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  • A Bidirectional Electrostatic Microvalve With Microsecond Switching Performance, B. Bae et al. (2007)
    TitleA Bidirectional Electrostatic Microvalve With Microsecond Switching Performance
    AuthorsB. Bae, J. Han, R. I. Masel
    PublicationJournal of Microelectromechanical Systems
    AbstractThis paper describes a new bidirectional high-pressure gas electrostatic microvalve that opens and closes in 50 $muhboxs$ or less. The microvalve consists of a valve-closing electrode, a flexible movable membrane, and a valve-opening electrode that is directly opposed to the valve-closing electrode. The membrane contains an embedded electrode, so the valve can zip closed when a potential is applied between the membrane and the valve-closing electrode. The valve-opening electrode allows the valve to open again in a rapid discontinuous motion, without requiring a large applied potential. A pressure-balance port is used to enhance the microvalve switching speed and to allow the valve to close against applied pressures greater than 8.3 atm (840 kPa). The gas conductance through the valve is 2.8 nl/Pa $ cdot$ s (17 sccm/atm), and the fluid leakage measured zero over the entire pressure range up to a burst pressure of 10.8 atm (1.1 MPa). Measurements show that the valve can open or close in 50 $muhboxs$ or less for applied pressures up to 126 kPa. In an extended lifetime test, a sample microvalve has been opened and closed 47 million times before failure. $hfill$[2007-0037]
  • A bistable electromagnetically actuated rotary gate microvalve, Rajesh Luharuka et al. (2008)
    TitleA bistable electromagnetically actuated rotary gate microvalve
    AuthorsRajesh Luharuka, Peter J. Hesketh
    PublicationJournal of Micromechanics and Microengineering
    AbstractTwo types of rotary gate microvalves are developed for flow modulation in microfluidic systems. These microvalves have been tested for an open flow rate of up to 100 sccm and operate under a differential pressure of 6 psig with flow modulation of up to 100. The microvalve consists of a suspended gate that rotates in the plane of the chip to regulate flow through the orifice. The gate is suspended by a novel fully compliant in-plane rotary bistable micromechanism (IPRBM) that advantageously constrains the gate in all degrees of freedom except for in-plane rotational motion. Multiple inlet/outlet orifices provide flexibility of operating the microvalve in three different flow configurations. The rotary gate microvalve is switched with an external electromagnetic actuator. The suspended gate is made of a soft magnetic material and its electromagnetic actuation is based on the operating principle of a variable-reluctance stepper motor.
  • A bonding technique using hydrophilic SU-8, Yu-Tzu Chen et al. (2007)
    TitleA bonding technique using hydrophilic SU-8
    AuthorsYu-Tzu Chen, Denz Lee
    PublicationJournal of Micromechanics and Microengineering
    AbstractIn this study, we present a bonding technique for fabricating microfluidic devices with surfactant-added SU-8 (hydrophilic SU-8) as the structure. The technique is based on an adhesive wafer bonding process. The hydrophilic SU-8 plays the roles of both an adhesive layer (glue) as well as a structural layer. Due to its special feature, bonding with hydrophilic SU-8 could be conducted without pressurizing equipment. The material could define structure satisfactorily and it has a hydrophilic surface in a cured state, and has a good adhesion capability with various substrates (glass, silicon or PDMS) after oxygen plasma treatment. The performance of the material was verified by using the Raman spectroscopy to analyze the possible changes in chemical structure, measuring contact angle to characterize hydrophilicity and several tests to confirm the bonding capability. The effect of different parameters on the bonding has also been explored. 2D (one-layer hydrophilic SU-8) and 3D (two-layer hydrophilic SU-8) sandwich configurations were constructed using this bonding technique. The tests showed the bonding strength to be in the range of 2-14 kg cm[?]2 measured by the pull test, and the microchannels could stand up to 0.4 atm pressure drop in the hydrodynamic testing. The present material has good properties in bonding, and the procedure is fast, compatible and easily implementable with a standard photolithography. It is suitable for microstructure and microelectronics integration, and highly involved three-dimensional (3D) microstructures.
  • About Coercivity and Intrinsic Coercivity, Magnetic Component Engineering (2007)
    TitleAbout Coercivity and Intrinsic Coercivity
    AuthorMagnetic Component Engineering
    PublisherMagnetic Component Engineering
    AbstractIn this article we will discuss a magnet's coercivity and intrinsic coercivity so as to give the reader a grasp of what these terms are and how they relate to permanent magnets. There is ample confusion about these terms, therefore, this article was written to give a better understanding of what these really mean with regards to the performance of permanent magnets and how these values should be specified on drawings.
  • A chaotic micromixer modulated by constructive vortex agitation, Jing-Tang Yang et al. (2007)
    TitleA chaotic micromixer modulated by constructive vortex agitation
    AuthorsJing-Tang Yang, Ker-Jer Huang, Kai-Yang Tung, I.-Chen Hu, Ping-Chiang Lyu
    PublicationJournal of Micromechanics and Microengineering
    AbstractA novel design for vortex modulation of a passive micromixer, named as the circulation-disturbance micromixer (CDM), has been achieved and analyzed experimentally and numerically. The micromixer consists of slanted grooves on the bottom and a zigzag barrier on the top. In this micromixer, the fluid produces a transverse motion perpendicular to the main field, and two modulated and hyperbolic vortices of disparate size are induced. The active-like agitation produced by the constructive interference of these two vortices induces increased flow through the grooves and the mixing efficiency is hence improved significantly. The 3D flow structure in CDM has been analyzed through both numerical simulation (CFD-ACE+) and two methods of visualization--using dyes and using micro laser-induced fluorescence (m-LIF, B-phycoerythrin (BPE) and Allophycocyanin alpha subunit (ApcA)) with a confocal microscope. Our results contribute to an understanding of the resulting enhanced hyperbolic flow mixing and provide also a superior microfluidic element for a 'lab on a chip'. Compared with a slanted groove micromixer, the mixing index of the designed CDM-2T increases 132%, whereas CDM-4T and CDM-8T respectively increase 183% and 280% at Reynolds number 10.
  • Active micromixer based on artificial cilia, Vinayak V. Khatavkar et al. (2007)
    TitleActive micromixer based on artificial cilia
    AuthorsVinayak V. Khatavkar, Patrick D. Anderson, Jaap M. J. den Toonder, Han E. H. Meijer
    PublicationPhysics of Fluids
    AbstractWe propose a design for an active micromixer that is inspired by the motion of ciliated micro-organisms occurring in nature. The conceptual design consists of an array of individually addressable artificial cilia in the form of microactuators covering the channel wall. The microactuators can be set into motion by an external stimulus such as an electric or a magnetic field, inducing either a primary or secondary motion in the surrounding fluid. To validate the concept and to help to design the precise mixer configuration, we developed a computational fluid-structure model. This model is based on a fictitious domain method that couples the microactuator motion to the concomitant fluid flow, fully capturing the mutual fluid-structure interactions. The simulated flow patterns resulting from the motion of single and multiple actuated elements (in a microchannel filled with a Newtonian fluid) under the action of a time-periodic forcing function are analyzed using dynamical systems theory to quantify the mixing efficiency. The results show that with a proper actuation scheme, two microactuators placed on the same wall of a microchannel can indeed induce effective mixing by chaotic advection; their distance should be small, but collisions should be avoided, and they can be actuated in a rather broad regime around 90° out of phase. Placing actuators on opposite walls also induces exponential stretching in the fluid, but if their length is relatively small, of the order of 20% of the channel height, mixing effectiveness is higher when they are arranged on the same wall
  • A decade of microfluidic analysis coupled with electrospray mass spectrometry: An overview, Sander Koster et al. (2007)
    TitleA decade of microfluidic analysis coupled with electrospray mass spectrometry: An overview
    AuthorsSander Koster, Elisabeth Verpoorte
    PublicationLab on a Chip
    AbstractThis review presents a thorough overview covering the period 1997-2006 of microfluidic chips coupled to mass spectrometry through an electrospray interface. The different types of fabrication processes and materials used to fabricate these chips throughout this period are discussed. Three 'eras' of interfaces are clearly distinguished. The earliest approach involves spraying from the edge of a chip, while later devices either incorporate a standard fused-silica emitter inserted into the device or fully integrated emitters formed during chip fabrication. A summary of microfluidic-electrospray devices for performing separations and sample pretreatment steps before sample introduction into the mass spectrometer is also presented.
  • Adhesion and friction of PDMS networks: molecular weight effects, A. Galliano et al. (2003)
    TitleAdhesion and friction of PDMS networks: molecular weight effects
    AuthorsA. Galliano, S. Bistac, J. Schultz
    PublicationJournal of Colloid and Interface Science
    DateSeptember 15, 2003
    AbstractThe objective of this work is to find relations between adherence and friction behaviors of elastomer networks. The chosen approach is based on the parallel study of the initial molecular weight (i.e., the degree of cross-linking) dependence of both adherence and friction. The polymers used are cross-linked polydimethylsiloxane (PDMS) and the substrate is a smooth glass plate. The experimental procedure uses both friction (pin on disk tribometer) and adhesion (tack test) measurements, associated with surface analysis and mechanical and rheological characterizations. Tack results show that high molecular weight PDMS exhibits the greater adherence energy. This can be explained by the role of both chain length and free and pendant chains: more numerous and longer free chains favor the substrate wetting (at a molecular scale) and increases the energy dissipation during separation (extraction and reptation mechanisms). However, friction results indicate a higher friction resistance for low molecular weight PDMS. This result could be quite surprising. An explanation based on interfacial sliding properties of free and pendant chains can be proposed. Elsewhere, for the lower molecular weight polymer, elastic contact present during friction is able to act as a forced wetting, constraining the network and consequently leading to a greater energy dissipation.
  • A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties, Tanushree Bala et al. (2004)
    TitleA facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to NicoreAgshell particles: structural characterization and investigation of magnetic properties
    AuthorsTanushree Bala, S. D. Bhame, P. A. Joy, B. L. V. Prasad, Murali Sastry
    PublicationJournal of Materials Chemistry
    AbstractA facile route for the synthesis of nickel nanoparticles in stable aqueous foams is reported. The Ni nanoparticles were roughly 12-15 nm in size and were stable as aqueous suspensions or powders when oleic acid was used as a capping agent. These Ni nanoparticles were subsequently coated with a silver shell in view of the extra stability and the enhanced manipulative ability afforded by the silver nanocoating. This was accomplished by a simple transmetallation reaction wherein the nanoparticle surface nickel atoms act as localized reducing agents for the silver ions in solution. As the silver shell is formed through the surface reaction a reduction in the average size of the Nicore occurs. After the core-shell structure formation, the Nicore has an average diameter of 10-20 nm while the Agshell has a thickness of 2-4 nm. The pristine oleic acid coated Ni and NicoreAgshell nanoparticles were probed for their magnetic characteristics by a vibrating sample magnetometer. The nascent, oleic acid coated Ni nanoparticles display a low superparamagnetic blocking temperature, TB, of 20 K. The field dependent magnetic behaviour above and below TB displays the standard features corresponding to superparamagnetism, as expected for very small Ni crystallites suggesting again that each 12 nm particle is polycrystalline. The magnetic contribution in the NicoreAgshell system comes from only the Ni core and predictably, the blocking temperature of this system is below 12 K due to the smaller size of the Ni core.
  • A Highly Symmetrical Capacitive Triaxial Accelerometer, Joost Conrad Lötters (1997)
    TitleA Highly Symmetrical Capacitive Triaxial Accelerometer
    AuthorJoost Conrad Lötters
    DateAug 1997
  • Aldrich Polymer Products Applicaton & Reference Information: Free Radical Initiators, Aldrich Chemical Co., Inc. (1999)
    TitleAldrich Polymer Products Applicaton & Reference Information: Free Radical Initiators
    Author Aldrich Chemical Co., Inc.
  • A Magnetically Driven Micro-Mixing Device and its Numerical Analysis, A.M. Morega et al. (2007)
    TitleA Magnetically Driven Micro-Mixing Device and its Numerical Analysis
    AuthorsA.M. Morega, J.C. Ordonez, M. Morega
    Conference NameCOMSOL Users Conference 2007
    AbstractIn this paper, we present a FEM model of a mixing MEMS μTAS device. A quasistatic magnetic field, produced by sequentially switched DC currents advected through conductors embedded in the device substrate beneath the flow channel, is used to mix the working magnetic fluid, while it is forced to flow through a rib walled channel. The body forces in the magnetized fluid perturb the otherwise laminar flow, into a mixing flow. The study is also concerned with the heat transfer problem posed by the Joule effect produced by the electric currents. For the assumed working conditions, the temperature profile within the structure exhibits moderate levels of Joule heating, hence there is no stringent need to consider the temperature dependence of the fluid’s magnetization.
  • A magnetic microstirrer and array for microfluidic mixing, Liang-Hsuan Lu et al. (2002)
    TitleA magnetic microstirrer and array for microfluidic mixing
    Authors Liang-Hsuan Lu, Kee Suk Ryu, Chang Liu
    PublicationJournal of Microelectromechanical Systems
    AbstractWe report the development of a micromachined magnetic-bar micromixer for microscale fluid mixing in biological laboratory-on-a-chip applications. The mixer design is inspired by large scale magnetic bar mixers. A rotating magnetic field causes a single magnetic bar or an array of them to rotate rapidly within a fluid environment. A fabrication process of the magnetic bar mixer is developed. Results of fluid mixing in micro channels and chambers are investigated using experimental means and computer-aided fluid simulation.
  • A magneto-hydrodynamically controlled fluidic network, Haim H. Bau et al. (2003)
    TitleA magneto-hydrodynamically controlled fluidic network
    AuthorsHaim H. Bau, Jianzhong Zhu, Shizhi Qian, Yu Xiang
    PublicationSensors and Actuators B: Chemical
    DateJanuary 15, 2003
    AbstractThe paper describes fluidic networks consisting of individually controlled branches. The networks' basic building blocks are conduits equipped with two electrodes positioned on opposing walls. The entire device is either subjected to an external uniform magnetic field or fabricated within a magnetic material. When a prescribed potential difference is applied across each electrode pair, it induces current in the liquid (assumed to be at least weakly conductive solution). Analogously with electric circuits, by judicious application of the potential differences at various branches, one can direct liquid flow in any desired way without a need for mechanical pumps or valves. Equipped with additional, internally located electrodes, the network branches double as stirrers capable of generating chaotic advection. The paper describes the basic building blocks for such a network, the operation of these branches as stirrers, a general linear graph-based theory for the analysis and optimal control of fluidic magneto-hydrodynamic (MHD) networks, an example of a network fabricated with low temperature, co-fired ceramic tapes, and preliminary experimental observations that illustrate that the ideas described in this paper can, indeed, be implemented in practice.
  • A Mechanism of Magnetic Hysteresis in Heterogeneous Alloys, E. C. Stoner et al. (1948)
    TitleA Mechanism of Magnetic Hysteresis in Heterogeneous Alloys
    AuthorsE. C. Stoner, E. P. Wohlfarth
    PublicationPhilosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
    DateMay 04, 1948
    AbstractThe Becker-Kersten treatment of domain boundary movements is widely applicable in the interpretation of magnetization curves, but it does not account satisfactorily for the higher coercivities obtained, for example, in permanent magnet alloys. It is suggested that in many ferromagnetic materials there may occur 'particles' (this term including atomic segregates or 'islands' in alloys), distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector, I 0 . As the field changes continuously, the resolved magnetization, I H , may change discontinuously at critical values, H 0 , of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle, and on the orientation of 'easy axes' with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magneto-crystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution (section section 2,3,4), and a less detailed treatment for the general ellipsoidal form (section 5). For the first it is convenient to use the non-dimensional parameter h, such that h = H/(|N a -N b |) I 0 , N a and N b being the demagnetization coefficients along the polar and equatorial axes. The results are presented in tables and diagrams giving the variation with h of I H /I 0 . For the special limiting form of the oblate spheroid there is no hysteresis. For the prolate spheroid, as the orientation angle, θ , varies from 0 to 90 degrees, the cyclic magnetization curves change from a rectangular form with |h 0 | = 1, to a linear non-hysteretic form, with an interesting sequence of intermediate forms. Exact expressions are obtained for the dependence of h 0 and θ , and curves for random distribution are computed. All the numerical results are applicable when the anisotropy is due to longitudinal stress, when h = HI 0 /3 λσ, where λ is the saturation magnetostriction coefficient, and σ the stress. The results also apply to magneto-crystalline anisotropy in the important and representative case in which there is a unique axis of easy magnetization as for hexagonal cobalt. Estimates are made of the magnitude of the effect of the various types of anisotropy. For iron the maximum coercivities, for the most favourable orientation, due to the magneto-crystalline and strain effects are about 400 and 600 respectively. These values are exceeded by those due to the shape effect in prolate spheroids if the dimensional ratio, m, is greater than 1 ⋅1; for m = 10, the corresponding value would be about 10,000 (section 7). A fairly precise estimate is made of the lower limit for the equatorial diameter of a particle in the form of a prolate spheroid below which boundary formation cannot occur. As m varies from 1 (the sphere) to 10, this varies from 1 ⋅5 to 6 ⋅1 × 10 -6 for iron, and from 6 ⋅2 to 25 × 10 -6 for nickel (section 6). A discussion is given (section 7) of the application of these results to (a) non-ferromagnetic metals and alloys containing ferromagnetic 'impurities', (b) powder magnets, (c) high coercivity alloys of the dispersion hardening type. In connexion with (c) the possible bearing on the effects of cooling in a magnetic field is indicated.
  • A MEMS-based valveless impedance pump utilizing electromagnetic actuation, Chia-Yen Lee et al. (2008)
    TitleA MEMS-based valveless impedance pump utilizing electromagnetic actuation
    AuthorsChia-Yen Lee, Hsien-Tsung Chang, Chih-Yung Wen
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis study presents a planar valveless impedance-based micro pump for biomedical applications. The micro pump comprises four major components, namely a lower glass substrate containing a copper micro coil, a microchannel, an upper glass cover plate and a PDMS diaphragm with a magnet mounted on its upper surface. When a current is passed through the micro coil, an electromagnetic force is established between the coil and the magnet. The resulting deflection of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. The performance of the micro pump is characterized both experimentally and numerically using Ansoft/Maxwell3D FEA software. The results show that the mechanical integrity of the micro pump is assured provided that the diaphragm deflection does not exceed 110 µm. This deflection is obtained by supplying the micro coil with an input current of 0.6 A, and results in a flow rate of 7.2 ml min[?]1 when the PDMS membrane is driven by an actuating frequency of 200 Hz.
  • A microfabricated device for sizing and sorting DNA molecules, Hou-Pu Chou et al. (1999)
    TitleA microfabricated device for sizing and sorting DNA molecules
    AuthorsHou-Pu Chou, Charles Spence, Axel Scherer, Stephen Quake
    PublicationProceedings of the National Academy of Sciences of the United States of America
    AbstractWe have demonstrated a microfabricated single-molecule DNA sizing device. This device does not depend on mobility to measure molecule size, is 100 times faster than pulsed-field gel electrophoresis, and has a resolution that improves with increasing DNA length. It also requires a million times less sample than pulsed-field gel electrophoresis and has comparable resolution for large molecules. Here we describe the fabrication and use of the single-molecule DNA sizing device for sizing and sorting DNA restriction digests and ladders spanning 2–200 kbp.
  • A Microfabricated Rotary Pump, Chou et al. (2001)
    TitleA Microfabricated Rotary Pump
    Authors Chou, Unger, Quake
    PublicationBiomedical Microdevices
    DateDecember 01, 2001
    AbstractBecause microfluidic devices operate at low Reynolds number, many fluidic operations are limited by diffusion. We have developed a microfabricated rotary pump and demonstrated that active mixing can be used to overcome the slow diffusion process in two applications. First, we showed that mixing of reagents could be efficiently accomplished for objects of a wide range of diffusion constants. Second, we showed how reaction kinetics of a surface-binding assay can be enhanced by nearly two orders of magnitude.
  • A microfluidic processor for gene expression profiling of single human embryonic stem cells, Jiang F. Zhong et al. (2008)
    TitleA microfluidic processor for gene expression profiling of single human embryonic stem cells
    AuthorsJiang F. Zhong, Yan Chen, Joshua S. Marcus, Axel Scherer, Stephen R. Quake, Clive R. Taylor, Leslie P. Weiner
    PublicationLab on a Chip
    AbstractThe gene expression of human embryonic stem cells (hESC) is a critical aspect for understanding the normal and pathological development of human cells and tissues. Current bulk gene expression assays rely on RNA extracted from cell and tissue samples with various degree of cellular heterogeneity. These 'cell population averaging' data are difficult to interpret, especially for the purpose of understanding the regulatory relationship of genes in the earliest phases of development and differentiation of individual cells. Here, we report a microfluidic approach that can extract total mRNA from individual single-cells and synthesize cDNA on the same device with high mRNA-to-cDNA efficiency. This feature makes large-scale single-cell gene expression profiling possible. Using this microfluidic device, we measured the absolute numbers of mRNA molecules of three genes (B2M, Nodal and Fzd4) in a single hESC. Our results indicate that gene expression data measured from cDNA of a cell population is not a good representation of the expression levels in individual single cells. Within the G0/G1 phase pluripotent hESC population, some individual cells did not express all of the 3 interrogated genes in detectable levels. Consequently, the relative expression levels, which are broadly used in gene expression studies, are very different between measurements from population cDNA and single-cell cDNA. The results underscore the importance of discrete single-cell analysis, and the advantages of a microfluidic approach in stem cell gene expression studies.
  • A micromagnetic study of domain-structure modeling, Tetsuji Matsuo et al. (2008)
    TitleA micromagnetic study of domain-structure modeling
    AuthorsTetsuji Matsuo, Naoki Mimuro, Masaaki Shimasaki
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    Date18 April 2008
    AbstractTo develop a mesoscopic model for magnetic-domain behavior, a domain structure model (DSM) was examined and compared with a micromagnetic simulation. The domain structure of this model is given by several domains with uniform magnetization vectors and domain walls. The directions of magnetization vectors and the locations of domain walls are determined so as to minimize the magnetic total energy of the magnetic material. The DSM was modified to improve its representation capability for domain behavior. The domain wall energy is multiplied by a vanishing factor to represent the disappearance of magnetic domain. The sequential quadratic programming procedure is divided into two steps to improve an energy minimization process. A comparison with micromagnetic simulation shows that the modified DSM improves the representation accuracy of the magnetization process.
  • An Account of an Extraordinary Effect of Lightning in Communicating Magnetism. Communicated by Pierce Dod, M. D. F. R. S. from Dr. Cookson of Wakefield in Yorkshire, Pierce Dod (1735)
    TitleAn Account of an Extraordinary Effect of Lightning in Communicating Magnetism. Communicated by Pierce Dod, M. D. F. R. S. from Dr. Cookson of Wakefield in Yorkshire
    AuthorPierce Dod
    PublicationPhilosophical Transactions (1683-1775)
    Date1735 - 1736
  • An AC Magnetohydrodynamic Microfluidic Switch for Micro Total Analysis Systems, Lemoff et al. (2003)
    TitleAn AC Magnetohydrodynamic Microfluidic Switch for Micro Total Analysis Systems
    Authors Lemoff, Lee
    PublicationBiomedical Microdevices
    DateMarch 01, 2003
    AbstractIn this paper, a magnetohydrodynamic (MHD) microfluidic switch, which could form the basis for general microfluidic circuits, is reported. The switch uses an AC MHD pumping mechanism in which the Lorentz force is used to pump electrolytic solutions. By integrating two AC MHD pumps into different arms of a Y-shaped fluidic circuit, flow can be switched between the two arms by activating one of the micropumps and setting the other one at a counteracting pressure to prevent flow. Flow could be switched from one microchannel to another at a velocity of 0.3 mm/sec. This type of switch is easily integrated with other biochips and can be used to produce complex fluidic routing, which may have multiple applications in micro total analysis systems (µTAS). Examples of applications include on-chip combinatorial chemistry for drug discovery and drug testing, connectors for routing samples to different detectors, and general reconfigurable assays.
  • Analysis of the Demagnetisation Process and Possible Alternative Magnetic Treatments for Naval Vessels, T. Baynes (2002)
    TitleAnalysis of the Demagnetisation Process and Possible Alternative Magnetic Treatments for Naval Vessels
    AuthorT. Baynes
    DateFebruary, 2002
    AbstractNaval submarines and surface ships are regularly subjected to a treatment called “deperming” that seeks to design the vessel’s permanent magnetisation for optimal magnetic camouflage. A scaled model of a magnetic treatment facility (MTF) has been established as a valid system to simulate deperming and used to investigate various aspects of the deperm process including: magnetic anisotropy and demagnetising fields as factors in the physical modelling of magnetism in whole vessels; a comparison of current and alternative deperm procedures; the application of theoretical models of bulk magnetisation to calculate deperm outcomes in the physical model and in actual vessels. A “laboratory MTF” was constructed to imitate the applied field geometry at a naval MTF. The system was calibrated and it was determined that the laboratory MTF could make magnetic measurements on a CU200T-G steel bar sample with an equivalent accuracy (error = ±5%) to that of standard magnetometric equipment. Experiments were conducted with emphasis on a holistic approach to modelling the deperm process and describing magnetisation changes in whole objects. The importance of the magnetic anisotropic changes to steel with cold rolling was confirmed. In CU200T-G steel sheet the initial susceptibility (ci) was found to increase by a factor of 3 ±0.1 in the rolling direction, from a value of ~ 110 in the un-rolled steel sheet (thickness dependent). ci in the rolled sheet transverse to the rolling direction was decreased by a factor of 0.94 ±0.09 to ci in the un-rolled sheet steel. Previous studies on hull steel have neglected to account for this transformation through cold work. The demonstration on mild steel here is expected to have an analogy in the final state of the hull sheet steel as it resides in a submarine pressure hull. Future studies either on hull material or on modelling whole vessels should include the same or similar magnetic anisotropic properties in the steel(s) under investigation. Hollow circular tubes made from CA2S-E and CU200T-G steel sheet were selected as models for vessels. It was shown that these steel tubes were a good choice in this regard: minimising the complexity of the experiment whilst maintaining the validity of XI a deperm simulation. During a deperm there was an excellent qualitative likeness in the permanent longitudinal magnetisation (PLM) for the steel tubes to PLM in both a submarine and a surface vessel. Permanent vertical magnetisation (PVM) deperm results from the tubes displayed a close qualitative match with PVM in a submarine but not in a surface vessel. A theoretical treatment for demagnetisation factors (Nd) in hollow ellipsoids was used in conjunction with a geometrical approximation to calculate Nd for finite hollow objects of revolution. Subsequent theoretical calculations correlated well with experimental results for measured effective ci (ceff) in hollow circular CU200T-G steel tubes of various lengths and aspect ratios. Using an estimate of 100 as ci for submarine hull steel, the same analysis produces Nd for the axial and transaxial directions in a submarine equal to 5.97´10-3 and 0.0142 respectively. Three items for potential improvement were identified in the current deperm protocol used on naval vessels (Flash-D): redundancy in the protocol; the duration of the deperm and a theoretical basis for predicting the final magnetisation or changes in magnetisation during a deperm. Simulations of a novel “anhysteretic deperm” method, designed to combat these issues, compared favourably to the Flash-D protocol. The standard deviation (s) of the final PVM from 30 Flash-D deperms on steel tubes was 206 A/m; for the final PVM from 30 anhysteretic deperms of the same duration, this was 60 A/m. The s for the final PLM for Flash-D and anhysteretic deperms of the same duration were 416 A/m and 670 A/m respectively. The conclusion is that adopting the anhysteretic deperm on actual vessels would improve the reliability of the PVM outcome. Though the procedure would demand the same duration as Flash-D, there is the advantage of saving time by not having to repeat deperms to obtain the desired result. Additionally the anhysteretic deperm is considerably more amenable to theoretical analysis. A modified version of Langevin’s equation was used to predict the final PLM and PVM results for anhysteretic deperms and to provide a useful analysis of the anhysteretic processes in the Flash-D procedure. Using a Preisach analysis of hysteresis, a mathematical description of bulk magnetic changes that occur to a specific object, XII within a deperm, has been developed. Theoretical calculations of PLM in a steel tube during and after both types of deperm are in excellent agreement with experimental data. The same theoretical approach was also used to retrospectively model PLM results from previous Flash-D deperms on a submarine with equal success. With this analysis it is proposed that anhysteretic deperm outcomes could be predicted a priori. The influence of magnetic cargo on hull magnetisation was demonstrated to be of significance during and after deperming. “Sympathetic deperming” occurs where a magnetic source is located close to the hull during a deperm. It was found that a vessel or model vessel hull could still be demagnetised even when they contain magnetic cargo that would normally resist the direct application of the same magnetic fields. This was explained using the principles of demagnetising fields and anhysteretic magnetisation. A possible explanation was provided for a PVM measurement anomaly common to the model and vessel deperm results. From measurement, alternating longitudinal applied fields apparently induce corresponding changes in the PVM. This effect could be explained by the depermed object being offset longitudinally from the position expected by the measurement system. This offset could be estimated using an analysis of the changes to PLM and PVM after a longitudinal applied field. The offset displacements calculated for the vessels were too small to be verified experimentally (< 0.1m), but the predicted offset for the steel tubes coincided with the limit of precision for their placement in the laboratory MTF = 0.5mm The aim of this work was to look at the deperm process with reference to a system that demonstrated qualitative similarities to deperms on actual vessels. The laboratory MTF is a unique facility, permitting a useful practical analysis of deperming based on sound magnetostatic measurements The experimental and theoretical results gained here have direct application to future deperms on naval vessels with particular reference to submarines.
  • Analytical description of magnetization curves, Zdzislaw Wlodarski (2006)
    TitleAnalytical description of magnetization curves
    AuthorZdzislaw Wlodarski
    PublicationPhysica B: Condensed Matter
    DateMarch 15, 2006
    AbstractMagnetization process is described by the two-component expression based on the Brillouin equation and the Rayleigh model. Such approach leads to very accurate approximation of typical main magnetization curves, and adequate approximation of related hysteresis loops and demagnetization curves in the whole range of magnetization. Model parameters may be determined from the measured magnetization curves or standard physical parameters of magnetic materials.
  • A new and simple method for thin graphitic coating of magnetic-metal nanoparticles, Satoshi Tomita et al. (2000)
    TitleA new and simple method for thin graphitic coating of magnetic-metal nanoparticles
    AuthorsSatoshi Tomita, Masahiro Hikita, Minoru Fujii, Shinji Hayashi, Keiichi Yamamoto
    PublicationChemical Physics Letters
    DateJanuary 21, 2000
    AbstractA new and simple method for synthesizing graphitic carbon-coated magnetic-metal (Co, Ni and Fe) nanoparticles has been reported. The mixture of metal and diamond nanoparticles was just annealed at 1700[degree sign]C in vacuum. The annealed samples were studied by high-resolution transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. These analyses revealed that magnetic-metal particles are coated with uniform graphitic layers several nanometers in thickness.
  • A new model to describe the crossover from superparamagnetic to blocked magnetic nanoparticles, E. De Biasi et al. (2008)
    TitleA new model to describe the crossover from superparamagnetic to blocked magnetic nanoparticles
    AuthorsE. De Biasi, R.D. Zysler, C.A. Ramos, M. Knobel
    PublicationJournal of Magnetism and Magnetic Materials
    DateJuly 2008
    AbstractA new model that considers the thermal probability of uniform magnetization inversion in magnetic nanoparticles is presented. We included the temporal window in consideration of the thermal average, which allowed us to take into account the hysteretic behavior, leading to a more clear description of the passage from one regime to another. From this formalism appears a superparamagnetic probability L that indicated the fraction of superparamagnetic particles we find on the ensemble at a given T, H and experimental time window. We have performed numerical simulations, including different time windows and considering the high- and low-temperature regimes. We compare our model with the analytic solution in zero and high-temperature limits and find that the proposed model agrees with the simulations. Measurements of field-cooling and zero-filed-cooling magnetization as well as hysteresis loops were simulated applying this model, from which relevant considerations regarding the importance, applicability and limitations of this treatment could be obtained.
  • Angular dependence of coercivity in sintered magnets, D. Givord et al. (1988)
    TitleAngular dependence of coercivity in sintered magnets
    AuthorsD. Givord, P. Tenaud, T. Viadieu
    PublicationJournal of Magnetism and Magnetic Materials
    DateApril 2, 1988
    AbstractThe angular dependence of coercivity in sintered magnets is analysed within the framework of a model for magnetization reversal described previously. In systems where the coercive field is much weaker than the anisotropy field, magnetization reversal in each grain is determined by a 1/cos [theta] law, i.e. only the projection of the field along the magnetization is effective. The angular dependence of coercivity in magnets corresponds to such a law, convoluted with the angular distribution of grain orientations. In systems, where the coercive field is not negligible with respect to the anisotropy field, a coherent reversible rotation of the moments apart from their easy direction occurs prior to magnetization reversal and modifies the 1/cos [theta] law. Analysis of the observed behavior reveals then that, in the nucleus in which magnetization reversal is initiated, the anisotropy is not strongly reduced with respect to the bulk.
  • Angular dependence of coercivity of grains in nanocrystalline permanent magnets, Gong Yi-Min et al. (2008)
    TitleAngular dependence of coercivity of grains in nanocrystalline permanent magnets
    AuthorsGong Yi-Min, Lan Zhi-Huan, Yan Yu, Du Xiao-Bo, Wang Wen-Quan, Wang Xue-Feng, Su Feng, Lu Lei, Zhang Zhi-Sheng, Jin Han-Min, Wen Ge-Hui
    PublicationChinese Physics B
    AbstractIn this paper magnetization remanence curves were studied for nanocrystalline Pr8Fe87B5, Pr12Fe82B6 and Pr15Fe77B8. Initially the sample was at remanence following saturation along z-axis. After rotating the magnet by 5n degrees (n = 0, 1, ..., 18) a field H was applied along z-axis and then decreased to zero, and the remanence Jnr was measured as a function of H. The curves were compared with those calculated based on the nucleation of reverse domain model and domain wall pinning model. The latter model succeeds in simulation much better than the former, and it is concluded that the magnetization reversal is dominated by domain wall pinning for all the samples. The nucleation mechanism contribution, while remains small, increases with the increase of Pr content.
  • An integrated liquid mixer/valve, J. Voldman et al. (2000)
    TitleAn integrated liquid mixer/valve
    AuthorsJ. Voldman, M.L. Gray, M.A. Schmidt
    PublicationJournal of Microelectromechanical Systems
    AbstractWe present an integrated liquid mixer/valve to be used for sample preparation for bioscience analysis systems. The mixer/valve is a glass-silicon bonded structure with a wafer-bonded cantilever-plate flapper valve and deep reactive-ion etched ports. It is passively pressure actuated and is distinguished by the fact that it can perform both a mixing and valving function simultaneously to mix two liquids noncontinuously. We present the design and fabrication of the mixer/valve and show that it successfully performs both its valving and mixing functions, including the discontinuous mixing of two liquids. We propose a method for characterizing mixing in this device using fluorescence microscopy and the pH dependence of fluorescein fluorescence. This method aims to allow one to extract the mixing length from a quantifiable observable. We present modeling and results of mixing length measurements using this method
  • An Integrative Computational Model of Multiciliary Beating, Xingzhou Yang et al. (2008)
    TitleAn Integrative Computational Model of Multiciliary Beating
    AuthorsXingzhou Yang, Robert Dillon, Lisa Fauci
    PublicationBulletin of Mathematical Biology
    DateMay 04, 2008
    AbstractThe coordinated beating of motile cilia is responsible for ovum transport in the oviduct, transport of mucus in the respiratory tract, and is the basis of motility in many single-celled organisms. The beating of a single motile cilium is achieved by the ATP-driven activation cycles of thousands of dynein molecular motors that cause neighboring microtubule doublets within the ciliary axoneme to slide relative to each other. The precise nature of the spatial and temporal coordination of these individual motors is still not completely understood. The emergent geometry and dynamics of ciliary beating is a consequence of the coupling of these internal force-generating motors, the passive elastic properties of the axonemal structure, and the external viscous, incompressible fluid. Here, we extend our integrative model of a single cilium that couples internal force generation with the surrounding fluid to the investigation of multiciliary interaction. This computational model allows us to predict the geometry of beating, along with the detailed description of the time-dependent flow field both near and away from the cilia. We show that synchrony and metachrony can, indeed, arise from hydrodynamic coupling. We also investigate the effects of viscosity and neighboring cilia on ciliary beat frequency. Moreover, since we have precise flow information, we also measure the dependence of the total flow pumped per cilium per beat upon parameters such as viscosity and ciliary spacing.
  • Anisotropic magnetism in field-structured composites, James E. Martin et al. (2000)
    TitleAnisotropic magnetism in field-structured composites
    AuthorsJames E. Martin, Eugene Venturini, Judy Odinek, Robert A. Anderson
    PublicationPhysical Review E
    DateMarch 2000
  • Anisotropy and phase transitions in atomically thin magnetic microstructures, A. Marty (2000)
    TitleAnisotropy and phase transitions in atomically thin magnetic microstructures
    AuthorA. Marty
    AbstractA recently developed technique allows the in situ fabrication of real two dimensional ferromagnetic particles. In this thesis a Scanning Kerr Microscope (SKEM) with a resolution of about 1mu is used to study the in-plane magnetization of such ultrathin particles on the micrometer size scale. The SKEM provides the possibility to measure the temperature dependent magnetization not only in zero magnetic field, but also in an applied external field. Magnetization loops M(H) can be collected at diferent spots on the sample. In addition, by scanning an interesting area we are able to map the magnetization in any external magnetic field along an in-plane direction. In the first part of this thesis a detailed study, of the magnetization of ultrathin Co particles evaporated on a Cu(100) single crystal is presented. The outstanding property is their single domain remanent state. They show square hysteresis loops along the easy magnetization axis with slightly varying fields Hc. The single domain state is stable and independent on the lateral extent of the structures, at least down to 1mu. Hysteresis loops are collected on particles of various lateral sizes and shapes to measure the switching behavior and the influence of their shape on their magnetization. We found that local changes in the substrate dominates over eventual size or shape dependence. No mutual interaction was observed for particles with a distance between each other down to 2mu. In the second part of this thesis the critical behaviour of in-plane magnetized Co/Cu(100) films and particles are investigated. The system exhibits a second-order phase transition from a ferromagnetic phase to a paramagnetic phase. In addition to the fourfold symmetry breaking field, a misfit in the Cu substrate causes a weak twofold anisotropy field. Both anisotropies scales differently with temperature and the transition is probably dominated by the uniaxial crystal field. However. the fourfold symmetry breaking cannot be neglected and causes non-universal behavior. Simultaneously collected M(H) curves parallel and perpendicular to the easy magnetization axis during phase transition reveal an anisotrupic behavior up to about 10 Kelvin above Tc and pronounced peaks in both susceptibilities at Tc. An analysis of the shape of the magnetization curves indicates that the fourfold symmetry breaking vanish slightly below T, while the twofold field persists. The relevant length at phase transition - the correlation length of the electron spins - develops to the maximum of about 1mu in our system. This is about the maximal particle size detectable with the SKEM. Finite size effects are therefore hard to observe. The values for the critical exponents beta, delta and gamma measured at 10x6mu2 and 4x4mu2 particles are slightly enhanced compared with the extended film values. In addition they exhibit a slightly different scaling function.
  • A novel metal-protected plasma treatment for the robust bonding of polydimethylsiloxane, Natasha Patrito et al. (2007)
    TitleA novel metal-protected plasma treatment for the robust bonding of polydimethylsiloxane
    AuthorsNatasha Patrito, Jessica Mary McLachlan, Sarah Nicole Faria, Jayna Chan, Peter R. Norton
    PublicationLab on a Chip
    AbstractWe describe a method for the irreversible bonding of PDMS-based microfluidic components by exploiting the first reported "shelfable" plasma treatment of PDMS. Simultaneous plasma activation and protection of PDMS surfaces are achieved via RF magnetron sputtering of thin aluminium films in the presence of an argon plasma. In this process, Ar plasma exposure generates a hydrophilic, silanol-enriched polymer surface amenable to irreversible bonding to glass, PDMS or silicon substrates, while the aluminium film functions as a capping layer to preserve the surface functionality over several weeks of storage in ambient conditions. Prior to bonding, this protective aluminium layer is removed by immersion in an aqueous etchant, exposing the adhesive surface. Employing this technology, PDMS-glass and PDMS-PDMS microfluidic devices were fabricated and the adhesive strength was quantified by tensile and leakage testing. Bonding success rates in excess of 80% were demonstrated for both PDMS-glass and PDMS-PDMS assemblies sealed 24 h and 7 days following initial polymer surface activation. PDMS-glass microdevices performed optimally, displaying maximum adhesive strengths on the order of 5 MPa and burst flow rates of [similar]1 mL min-1 (channel dimensions: l = 25 mm; w = 300 [micro sign]m; h = 20 [micro sign]m). These data demonstrate a significant improvement in performance over previously reported bonding technologies, resulting in the production of more robust, longer-lasting microfluidic systems that can withstand higher pressures and flow rates.
  • A novel micromachined magnetic membrane microfluid pump, M. Khoo et al. (2000)
    TitleA novel micromachined magnetic membrane microfluid pump
    AuthorsM. Khoo, C. Liu
    Pages2394-2397 vol.3
    Conference NameEngineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE
    AbstractWe present results on the design, fabrication, and testing of a new, micromachined magnetic pump for integrated microfluidic systems. Structurally, the pump consists of a magnetic microactuator and two polymer-based one-way diffuser valves. The microactuator is based on a thin membrane made of polydimethylsiloxane (PDMS), a soft silicone elastomer. Membrane displacement is caused by the interaction between ferromagnetic pieces (embedded within the thickness of the membrane) and an external magnet. This novel mechanism reduces fabrication and packaging complexity, and allows for remote operation of the micropump without any tether wires for power input. The operation is simple as no precise alignment is required between the external magnet and the pump. PDMS is biocompatible compared to silicon. One future application of this tetherless micropump is implanted biomedical microfluidic systems. We developed a novel micromachining process for embedding ferromagnetic materials within a thin, spin-cast PDMS membrane. Unique pump and diffuser mechanisms that allow for continuous pumping are also developed. Diffuser elements containing no moving parts are fabricated using polymer micromachining techniques. Micro Permalloy pieces are strategically positioned within a 2×2 mm2, 40-μm-thick PDMS membrane. Dimensions and locations of the membrane and the Permalloy pieces are optimized for maximum membrane vertical displacement under a given magnetic field. Experimentally, we have demonstrated successful on-chip fluid pumping. In the presence of an oscillating 2.85×105-A/m external magnetic field, a 1.2-μl/min flow rate was measured for an actuation frequency of 2.9-Hz. The flow rate can be easily varied by the frequency
  • An Ultraviolet-Curable Mold for Sub-100-nm Lithography, S. Choi et al. (2004)
    TitleAn Ultraviolet-Curable Mold for Sub-100-nm Lithography
    AuthorsS. Choi, P.J. Yoo, S.J. Baek, T.W. Kim, H.H. Lee
    PublicationJournal of the American Chemical Society
    DateJune 30, 2004
    AbstractWe describe a novel UV-curable mold that is stiff enough for replicating dense sub-100-nm features even with a high aspect ratio. It also allows for flexibility when the mold is prepared on a flexible support such that large area replication can be accomplished. The composite material of the mold is inert to chemicals and solvents. The surface energy is made low with a small amount of releasing agent such that the mold can be removed easily and cleanly after patterning. In addition, the material allows self-replication of the mold. These unique features of the mold material should make the mold quite useful for various patterning purposes.
  • A Photocurable Poly(dimethylsiloxane) Chemistry Designed for Soft Lithographic Molding and Printing in the Nanometer Regime, K.M. Choi et al. (2003)
    TitleA Photocurable Poly(dimethylsiloxane) Chemistry Designed for Soft Lithographic Molding and Printing in the Nanometer Regime
    AuthorsK.M. Choi, J.A. Rogers
    PublicationJournal of the American Chemical Society
    DateApril 9, 2003
    AbstractPatterning techniques that rely on high-resolution elastomeric elements such as stamps, molds, and conformable photomasks are operationally simple methods for nanofabrication that may find applications in areas such as molecular and organic electronics. The resolution of these "soft" lithographic procedures is often limited by the mechanical properties of the elastomers. We introduce here a chemically modified poly(dimethylsiloxane) material that is designed and optimized specifically for soft lithography, particularly in the nanometer regime. We demonstrate its use for nanopatterning tasks that are challenging with the commercially available elastomers that have been used in the past.
  • A PMMA valveless micropump using electromagnetic actuation, C. Yamahata et al. (2005)
    TitleA PMMA valveless micropump using electromagnetic actuation
    AuthorsC. Yamahata, C. Lotto, E. Al-Assaf, M. A. M. Gijs
    PublicationMicrofluidics and Nanofluidics
    DateJuly 01, 2005
    AbstractWe have fabricated and characterized a polymethylmethacrylate (PMMA) valveless micropump. The pump consists of two diffuser elements and a polydimethylsiloxane (PDMS) membrane with an integrated composite magnet made of NdFeB magnetic powder. A large-stroke membrane deflection (~200 µm) is obtained using external actuation by an electromagnet. We present a detailed analysis of the magnetic actuation force and the flow rate of the micropump. Water is pumped at flow rates of up to 400 µl/min and backpressures of up to 12 mbar. We study the frequency-dependent flow rate and determine a resonance frequency of 12 and 200 Hz for pumping of water and air, respectively. Our experiments show that the models for valveless micropumps of A. Olsson et al. (J Micromech Microeng 9:34, 1999) and L.S. Pan et al. (J Micromech Microeng 13:390, 2003) correctly predict the resonance frequency, although additional modeling of losses is necessary.
  • A Rapid and Low-Cost Procedure for Fabrication of Glass Microfluidic Devices, Q. Chen et al. (2007)
    TitleA Rapid and Low-Cost Procedure for Fabrication of Glass Microfluidic Devices
    AuthorsQ. Chen, G. Li, Q.-H. Jin, J.-L. Zhao, Q.-S. Ren, Y.-S. Xu
    PublicationJournal of Microelectromechanical Systems
    AbstractIn this paper, we present a simple, rapid, and low-cost procedure for fabricating glass microfluidic chips. This procedure uses commercially available microscopic slides as substrates and a thin layer of AZ 4620 positive photoresist (PR) as an etch mask for fabricating glass microfluidic components, rather than using expensive quartz glasses or Pyrex glasses as substrates and depositing an expensive metal or polysilicon/amorphous silicon layer as etch masks in conventional method. A long hard-baking process is proposed to realize the durable PR mask capable of withstanding a long etching process. In order to remove precipitated particles generated during the etching process, a new recipe of buffered oxide etching with addition of 20% HCl is also reported. A smooth surface microchannel with a depth of more than 110 $muhboxm$ is achieved after 2 h of etching. Meanwhile, a simple, fast, but reliable bonding process based on UV-curable glue has been developed which takes only 10 min to accomplish the efficient sealing of glass chips. The result shows that a high bonding yield ( $sim$100%) can be easily achieved without the requirement of clean room facilities and programmed high-temperature furnaces. The presented simple fabrication process is suitable for fast prototyping and manufacturing disposable microfluidic devices.$hfill$ [2007-0032]
  • A rapid magnetic particle driven micromixer, Wang et al. (2007)
    TitleA rapid magnetic particle driven micromixer
    Authors Wang, Zhe, Chung, Dutta
    PublicationMicrofluidics and Nanofluidics
    AbstractPerformances of a magnetic particle driven micromixer are predicted numerically. This micromixer takes advantages of mixing enhancements induced by alternating actuation of magnetic particles suspended in the fluid. Effects of magnetic actuation force, switching frequency and channel’s lateral dimension have been investigated. Numerical results show that the magnetic particle actuation at an appropriate frequency causes effective mixing and the optimum switching frequency depends on the channel’s lateral dimension and the applied magnetic force. The maximum efficiency is obtained at a relatively high operating frequency for large magnetic actuation forces and narrow microchannels. If the magnetic particles are actuated with a much higher or lower frequency than the optimum switching frequency, they tend to add limited agitation to the fluid flow and do not enhance the mixing significantly. The optimum switching frequency obtained from the present numerical prediction is in good agreement with the theoretical analysis. The proposed mixing scheme not only provides an excellent mixing, even in simple microchannel, but also can be easily applied to lab-on-a-chip applications with a pair of external electromagnets.
  • A review of micropumps, D. J. Laser et al. (2004)
    TitleA review of micropumps
    AuthorsD. J. Laser, J. G. Santiago
    PublicationJournal of Micromechanics and Microengineering
    AbstractWe survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.
  • A review of microvalves, Kwang W. Oh et al. (2006)
    TitleA review of microvalves
    AuthorsKwang W. Oh, Chong H. Ahn
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis review gives a brief overview of microvalves, and focuses on the actuation mechanisms and their applications. One of the stumbling blocks for successful miniaturization and commercialization of fully integrated microfluidic systems was the development of reliable microvalves. Applications of the microvalves include flow regulation, on/off switching and sealing of liquids, gases or vacuums. Microvalves have been developed in the form of active or passive microvalves employing mechanical, non-mechanical and external systems. Even though great progress has been made during the last 20 years, there is plenty of room for further improving the performance of existing microvalves.
  • A review of passive and active mixing systems in microfluidic devices, James Green et al. (2007)
    TitleA review of passive and active mixing systems in microfluidic devices
    AuthorsJames Green, Arne E Holdo, Aman Khan
    PublicationThe International Journal of Multiphysics
    AbstractA review of mixing elements and devices for microscale fluidic devices is presented. The application, principles and characterisation of these devices is discussed, and the classifications based on these factors highlighted. A review of published works relating both experimental and simulation profiling of both passive and active mixing systems is presented. Each mixing principle upon which a design is based is discussed with regard to the fundamental physics that governs fluid behaviour. Passive systems covered include multi-lamination, split/recombination, chaotic advection, jet based, recirculation and droplet internal convection. Active systems covered include longitudinal and transverse pulsing, micro-stirrers, electro-kinetic methods, and acoustic/ultrasonic excitation. The review shows that the majority of devices have been designed within the past five years. Furthermore, at present, devices based on the multi-laminate method appear to outperform most other systems.
  • A review of some current research in microelectromechanical systems (MEMS) with defence applications, A. White (2006)
    TitleA review of some current research in microelectromechanical systems (MEMS) with defence applications
    Author A. White
    AbstractThis reviews reviews some research in microelectromechanical systems (MEMS) published during the period 1999-2000. Research in defence applications of MEMS or MEMS research with potential applications for the Australian Defence Organisation are also discussed.
  • A Robust Low-Cost PDMS Peristaltic Micropump With Magnetic Drive, E. Kai et al. (2004)
    TitleA Robust Low-Cost PDMS Peristaltic Micropump With Magnetic Drive
    Authors E. Kai, T. Pan, B. Ziaie
    PublisherUniversity of Minnesota
    AbstractIn this paper, we present a low-cost PDMS peristaltic micropump with magnetic drive. The fabrication process is based on soft molding and bonding of three PDMS layers. A base layer incorporates the microchannels while a middle actuating layer houses three miniature permanent magnets covered by a top flat layer. A small DC motor (6mm in diameter and 15mm in length) with three permanent magnets (NdFeB) stagger-mounted on its shaft is used to pull down and actuate the membrane-mounted magnets. A maximum flow rate of about 24 muL/min at the speed of 4000rpm with power consumption of 14mW was demonstrated.
  • Arrayed pH-responsive microvalves controlled by multiphase laminar flow, Chenwei Liu et al. (2007)
    TitleArrayed pH-responsive microvalves controlled by multiphase laminar flow
    AuthorsChenwei Liu, Joong Yull Park, Yugong Xu, SangHoon Lee
    PublicationJournal of Micromechanics and Microengineering
    AbstractIn chemical and biological assays, the synchronized control of multiple valves is very important. Currently there is no control scheme for the use of a large number of valves without adopting bulky peripheral control devices such as pumps or electrical equipment. Therefore, we propose a simple pH-responsive microvalve array system and a new multiplexing technology that, through its reliance on multiphase laminar flow, facilitates the operation of arrayed multiple microvalves. For the fabrication of the microvalve arrays, we have used pH-responsive hydrogel microspheres produced by a microfluidic chip. By incorporating these microspheres inside an arrayed microvalve polydimethylsiloxane (PDMS) platform, we produced pH-responsive arrayed microvalves with 'open' and 'close' operations carried out by the multiphase laminar streams of pH solutions. The constructed arrayed microvalves were adequately controlled by the multiphase pH buffer; the pressure of the pH-buffer solutions controlled the widths of the sample flow. Based on the simplicity and reliability of the operating principles, this new arrayed-valve system will decrease the need for complicated peripheral lines and will remove the need for many solenoid valves, which are currently used for the individual control of arrayed valves.
  • Artificial cilia for active micro-fluidic mixing, Jaap den Toonder et al. (2008)
    TitleArtificial cilia for active micro-fluidic mixing
    AuthorsJaap den Toonder, Femke Bos, Dick Broer, Laura Filippini, Murray Gillies, Judith de Goede, Titie Mol, Mireille Reijme, Wim Talen, Hans Wilderbeek, Vinayak Khatavkar, Patrick Anderson
    PublicationLab on a Chip
    DateApril 2008
    AbstractIn lab-on-chip devices, on which complete (bio-)chemical analysis laboratories are miniaturized and integrated, it is essential to manipulate fluids in sub-millimetre channels and sub-microlitre chambers. A special challenge in these small micro-fluidic systems is to create good mixing flows, since it is almost impossible to generate turbulence. We propose an active micro-fluidic mixing concept inspired by nature, namely by micro-organisms that swim through a liquid by oscillating microscopic hairs, cilia, that cover their surface. We have fabricated artificial cilia consisting of electro-statically actuated polymer structures, and have integrated these in a micro-fluidic channel. Flow visualization experiments show that the cilia can generate substantial fluid velocities, up to 0.6 mm s-1. In addition, very efficient mixing is obtained using specially designed geometrical cilia configurations in a micro-channel. Since the artificial cilia can be actively controlled using electrical signals, they have exciting applications in micro-fluidic devices.
  • A single layer negative tone lift-off photo resist for patterning a magnetron sputtered Ti/Pt/Au contact system and for solder bumps, A. Voigt et al. (2005)
    TitleA single layer negative tone lift-off photo resist for patterning a magnetron sputtered Ti/Pt/Au contact system and for solder bumps
    AuthorsA. Voigt, M. Heinrich, K. Hauck, R. Mientus, G. Gruetzner, M. T�pper, O. Ehrmann
    PublicationMicroelectronic Engineering
    DateMarch 2005
    AbstractIn this paper, we present the suitability of easy to handle negative tone photoresists providing examples of lift-off applications. The lithographic process of this single layer resist system requires standard broadband or i-line process conditions. At first, the capability to obtain an undercut pattern and the thermal stability of the resist ma-N 1400 is demonstrated in the lift-off patterning of magnetron sputtered thin three layer contact system Ti/Pt/Au. Temperature of the substrate during sputtering was measured time-resolved using a thermal couple. Secondly, an example to achieve AuSn solder bumps of 7.5�[mu]m diameter by a combination of sputtering and metal evaporation using the lift-off resist ma-N 400 is given. Regarding the further miniaturization of electronic devices, this process is a cost-effective method to achieve solder depots for flip chip bonding of ultra thin chips.
  • A split and recombination micromixer fabricated in a PDMS three-dimensional structure, Seok Woo Lee et al. (2006)
    TitleA split and recombination micromixer fabricated in a PDMS three-dimensional structure
    AuthorsSeok Woo Lee, Dong Sung Kim, Seung S. Lee, Tai Hun Kwon
    PublicationJournal of Micromechanics and Microengineering
    AbstractIn this paper we propose a new split and recombination (SAR) micromixer that is compatible with the microfabrication process of polydimethylsiloxane (PDMS). We evaluate the mixing efficiency of the fabricated SAR micromixer and find that it increases interfaces exponentially. Simulation using CFD-ACE+ shows a cross-sectional view of the flow and estimates the mixing efficiency of the SAR micromixer and the pressure drop for a unit of the SAR micromixer. A mixing experiment involving phenolphthalein and NaOH solutions shows that interfaces, represented as red lines, are increased by SAR mixing. The result of our mixing experiment involving blue dye and water is evaluated to determine the mixing efficiency by calculating the standard deviation (stdev) of the pixel intensity of the observed image. After the seventh unit of the SAR micromixer, solutions are mixed to 90% at Re 0.6. The number of units needed to reach a mixed state in which the stdev is lower than 0.05, a 90% mixed state, increases from 5 to 10 for a flow rate ranging from 0.1 µ min[?]1 (Re 0.012) to 1000 µ min[?]1 (Re 120) including numerical analysis results. The pressure drop increases proportionally from 2.8 Pa to 35 000 Pa when the flow rate increases from 0.1 µ min[?]1 (Re 0.012) to 1000 µ min[?]1 (Re 120) in the numerical analysis results.
  • Assembly of Phase Transferred Nickel Nanoparticles at AirWater Interface Using Langmuir-Blodgett Technique, Tanushree Bala et al. (2006)
    TitleAssembly of Phase Transferred Nickel Nanoparticles at AirWater Interface Using Langmuir-Blodgett Technique
    AuthorsTanushree Bala, Bhagyashree Joshi, Neelima Iyer, Murali Sastry, B. L.V Prasad
    PublicationJournal of Nanoscience and Nanotechnology
    DateDecember 2006
    AbstractDevelopment of simple and efficient protocol for the synthesis of Ni nanoparticles in aqueous media and their subsequent phase transfer to organic media is reported. The synthesis of nickel nanoparticles in aqueous medium is accomplished by reducing the nickel nitrate with sodium borohydride in presence of oleic acid. It results in the formation of nickel nanoparticles capped with oleic acid. The pristine oleic acid capped nickel nanoparticles were then phase transferred to nonpolar solvents such as toluene using stearic acid. The phase transfer was effective probably due to the space exchange between the oleic acid moiety and stearic acid molecules. The hydrophobized Ni thus obtained was organized at the air-water interface and it was observed that by controlling the pressure and concentration of hydrophobized Ni nanoparticles at air-water interface, linear ribbon like assemblies could be obtained. The organization process was followed by surface pressure-area isotherm measurement and Brewster Angle Microscopy.
  • A thermomechanical model for adhesion reduction of MEMS cantilevers, J.W. Rogers et al. (2002)
    TitleA thermomechanical model for adhesion reduction of MEMS cantilevers
    AuthorsJ.W. Rogers, T.J. Mackin, L.M. Phinney
    PublicationJournal of Microelectromechanical Systems
    DateOct. 2002
    AbstractPresents a thermomechanical model that describes adhesion reduction in MEMS structures using laser heating. A fracture mechanics model is developed where the interface between the stiction-failed microcantilever and the substrate is treated as a crack, and the energy release rate is calculated using elastic theory. In order to include the effect of a temperature difference between the microcantilever and the substrate, an associated thermal strain energy is included in the fracture model. If the free length is longer than the critical buckling length, the beam buckles decreasing the strain energy of the system. For surface-micromachined polycrystalline silicon cantilevers with an initial crack length of 400 /spl mu/m, the model predicts that a temperature difference of 100 K repairs microcantilevers as long as 1300 /spl mu/m. The peeling of adhered beams from the substrate after laser irradiation is experimentally shown with measured crack lengths within 15% of predicted values indicating that the proposed model establishes the mechanism of adhesion reduction by laser irradiation.
  • A three-dimensional microfabrication system for biodegradable polymers with high resolution and biocompatibility, Akira Yamada et al. (2008)
    TitleA three-dimensional microfabrication system for biodegradable polymers with high resolution and biocompatibility
    AuthorsAkira Yamada, Fuminori Niikura, Koji Ikuta
    PublicationJournal of Micromechanics and Microengineering
    AbstractBiodegradable polylactide polymers are already widely used in medicine. While further applications are eagerly awaited, progress has been impeded by a lack of appropriate processing methods. Our group attempted to construct a novel three-dimensional microfabrication system for the free processing of three-dimensional micro-level forms. The system processed the polymers with extremely high precision using a fine nozzle. An evaluation of one of the piled-up layers of the extruded lines revealed lateral and depth resolutions of 40 µm and 45 µm, respectively. Micro-pipes, micro-bends and micro-coil springs were fabricated in less than 15 min by stacking up melted polymers from a nozzle. A batch process was adopted for the supply of the materials in order to eliminate the use of toxic solvents, one of the necessary evils with earlier fabrication techniques. Microstructures fabricated by our system and by a conventional method were tested in tensile strength tests to compare the mechanical strengths. The biocompatibility of a newly fabricated structure was tested by cultivating a cell line (PC12) in a small poly(lactic acid) (PLA) vessel with a transparent base, then comparing the morphology and growth with those of the same PC12 line cultivated by a standard vessel.
  • Atomically thin magnetic microstructures , C. Stamm (2000)
    TitleAtomically thin magnetic microstructures
    AuthorC. Stamm
    AbstractIn this thesis the magnetic properties of atomically thin microstructures are investigated. By drastically decreasing the size of a ferromagnet along one space dimension a two-dimensional particle results, which exhibits new magnetic behaviour. Domains in ferromagnetic bodies are the result of two competing interactions. The magnetostatic self-energy is reduced by the formation of magnetic domains with opposite magnetization. On the other hand exchange and anisotropy energy increase with each additional domain wall. The reason why in three-dimensional ferromagnets domains occur is that the agnetostatic energy is a volume energy, whereas the wall energy is a surface energy. Therefore, only small magnets are expected to be in a single-domain state. This is not necessarily true for two-dimensional magnets, where two different situations must be considered. In the first case, the magnetization is oriented parallel to the film plane. The physical systems investigated in this thesis are Co on a Cu(001) surface and Fe on a W(110) surface. The main result for in-plane magnetized structures is that they do not exhibit domains, irrespective of their size and shape. The smallest particle with rema- nent magnetization at room temperature was 130nm wide and 2 atomic layers thick. The shape anisotropy of stripes with in-plane aspect ratio R = 80 is negligible compared to the crystalline anisotropy. The mutual interaction between atomically thin magnets is too small to determine the magnetic configuration. In the second case, the magnetization stands perpendicular to the film plane, real- ized in this work by a few layers of Fe on Cu(001). Continuous films exhibit a striped domain configuration with local orientational order. When confining its lat- eral size on the micron scale a transition becomes visible, where magnetic particles below a critical size become single-domain. The phase transition of a perpendicular magnetized thin film to the paramagnetic state is found to happen in two steps, which is reminiscent of a two-dimensional melting process.
  • Atomic force microscope based nanofabrication of master pattern molds for use in soft lithography, Matthew S. Johannes et al. (2007)
    TitleAtomic force microscope based nanofabrication of master pattern molds for use in soft lithography
    AuthorsMatthew S. Johannes, Daniel G. Cole, Robert L. Clark
    PublicationApplied Physics Letters
    AbstractThe authors have developed a technique that couples nanolithographic patterning using an atomic force microscope with the parallel patterning abilities of soft lithography. Master pattern generation is accomplished using local anodic oxidation as a mask pattern for anisotropic wet etching of Si(110). The resulting nanostructures are then used as master patterns for the molding of polymeric stamps to be used for microcontact printing of alkanethiols. Analysis of the resulting patterns demonstrates the validity of this method as a simple, effective, and low cost alternative to conduct and prototype nanoscale patterning in a parallel fashion.
  • Automated chip-based device for simple and fast nucleic acid amplification, Gotz Munchow et al. (2005)
    TitleAutomated chip-based device for simple and fast nucleic acid amplification
    Authors Gotz Munchow, Dalibor Dadic, Frank Doffing, Steffen Hardt, Klaus-Stefan Drese
    PublicationExpert Review of Molecular Diagnostics
    DateJuly 2005
    AbstractA chip-based PCR device is presented that is capable of rapid temperature ramping and handling sample volumes in the microliter range. The PCR chip comprises a microchannel thermally connected to three temperature zones. Inside this microchannel, the PCR sample plug is driven and precisely positioned by a ferrofluidic actuator for more than 40cycles within 5 min. Computer simulations predict that the sample plugs are thermally equilibrated on a time scale of some 10ms when transported to a different temperature zone. Hence, the thermal limitations on the cycle speed of the system are considerably reduced compared with conventional cyclers. The system was developed on a modular platform suitable for handling further microfluidic tasks such as DNA extraction and preparation of the PCR mix. Thus, the aspired chip-based platform represents not only a PCR system but a complete analysis system, from the injection of a patient’s blood sample to its final appraisal.
  • A versatile surface channel concept for microfluidic applications, M. Dijkstra et al. (2007)
    TitleA versatile surface channel concept for microfluidic applications
    AuthorsM. Dijkstra, M. J. de Boer, J. W. Berenschot, T. S. J. Lammerink, R. J. Wiegerink, M. Elwenspoek
    PublicationJournal of Micromechanics and Microengineering
    AbstractMEMS fluidic devices often require the integration of transducer structures with freely suspended microchannels. In this paper a versatile microchannel fabrication concept is presented, allowing for easy fluidic interfacing and integration of transducer structures in close proximity to the fluid. This is achieved by the reliable fabrication of completely sealed microchannels directly below the substrate surface. The resulting planar substrate surface allows for the deposition of transducer material and pattern transfer by lithography. The microchannels are subsequently released and fluidic entrance holes are created, while the transducer structures can be protected by photoresist. Several monolithic microfluidic device structures have been fabricated, demonstrating the versatility of the concept. Fabricated surface microchannel devices can optionally be vacuum sealed by anodic bonding.
  • A virtual hair cell: I. Addition of gating spring theory into a 3-D bundle mechanical model, Jong-Hoon Nam et al. (2007)
    TitleA virtual hair cell: I. Addition of gating spring theory into a 3-D bundle mechanical model
    AuthorsJong-Hoon Nam, John R. Cotton, Wally Grant
    PublicationBiophysical Journal
    DateJanuary 5, 2007
    AbstractWe have developed a virtual hair cell that simulates hair cell mechano-electrical transduction (MET) in the turtle utricle. This study combines a full 3-D hair bundle mechanical model with a gating spring theory. Previous mathematical models represent the hair bundle with a single degree of freedom system which, we have argued, cannot fully explain hair bundle mechanics. In our computer model, the tip link tension and fast adaptation modulator kinetics determine the opening and closing of each channel independently. We observed the response of individual transduction channels with our presented model. The simulated results showed three features of hair cells in vitro: First, a transient rebound of the bundle tip appeared when fast adaptation dominated the dynamics. Second, the dynamic stiffness of the bundle was minimized when the response-displacement (I-X) curve was steepest. Third, the hair cell showed "polarity", i.e. activation decreased from a peak to zero as the forcing direction rotated from the excitatory to inhibitory direction.
  • Bio-inspired electric cilia development for biomedical applications: use of ionic electro-active polymer, nanowire arrays, and micro-stereo-lithography, Hargsoon Yoon et al. (2007)
    TitleBio-inspired electric cilia development for biomedical applications: use of ionic electro-active polymer, nanowire arrays, and micro-stereo-lithography
    AuthorsHargsoon Yoon, Vasuda Ramachandran, Devesh C. Deshpande, Vijay K. Varadan
    DateApril 06, 2007
    Proceedings TitleNanosensors, Microsensors, and Biosensors and Systems 2007
    Conference NameNanosensors, Microsensors, and Biosensors and Systems 2007
    PlaceSan Diego, California, USA
  • Biological cell detection using ferromagnetic microbeads, T. Mitrelias et al. (2007)
    TitleBiological cell detection using ferromagnetic microbeads
    AuthorsT. Mitrelias, J. Palfreyman, Z. Jiang, J. Llandro, J.A.C. Bland, R.M. Sanchez-Martin, M. Bradley
    PublicationJournal of Magnetism and Magnetic Materials
    Issue2, Part 3
    DateMarch 2007
    AbstractThe successful capture of different sized fluorescently labeled ferromagnetic microbeads by different cell lines is reported here. The cells have subsequently been analyzed by flow cytometry and the degree of uptake was found to be dependent on the bead size/concentration and the incubation time. In contrast to previous studies where superparamagnetic beads had mainly been used, we show that ferromagnetic beads, which have two orders of magnitude higher magnetic moments, can be successfully incubated with biological cells. The design of a "Y"-shaped microfluidic device that was successfully used to hydrodynamically focus and sort the fluorescent beads is also presented here.
  • Biomimetic Autoseparation of Leukocytes from Whole Blood in a Microfluidic Device, S.S. Shevkoplyas et al. (2005)
    TitleBiomimetic Autoseparation of Leukocytes from Whole Blood in a Microfluidic Device
    AuthorsS.S. Shevkoplyas, T. Yoshida, L.L. Munn, M.W. Bitensky
    PublicationAnalytical Chemistry
    DateFebruary 1, 2005
    AbstractLeukocytes comprise less than 1% of all blood cells. Enrichment of their number, starting from a sample of whole blood, is the required first step of many clinical and basic research assays. We created a microfluidic device that takes advantage of the intrinsic features of blood flow in the microcirculation, such as plasma skimming and leukocyte margination, to separate leukocytes directly from whole blood. It consists of a simple network of rectangular microchannels designed to enhance lateral migration of leukocytes and their subsequent extraction from the erythrocyte-depleted region near the sidewalls. A single pass through the device produces a 34-fold enrichment of the leukocyte-to-erythrocyte ratio. It operates on microliter samples of whole blood, provides positive, continuous flow selection of leukocytes, and requires neither preliminary labeling of cells nor input of energy (except for a small pressure gradient to support the flow of blood). This effortless, efficient, and inexpensive technology can be used as a lab-on-a-chip component for initial whole blood sample preparation. Its integration into microanalytical devices that require leukocyte enrichment will enable accelerated transition of these devices into the field for point-of-care clinical testing.
    DOI10.1021/ac049037i S0003-2700(04)09037-7
  • Cantilevered actuator using magnetostricitive thin film, Kazushi Ishiyama et al. (2008)
    TitleCantilevered actuator using magnetostricitive thin film
    AuthorsKazushi Ishiyama, Chikako Yokota
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    DateApril 2008
  • Chaotic Mixer for Microchannels, Abraham D. Stroock et al. (2002)
    TitleChaotic Mixer for Microchannels
    AuthorsAbraham D. Stroock, Stephan K. W. Dertinger, Armand Ajdari, Igor Mezic, Howard A. Stone, George M. Whitesides
    DateJanuary 25, 2002
  • Chaotic mixing using periodic and aperiodic sequences of mixing protocols in a micromixer, Kang et al. (2007)
    TitleChaotic mixing using periodic and aperiodic sequences of mixing protocols in a micromixer
    Authors Kang, Singh, Kwon, Anderson
    PublicationMicrofluidics and Nanofluidics
    DateAugust 2007
    AbstractWe conducted a numerical study on mixing in a barrier embedded micromixer with an emphasis on the effect of periodic and aperiodic sequences of mixing protocols on mixing performance. A mapping method was employed to investigate mixing in various sequences, enabling us to qualitatively observe the progress of mixing and also to quantify both the rate and the final state of mixing. First, we introduce the design concept of the four mixing protocols and the route to achieve chaotic mixing of the mixer. Then, several periodic sequences consisting of the four mixing protocols are used to investigate the mixing performance depending on the sequence. Chaotic mixing was observed, but with different mixing rates and different final mixing states significantly influenced by the specific sequence of mixing protocols and inertia. As for the effect of inertia, the higher the Reynolds number the larger the rotational motion of the fluid leading to faster mixing. We found that a sequence showing the best mixing performance at a certain Reynolds number is not always superior to other sequences in a different Reynolds number regime. A properly chosen aperiodic sequence results in faster and more uniform mixing than periodic sequences.
  • Characterization of laterally deformable elastomer membranes for microfluidics, S. J. Lee et al. (2007)
    TitleCharacterization of laterally deformable elastomer membranes for microfluidics
    AuthorsS. J. Lee, J. C.-Y. Chan, K. J. Maung, E. Rezler, N. Sundararajan
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis work presents experimental characterization and numerical modeling of laterally deflecting polydimethylsiloxane (PDMS) membranes under pneumatic actuation. The device for this study is a membrane valve seat that partially closes a perpendicular fluid microchannel, fabricated using single-layer soft lithography. Membranes with thickness between 8 and 14 µm have been experimentally tested up to 207 kPa, and maximum lateral displacement beyond 20 µm has been demonstrated. Investigation of geometric parameters by factorial design shows that the height of the membrane is more dominant than the width and thickness, and this is attributed to the zero-displacement boundary condition at the foot of the membrane where it is bonded to a flat substrate. A numerical model that incorporates hyperelastic material testing data shows close agreement with the deflection behavior of experimental samples, accurately predicting that a membrane of 10 µm thick, 100 µm wide and 45 µm tall deflects approximately 13 µm at 207 kPa. Simulation further shows that sidewall effects from bulk compression of the elastomer material in the actuation cavity have a significant effect, reducing maximum displacement by as much as 15% over predictions based on deformation that is limited strictly to the membrane only. Experimental yield, SEM imaging and stress simulations emphasize that the membrane foot region requires the greatest attention in terms of process development.
  • Characterization of Polydimethylsiloxane (PDMS) Properties for Biomedical Micro/Nanosystems, Mata et al. (2005)
    TitleCharacterization of Polydimethylsiloxane (PDMS) Properties for Biomedical Micro/Nanosystems
    Authors Mata, Fleischman, Roy
    PublicationBiomedical Microdevices
    DateDecember 08, 2005
    AbstractPolydimethylsiloxane (PDMS Sylgard 184, Dow Corning Corporation) pre-polymer was combined with increasing amounts of cross-linker (5.7, 10.0, 14.3, 21.4, and 42.9 wt.%) and designated PDMS1, PDMS2, PDMS3, PDMS4, and PDMS5, respectively. These materials were processed by spin coating and subjected to common microfabrication, micromachining, and biomedical processes: chemical immersion, oxygen plasma treatment, sterilization, and exposure to tissue culture media. The PDMS formulations were analyzed by gravimetry, goniometry, tensile testing, nanoindentation, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Spin coating of PDMS was formulation dependent with film thickness ranging from 308 μm on PDMS1 to 171 μm on PDMS5 at 200 revolutions per minute (rpm). Ultimate tensile stress (UTS) increased from 3.9 MPa (PDMS1) to 10.8 MPa (PDMS3), and then decreased down to 4.0 MPa (PDMS5). Autoclave sterilization (AS) increased the storage modulus (σ) and UTS in all formulations, with the highest increase in UTS exhibited by PDMS5 (218%). PDMS surface hydrophilicity and micro-textures were generally unaffected when exposed to the different chemicals, except for micro-texture changes after immersion in potassium hydroxide and buffered hydrofluoric, nitric, sulfuric, and hydrofluoric acids; and minimal changes in contact angle after immersion in hexane, hydrochloric acid, photoresist developer, and toluene. Oxygen plasma treatment decreased the contact angle of PDMS2 from 109∘ to 60∘. Exposure to tissue culture media resulted in increased PDMS surface element concentrations of nitrogen and oxygen.
  • Characterization of poly(isobornyl acrylate) as a construction material for microfluidic applications, M. d.C López-García et al. (2007)
    TitleCharacterization of poly(isobornyl acrylate) as a construction material for microfluidic applications
    AuthorsM. d.C López-García, D. J Beebe, W. C Crone
    PublicationJournal of Applied Polymer Science
    AbstractIsobornyl acrylate (IBA) is a photopolymerizable monomer that is employed in microfluidic devices because of desirable properties, such as inertness, transparency, and resolution. However, some of the mechanical properties of poly(isobornyl acrylate) are greatly affected by subtle changes in the manufacturing techniques. In this study, the parameters of exposure time, UV intensity, and aging are varied to study their effect on the material properties of thin samples of isobornyl acrylate construction material (&lt;0.25 mm). Mechanical testing was used to obtain properties, such as elasticity, maximum strength, and maximum strain. It was observed that when using high levels of both exposure time and intensity, the polymers strength was increased. Lowering one of these two parameters immediately reduced the construction materials strength. It was also noted that aging weakens the material in as little as 1 day. In addition, an anisotropic response that produces curling in samples has been studied. It showed to have a negligible effect on the mechanical properties of the material; however it may have a major effect on device quality and shelf-life. \textcopyright 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
  • Cilia and Flagella: Structure and Movement (Chapter 19.4), Harvey Lodish et al. (2000)
    TitleCilia and Flagella: Structure and Movement (Chapter 19.4)
    AuthorsHarvey Lodish, Arnold Berk, Lawrence S. Zipursky, Paul Matsudaira, David Baltimore, James Darnell
    PlaceNew York
    PublisherW.H. Freeman and Company
  • Cofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane), Adam C. Siegel et al. (2006)
    TitleCofabrication of Electromagnets and Microfluidic Systems in Poly(dimethylsiloxane)
    AuthorsAdam C. Siegel, Sergey S. Shevkoplyas, Douglas B. Weibel, Derek A. Bruzewicz, Andres W. Martinez, George M. Whitesides
    PublicationAngewandte Chemie International Edition
  • Comparison between various hysteresis models and experimental data , F. Ossart et al. (1990)
    TitleComparison between various hysteresis models and experimental data
    AuthorsF. Ossart, F. Ossart, G. Meunier
    PublicationMagnetics, IEEE Transactions on
    AbstractThe authors present a comparison between results predicted by four mathematical models of hysteresis and experimental data measured on a CoNiCr alloy for longitudinal recording. Two of those models are simple analytical formulas and can be used in a first approach to the phenomena, but are deficient in terms of modeling the behavior of minor loops. The other two models are more sophisticated. The first assumes a differential equation between B and H, while the other is derived from the Preisach model. The authors present results showing that, for the material studied, the last model gives the best fitting to experimental data
  • Complete UV emission of ZnO nanoparticles in a PMMA matrix, Xi-Wen Du et al. (2006)
    TitleComplete UV emission of ZnO nanoparticles in a PMMA matrix
    AuthorsXi-Wen Du, Ying-Song Fu, Jing Sun, Xue Han, Jim Liu
    PublicationSemiconductor Science and Technology
    AbstractPreparation and photoluminescence (PL) properties of zinc oxide (ZnO) nanoparticles embedded in a lipophilic polymethyl methacrylate (PMMA) matrix are reported in detail with an unbalanced sol-gel route. A high-resolution transmission electron microscope (HRTEM) indicates that ZnO particles are highly crystallized, with a size of 5-6 nm and hexagonal wurtzite structure. During the sol-gel reaction, partial ester groups of R-COOCH3 in PMMA are hydrolyzed to form carboxylic ion groups, which chemisorb on the surface of ZnO nanoparticles to eliminate the defects; thus ZnO nanoparticles in the PMMA matrix exhibit complete ultraviolet (UV) emissions, while emissions in the visible region are fully quenched.
  • Composite elastic magnet films with hard magnetic feature, Weisong Wang et al. (2004)
    TitleComposite elastic magnet films with hard magnetic feature
    AuthorsWeisong Wang, Zhongmei Yao, Jackie C. Chen, Ji Fang
    PublicationJournal of Micromechanics and Microengineering
    AbstractHard magnetic materials with high remnant magnetic moment, Mr, have unique advantages that can achieve bi-directional (push-pull) movement in an external magnetic field. This paper presents the results on the fabrication and testing of novel composite elastic permanent magnet films. The microsize hard barium ferrite powder, NdFeB powder, and different silicone elastomers have been used to fabricate various large elongation hard magnetic films. Three different fabrication methods, screen-coating processing, moulding processing and squeegee-coating processing, have been investigated, and the squeegee-coating process was proven to be the most successful method. The uniform composite elastic permanent magnet films range from 40 µm to 216 µm in thickness have been successfully fabricated. These films were then magnetized in the thickness direction after fabrication. They exhibited permanent magnet behaviour; for instance, the film (0.640 mm3 in volume) made of polydimethyl siloxane (PDMS) and hard barium ferrite powders is measured to give a coercive force, Hc, of 3.24 × 105 A m[?]1 and Mr of 1.023 × 10[?]5 A m2, and the film (0.504 mm3 in volume) made of PDMS and NdFeB powders gives 1.55 × 105 A m[?]1 Hc and 8.081 × 10[?]5 A m2 Mr. These composite elastic permanent magnet films' mechanical properties, like Young's modulus and deflection force, have been evaluated. To validate the films' Young's modulus, a finite-element computer simulation (ANSYS®) is used and one film is chosen whose Young's modulus (16.60 MPa) is confirmed by the simulation results with ANSYS®. The large elongation composite elastic permanent magnet film provides an excellent diaphragm material, which plays an important role in the micropump or valve. The movement of the 126 µm thick film with 4.5 mm diameter made of PDMS and NdFeB powders has been tested in a 0.21 Tesla external magnetic field. It was proven to have large deflection of 125 µm.
  • Concepts for the incorporation of inorganic building blocks into organic polymers on a nanoscale, Guido Kickelbick (2003)
    TitleConcepts for the incorporation of inorganic building blocks into organic polymers on a nanoscale
    AuthorGuido Kickelbick
    PublicationProgress in Polymer Science
    DateJanuary 2003
    AbstractHybrid inorganic-organic materials are promising systems for a variety of applications due to their extraordinary properties based on the combination of the different building blocks. The combination of nanoscale inorganic moieties with organic polymers has a high potential for future applications and has therefore attracted a lot of attention during the last years. Since there are countless different combinations of the two moieties, there are also a large number of methodologies to combine them in one material. This review is written with the intention to give an overview of principal concepts of the preparation of such materials for different applications. It focuses on the chemical aspects of the incorporation of inorganic building blocks such as silica networks, porous materials, metals, etc. into an organic polymeric matrix.
  • Connection between microstructure and magnetic properties of soft magnetic materials, G. Bertotti (2008)
    TitleConnection between microstructure and magnetic properties of soft magnetic materials
    AuthorG. Bertotti
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    Date7 April 2008
    AbstractThe magnetic behavior of soft magnetic materials is discussed with some emphasis on the connection between macroscopic properties and underlying micromagnetic energy aspects. It is shown that important conceptual gaps still exist in the interpretation of macroscopic magnetic properties in terms of the micromagnetic formulation. Different aspects of hysteresis modeling, power loss prediction and magnetic non-destructive evaluation are discussed in this perspective.
  • Construction and actuation of microscopic superparamagnetic polymer slabs (confidential), M.W.P.E. Lamers (2006)
    TitleConstruction and actuation of microscopic superparamagnetic polymer slabs (confidential)
    AuthorM.W.P.E. Lamers
    DateMay 19, 2006
    AbstractIn recent years the concept of a ‘lab-on-a-chip’ has been proposed for e.g. analyzing proteins. For efficient operation on a microscale level several functions are required, like transport and mixing of fluids. Mixing can be achieved with the use of a microactuator. This research is focussed on the design and realization of such an actuator. The proposed actuator is a microscopic polymer slab with a high aspect ratio. These slabs can be made using ion beam lithography. The suitability of poly(butyl methacrylate) PBMA for ion beam lithography has been investigated, as this polymer has not been used for this purpose before. In the PBMA slab superparamagnetic particles are embedded upon which a magnetic force can act that causes deflection. The magnetic force arises from the gradient in the mag- netic field, caused by a current in a wire in the substrate positioned above the slab, and the magnetization of the slab. The achieved deflection is maximal if the force is maximal at the tip of the slab and depends significantly on the storage elastic modulus of the slab. Experiments have been performed to determine the storage elastic modulus of PBMA and the parameters that determine this. Also experiments have been performed to determine the magnetization. Experiments show that the storage elastic modulus of PBMA starts to decrease rapidly at temperatures above 33 ± 5 . The storage elastic modulus decreases significantly if the frequency with which the slabs are actuated decreases. A decrease in the applied frequency from 10 to 1 Hz results in a decrease in the modulus from 131 to 34 Hz for T = 37 . In addition, the Payne effect reduces the storage elastic modulus with a factor up to two. Experiments indicate that the magnetization increases significantly due to a distribution in the particle size and dipole-dipole interactions. Calculations show that an aspect ratio of 40 is required to obtain an angle of deflection of 3–5° for a current of 100 mA. Slabs are produced using a fluence between 3.35 and 17·106 H+ .μm−2 using IPA:ethanol = 1:3 as a developer. Reproducibility has shown to present problems, which is probably due to the temperature dependence of the dissolution rate of the developer in PBMA. Preliminary investigations have been performed to determine if ion beam lithography is possible in polymer films with magnetite particles. Ion beam lithography in poly(methyl methacrylate) (PMMA) with magnetite particles is shown to be successful, though a new developer is required to remove the irradiated PMMA completely.
  • Construction of individual addressable PDMS slabs for microfluidic mixing, Maarten Hermans (2007)
    TitleConstruction of individual addressable PDMS slabs for microfluidic mixing
    AuthorMaarten Hermans
    DateAugust, 2007
    AbstractIn this report a method has been investigated to fabricate active mixing elements in a microfluidic system. Mixing is performed in this method by means of flexible, individual addressable PDMS slabs, containing dispersed superparamagnetic particles. These slabs are set into motion by placing them in a magnetic field gradient. The best way to disperse the magnetic particles in the PDMS is by first solving the magnetic particles together with the PDMS base in the solvent tetrahydrofuran (THF), letting the THF evaporate and finally add the PDMS curing agent. Up to a volume percentage magnetic content of 5 % is achieved in this report. As a result of the dispersed particles, the Young modulus of the magnetic PDMS decreases with an increase of the volume percentage of magnetic content. By making use of a double mould process, a method to fabricate a channel with slabs into PDMS with superparamagnetic particles dispersed in it is studied. The resulting slabs have dimensions about 13 mu x 70 mu and contain a volume percentage of magnetic content of 5 %. Finally, a first insight on the production and the properties of the current wires used to induce the magnetic field gradient is performed. Gold current wires with dimensions 15 mu x 300 nm are fabricated. The maximum current they can handle is about 200 mA.
  • Controlling magnetic ordering in coupled nanomagnet arrays, R. P. Cowburn et al. (1999)
    TitleControlling magnetic ordering in coupled nanomagnet arrays
    AuthorsR. P. Cowburn, A. O. Adeyeye, M. E. Welland
    PublicationNew Journal of Physics
    AbstractWe have fabricated using high-resolution electron beam lithography circular magnetic particles (nanomagnets) of diameter 60 nm and thickness 7 nm out of the common magnetic alloy supermalloy. The nanomagnets were arranged on rectangular lattices of different periods. A high-sensitivity magneto-optical method was used to measure the magnetic properties of each lattice. We show experimentally how the magnetic properties of a lattice of nanomagnets can be profoundly changed by the magnetostatic interactions between nanomagnets within the lattice. We find that simply reducing the lattice spacing in one direction from 180 nm down to 80 nm (leaving a gap of only 20 nm between edges) causes the lattice to change from a magnetically disordered state to an ordered state. The change in state is accompanied by a peak in the magnetic susceptibility. We show that this is analogous to the paramagnetic-ferromagnetic phase transition which occurs in conventional magnetic materials, although low-dimensionality and kinetic effects must also be considered.
  • Control of microfluidic systems: two examples, results, and challenges, M. Armani et al. (2005)
    TitleControl of microfluidic systems: two examples, results, and challenges
    AuthorsM. Armani, S. Chaudhary, R. Probst, S. Walker, B. Shapiro
    PublicationInternational Journal of Robust and Nonlinear Control
    AbstractThis paper describes results and challenges in feedback control of microfluidic systems. Results are provided for two representative examples: control of liquid droplets by electrically actuated surface tension forces and steering of many particles at once by micro flow control. Common themes and challenges are outlined based on the authors\textquoteright research programs and on the results of the March 2004 NSF workshop on ?Control and System Integration of Micro- and Nano-Scale Systems? organized by the author. Copyright ? 2005 John Wiley & Sons, Ltd.
  • CRC Handbook of Chemistry and Physics, Internet Version, (2007)
    TitleCRC Handbook of Chemistry and Physics, Internet Version
    PlaceBoca Raton, Fl, USA
    PublisherTaylor and Francis
  • Critical superparamagnetism, K. Stierstadt N. Steigenberger (1972)
    TitleCritical superparamagnetism
    AuthorK. Stierstadt N. Steigenberger
    PublicationPhysica Status Solidi (a)
    AbstractThe behaviour of a magnetic system, which becomes superparamagnetic at a blocking temperature inside its critical region, is called critical superparamagnetism. The system may consist either of small ferromagnetic particles in a non-ferromagnetic matrix, or likewise of a large crystal containing small regions with different Curie temperatures. The conditions for the existence of critical superparamagnetism are studied as functions of temperature, particle size, packing fraction, and anisotropy. The initial susceptibility of such a system depends in a characteristic manner on the measuring frequency. At a frequency corresponding to the reciprocal superparamagnetic relaxation time the susceptibility changes rather abruptly from its rotational to its superparamagnetic value. Numerical calculations are carried out for nickel showing the existence of critical superparamagnetism in this material. The susceptibility difference can reach several orders of magnitude under suitable conditions
  • Crucial Experiment Demonstrating Single Domain Property of Fine Ferromagnetic Powders, C. Kittel et al. (1950)
    TitleCrucial Experiment Demonstrating Single Domain Property of Fine Ferromagnetic Powders
    AuthorsC. Kittel, J. K. Galt, W. E. Campbell
    PublicationPhysical Review
    DateMarch 01, 1950
  • Current-induced magnetic vortex core switching in a Permalloy nanodisk, Y. Liu et al. (2007)
    TitleCurrent-induced magnetic vortex core switching in a Permalloy nanodisk
    AuthorsY. Liu, S. Gliga, R. Hertel, C. M. Schneider
    PublicationApplied Physics Letters
    AbstractThe authors report on the switching of a magnetic vortex core in a submicron Permalloy disk, induced by a short current pulse applied in the film plane. Micromagnetic simulations including the adiabatic and nonadiabatic spin-torque terms are used to investigate the current-driven magnetization dynamics. They predict that a core reversal can be triggered by current bursts a tenth of a nanosecond long. The vortex core reversal process is found to be the same as when an external field pulse is applied. The control of a vortex core's orientation using current pulses introduces the technologically relevant possibility to address individual nanomagnets within dense arrays.
  • Current induced switching of vortex polarity in magnetic nanodisks, Denis D. Sheka et al. (2007)
    TitleCurrent induced switching of vortex polarity in magnetic nanodisks
    AuthorsDenis D. Sheka, Yuri Gaididei, Franz G. Mertens
    PublicationApplied Physics Letters
    AbstractIt is shown that the vortex polarity can be irreversibly switched by injecting a spin-polarized direct electrical current, which flows perpendicular to the disk plane. Intensive numerical spin-lattice simulations demonstrate that the switching process involves a vortex-antivortex pair creation. This differs from magnets with no dipolar interaction, where the spin dc acts similar to a static magnetic field.
  • Das magnetische Einmündungsgesetz bei plastisch verformten Nickel- und Nickel-Kobalt-Einkristallen, Kronmüller (1959)
    TitleDas magnetische Einmündungsgesetz bei plastisch verformten Nickel- und Nickel-Kobalt-Einkristallen
    Author Kronmüller
    PublicationZeitschrift für Physik A Hadrons and Nuclei
    DateOctober 01, 1959
    AbstractZusammenfassung In der vorliegenden Arbeit wird der Einfluß einer plastischen Verformung auf die Einmündung in die ferromagnetische Sättigung experimentell untersucht. Ni-und NiCo-Einkristalle wurden bei Raumtemperatur und -183° C im Zugversuch plastisch verformt. Abweichend von dem Vorgehen früherer Autoren wurde zur Auswertung der magnetischen Messungen nicht die Feldstärkeabhängigkeit, sondern die Abhängigkeit von der plastischen Verformung benützt. Aus der Temperaturabhängigkeit der differentiellen Suszeptibilität ? ergibt sich, daß die Zunahme von ? mit wachsender Verformung der magnetostriktiven Wirkung der während der Verformung entstandenen Fehlstellen, insbesondere der Versetzungen, zuzuschreiben ist.
  • Demagnetizing factors for cylinders, D.-X. Chen et al. (1991)
    TitleDemagnetizing factors for cylinders
    AuthorsD.-X. Chen, J.A. Brug, R.B. Goldfarb
    PublicationIEEE Transactions on Magnetics
    AbstractFluxmetric (ballistic) and magnetometric demagnetizing factors Nf and Nm for cylinders as functions of susceptibility χ and the ratio γ of length to diameter have been evaluated. Using a one-dimensional model when γ&ges;10, Nf was calculated for -1&les;χ<∞ and Nm was calculated for χ→∞. Using a two-dimensional model when 0.01&les;γ&les;50, an important range for magnetometer measurements, Nm and Nf were calculated for -1&les;χ<∞. Demagnetizing factors for χ<0 are applicable to superconductors. For χ=0, suitable for weakly magnetic or saturated ferromagnetic materials, Nf and Nm were computed exactly using inductance formulas
  • Demagnetizing factors for rectangular ferromagnetic prisms, Amikam Aharoni (1998)
    TitleDemagnetizing factors for rectangular ferromagnetic prisms
    AuthorAmikam Aharoni
    PublicationJournal of Applied Physics
    DateMarch 15, 1998
  • Demagnetizing Factors of the General Ellipsoid, J. A. Osborn (1945)
    TitleDemagnetizing Factors of the General Ellipsoid
    AuthorJ. A. Osborn
    PublicationPhysical Review
    DateJune 01, 1945
  • Demagnetizing Field in Nonellipsoidal Bodies, R. I. Joseph et al. (1965)
    TitleDemagnetizing Field in Nonellipsoidal Bodies
    AuthorsR. I. Joseph, E. Schlomann
    PublicationJournal of Applied Physics
    DateMay 00, 1965
  • Design and analysis of a high pressure piezoelectric actuated microvalve, I. Fazal et al. (2007)
    TitleDesign and analysis of a high pressure piezoelectric actuated microvalve
    AuthorsI. Fazal, M. C. Elwenspoek
    PublicationJournal of Micromechanics and Microengineering
    AbstractA normally open piezoelectric actuated microvalve which modulates a gas flow is fabricated and tested. This work is based on the novel concept of combining micro-machining- and fine machining. The microvalve was tested for air flow. It is shown that a flow rate of 250 ml min[?]1 for a pressure difference of 4 bars can be achieved. The continuous and controlled flow of gas at any stage of valve operation can be obtained. Additionally, it has been shown that almost no hysteresis occurs during the valve operation and the power consumption is very low.
  • Design and microfabrication of a high-aspect-ratio PDMS microbeam array for parallel nanonewton force measurement and protein printing, F. M. Sasoglu et al. (2007)
    TitleDesign and microfabrication of a high-aspect-ratio PDMS microbeam array for parallel nanonewton force measurement and protein printing
    AuthorsF. M. Sasoglu, A. J. Bohl, B. E. Layton
    PublicationJournal of Micromechanics and Microengineering
    AbstractCell and protein mechanics has applications ranging from cellular development to tissue engineering. Techniques such as magnetic tweezers, optic tweezers and atomic force microscopy have been used to measure cell deformation forces of the order of piconewtons to nanonewtons. In this study, an array of polymeric polydimethylsiloxane (PDMS) microbeams with diameters of 10-40 µm and lengths of 118 µm was fabricated from Sylgard® with curing agent concentrations ranging from 5% to 20%. The resulting spring constants were 100-300 nN µm[?]1. The elastic modulus of PDMS was determined experimentally at different curing agent concentrations and found to be 346 kPa to 704 kPa in a millimeter-scale array and [?]1 MPa in a microbeam array. Additionally, the microbeam array was used to print laminin for the purpose of cell adhesion. Linear and nonlinear finite element analyses are presented and compared to the closed-from solution. The highly compliant, transparent, biocompatible PDMS may offer a method for more rapid throughput in cell and protein mechanics force measurement experiments with sensitivities necessary for highly compliant structures such as axons.
  • Detection of ferromagnetic particles using spin valve sensors, L. W. Y. Lui et al. (2006)
    TitleDetection of ferromagnetic particles using spin valve sensors
    AuthorsL. W. Y. Lui, Y. Y. Tan, K. B. Li, C. H. Sow, S. J. O'Shea
    PublicationJournal of Applied Physics
  • Determining refractive index of single living cell using an integrated microchip, X.J. Liang et al. (2007)
    TitleDetermining refractive index of single living cell using an integrated microchip
    AuthorsX.J. Liang, A.Q. Liu, C.S. Lim, T.C. Ayi, P.H. Yap
    PublicationSensors and Actuators A: Physical
    DateFebruary 12, 2007
    AbstractWe report a novel method for measuring the effective refractive index (RI) of single living cell using a small integrated chip, which might be an efficient approach for diseases diagnosis. This microchip is able to determine the refractive index of single living cell in real time without any extra cell treatments such as fluorescence labelling, chemical modification and so forth, meanwhile, providing low cost, small size, easy operation and high accuracy. The measurement system integrates an external cavity laser, a microlens, and some microfluidic channels onto a monolithic chip. In the experiments, two standard polystyrene beads with nominal RI are utilized to calibrate the measurement system and five different types of cancerous cells are subsequently measured in the chip. The experimental results show that the refractive indices of the cancerous cells tested ranges from 1.392 to 1.401, which is larger than typical value of normal cell of 1.35-1.37. This integrated chip potentially has a serial of applications on biodefense, disease diagnosis, biomedical and biochemical analysis.
  • Development of a miniaturised drug delivery system with wireless power transfer and communication, S. Smith et al. (2007)
    TitleDevelopment of a miniaturised drug delivery system with wireless power transfer and communication
    AuthorsS. Smith, T.B. Tang, J.G. Terry, J.T.M. Stevenson, B.W. Flynn, H.M. Reekie, A.F. Murray, A.M. Gundlach, D. Renshaw, B. A10 - Dhillon Dhillon, A. A11 - Ohtori Ohtori, Y. A12 - Inoue Inoue, A.J. A13 - Walton Walton
    PublicationNanobiotechnology, IET
  • Development of Elongated Particle Magnets, Fred E. Luborsky (1961)
    TitleDevelopment of Elongated Particle Magnets
    AuthorFred E. Luborsky
    PublicationJournal of Applied Physics
    DateMarch 00, 1961
  • Development of Ni-Zn nanoferrite core material with improved saturation magnetization and DC resistivity, A. Mahesh Kumar et al. (2008)
    TitleDevelopment of Ni-Zn nanoferrite core material with improved saturation magnetization and DC resistivity
    AuthorsA. Mahesh Kumar, M. Chaitanya Varma, Charu Lata Dube, K.H. Rao, Subhash C. Kashyap
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
  • Deviation from the superparamagnetic behaviour of fine-particle systems, I. Malaescu et al. (2000)
    TitleDeviation from the superparamagnetic behaviour of fine-particle systems
    AuthorsI. Malaescu, C. N. Marin
    PublicationJournal of Magnetism and Magnetic Materials
    DateJuly 2, 2000
    AbstractStudies concerning superparamagnetic behaviour of fine magnetic particle systems were performed using static and radiofrequency measurements, in the range 1-60 MHz. The samples were: a ferrofluid with magnetite particles dispersed in kerosene (sample A), magnetite powder (sample B) and the same magnetite powder dispersed in a polymer (sample C). Radiofrequency measurements indicated a maximum in the imaginary part of the complex magnetic susceptibility, for each of the samples, at frequencies with the magnitude order of tens of MHz, the origin of which was assigned to Neel-type relaxation processes. The static measurements showed a Langevin-type dependence of magnetisation M and of susceptibility [chi], on the magnetic field for sample A. For samples B and C deviations from this type of dependence were found. These deviations were analysed qualitatively and explained in terms of the interparticle interactions, dispersion medium influence and surface effects.
  • Direct Measurements of the Stiffness of Echinoderm Sperm Flagella, Makato Okuno et al. (1979)
    TitleDirect Measurements of the Stiffness of Echinoderm Sperm Flagella
    AuthorsMakato Okuno, Yukio Hiramoto
    PublicationJournal of Experimental Biology
    DateApril 1, 1979
    Abstract1. The stiffness (flexural rigidity) of some echinoderm sperm flagella was measured, using a flexible glass microneedle.2. Values of 0.3-1.5 x 10-21 N m2 were obtained for the stiffness of live flagella which were immobilized with CO2-saturated sea water.3. The immobilized live flagellum was uniform in stiffness along its entire length, except in a particular plane of imposed bending in which flexible regions were observed.4. Demembranated flagella (Hemicentrotus pulcherrimus) in an ATP-free solution were about ten times stiffer (1.1 x 10-20 N m2) than immobilized live ones (0.5-0.9 x 10-21 N m2). The stiffness was decreased by addition of ATP to the solution and became equivalent to that of live ones when the solution contained 10 mM ATP.5. In the demembranated flagella, the effects of ADP and ATP on the stiffness were similar. Other nucleotide phosphates and inorganic phosphate did not reduce the stiffness.6. Young's modulus of microtubules is estimated to be 2.5 x 109 Nm2 on the basis that the microtubules have no tight connexion with one another in immobilized live flagella.
  • Discovery of a Magnetic Ionic Liquid FeCl4, Satoshi Hayashi et al. (2004)
    TitleDiscovery of a Magnetic Ionic Liquid FeCl4
    AuthorsSatoshi Hayashi, Hiro-o Hamaguchi
    PublicationChemistry Letters
    AbstractA magnetic ionic liquid, which shows a strong response to magnetic field, has been discovered. We synthesized an ionic liquid by mixing 1-butyl-3-methylimidazolium chloride ([bmim]Cl) and FeCl3, in anticipation of unique magnetic properties due to the possible local ordering of the magnetic anions. The visible absorption spectroscopy has shown that this liquid contains the high spin FeCl4− as the anion. Raman spectroscopy has indicated that it contains bmim+ as the cation. It has thus been confirmed that the prepared liquid is [bmim]FeCl4. The liquid [bmim]FeCl4 responded strongly to magnetic field. The SQUID measurements have shown that it is paramagnetic having a large magnetic susceptibility of 40.6 × 10−6 emu g−1. The present discovery of a magnetic ionic liquid has opened up a new research area of the magnetism of liquids.
  • Disposable smart lab on a chip for point-of-care clinical diagnostics, C.H. Ahn et al. (2004)
    TitleDisposable smart lab on a chip for point-of-care clinical diagnostics
    AuthorsC.H. Ahn, Jin-Woo Choi, G. Beaucage, J.H. Nevin, Jeong-Bong Lee, A. Puntambekar, J.Y. Lee
    PublicationProceedings of the IEEE
    AbstractThis paper presents the development of a disposable plastic biochip incorporating smart passive microfluidics with embedded on-chip power sources and integrated biosensor array for applications in clinical diagnostics and point-of-care testing. The fully integrated disposable biochip is capable of precise volume control with smart microfluidic manipulation without costly on-chip microfluidic components. The biochip has a unique power source using on-chip pressurized air reservoirs, for microfluidic manipulation, avoiding the need for complex microfluidic pumps. In addition, the disposable plastic biochip has successfully been tested for the measurements of partial oxygen concentration, glucose, and lactate level in human blood using an integrated biosensor array. This paper presents details of the smart passive microfluidic system, the on-chip power source, and the biosensor array together with a detailed discussion of the plastic micromachining techniques used for chip fabrication. A handheld analyzer capable of multiparameter detection of clinically relevant parameters has also been developed to detect the signals from the cartridge type disposable biochip. The handheld analyzer developed in this work is currently the smallest analyzer capable of multiparameter detection for point-of-care testing.
  • Doping nanoparticles into polymers and ceramics using ultrasound radiation, Aharon Gedanken (2007)
    TitleDoping nanoparticles into polymers and ceramics using ultrasound radiation
    AuthorAharon Gedanken
    PublicationUltrasonics Sonochemistry
    DateApril 2007
    AbstractIn materials science, sonochemistry is mostly used for the fabrication of nanomaterials, but it has also been used for the polymerization of monomers. The current review is aimed at introducing a new application of sonochemistry to materials science, i.e., the doping of nanoparticles into polymers and ceramic bodies. The introduction will present a short overview of sonochemistry, and will outline the advantages of sonochemistry as a tool for fabricating nanomaterials.
  • Effects of grain size distribution on coercivity and permeability of ferromagnets, Desheng Xue et al. (2008)
    TitleEffects of grain size distribution on coercivity and permeability of ferromagnets
    AuthorsDesheng Xue, Guozhi Chai, Xiling Li, Xiaolong Fan
    PublicationJournal of Magnetism and Magnetic Materials
    DateApril 2008
    AbstractGrain size dependence of coercivity and permeability (GSDCP) theory is extended to include grain size distribution in ferromagnets. It is found that the experimental data do not agree with the GSDCP theory on the transition location of different grain size ranges (The GSDCP theory has three different grain size ranges for different magnetization processes.). Correspondingly, including the grain size distribution the GSDCP theory fits the experimental data very well. These results prove that the grain size distribution indeed affects the magnetic properties of nanocrystalline ferromagnets.
  • Elastic energy methods of design analysis, Ralph J. Harker (1986)
    TitleElastic energy methods of design analysis
    AuthorRalph J. Harker
  • Elastic Properties of the Sea Urchin Sperm Flagellum, Robert Rikmenspoel (1966)
    TitleElastic Properties of the Sea Urchin Sperm Flagellum
    AuthorRobert Rikmenspoel
    PublicationBiophysical Journal
    DateJuly 1, 1966
    AbstractThe theory of flexural vibrations in thin rods, applied to the movement of flagella, has been extended to include an investigation of the influence of the boundary conditions on the theoretical waveforms. It was found that for flagella which are flexible enough, the flexibility can be estimated solely from the wavelength of the wave traveling in it. This can be expected to hold for those flagella which do not possess a fibrous sheath. The bending moment in flagella in which the ampitude of the wave is maintained as the wave travels distally is almost completely produced by active contractile elements. This means that the active bending moment can be estimated from the radius of curvature of the flagellum and the stiffness. The above findings were applied to the case of the sea urchin sperm flagellum. One finds that the stiffness of the flagellum is caused mainly by the nine longitudinal fibers which must have a Young's modulus of slightly less than 108dyne/cm2. The longitudinal fibers need to develop a tension of 1.6 x 108dyne/cm2 to account for the bending moment in the flagellum. These two figures are in line with those found for muscle fibers.
  • Elastomer-supported cold welding for room temperature wafer-level bonding, W.Y. Zhang et al. (2004)
    TitleElastomer-supported cold welding for room temperature wafer-level bonding
    AuthorsW.Y. Zhang, G.S. Ferguson, S. Tatic-Lucic
    Conference NameMicro Electro Mechanical Systems, 2004. 17th IEEE International Conference on. (MEMS)
    AbstractThis paper presents a method for room-temperature wafer-level bonding that is applicable for the MEMS and NEMS packaging and fabrication processes, but does not require an applied voltage, high pressure or vacuum. By applying a layer of elastomer between the wafer and gold overlayer, we successfully bonded two silicon wafers under limited load (/spl sim/3 KPa) at room temperature (25/spl deg/C). One of the important potential applications of this technique is to create a temporary cap wafer that would protect already released, bulk or surface-micromachined structures during the dicing process. The initial results of experiments on the detachment of the temporary cap wafers bonded using this method are presented.
  • Electrical switching of the vortex core in a magnetic disk, Keisuke Yamada et al. (2007)
    TitleElectrical switching of the vortex core in a magnetic disk
    AuthorsKeisuke Yamada, Shinya Kasai, Yoshinobu Nakatani, Kensuke Kobayashi, Hiroshi Kohno, Andre Thiaville, Teruo Ono
    PublicationNat Mater
    DateApril 2007
  • Electric and Magnetic Field-Structured Smart Composites, Zsolt Varga et al. (2005)
    TitleElectric and Magnetic Field-Structured Smart Composites
    AuthorsZsolt Varga, Genov�va Filipcsei, Andr�s Szil�gyi, Mikl�s Zr�nyi
    PublicationMacromolecular Symposia
    AbstractThe combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The electric- and magnetic- field-sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in high elastic polymeric matrix. Coupling of electric and/or magnetic fields with elastic properties leads to a number of striking phenomena that are exhibited in response to impressed external fields.The ability of such materials to change their size and mechanical properties in a reversible manner has inherent interest, if for no other reason than the uniqueness having giant elastic response to polarization. The giant deformational effect, high elasticity, anisotropic properties, and quick response to either electric or magnetic fields open new opportunities for using such materials for various applications. Since electric and magnetic fields are convenient stimuli from the point of signal control, it is of great importance to develop and study such flexible, smart polymeric systems.
  • Electromagnetic actuation and microchannel engineering of a polymer micropen array integrated with microchannels and sample reservoirs for biological assay patterning, Maesoon Im et al. (2007)
    TitleElectromagnetic actuation and microchannel engineering of a polymer micropen array integrated with microchannels and sample reservoirs for biological assay patterning
    AuthorsMaesoon Im, Il-Joo Cho, Kwang-Seok Yun, Euisik Yoon
    PublicationApplied Physics Letters
  • Electromigration—A brief survey and some recent results, J.R. Black (1969)
    TitleElectromigration—A brief survey and some recent results
    AuthorJ.R. Black
    PublicationElectron Devices, IEEE Transactions on
    AbstractRecently, electromigration has been identified as a potential wear-out failure mode for semiconductor devices employing metal film conductors of inadequate cross-sectional area. A brief survey of electromigration indicates that although the effect has been known for several decades, a great deal of the processes involved is still unknown, especially for complex metals and solute ions. Earlier design equations are improved to account for conductor film cross-sectional area as well as film structure, film temperature, and current density. Design curves are presented which permit the construction of high reliability "infinite life" aluminum conductors for specific conditions of maximum current and temperature stress expected in use. It is also shown that positive gradients, in terms of electron flow, of temperature, current density, or ion diffusion coefficient foreshorten conductor life because they present regions where vacancies condense to form voids.
  • Electromigration-Induced Failures in, and Microstructure and Resistivity of, Sputtered Gold Films, J. C. Blair et al. (1972)
    TitleElectromigration-Induced Failures in, and Microstructure and Resistivity of, Sputtered Gold Films
    AuthorsJ. C. Blair, C. R. Fuller, P. B. Ghate, C. T. Haywood
    PublicationJournal of Applied Physics
    DateFebruary 00, 1972
  • Electron behavior and magnetic properties of polymer nanocomposites, D. Y. Godovski (1995)
    TitleElectron behavior and magnetic properties of polymer nanocomposites
    AuthorD. Y. Godovski
    PublisherSpringer Berlin / Heidelberg
    AbstractIn this review article, an attempt has been made to describe the relatively new class of composite systems, polymer nanocomposites. The study of nanocomposites is determined by a number of anomalous properties, exhibited by both the nanoparticles themselves and the systems of such objects immersed in a polymer matrix. The anomalous character of nanoparticle properties is determined by their medium position between continuous bulk and single atoms. Such particles between 10 to 1000 Å sometimes exhibit a number of quantum size effects that determine anomalous optical and magnetic properties. The cooperative effects of composites with interacting nanoparticles is another distinctive feature of such systems. These effects occur at the so-called percolation threshold, where the particles begin having contact with one another, whereby the interparticle contacts increase with the increase in their number. The electronic, optical and magnetic properties of composites, which change with the changes in cluster structure, are also discussed in this review.
  • Evaluation of polydimethylsiloxane scaffolds with physiologically-relevant elastic moduli: interplay of substrate mechanics and surface chemistry effects on vascular smooth muscle cell response, Xin Q. Brown et al. (2005)
    TitleEvaluation of polydimethylsiloxane scaffolds with physiologically-relevant elastic moduli: interplay of substrate mechanics and surface chemistry effects on vascular smooth muscle cell response
    AuthorsXin Q. Brown, Keiko Ookawa, Joyce Y. Wong
    DateJune 2005
    AbstractPolydimethylsiloxane (PDMS) is used extensively to study cell-substrate interactions because its mechanical properties are easily tuned in physiologically relevant ranges. However, changes in mechanical properties also modulate surface chemistry and cell response. Here, we correlate the mechanical and surface properties of PDMS to vascular smooth muscle cell (VSMC) behavior. We find that a 5-fold increase in base:crosslinker ratio leads to ~40-fold decrease in elastic modulus but no significant differences in surface wettability. However, when polyelectrolyte multilayers are adsorbed to promote cell adhesion, wettability varies inversely with substrate stiffness. Despite these differences in hydrophobicity, the amount of adsorbed protein remains the same. In the absence of serum, there is a 39% decrease in cell attachment and a 42% decrease in spreading as the elastic modulus decreases from 1.79 to 0.05�MPa. In the presence of serum or adsorbed fibronectin, the differences in attachment and spreading are diminished. This is not the case for the rate of serum-stimulated cell proliferation, which remains inversely dependent on crosslinker concentration. We conclude that for the range of crosslinker concentrations investigated, the surface properties dominate the initial cell attachment and spreading, whereas the mechanical properties influence the long-term cell growth.
  • Exchange bias, J. Nogués et al. (1999)
    TitleExchange bias
    AuthorsJ. Nogués, Ivan K. Schuller
    PublicationJournal of Magnetism and Magnetic Materials
    DateFebruary 15, 1999
    AbstractWe review the phenomenology of exchange bias and related effects, with emphasis on layered antiferromagnetic (AFM)-ferromagnetic (FM) structures. A compilation of materials exhibiting exchange bias and some of the techniques used to study them is given. Some of the applications of exchange bias are discussed. The leading theoretical models are summarized. Finally some of the factors controlling exchange bias as well as some of the unsolved issues associated with exchange bias are discussed.
  • Exchange bias theory, Miguel Kiwi (2001)
    TitleExchange bias theory
    AuthorMiguel Kiwi
    PublicationJournal of Magnetism and Magnetic Materials
    DateSeptember 2001
    AbstractResearch on the exchange bias (EB) phenomenon has witnessed a flurry of activity during recent years, which stems from its use in magnetic sensors and as stabilizers in magnetic reading heads. EB was discovered in 1956 but it attracted only limited attention until these applications, closely related to giant magnetoresistance, were developed during the last decade. In this review, I initially give a short introduction, listing the most salient experimental results and what is required from an EB theory. Next, I indicate some of the obstacles in the road towards a satisfactory understanding of the phenomenon. The main body of the text reviews and critically discusses the activity that has flourished, mainly during the last 5 years, in the theoretical front. Finally, an evaluation of the progress made, and a critical assessment as to where we stand nowadays along the road to a satisfactory theory, is presented.
  • Fabrication and Characterization of Nickel Nanowire Polymer Composites, H. Denver et al. (2007)
    TitleFabrication and Characterization of Nickel Nanowire Polymer Composites
    AuthorsH. Denver, J. Hong, D. Borca-Tasciuc
    PublisherMaterials Research Society
    AbstractMagnetic polymers are multi-functional composites emerging as a new category of smart materials. This work focuses on fabrication and characterization of magnetic polymer nanocomposites based on polydimethylsiloxane (PDMS) elastomer matrix. The magnetic fillers are commercially available Ni nanoparticles and respectively in-house fabricated Ni nanowires. Synthesis of Ni nanowires is achieved by electroless deposition inside nanoporous anodic alumina templates. After template removal, the nanowires are coated with 1-Octodecanethiol surfactant and mixed with PDMS using a FlackTek SpeedMixer. In parallel, nanoparticles are mixed with PDMS, without undergoing surfactant coating. Both composites are evaluated by scanning electron microscope (SEM) to determine dispersion uniformity. Mechanical properties are resolved by tensile tests performed by an instron. Preliminary results suggest that surfactant addition enhances dispersion, while mechanical properties of the composites for up to 5 vol. % of added nickel remain close to that of the polymer matrix without filler.
  • Fabrication of a peristaltic micro pump with novel cascaded actuators, Ok Chan Jeong et al. (2008)
    TitleFabrication of a peristaltic micro pump with novel cascaded actuators
    AuthorsOk Chan Jeong, Satoshi Konishi
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis paper presents the fabrication of an all-PDMS (polydimethylsiloxane) micro pump with novel cascaded actuators as dynamic valves. The micro pump consists of three pneumatic actuators in series and a micro fluidic channel connecting two fluidic inlet and outlet ports. The three-layer bonded pump structure is fabricated through a typical moulding process of PDMS and a simple heating process for the PDMS-to-PDMS bonding. The total size of the micro pump is 5 mm × 5 mm. The dynamic valve pattern of the single actuator is observed under various operational conditions of the square-wave input signal for the estimation of its volume stroke. The maximum volume stroke of the pneumatic actuator for liquid is about 85% of the volume of the liquid chamber. Three types of liquid-pumping tests are performed for characterization of the micro pump such as backpressure, frequency and viscous liquids. The flow rate of the de-ionized (DI) water is about 73.9 nl min[?]1 at zero backpressure. As the hydraulic difference between inlet and outlet ports increases, the flow rate gradually decreases. In the case of the frequency responses, the micro pump has the maximum flow rate of the DI water at 2 Hz. The viscosity-dependent flow rate of the working fluids is also observed.
  • Fabrication of beam structures with micro-scale cross-sections and meso-scale spans, Michael James Martin et al. (2007)
    TitleFabrication of beam structures with micro-scale cross-sections and meso-scale spans
    AuthorsMichael James Martin, Robert D. White, Katsuo Kurabayashi, Iain D. Boyd
    PublicationJournal of Micromechanics and Microengineering
    AbstractTo allow testing of micro-scale aerodynamics, a process was created to manufacture beam structures that combine spans of 1 cm with a cross-section of 5 µm by 100 µm. The structural considerations limiting the fabrication of a structure combining macro-scale spans with a micro-scale cross-section are analyzed. Limiting considerations include forces during operation, fluid forces during release, vibrational limitations and beam buckling. Based on these results, a fabrication process for creating a beam structure for large spans without support structures is devised, incorporating the use of back-side etches and extra handling wafers to avoid stiction. This process is used to successfully fabricate the desired structure.
  • Fabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters, Kwang-Seok Yun et al. (2008)
    TitleFabrication of complex multilevel microchannels in PDMS by using three-dimensional photoresist masters
    AuthorsKwang-Seok Yun, Euisik Yoon
    PublicationLab on a Chip
    AbstractThis paper demonstrates a new method of implementing complex microchannels in PDMS, which is simply constructed using three-dimensional photoresist structures as a master mold for the PDMS replica process. The process utilizes UV-insensitive LOR resist as a sacrificial layer to levitate the structural photoresist. In addition, the thickness of photoresist structures can be controlled by multi-step UV exposure. By using these techniques, various three-dimensional photoresist structures were successfully implemented, including the recessed cantilevers, suspended bridges, and the complex plates with micro-pits or micro-villi. We demonstrate that the three-dimensional photoresist structures are applicable to implementing complex multiple microchannels in PDMS by using the PDMS replica method.
  • Fabrication of complex nanoscale structures on various substrates, Kang-Soo Han et al. (2007)
    TitleFabrication of complex nanoscale structures on various substrates
    AuthorsKang-Soo Han, Sung-Hoon Hong, Heon Lee
    PublicationApplied Physics Letters
  • Fabrication of high-aspect-ratio nano structures using a nano x-ray shadow mask, Yong Chul Kim et al. (2008)
    TitleFabrication of high-aspect-ratio nano structures using a nano x-ray shadow mask
    AuthorsYong Chul Kim, Seung S. Lee
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis paper describes a novel method for the fabrication of high-aspect-ratio nano structures (HAR-nano structures) using a nano x-ray shadow mask and deep x-ray lithography (DXRL). The nano x-ray shadow mask is fabricated by depositing an x-ray absorber layer (Au, 3 µm) onto the back side of a nano shadow mask. The nano shadow mask is produced with nano-sized apertures whose dimensions are reduced to several tens of nanometers by the accumulation of low-stress silicon nitride (SixNy) using the LPCVD process on the shadow mask. A shadow mask containing apertures with a size of 1 µm is fabricated on a bulk micromachined SixNy membrane. The thickness of an absorber layer must be in the range of several tens of micrometers in order to obtain a contrast of more than 100 for the conventional DXRL process at the Pohang Light Source (PLS). However, a 3 µm thick absorber layer can provide a sufficient contrast if the modified DXRL of the central beam-stop method is used, which blocks high-energy x-rays. A nano shadow mask with 30 nm sized apertures is fabricated and a nano x-ray shadow mask with 250 nm sized apertures is fabricated by depositing a 3 µm thick absorber layer on a nano shadow mask with 500 nm sized apertures. HAR-nano structures (circles with a diameter of 420 nm and lines with a width of 274 nm) with aspect ratios of over 10:1 on a 3.2 µm SU-8 are successfully fabricated by using the nano x-ray shadow mask and the central beam-stop method.
  • Fabrication of microfluidic systems in poly(dimethylsiloxane), J. Cooper McDonald et al. (2000)
    TitleFabrication of microfluidic systems in poly(dimethylsiloxane)
    AuthorsJ. Cooper McDonald, David C. Duffy, Janelle R. Anderson, Daniel T. Chiu, Hongkai Wu, Olivier J. A. Schueller, George M. Whitesides
    AbstractMicrofluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.
  • Fabrication of polymer microstructures for MEMS: sacrificial layer micromolding and patterned substrate micromolding, Ferrell et al. (2007)
    TitleFabrication of polymer microstructures for MEMS: sacrificial layer micromolding and patterned substrate micromolding
    Authors Ferrell, Woodard, Hansford
    PublicationBiomedical Microdevices
    DateDecember 26, 2007
    AbstractTwo soft lithography based fabrication techniques are employed for fabricating mechanically independent, freely suspended polymer microstructure from poly(n-propyl methacrylate) (PPMA), poly(methyl methacrylate) (PMMA), and polystyrene. Both methods involve a micromolding process followed by thermal bonding to the substrate. The first method, sacrificial layer micromolding, uses a water soluble sacrificial layer, allowing functional structures to be released by immersion in water. The second method, patterned substrate micromolding, uses a permanent substrate patterned via photolithography. Functional regions of the polymer MEMS are suspended over the voids in the photoresist pattern. The processes have been applied to the fabrication of polymer microstructures with a variety of geometries for specific applications. Devices have included microcantilevers, beams, and other more complicated microstuctures. The thermal molding process is conceivably applicable to the fabrication of microstructures from a wide variety of thermoplastic polymers, allowing material selection to be tailored based on application.
  • Fabrication of SU-8 free-standing structures embedded in microchannels for microfluidic control, A. Ezkerra et al. (2007)
    TitleFabrication of SU-8 free-standing structures embedded in microchannels for microfluidic control
    AuthorsA. Ezkerra, L. J. Fernández, K. Mayora, J. M. Ruano-López
    PublicationJournal of Micromechanics and Microengineering
    AbstractThe application of cantilevered structures as check valves or flow sensors can provide new possibilities towards the integration of accurate sample preparation systems within a lab-on-a-chip. The cantilevers presented in this paper act as flaps enclosed within a channel in a direction perpendicular to the flow. This orientation allows simpler designs and easier integration of the valve or flow sensor within the microfluidic network. The cantilevers have been embedded in a microfluidic channel by low temperature full wafer adhesive bonding. In this way, electrodes, microchannels, microchambers and cantilevers can be fabricated and sealed at the same time at a wafer level. To the author's knowledge, this is the first example of flap cantilevers embedded in a polymeric microfluidic channel. The mobility of the structure and the leakage are dependent on the size of the sealing gaps between the cantilever and the enclosing channel. In this paper, we present three different fabrication methods for a range of bottom sealing gaps from the micro to the nanometer size. The top sealing gap is determined by the adhesive bonding and is 11 µm wide. Furthermore, various geometrical features have been introduced in order to optimize a valve or flow sensor. The characterization of the structures comprises measurements of the sensitivity of each cantilever design by obtaining their relative spring constant, measurements of their elastic and plastic working regimes and Young's modulus of the SU-8.
  • Ferrofluid-based microchip pump and valve, Herb Hartshorne et al. (2004)
    TitleFerrofluid-based microchip pump and valve
    AuthorsHerb Hartshorne, Christopher J. Backhouse, William E. Lee
    PublicationSensors and Actuators B: Chemical
    DateMay 1, 2004
    AbstractFluid control is a key element in the performance of microfluidic "lab-on-a-chip" devices. The development of integrated multi-function micro-chemical reactors and analysis platforms depends upon on-chip valving and pumping. In this work, microfluidic valves and pumps were fabricated from etched glass substrates each bonded to a second glass substrate lid that had ultrasonically drilled access holes. The devices contained ferrofluid plugs of approximately 10 mm in length that were actuated by external magnets. The ferrofluid used in the devices was a colloidal suspension of ferromagnetic particles in a hydrophobic fluorocarbon carrier and was immiscible in water. With air in the channels, ferrofluid devices could withstand pressures of 12 kPa and could be opened and closed against pressures of 8.5 and 5.0 kPa, respectively, under a magnetic field of 2.8 kG. A ferrofluid pump comprising a ferrofluid piston and two ferrofluid valves was able to generate air pressures in excess of 5 kPa. In untreated glass channels, leakage of water around ferrofluid seals was significant. However, when the portions of the channel network that contained the ferrofluid were coated with a hydrophobic organo-silane, leakage was not detectable.
  • Ferromagnetic coercivity and applied field orientation, Brandon Edwards et al. (1995)
    TitleFerromagnetic coercivity and applied field orientation
    AuthorsBrandon Edwards, D. I. Paul
    PublicationJournal of Magnetism and Magnetic Materials
    DateJune 1995
    AbstractWe analyze the relationship between the coercive force of a ferromagnetic material and the angle of the applied magnetic field. The material is assumed to contain a ferromagnetic domain wall as well as a planar defect parallel to the wall and it is further assumed that the dominant mechanism determing the coercivity is that of pinning of the wall by the defect. Our formulation takes into account the spatial dependence of the direction of magnetization along the normal to the plane of the defect. Numerical solutions are obtained for the resulting nonlinear differential equations and analysis is done on the roles of the anisotropic, magnetostatic, and exchange energies in determining the behavior of the coercivity as the direction of the applied magnetic field is varied. Our results show that, in contradiction to previous thought, the inverse cosine of the applied field angle is not a good approximation to the coercivity dependence unless the coercivity is about two orders of magnitude smaller than the anisotropy field. Also, there exist ranges of parameter values for which the domain wall pinning coercivity decreases as the angle between the applied magnetic field and the anisotropy field increases - a behavior previously assumed to occur only when the coercivity is dominated by nucleation rather than pinning of domain walls. Thus, caution must be exercised when using the angular dependence of the applied field to determine the mechanism of magnetic reversal of a given material.
  • Ferromagnetism, R.M. Bozorth (1951)
    AuthorR.M. Bozorth
    PublisherVan Nostrand
    AbstractA reissue of a broadly recognized classic text, Ferromagnetism covers the basics of magnetics as well as in-depth coverage of magnetic materials. This timeless and invaluable reference also includes: * complete definitions of magnetic phenomena and theories * illustrations of magnetic materials * detailed explanations of basic magnetization and domain theory * practical use of many fundamental expressions * useful technical data on magnetic materials Ferromagnetism will provide a useful resource to any electrical engineer, physicist, researcher or designer, interested in the field of magnetics.
  • Field-induced flocculation on biocompatible magnetic colloids, E.R. Cintra et al. (2008)
    TitleField-induced flocculation on biocompatible magnetic colloids
    AuthorsE.R. Cintra, J.L. Santos Jr., L.M. Socolovsky, N. Buske, A.F. Bakuzis
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Uncorrected Proof
    AbstractField dependence of the optical transmission of a polyaspartic-coated magnetite magnetic fluid dispersed in water was investigated at different particle volume fractions. The particle size distribution of the sample was obtained from the analysis of the transmission electron microscopy pictures. The transmissivity decreased increasing the magnetic field until a critical field is achieved. Above this value, the opposite effect was observed. Indeed, the critical field decreases the higher the particle volume fraction being in qualitative similarity with phase separation behavior. However, the origin of the effect is attributed to the precipitation of field-induced nanoparticle chains. These phenomena might be useful on obtaining one-dimensional nanoparticle arrangements.
  • Fine pattern transfer by nanocasting lithography, Yoshihiko Hirai et al. (2005)
    TitleFine pattern transfer by nanocasting lithography
    AuthorsYoshihiko Hirai, Takashi Yoshikawa, Masatoshi Morimatsu, Masaki Nakajima, Hiroaki Kawata
    PublicationMicroelectronic Engineering
    DateMarch 2005
    AbstractA novel pattern transfer technique has been demonstrated by simple procedure based on a nanoimprint lithography. A polymer is coated on a mold by a spin coater and cast into fine grooves on the mold. After evaporation of a solvent, an adhesive resin is coated on the polymer and put a substrate plate. After releasing the mold, fine pattern is successfully transferred to the polymer. Applying this process, fine pattern transfer using various polymers, high aspect ratio pattern and sub-100�nm patterns have been demonstrated on various substrates.
  • Flexural Rigidity and Elastic Constant of Cilia, Shoji A. Baba (1972)
    TitleFlexural Rigidity and Elastic Constant of Cilia
    AuthorShoji A. Baba
    PublicationJournal of Experimental Biology
    DateApril 1, 1972
    Abstract1. The flexural rigidity of the large abfrontal cilia of Mytilus has been measured with a flexible glass micro-needle.2. The same cilium has similar values to the flexural rigidity irrespective of the phases of beat cycle (including the recovery phase) and of the direction of force applied.3. The values of 3-13 x 10-9 dyne. cm2 have been obtained for the flexural rigidity of compound cilia of various sizes; 2-3 x 10-10 dyne.cm2 for that of the component cilia.4. The Young's modulus of the microtubule is estimated to be 5-9 x 1010 dyne/cm2 on the basis that the outer doublet microtubules are tightly connected with one another.
  • Flexural Rigidity of Echinoderm Sperm Flagella, Sumio Ishijima et al. (1994)
    TitleFlexural Rigidity of Echinoderm Sperm Flagella
    AuthorsSumio Ishijima, Yukio Hiramoto
    PublicationCell Structure and Function
    AbstractThe stiffness (flexural rigidity) of live sperm flagella, Triton-demembranated flagella (axonernes), trypsin-digested axonemes, and doublet microtubules of the axonemes in echinoderms was determined from the relationship between their deformation when a stream of medium was applied and the viscous resistance of the medium acting on the flagellum. The stiffness of the flagellum beating in seawater was 5.8×10-21 Nm2 for bending in the direction perpendicular to the beating plane and 4.2×10-22 Nm2 for bending within the beating plane. A similar difference in stiffness from the difference in bending directions was found in reactivated flagella with 1 Mm ATP. The stiffness of live flagella immobilized in CO2-saturated seawater and axonemes in ATP-free medium was similar to that of beating flagella for bending in the direction perpendicular to the beating plane. The stiffness of motionless flagella significantly decreased with erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and vanadate. The trypsin-digestion of motionless axonemes did not change their stiffness. The stiffness of doublet microtubules was 1.4 ×10-23 Nm2 in 0.1 mM ATP medium and 6.1×10-23 Nm2 in ATP-free medium. These results suggest that doublet pairs lying parallel to the beating plane of the flagellum retain fewer cross-bridges than doublet pairs lying perpendicular to the beating palne.
  • Fluidic Microchannel Arrays for the Electrophoretic Separation and Detection of Bioanalytes using Electrochemiluminescence, Yan et al. (2000)
    TitleFluidic Microchannel Arrays for the Electrophoretic Separation and Detection of Bioanalytes using Electrochemiluminescence
    Authors Yan, Smith, Collins
    PublicationBiomedical Microdevices
    DateJune 01, 2000
    AbstractIn this paper a low cost, multi-channel separation and detection system is reported for use in fast, high throughput screening of bioanalytes. Applications include genetic engineering and drug discovery, particularly combinatorial chemistry. A prototype detection system is presented which is comprised of an array of 50 microchannels fabricated on 25 mm×75 mm glass substrates with planar, thin film metal electrodes for electrophoresis and electrochemiluminescence excitation. Fluidic interconnects to the microchannels via standard tubing provide quick and facile interfacing to external macro components, controllers and/or other microsystems. The fabrication process is readily scalable to higher density arrays.
  • Fluid Mechanics of Propulsion by Cilia and Flagella, C. Brennen et al. (1977)
    TitleFluid Mechanics of Propulsion by Cilia and Flagella
    AuthorsC. Brennen, H. Winet
    PublicationAnnual Review of Fluid Mechanics
  • Fluid transport by cilia between parallel plates, N. Liron (1977)
    TitleFluid transport by cilia between parallel plates
    AuthorN. Liron
    PublicationJournal of Fluid Mechanics
    DateSeptember 8 1977
    AbstractThe problem of fluid transport by cilia is investigated using the Green's function for a Stokeslet between two parallel plates. The discrete-cilia approach is used in building the model, and a readily usable expression for the velocities is obtained. Dependence on the direction of the metachronal wave and on time is not averaged out. Velocity fields, pressure fields and fluxes due to a single Stokeslet and to an infinite line of Stokeslets are discussed. It is found that the flux associated with Stokeslets in between two parallel plates is always zero, in contrast to a Stokeslet parallel to, and above, one plate. In the model one also has to add a plane Poiseuille flow, which incorporates non-zero flux. The flow due to the Stokeslet solution imposes a positive pressure gradient downstream, and the Poiseuille flow a negative pressure gradient. Calculated velocity profiles, in the pumping range, are seen to be time-independent in the centre of the channel and vary between a negative parabolic profile and a plug flow. The reason for these profiles and some possible biological applications are discussed.
  • Formulas for stress and strain, Raymond J Roark (1975)
    TitleFormulas for stress and strain
    AuthorRaymond J Roark
  • From Micro- to Nanofabrication with Soft Materials, Stephen R. Quake et al. (2000)
    TitleFrom Micro- to Nanofabrication with Soft Materials
    AuthorsStephen R. Quake, Axel Scherer
    DateNovember 24, 2000
  • From superhydrophobic to superhydrophilic surfaces tuned by surfactant solutions, Feng-Ming Chang et al. (2007)
    TitleFrom superhydrophobic to superhydrophilic surfaces tuned by surfactant solutions
    AuthorsFeng-Ming Chang, Yu-Jane Sheng, Hui Chen, Heng-Kwong Tsao
    PublicationApplied Physics Letters
  • Fundamentals of microfabrication, M. Madou (1997)
    TitleFundamentals of microfabrication
    AuthorM. Madou
    PublisherCRC Press
    AbstractMEMS technology and applications have grown at a tremendous pace, while structural dimensions have grown smaller and smaller, reaching down even to the molecular level. With this movement have come new types of applications and rapid advances in the technologies and techniques needed to fabricate the increasingly miniature devices that are literally changing our world. A bestseller in its first edition, Fundamentals of Microfabrication, Second Edition reflects the many developments in methods, materials, and applications that have emerged recently. Renowned author Marc Madou has added exercise sets to each chapter, thus answering the need for a textbook in this field. Fundamentals of Microfabrication, Second Edition offers unique, in-depth coverage of the science of miniaturization, its methods, and materials. From the fundamentals of lithography through bonding and packaging to quantum structures and molecular engineering, it provides the background, tools, and directions you need to confidently choose fabrication methods and materials for a particular miniaturization problem.
  • General relation for the vector magnetic field of a circular current loop: a closer look, R.A. Schill (2003)
    TitleGeneral relation for the vector magnetic field of a circular current loop: a closer look
    AuthorR.A. Schill
    PublicationMagnetics, IEEE Transactions on
    AbstractThis paper presents a general theory for the fields generated by a circular current loop and compares it with existing theories. The existing, general, closed solution for the vector magnetic field may be expressed in a number of seemingly different but equivalent forms. These relations offer alternative closed-form solutions that may find various applications, including the characterization of Helmholtz coils. The paper provides alternative closed forms in both spherical and cylindrical coordinate systems. It employs Gauss's magnetic law to show that the alternative closed form is self-consistent and correct and also shows agreement with well-known solutions. Finally, it develops a new (or not readily found) tabulated mathematical identity.
  • Giant magnetic susceptibility enhancement in field-structured nanocomposites, James.E. Martin et al. (2008)
    TitleGiant magnetic susceptibility enhancement in field-structured nanocomposites
    AuthorsJames.E. Martin, E.L. Venturini, D.L. Huber
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
    Date18 April 2008
    AbstractWe demonstrate through experiment and simulation that when mono-domain Fe nanoparticles are formed into chains by the application of a magnetic field, the susceptibility of the resulting structure is greatly enhanced (11.4-fold) parallel to the particle chains, and is much larger than transverse to the chains. Simulations show that this significant enhancement is expected when the susceptibility of the individual particles approaches 5 in MKS units, and is due to the spontaneous magnetization of individual particle chains, which occurs because of the strong dipolar interactions. This large enhancement is only possible with nanoparticles, because demagnetization fields limit the susceptibility of a spherical multi-domain particle to 3 (MKS). Experimental confirmation of the large susceptibility enhancement is presented, and both the enhancement and the susceptibility anisotropy are found to agree with simulation. The specific susceptibility of the nanocomposite is 54 (MKS), which exceeds the highest value we have obtained for field-structured composites of multi-domain particles by a factor of four.
  • Glass coating for PDMS microfluidic channels by sol–gel methods, A.R. Abate et al. (2008)
    TitleGlass coating for PDMS microfluidic channels by sol–gel methods
    Authors A.R. Abate, D. Lee, T. Do, C. Holtze, D.A. Weitz
    PublicationLab on a Chip
    AbstractSoft lithography using polydimethylsiloxane (PDMS) allows one to fabricate complex microfluidic devices easily and at low cost. However, PDMS swells in the presence of many organic solvents significantly degrading the performance of the device. We present a method to coat PDMS channels with a glass-like layer using sol–gel chemistry. This coating greatly increases chemical resistance of the channels; moreover, it can be functionalized with a wide range of chemicals to precisely control interfacial properties. This method combines the ease of fabrication afforded by soft-lithography with the precision control and chemical robustness afforded by glass.
  • Glass valveless micropump using electromagnetic actuation, Christophe Yamahata et al. (2005)
    TitleGlass valveless micropump using electromagnetic actuation
    AuthorsChristophe Yamahata, Frédéric Lacharme, Martin A.M. Gijs
    PublicationMicroelectronic Engineering
    DateMarch 2005
    AbstractWe present a valveless micropump in glass, which is magnetically actuated using the sinusoidal current of an external electromagnet. We employ a powder blasting microerosion process for microstructuring the glass substrates and fusion bonding for assembly of the multi-layered microfluidic chip. The reciprocating type micropump contains two nozzle/diffuser elements and a poly(dimethylsiloxane) membrane with embedded permanent magnet. The micropump is self-priming and exhibits a backpressure of 50 mbar and water flow rates up to 1 mL/min. The flow resonance frequency is in excellent agreement with the model of Olsson et al. [Journal of Micromechanics and Microengineering 9 (1999) 34].
  • Gold-coated iron nanoparticles: a novel magnetic resonance agent for T1 and T2 weighted imaging, Sung-Jin Cho et al. (2006)
    TitleGold-coated iron nanoparticles: a novel magnetic resonance agent for T1 and T2 weighted imaging
    AuthorsSung-Jin Cho, Benjamin R. Jarrett, Angelique Y. Louie, Susan M. Kauzlarich
    AbstractCore/shell structured iron(Fe)/gold(Au) nanoparticles have been prepared by a reverse micelle method, and their potential application as magnetic resonance (MR) contrast agent investigated. The average nanoparticle size is 19 nm, as determined by x-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties and relaxivities of nanoparticles are presented and compared. The saturation magnetization is 81 emu g[?]1 Fe for freshly prepared nanoparticles and the particles have high r1(6.87 mM[?]1 s[?]1) when the Fe core is kept from oxidation. These nanoparticles may be used as T1 agents in the unoxidized form.
  • Handbook of Magnetic Materials : Volume 1, E.P. Wohlfarth (1980)
    TitleHandbook of Magnetic Materials : Volume 1
    AuthorE.P. Wohlfarth
    PublisherNorth Holland
  • Hemocompatibility, biocompatibility, inflammatory and in vivo studies of primary reference materials low-density polyethylene and polydimethylsiloxane: A review, Yves Marois Marie-Claire Bélanger (2001)
    TitleHemocompatibility, biocompatibility, inflammatory and in vivo studies of primary reference materials low-density polyethylene and polydimethylsiloxane: A review
    AuthorYves Marois Marie-Claire Bélanger
    PublicationJournal of Biomedical Materials Research
    AbstractIn 1984, low-density polyethylene (LDPE) and polymethylsiloxane (PDMS), two primary reference materials (PRM), were made available by the National Heart, Lung, and Blood Institute (NHLBI) as discriminatory tools for the validation of standardized and novel in vitro and in vivo tests in the evaluation of biomaterials. This article reviews the results and conclusions obtained by several studies investigating the hemocompatibility, in vitro biocompatibility, inflammatory response, and in vivo tissue reactions of these two reference materials. Variable results obtained with LDPE and PDMS in ex vivo hemocompatibility studies were attributed to the type of animal model used, the flow velocity of the circulating blood, the time of exposure, and the methodology used to measure blood cell adhesion or activation at the surface of the materials. In contrast, both the LDPE and PDMS appeared to be suitable reference materials when used in in vitro biocompatibility, inflammatory response, and in vivo studies. However, caution must be taken when interpreting the results, because gamma sterilization of these two materials as well as their origin (for example PDMS) are two critically important factors. In conclusion, we see a definite need for standardized hemocompatible parameters and better high-quality hemocompatibility studies on PRM. This review also suggests other materials as potential PRM candidates, namely, Biomer® and IntramedicTM polyethylene. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 467-477, 2001
  • High-frequency ultrasound array element using thermoelastic expansion in an elastomeric film, T. Buma et al. (2001)
    TitleHigh-frequency ultrasound array element using thermoelastic expansion in an elastomeric film
    AuthorsT. Buma, M. Spisar, M. O'Donnell
    PublicationApplied Physics Letters
    DateJuly 23, 2001
    AbstractThe thermoelastic effect was used to produce high-frequency, broadband ultrasound in water. A pulsed diode laser, followed by an erbium-doped fiber amplifier, was focused onto a light-absorbing film deposited on a glass substrate. Conversion efficiency was improved by over 20 dB using an elastomeric film instead of a more commonly used metallic one. Radiation pattern measurements show that considerable energy is radiated at +/–45° for frequencies beyond 50 MHz. These results show that the thermoelastic effect can be used to produce phased arrays for high-frequency ultrasound imaging.
  • Highly parallel mix-and-match fabrication of nanopillar arrays integrated in microfluidic channels for long DNA molecule separation, J. Shi et al. (2007)
    TitleHighly parallel mix-and-match fabrication of nanopillar arrays integrated in microfluidic channels for long DNA molecule separation
    AuthorsJ. Shi, A. P. Fang, L. Malaquin, A. Pepin, D. Decanini, J. L. Viovy, Y. Chen
    PublicationApplied Physics Letters
    DateOctober 08, 2007
    AbstractWe report on a mix-and-match method based on a combination of soft UV nanoimprint lithography, contact optical lithography, and reactive-ion-etch techniques, which is applicable for high throughput manufacturing of nanostructure integrated microfluidic devices. We demonstrate the integration of high density and high aspect ratio nanopillars into microfluidic channels as electrophoresis sieving matrices. As a result, lambda DNA and T4 DNA can be separated within a few minutes. By changing the pattern design, the device could be used for separation of other types of molecules.
  • Implementation of Hysteresis Material Characteristics in Finite Element Computations, P. Sergeant et al. (2007)
    TitleImplementation of Hysteresis Material Characteristics in Finite Element Computations
    AuthorsP. Sergeant, L. Dupré
    Conference NameCOMSOL Users Conference 2007
    AbstractThe hysteresis loss in a sample is obtained by evaluating the drag force profile when slowly moving the sample forward and backward through the strong field of a permanent magnet. A numerical time-stepping model is presented that calculates the drag force profile. At every time step, the sample is slightly moved relative to the magnet. The model is based on 2D-FE computations (COMSOL AC/DC module, magnetostatics, perpendicular currents) including magnetic hysteretic material behavior using the Preisach model. The material behavior is described through differential permeabilities. The drag force is obtained by using the Maxwell stress tensor. A study was carried out of the numerical accuracy, and the model was also validated by comparing with measurements. The results show that the method is able to detect defects in the sample.
  • Including effects of microstructure and anisotropy in theoretical models describing hysteresis of ferromagnetic materials, H. Hauser et al. (2007)
    TitleIncluding effects of microstructure and anisotropy in theoretical models describing hysteresis of ferromagnetic materials
    AuthorsH. Hauser, Y. Melikhov, D. C. Jiles
    PublicationApplied Physics Letters
    DateOctober 22, 2007
  • Influence des fluctuations thermiques sur l'aimantation de grains ferromagnétiques très fins, L. Néel (1949)
    TitleInfluence des fluctuations thermiques sur l'aimantation de grains ferromagnétiques très fins
    AuthorL. Néel
    PublicationSéance du académie des sciences
    Date21 Feb 1949
  • Information about Dow Corning® brand Silicone Encapsulants, Dow Corning Corporation (2005)
    TitleInformation about Dow Corning® brand Silicone Encapsulants
    AuthorDow Corning Corporation
  • Information About High Technology Silicone Materials, Dow Corning Corporation (1991)
    TitleInformation About High Technology Silicone Materials
    AuthorDow Corning Corporation
  • In-situ synthesis of poly(dimethylsiloxane)–gold nanoparticles composite films and its application in microfluidic systems, Q. Zhang et al. (2007)
    TitleIn-situ synthesis of poly(dimethylsiloxane)–gold nanoparticles composite films and its application in microfluidic systems
    AuthorsQ. Zhang, J. Xu, Y. Liu, H. Chen
    PublicationLab on a Chip
    DateNov, 2007
    AbstractWe presented a simple approach for in-situ synthesis of poly(dimethylsiloxane) (PDMS)–gold nanoparticles composite film based on the special characteristics of PDMS itself. It is an environmentally safe synthesis method without the requirement of additional reducing/stabilizing agents. The region where the resulting gold nanoparticles distribute (in the matrix or on the surface of the polymer) and the size of the nanoparticles, as well as the colour of the free-standing films, can be simply controlled by adjusting the ratio of curing agent and the PDMS monomer. The chemical and optical properties of these composite films were studied. Using such a method, gold nanoparticle micropatterns on PDMS surfaces can be performed. And based on the gold nanoparticles micropattern, further modification with antibodies, antigens, enzymes and other biomolecules can be achieved. To verify this ability, an immobilized glucose oxidase (GOx) reactor in microchannels was built and its performance was studied. The experiments have shown that the resulting composite film may have a lot of potential merits in protein immobilization, immunoassays and other biochemical analysis on PDMS microchips.
  • Integrated Micromachined Magnetic Bead Separator, K. Smistrup (2003)
    TitleIntegrated Micromachined Magnetic Bead Separator
    AuthorK. Smistrup
    DateDecember, 2003
    AbstractThis thesis describes the design, modelling, fabrication, and characterization of an integrated micromachined magnetic bead separator. A microsystem capable of separating magnetic beads from a suspension flowing in a microfluidic channel is designed. Improvements are made compared to a current design by bringing the microfluidic channel closer to the magnetic structures. The microelectromagnets of the design are planar spiral coils with soft magnetic yokes. The magnetic field originating from such a magnetic structure is investigated using three different methods and approximations for the physical system. The magnetic beads experience a magnetic force while flowing in the microfluidic channel. This force is found using the effective moment approximation and by calculating the gradient with respect to the bead coordinates of the total magnetic energy found by integration of the magnetic field over all space. The flow of the magnetic beads in the microfluidic channel under the influence of the microelectromagnets is simulated using the knowledge of the magnetic force, buoyancy, and Stokes drag on the beads. The simulations predict the efficiency of separating magnetic beads from the fluid flow at different volumetric flows. A fabrication scheme for the chosen design is developed and the fabrication is successfully demonstrated. This includes making thick photoresist moulds for electroplating of semi-high aspect ratio copper wires for the electromagnetic coil and electroplating of a magnetic yoke using both PermAlloy and pure nickel. The electromagnetic structures are integrated with the microfluidic channel. The fabricated electromagnetic structures are characterized electronically by measuring the impedance and relating the impedance to an equivalent electronic circuit. The ability to separate magnetic beads from a suspension in a microfluidic channel is demonstrated and it is investigated how the bead capture efficiency changes with the operational parameters of the system. Finally the bead settling pattern in the microfluidic channel is recorded and compared to the pattern predicted by the simulations.
  • Integration of large-area polymer nanopillar arrays into microfluidic devices using in situ polymerization cast molding, Guofang Chen et al. (2007)
    TitleIntegration of large-area polymer nanopillar arrays into microfluidic devices using in situ polymerization cast molding
    AuthorsGuofang Chen, Gregory T. McCandless, Robin L. McCarley, Steven A. Soper
    PublicationLab on a Chip
    AbstractPresented here is a simple and robust approach for the integration of mixed-scale (nm-cm) structures into fluidic devices. We report on devices composed of large-area polymer nanopillar arrays of high aspect ratio (33-667) integrated into microfluidic channels fabricated by cast-molding polymerization of methyl methacrylate with mechanically/lithographically patterned, nanoporous aluminium oxide (AAO) templates. The microchannels containing the nanopillar arrays can be chemically functionalized and used for a variety of applications, such as separation beds or solid-phase reactors/extractors.
  • Integrin-Mediated Mechanotransduction in Vascular Smooth Muscle Cells : Frequency and Force Response Characteristics, Marc E. Goldschmidt et al. (2001)
    TitleIntegrin-Mediated Mechanotransduction in Vascular Smooth Muscle Cells : Frequency and Force Response Characteristics
    AuthorsMarc E. Goldschmidt, Kenneth J. McLeod, W. Robert Taylor
    PublicationCirc Res
    DateApril 13, 2001
    Abstract--Blood vessels are continuously exposed to mechanical forces that lead to adaptive remodeling and atherosclerosis. Although there have been many studies characterizing the responses of vascular cells to mechanical stimuli, the precise mechanical characteristics of the forces applied to cells to elicit these responses are not clear. We designed a magnetic exposure system capable of producing a defined normal force on ferromagnetic beads that are specifically bound to cultured cells coated with extracellular matrix proteins or integrin-specific antibodies. Rat aortic smooth muscle cells were incubated with engineered fibronectin-coated ferromagnetic beads and then exposed to a magnetic field. With activation of extracellular signal-regulated mitogen-activated protein kinase 1/2 (ERK 1/2MAPK) used as a prototypical marker for cell responsiveness to mechanical forces, Western blot analysis demonstrated an increase in phosphorylated ERK 1/2MAPK expression reaching a maximal response of a 3.5-fold increase at a total force of approx2.5 pN per cell. The peak response occurred after 5 minutes of exposure and slowly decreased to baseline after 30 minutes. A cyclic, rather than static, force was required for this activation, and the frequency-response curve increased approx2-fold between 0.5 and 2.0 Hz. Vitronectin- and beta3 antibody-coated beads showed a response nearly identical to those coated with engineered fibronectin, whereas forces applied to beads coated with alpha2 and beta1 antibodies did not significantly activate ERK 1/2MAPK. Mechanical activation of the ERK 1/2MAPK system in rat aortic smooth muscle cells occurs through specific integrin receptors and requires a cyclic force with a magnitude estimated to be in the piconewton range.
  • Integrins regulate opioid receptor signaling in trigeminal ganglion neurons, K.A. Berg et al. (2007)
    TitleIntegrins regulate opioid receptor signaling in trigeminal ganglion neurons
    AuthorsK.A. Berg, G. Zardeneta, K.M. Hargreaves, W.P. Clarke, S.B. Milam
    DateFebruary 9, 2007
    AbstractThe binding of integrins to the extracellular matrix results in focal organization of the cytoskeleton and the genesis of intracellular signals that regulate vital neuronal functions. Recent evidence suggests that integrins modulate G-protein-coupled receptor (GPCR) signaling in hippocampal neurons. In this study we evaluated the hypothesis that integrins regulate the mu opioid receptor in rat trigeminal ganglion neurons. For these studies, primary cultures of adult rat trigeminal ganglion neurons were used to demonstrate the colocalization of [beta]1 and [beta]3 integrins with mu opioid receptor in caveolin-1-rich membrane fractions, and at focal adhesions sites generated by integrin ligand binding. Furthermore, we show that the mu opioid receptor agonist, DAMGO ([D-Ala2,N-MePhe4,Gly-ol5]enkephalin), inhibits cyclic AMP (cAMP) accumulation in response to prostaglandin E2 (PGE2) stimulation in bradykinin-primed, but not unprimed, cultured trigeminal ganglia neurons. Application of soluble GRGDS (Gly-Arg-Gly-Asp-Ser) peptides that bind specific integrins (i.e. RGD-binding integrins) completely abolished the DAMGO effect in bradykinin-primed trigeminal ganglia neurons, but did not alter bradykinin-mediated hydrolysis of phosphatidylinositol. Likewise, monospecific anti-[beta]1 and anti-[beta]3 integrin subunit antibodies blocked this DAMGO effect in bradykinin-primed trigeminal ganglia neurons. Indeed, application of anti-[beta]1 integrin subunit actually reversed DAMGO signaling, resulting in increased cAMP accumulation in these cells. This suggests that the relative amounts of specific activated integrins at focal adhesions may govern signaling by the mu opioid receptor, perhaps by altering interactions with G proteins (e.g. G[alpha]i vs. G[alpha]s). Collectively, these data provide the first evidence that specific integrins regulate opioid receptor signaling in sensory neurons.
  • Introduction: mixing in microfluidics, Julio M. Ottino et al. (2004)
    TitleIntroduction: mixing in microfluidics
    AuthorsJulio M. Ottino, Stephen Wiggins
    PublicationPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
    DateMay 15, 2004
    AbstractIn this paper we briefly review the main issues associated with mixing at the microscale and introduce the papers comprising the Theme Issue.
  • Introduction to Magnetic Materials, B. D. Cullity (1972)
    TitleIntroduction to Magnetic Materials
    AuthorB. D. Cullity
  • Introduction to the Theory of Ferromagnetism, Amikam Aharoni (2001)
    TitleIntroduction to the Theory of Ferromagnetism
    AuthorAmikam Aharoni
    PublisherOxford University Press
  • Investigation of capillary adhesion between the microcantilever and the substrate with electronic speckle pattern interferometry, Xide Li et al. (2006)
    TitleInvestigation of capillary adhesion between the microcantilever and the substrate with electronic speckle pattern interferometry
    AuthorsXide Li, Yun Peng
    PublicationApplied Physics Letters
    DateDecember 04, 2006
    AbstractIn this letter, the authors present an experimental study of the capillary adhesion of microcantilevers and substrate using electronic speckle pattern interferometry. The transient deformation of a microcantilever caused by the capillary force was measured and the energy function of the adhesion system was constructed based on the independent parameters of adhesion length and volume fraction of the adhesion medium. Therefore, the capillary force could be theoretically determined by the minimum energy function, and the deformation of the microcantilever at the equilibrium state could be calculated and compared with the experimental result.
  • Investigations on magnetic properties and structure for carbon encapsulated nanoparticles of Fe, Co, Ni, Xiangcheng Sun et al. (2000)
    TitleInvestigations on magnetic properties and structure for carbon encapsulated nanoparticles of Fe, Co, Ni
    AuthorsXiangcheng Sun, A. Gutierrez, M. Jose Yacaman, Xinglong Dong, Shouri Jin
    PublicationMaterials Science and Engineering A
    DateJune 30, 2000
    AbstractIn the present work, experiments aim at the encapsulation of foreign materials within hollow graphitic cage have been carried out for iron group metals (Fe, Co, Ni) using a modified arc-discharge (carbon arc) reactor. HRTEM (high resolution transmission electron miscroscope), and XRD (X-ray diffractometer) studies, for three carbon encapsulated materials, showing nanoparticles of both a metallic phase ([alpha]-Fe, [gamma]-Fe; hcp-Co, fcc-Co; fcc-Ni) and also a carbide phase (M3C, M=Fe, Co, Ni) are encapsulated in graphitic carbon. The magnetic measurement for the three as-made nanoparticles, indicating that the values of saturation magnetic moment of three nanoparticle are 37.6, 55.5 and 15.7% of the bulk ferromagnetic elements counterparts, respectively. The different comparison values (Mr/Ms) of remanent magnetization (Mr) and saturation magnetization (Ms) suggest, the encapsulated Fe and Co nanoparticles are shown to be ferromagnetic with a ratio of remnant to saturation magnetization Mr/Ms~0.3; whereas, the encapsulated Ni nanoparticles exhibits superparamagnetic behavior at room temperature.
  • Kinetic investigations on the UV-induced photopolymerization of nanocomposites by FTIR spectroscopy, Fusheng Li et al. (2006)
    TitleKinetic investigations on the UV-induced photopolymerization of nanocomposites by FTIR spectroscopy
    AuthorsFusheng Li, Shuxue Zhou, Bo You, Limin Wu
    PublicationJournal of Applied Polymer Science
    AbstractThe kinetics of the photopolymerization for nanocomposites containing nanosilica with 2,2-dimethoxy-1,2-diphenylethan-1-one or benzophenone/n-methyl diethanolamine (BP/MDEA)as photoinitiators were studied by FTIR spectroscopy. It was found that nanocomposites containing nanosilica had higher conversion in comparison with pristine EA. The presence of MPS and ethanol accelerated the photopolymerization of nanocomposites, while the presence of water decelerated it. The photopolymerization of nanocomposites was more sensitive to oxygen than that of pristine EA. � 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1429-1436, 2006
  • Large-area, high-aspect-ratio SU-8 molds for the fabrication of PDMS microfluidic devices, S. Natarajan et al. (2008)
    TitleLarge-area, high-aspect-ratio SU-8 molds for the fabrication of PDMS microfluidic devices
    AuthorsS. Natarajan, D. A. Chang-Yen, B. K. Gale
    PublicationJournal of Micromechanics and Microengineering
    AbstractA relatively low-cost fabrication method using soft lithography and molding for large-area, high-aspect-ratio microfluidic devices, which have traditionally been difficult to fabricate, has been developed and is presented in this work. The fabrication process includes novel but simple modifications of conventional microfabrication steps and can be performed in any standard microfabrication facility. Specifically, the fabrication and testing of a microfluidic device for continuous flow deposition of bio-molecules in an array format are presented. The array layout requires high-aspect-ratio elastomeric channels that are 350 µm tall, extend more than 10 cm across the substrate and are separated by as little as 20 µm. The mold from which these channels were fabricated consisted of high-quality, 335 µm tall SU-8 structures with a high-negative aspect ratio of 17 on a 150 mm silicon wafer and was produced using spin coating and UV-lithography. Several unique processing steps are introduced into the lithographic patterning to eliminate many of the problems experienced when fabricating tall, high-aspect-ratio SU-8 structures. In particular, techniques are used to ensure uniform molds, both in height and quality, that are fully developed even in the deep negative-aspect-ratio areas, have no leftover films at the top of the structures caused by overexposure and no bowing or angled sidewalls from diffraction of the applied UV light. Successful microfluidic device creation was demonstrated using these molds by casting, curing and bonding a polydimethylsiloxane (PDMS) elastomer. A unique microfluidic device, requiring these stringent geometries, for continuous flow printing of a linear array of 16 protein and antibody spots has been demonstrated and validated by using surface plasmon resonance imaging of printed arrays.
  • Layered Magnetic Structures: History, Highlights, Applications, Peter Grunberg (2001)
    TitleLayered Magnetic Structures: History, Highlights, Applications
    AuthorPeter Grunberg
    PublicationPhysics Today
    DateMay 00, 2001
    AbstractThe study of layered magnetic structures is one of the hottest topics in magnetism today, due largely to growing applications in magnetic sensors and in magnetic storage media like computer disks and random-access memories (see the article by L. M. Falicov in PHYSICS TODAY, October 1992, page 46, and the special issue of PHYSICS TODAY on magnetoelectronics, April 1995). Magnetic random-access memories (MRAMs) based on structures of magnetic metallic films interspersed with nonmagnetic metallic or insulating interlayers could be the next generation in magnetic-storage technology, replacing the semiconductor-based dynamic random-access memories (DRAMs) that are now the standard. Advantages of MRAMs include nonvolatility (they retain information when the computer is switched off), high storage density, and low energy consumption. Until the introduction of DRAMs in the 1970s, MRAM technology—using minute ferrite rings, or “core”—was dominant. Thin magnetic film was suggested as a replacement for core as early as 1955, and the first research results were presented in 1959, but problems with reliability of film-based MRAMs led instead to the adoption of DRAMs.
  • Long-Term Monitoring of Bacteria Undergoing Programmed Population Control in a Microchemostat, Frederick K. Balagadde et al. (2005)
    TitleLong-Term Monitoring of Bacteria Undergoing Programmed Population Control in a Microchemostat
    AuthorsFrederick K. Balagadde, Lingchong You, Carl L. Hansen, Frances H. Arnold, Stephen R. Quake
    DateJuly 1, 2005
    AbstractUsing an active approach to preventing biofilm formation, we implemented a microfluidic bioreactor that enables long-term culture and monitoring of extremely small populations of bacteria with single-cell resolution. We used this device to observe the dynamics of Escherichia coli carrying a synthetic "population control" circuit that regulates cell density through a feedback mechanism based on quorum sensing. The microfluidic bioreactor enabled long-term monitoring of unnatural behavior programmed by the synthetic circuit, which included sustained oscillations in cell density and associated morphological changes, over hundreds of hours.
  • Magnetically actuated micropumps using an Fe-PDMS composite membrane, J.J. Nagel et al. (2006)
    TitleMagnetically actuated micropumps using an Fe-PDMS composite membrane
    AuthorsJ.J. Nagel, G. Mikhail, H. Noh, J. Koo
    PublicationProceedings of SPIE, the International Society for Optical Engineering
    AbstractIn this paper we describe a novel Fe-PDMS composite that can be used to create magnetically actuated polymeric microstructures. The composite is formed by suspending <10µm iron (Fe) particles in polydimethylsiloxane (PDMS) at concentrations ranging from 25-75% by weight. Material properties and processing capabilities have been examined, and to demonstrate material's usefulness we have designed, fabricated, and tested two prototypical micropumps that utilize an Fe-PDMS actuator membrane.
  • Magnetically Actuated Nanorod Arrays as Biomimetic Cilia, B.A. Evans et al. (2007)
    TitleMagnetically Actuated Nanorod Arrays as Biomimetic Cilia
    AuthorsB.A. Evans, A.R. Shields, R.L. Carroll, S. Washburn, M.R. Falvo, R. Superfine
    PublicationNano Letters
    DateMay 9, 2007
    AbstractWe present a procedure for producing high-aspect-ratio cantilevered micro- and nanorod arrays of a PDMS-ferrofluid composite material. The rods have been produced with diameters ranging from 200 nm to 1 m and aspect ratios as high as 125. We demonstrate actuation of these superparamagnetic rod arrays with an externally applied magnetic field from a permanent magnet and compare this actuation with a theoretical energy-minimization model. The structures produced by these methods may be useful in microfluidics, photonic, and sensing applications.
  • Magnetically controlled valve for flow manipulation in polymer microfluidic devices, Gaspar et al. (2007)
    TitleMagnetically controlled valve for flow manipulation in polymer microfluidic devices
    Authors Gaspar, Piyasena, Daroczi, Gomez
    PublicationMicrofluidics and Nanofluidics
    Date15 August 2007
    AbstractA simple, external in-line valve for use in microfluidic devices constructed of polydimethylsiloxane (PDMS) is described. The actuation of the valve is based on the principle that flexible polymer walls of a liquid channel can be pressed together by the aid of a permanent magnet and a small metal bar. In the presence of a small NdFeB magnet lying below the channel of interest, the metal bar is pulled downward simultaneously pushing the thin layer of PDMS down thereby closing the channel stopping any flow of fluid. The operation of the valve is dependent on the thickness of the PDMS layer, the height of the channel, the gap between the chip and the magnet and the strength of the magnet. The microfluidic channels are completely closed to fluid flows ranging from 0.1 to 1.0 μL/min commonly used in microfluidic applications.
  • Magnetically Driven Colloidal Microstirrer, P. Tierno et al. (2007)
    TitleMagnetically Driven Colloidal Microstirrer
    AuthorsP. Tierno, T.H. Johansen, T.M. Fischer
    PublicationJournal of Physical Chemistry B
    DateMarch 29, 2007
    AbstractParamagnetic colloidal particles dispersed in water and deposited above magnetic bubble domains of a uniaxial ferrimagnetic garnet film are used as microscopic stirrer when subjected to external rotating magnetic fields. The hydrodynamic flow field above the stirrer is detected by tracking of nonmagnetic microspheres. The vorticity of the flow falls off inversely proportionally to the distance from the bubble center and is proportional to the field frequency. The device provides complete control over the mixing capability. This alternative method of active mixing might be used for microfluidics applications where mechanical stirring cannot be achieved easily with other machinery parts.
  • Magnetic-based microfluidic platform for biomolecular separation, Qasem Ramadan et al. (2006)
    TitleMagnetic-based microfluidic platform for biomolecular separation
    AuthorsQasem Ramadan, Victor Samper, Daniel Poenar, Chen Yu
    PublicationBiomedical Microdevices
    DateJune 11, 2006
    AbstractA novel microfluidic platform for manipulation of micro/nano magnetic particles was designed, fabricated and tested for applications dealing with biomolecular separation. Recently, magnetic immunomagnetic cell separation has attracted a noticeable attention due to the high selectivity of such separation methods. Strong magnetic field gradients can be developed along the entire wire, and the miniaturized size of these current-carrying conductors strongly enhances the magnetic field gradient and therefore produces large, tunable and localized magnetic forces that can be applied on magnetic particles and confine them in very small spots. Further increases in the values of the generated magnetic field gradients can be achieved by employing miniaturized ferromagnetic structures (pillars) which can be magnetized by an external magnetic field or by micro-coils on the same chip. In this study, we demonstrate magnetic beads trapping, concentration, transportation and sensing in a liquid sample under continuous flow by employing high magnetic field gradients generated by novel multi-functional magnetic micro-devices. Each individual magnetic micro-device consists of the following components: 1. Cu micro-coils array embedded in the silicon substrate with high aspect ratio conductors for efficient magnetic field generation 2. Magnetic pillar(s) made of the magnetic alloy NiCoP for magnetic field focusing and magnetic field gradient enhancement. Each pillar is magnetized by its corresponding coil 3. Integrated sensing coil for magnetic beads detection 4. Microfluidic chamber containing all the previous components. Magnetic fields of about 0.1 T and field gradients of around 300 T/cm have been achieved, which allowed to develop a magnetic force of 3 10−9 N on a magnetic particle with radius of 1 μm. This force is large enough to trap/move this particle as the required force to affect such particles in a liquid sample is on the order of ∼pN. Trapping rates of up to 80% were achieved. Furthermore, different micro-coil designs were realized which allowed various movement modes and with different step-sizes. These results demonstrate that such devices incorporated within a microfluidic system can provide significantly improved spatial resolution and force magnitude for quick, efficient and highly selective magnetic trapping, separation and transportation, and as such they are an excellent solution for miniaturized μ-total analysis systems.
  • Magnetic bead handling on-chip: new opportunities for analytical applications, Gijs (2004)
    TitleMagnetic bead handling on-chip: new opportunities for analytical applications
    Author Gijs
    PublicationMicrofluidics and Nanofluidics
    DateNovember 01, 2004
    AbstractThis review describes recent advances in the handling and manipulation of magnetic particles in microfluidic systems. Starting from the properties of magnetic nanoparticles and microparticles, their use in magnetic separation, immuno-assays, magnetic resonance imaging, drug delivery, and hyperthermia is discussed. We then focus on new developments in magnetic manipulation, separation, transport, and detection of magnetic microparticles and nanoparticles in microfluidic systems, pointing out the advantages and prospects of these concepts for future analysis applications.
  • Magnetic behavior of nearly spherical Fe3O4 particles in low magnetic fields at elevated temperatures, S. Arajs N. Amin (1986)
    TitleMagnetic behavior of nearly spherical Fe3O4 particles in low magnetic fields at elevated temperatures
    AuthorS. Arajs N. Amin
    Publicationphysica status solidi (a)
    AbstractNearly spherical Fe3O4 (magnetite) particles (0.09 to 0.62) ?m in diameter, prepared by hydrogen transformation of ?-Fe2O3 (hematite), are studied in weak (up to 50 Oe) magnetic fields as a function of increasing and decreasing temperatures from 300 K to the Curie temperature (TC = = 853 K). In smaller demagnetized particles the magnetization gradually increases with increasing temperature reaching a maximum just below TC and then rapidly disappears at TC. In larger particles the magnetization close to TC first slowly decreases, then increases as the temperature approaches TC, and goes again to zero at TC. These observations are discussed from the viewpoint of changes in domain configurations as a function of temperature
  • Magnetic Cell Separation: Characterization of Magnetophoretic Mobility, K.E. McCloskey et al. (2003)
    TitleMagnetic Cell Separation: Characterization of Magnetophoretic Mobility
    AuthorsK.E. McCloskey, J.J. Chalmers, M. Zborowski
    PublicationAnalytical Chemistry
    DateDecember 15, 2003
    AbstractMagnetic cell separation has become a popular technique to enrich or deplete cells of interest from a heterogeneous cell population. One important aspect of magnetic cell separation is the degree to which a cell binds paramagnetic material. It is this paramagnetic material that imparts a positive magnetophoretic mobility to the target cell, thus allowing effective cell separation. A mathematical relationship has been developed to correlate magnetic labeling to the magnetophoretic mobility of an immunomagnetically labeled cell. Four parameters have been identified that significantly affect magnetophoretic mobility of an immunomagnetically labeled cell: the antibody binding capacity (ABC) of a cell population, the secondary antibody amplification (), the particle-magnetic field interaction parameter (Vm), and the cell diameter (Dc). The ranges of these parameters are calculated and presented along with how the parameters affect the minimum and maximum range of magnetophoretic mobility. A detailed understanding of these parameters allows predictions of cellular magnetophoretic mobilities and provides control of cell mobility through selection of antibodies and magnetic particle conjugates.
  • Magnetic characterization of a single superparamagnetic bead by phase-sensitive micro-Hall magnetometry, Goran Mihajlovic et al. (2007)
    TitleMagnetic characterization of a single superparamagnetic bead by phase-sensitive micro-Hall magnetometry
    AuthorsGoran Mihajlovic, Khaled Aledealat, Peng Xiong, Stephan von Molnar, Mark Field, Gerard J. Sullivan
    PublicationApplied Physics Letters
    DateOctober 22, 2007
  • Magnetic characterization of superparamagnetic nanoparticles pulled through model membranes, Allison Barnes et al. (2007)
    TitleMagnetic characterization of superparamagnetic nanoparticles pulled through model membranes
    AuthorsAllison Barnes, Ronald Wassel, Fadee Mondalek, Kejian Chen, Kenneth Dormer, Richard Kopke
    PublicationBioMagnetic Research and Technology
    AbstractBACKGROUND:To quantitatively compare in-vitro and in vivo membrane transport studies of targeted delivery, one needs characterization of the magnetically-induced mobility of superparamagnetic iron oxide nanoparticles (SPION). Flux densities, gradients, and nanoparticle properties were measured in order to quantify the magnetic force on the SPION in both an artificial cochlear round window membrane (RWM) model and the guinea pig RWM.METHODS:Three-dimensional maps were created for flux density and magnetic gradient produced by a 24-well casing of 4.1 kilo-Gauss neodymium-iron-boron (NdFeB) disc magnets. The casing was used to pull SPION through a three-layer cell culture RWM model. Similar maps were created for a 4 inch (10.16 cm) cube 48 MGOe NdFeB magnet used to pull polymeric-nanoparticles through the RWM of anesthetized guinea pigs. Other parameters needed to compute magnetic force were nanoparticle and polymer properties, including average radius, density, magnetic susceptibility, and volume fraction of magnetite.RESULTS:A minimum force of 5.04 x 10-16 N was determined to adequately pull nanoparticles through the in-vitro model. For the guinea pig RWM, the magnetic force on the polymeric nanoparticles was 9.69 x 10-20 N. Electron microscopy confirmed the movement of the particles through both RWM models.CONCLUSION:As prospective carriers of therapeutic substances, polymers containing superparamagnetic iron oxide nanoparticles were succesfully pulled through the live RWM. The force required to achieve in vivo transport was significantly lower than that required to pull nanoparticles through the in-vitro RWM model. Indeed very little force was required to accomplish measurable delivery of polymeric-SPION composite nanoparticles across the RWM, suggesting that therapeutic delivery to the inner ear by SPION is feasible.
  • Magnetic Detection of Microstructural Change in Power Plant Steels , Victoria Anne Yardley (2003)
    TitleMagnetic Detection of Microstructural Change in Power Plant Steels
    AuthorVictoria Anne Yardley
    DateMay 2003
    AbstractPower plant components are expected to withstand service at high tem- perature and pressure for thirty years or more. One of the main failure mechanisms under these conditions is creep. The steel compositions and heat treatments for this application are chosen to confer microstructural sta- bility and creep resistance. Nevertheless, gradual microstructural changes, which eventually degrade the creep properties, occur during the long service life. Conservative design lives are used in power plant, and it is often found that components can be used safely beyond the original design life. How- ever, to benefit from this requires reliable monitoring methods. One such technique involves relating the microstructural state to measurable magnetic properties. Magnetic domain walls interact energetically with microstructural fea- tures such as grain boundaries, carbides and dislocations, and are ‘pinned’ in place at these sites until a sufficiently large field is applied to free them. When this occurs, the sudden change in magnetisation as the walls move can be detected as a voltage signal (Barkhausen noise). Previous work has suggested that grain boundaries and carbide particles in power plant steels act as pinning sites with characteristic strengths and strength distributions. In this study, the concept of pinning site strength distributions was used to develop a model for the variation of the Barkhausen noise signal with ap- plied field. This gave a good fit to published data. The modelling parameters characterising pinning site strengths showed good correlations with grain and carbide particle sizes. New Barkhausen noise data were obtained from tempered power plant steel samples for further model testing. The Orientation Imaging Microscopy (OIM) technique was used to investigate the grain orientations and grain boundary properties in the steel and their possible role in Barkhausen noise behaviour. The model again fitted the data well, and a clear relationship could be seen between the pinning strength parameter and the severity of tempering (as expressed by the Larson-Miller tempering parameter) to which the steel was subjected. The experimental results suggest that the Barkhausen noise characteris- tics of the steels investigated depend strongly on the strain at grain bound- aries. As tempering progresses and the grain boundary dislocation density falls, the pinning strength of the grain boundaries also decreases. A clear difference in Barkhausen noise response could be seen between a 2 1 Cr1Mo 4 traditional power-plant steel and an 11Cr1Mo steel designed for superior heat resistance. A study of an oxide dispersion strengthened ferrous alloy, in which the mi- crostructure undergoes dramatic coarsening on recrystallisation, was used to investigate further the effects of grain boundaries and particles on Barkhausen noise. The findings from these experiments supported the conclusion that grain boundary strain reduction gave large changes in the observed Barkhausen noise.
  • Magnetic, electrical and optical properties of metal-polymer nanocomposites, A.D. Pomogailo et al. (2005)
    TitleMagnetic, electrical and optical properties of metal-polymer nanocomposites
    AuthorsA.D. Pomogailo, V.N. Kestelman
    AbstractHighly dispersed nanoscale particles in polymer matrices are currently attracting great interest in many fields of chemistry, physics, and materials science. This book presents and analyzes the essential data on nanoscale metal clusters dispersed in, or chemically bonded with polymers. Special attention is paid to the in situ synthesis of the nanocomposites, their chemical interactions, and the size and distribution of the particles in the polymer matrix. Numerous novel nanocomposites are described with regard to their mechanical, electrophysical, optical, magnetic, catalytic, and biological properties. Their applications, present and future, are outlined. The book is addressed both to researchers who actively use these materials and to students entering this multidisciplinary field.
  • Magnetic field driven nanowire rotation in suspension, K. Keshoju et al. (2007)
    TitleMagnetic field driven nanowire rotation in suspension
    AuthorsK. Keshoju, H. Xing, L. Sun
    PublicationApplied Physics Letters
  • Magnetic Field-Responsive Smart Polymer Composites, Genovéva Filipcsei et al. (2007)
    TitleMagnetic Field-Responsive Smart Polymer Composites
    AuthorsGenovéva Filipcsei, Ildikó Csetneki, András Szilágyi, Miklós Zrínyi
    AbstractThe combination of polymers with nano- or microsized solid materials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. Materials whose physical properties can be varied by application of magnetic fields belong to a specific class of smart materials. The broad family of magnetic field-controllable soft materials includes ferrofluids, magneto-rheological fluids, magnetic gels, and magnetic elastomers. The magnetic gels and elastomers (magnetoelasts) represent a new type of composite and consist of small magnetic particles, usually in the nanometer to micron range, dispersed in a highly elastic polymeric matrix. The magnetic particles can be incorporated into the elastic body either randomly or in ordered structure. If a uniform magnetic field is applied to the reactive mixture during the cross-linking process, particle chains form and become locked into the elastomer. The resulting composites exhibit anisotropic properties. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic fields. The magnetic particles couple the shape and the elastic modulus with the external magnetic field. Giant deformational effects, high elasticity, anisotropic elastic and swelling properties, and quick response to magnetic fields open new opportunities for using such materials for various applications. Since the magnetic fields are convenient stimuli from the point of signal control, the magnetoelasts are promising smart materials in engineering due to their real-time controllable elastic properties. More recently, increasing interest has been devoted to exploration of multiresponsive magnetic polymers, which exhibit sensitivity to several external stimuli. Micro- and nanospheres that combine both magnetic, temperature, and pH sensitivity were also elaborated and studied. These new results provide novel possibilities for preparation of more complex magnetic field-responsive materials like membranes with on/off switching control. In this article, we review recent advances in mechanical and swelling behavior of magnetic field-responsive soft materials, including flexible polymer networks and gels.
  • Magnetic microactuators based on polymer magnets, L.K. Lagorce et al. (1999)
    TitleMagnetic microactuators based on polymer magnets
    AuthorsL.K. Lagorce, O. Brand, M.G. Allen
    PublicationJournal of Microelectromechanical Systems
    AbstractIntegrated permanent magnet microactuators have been fabricated using micromachined polymer magnets. The hard magnetic material utilized is a polymer composite, consisting of magnetically hard ceramic ferrite powder imbedded in a commercial epoxy resin to a volume loading of 80%. The magnets have the form of thin disks approximately 4 mm in diameter and 90 μm in thickness. These disks have been magnetized in the thickness direction, and even in this geometrically unfavorable direction showed typical permanent magnet behavior with an intrinsic coercivity Hci of 4000 Oe (320 kA/m) and a residual induction Br of 600 Gauss (60 mT). Cantilever beam-type magnetic actuators carrying a screen-printed disk magnet on their free ends have been fabricated on an epoxy board. A planar coil on the opposite side of the substrate is used to drive the beams vertically. The actuators exhibit hard magnetic behavior allowing both attraction and repulsion by reversing the current direction. Static and dynamic testing of the magnetic actuators have been performed. The experimental data are compared with theoretical results obtained from both finite element simulations and analytical models. Good agreement is obtained between simulation and experiment
  • Magnetic nanoparticles with surface modification enhanced gene delivery of HVJ-E vector, Norio Morishita et al. (2005)
    TitleMagnetic nanoparticles with surface modification enhanced gene delivery of HVJ-E vector
    AuthorsNorio Morishita, Hironori Nakagami, Ryuichi Morishita, Shin-ichi Takeda, Fumihito Mishima, BungoTerazono, Shigehiro Nishijima, Yasufumi Kaneda, Noriaki Tanaka
    PublicationBiochemical and Biophysical Research Communications
    DateSeptember 9, 2005
    AbstractTo enter the realm of human gene therapy, a novel drug delivery system is required for efficient delivery of small molecules with high safety for clinical usage. We have developed a unique vector "HVJ-E (hemagglutinating virus of Japan-envelope)" that can rapidly transfer plasmid DNA, oligonucleotide, and protein into cells by cell-fusion. In this study, we associated HVJ-E with magnetic nanoparticles, which can potentially enhance its transfection efficiency in the presence of a magnetic force. Magnetic nanoparticles, such as maghemite, with an average size of 29 nm, can be regulated by a magnetic force and basically consist of oxidized Fe which is commonly used as a supplement for the treatment of anemia. A mixture of magnetite particles with protamine sulfate, which gives a cationic surface charge on the maghemite particles, significantly enhanced the transfection efficiency in an in vitro cell culture system based on HVJ-E technology, resulting in a reduction in the required titer of HVJ. Addition of magnetic nanoparticles would enhance the association of HVJ-E with the cell membrane with a magnetic force. However, maghemite particles surface-coated with heparin, but not protamine sulfate, enhanced the transfection efficiency in the analysis of direct injection into the mouse liver in an in vivo model. The size and surface chemistry of magnetic particles could be tailored accordingly to meet specific demands of physical and biological characteristics. Overall, magnetic nanoparticles with different surface modifications can enhance HVJ-E-based gene transfer by modification of the size or charge, which could potentially help to overcome fundamental limitations to gene therapy in vivo.
  • Magnetic properties of NiO nanoparticles, S.D. Tiwari et al. (2006)
    TitleMagnetic properties of NiO nanoparticles
    AuthorsS.D. Tiwari, K.P. Rajeev
    PublicationThin Solid Films
    DateMay 18, 2006
    AbstractNickel oxide nanoparticles of different sizes are prepared by a sol-gel method. Samples are characterized by X-ray diffraction and transmission electron microscopy. Dc susceptibility measurements as a function of temperature and field are done for various particle sizes. We find peaks in zero field cooled susceptibility vs. temperature curves. In sufficiently low fields the peak temperature decreases with increasing particle size whereas at higher fields the peak temperature increases with increasing particle size. We propose that these nanoparticles consist of antiferromagnetically aligned core spins and a spin glass like surface layer.
  • Magnetic properties of sub-micrometer superparamagnetic beads used for biosensors, K. Ommering, van (2005)
    TitleMagnetic properties of sub-micrometer superparamagnetic beads used for biosensors
    AuthorK. Ommering, van
    AbstractMagnetic biosensors are being investigated as a new means to detect low concentrations of molecules in body fluids such as urine and blood. These biosensors are based on an immunoassay, where target molecules are labeled with superparamagnetic beads that can be detected with a giant magnetoresistance (GMR) sensor. The superparamagnetic beads can also be used for actuation, for example to enhance transport of molecules to the sensor surface. It is essential to know the magnetic properties of these beads for accurate detection and actuation in these biosensors. In this report, two techniques will be described that can measure the magnetic susceptibility of sub-micrometer superparamagnetic beads. Both the magnitude of the susceptibility and the statistical distribution between beads can be determined. The two techniques have in common that beads are observed in a biosensor environment, excluding possible influence of the environment. Beads are suspended in a fluid and applied to a chip. With current wires below the surface of this chip, a magnetic field is induced. A gradient in the magnetic field will cause the beads to move. The movement of the beads is monitored with a water-immersion microscope with very high magnification, a high-speed camera and image-processing software. The first technique is called magnetophoresis. The speed of the bead in a known magnetic field gradient is determined, which directly relates to the susceptibility. This technique already exists for about 10 years, but has never been employed with beads smaller than 1 μm. For these beads, Brownian motion complicates the measurements. In this report a set-up will be described that is suitable for characterizing sub-micrometer beads. Measurements have shown that the measured susceptibilities of individual 300 nm beads are around 0.2·10-19 m3 per bead. This is close to the value expected based on VSM measurements of bulk samples (0.38·10-19 m3). Differences between beads seem to exist, but Brownian motion still complicates the measurements considerably, so no definite results can be given. In the future, using a slightly different set-up might improve the results. Also, a chip is designed, which is even more suitable for magnetophoresis measurements. This chip is called the biochannel chip. Simulations have shown that, using this chip, it should be possible to measure the susceptibility with a higher accuracy. The biochannel chip is fabricated, but measurements have not yet been performed. The second technique uses Brownian motion to measure the susceptibility of sub-micrometer superparamagnetic beads. This technique is completely new in the field of bead characterization. By analyzing the Brownian motion of beads trapped in a known magnetic potential well on the surface of a chip, the susceptibility can be calculated. This technique has proven to be very suitable for this purpose. It is demonstrated that the susceptibility of beads can differ by a factor of ten. Also, the size of the beads is optically determined, making it possible to examine the correlation between size and susceptibility of individual beads. It is shown that larger beads usually have a larger susceptibility, but beads of the same size can also have a susceptibility that differs by an order of magnitude. This can be explained by factors like grain size, grain distribution, grain interaction and shape anisotropy. Using these two techniques, more insight is obtained in the magnetic susceptibility of individual beads. This can improve detection and manipulation in magnetic biosensors. Moreover, in the future, more suitable beads can be chosen or the result of separation techniques can be examined.
  • Magnetic properties of superparamagnetic γ-Fe2O3 nanoparticles prepared by coprecipitation technique, Jong-Ryul Jeong et al. (2005)
    TitleMagnetic properties of superparamagnetic γ-Fe2O3 nanoparticles prepared by coprecipitation technique
    AuthorsJong-Ryul Jeong, Sung-Chul Shin, Seung-Jun Lee, Jong-Duk Kim
    PublicationJournal of Magnetism and Magnetic Materials
    DateFebruary 2005
    Abstractγ-Fe2O3 nanoparticles have been synthesized by a chemical coprecipitation technique using the typical pipette drop method and the novel piezoelectric nozzle method. Nanoparticles made by the piezoelectric nozzle method show smaller size and very narrow size distribution compared to the nanoparticles produced by the pipette drop method. The superconducting quantum interference device (SQUID) measurements show superparamagnetism of nanoparticles and reveal that the anisotropy constants of the nanoparticles made by the pipette drop method and the piezoelectric nozzle method are 2.2x106 and 9.0x106 erg/cm3, respectively. By measuring the magnetic relaxation of the magnetization at 5 K, we also obtained magnetic viscosity of [gamma]-Fe2O3 nanoparticles.
  • Magnetic properties of ultrafine ferrite particles, Toshihiko Sato et al. (1987)
    TitleMagnetic properties of ultrafine ferrite particles
    AuthorsToshihiko Sato, Tetsuo Iijima, Masahiro Seki, Nobuo Inagaki
    PublicationJournal of Magnetism and Magnetic Materials
    DateMarch 1, 1987
    AbstractThe morphology and magnetic properties of ultrafine ferrite particles prepared by coprecipitation are studied. Saturation magnetization is found to decrease sharply when the particle size is reduced below 10 nm, and this decrease is found to be related to the crystalline magnetic anisotropy constant K1.
  • Magnetic properties of variable-sized Fe3O4 nanoparticles synthesized from non-aqueous homogeneous solutions of polyols, Daniela Caruntu et al. (2007)
    TitleMagnetic properties of variable-sized Fe3O4 nanoparticles synthesized from non-aqueous homogeneous solutions of polyols
    AuthorsDaniela Caruntu, Gabriel Caruntu, Charles J. O'Connor
    PublicationJournal of Physics D: Applied Physics
    AbstractThe magnetic behaviour of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8 nm prepared in a non-aqueous medium was investigated. The smaller nanocrystals exhibit superparamagnetism with the blocking temperatures increasing with the particle size, whereas the biggest particles are ferromagnetic at room temperature. The saturation magnetization values are slightly smaller than that of the bulk material, suggesting the existence of a disordered spin configuration on their surface. The thickness of the magnetically inert shell was estimated from the size variation of the magnetization at 1.9 . The dipole-dipole interactions between the particles were tuned by changing the interparticle distances, e.g. by diluting the nanopowders in a non-magnetic matrix at concentrations ranging from 0.25 to 100 wt%. As the strength of the interactions is decreased with dilution, the energy barrier is substantially lowered; this will induce a drastic decrease of both the blocking temperatures and the coercivity with decreasing concentration of the nanoparticles.
  • Magnetic separation in microfluidic systems, K. Smistrup (2007)
    TitleMagnetic separation in microfluidic systems
    AuthorK. Smistrup
    DateJanuary 31, 2007
    AbstractThis Ph.D. thesis presents theory, modeling, design, fabrication, experiments and results for microfluidic magnetic separators. A model for magnetic bead movement in a microfluidic channel is presented, and the limits of the model are discussed. The effective magnetic field gradient is defined, and it is argued that it is a good measure, when comparing the performance of magnetic bead separators. It is described how numeric modelling is used to aid the design of microfluidic magnetic separation systems. An example of a design optimization study is given. A robust fabrication scheme has been developed for fabrication of silicon based systems. This fabrication scheme is explained, and it is shown how, it is applied with variations for several designs of magnetic separators. An experimental setup for magnetic separation experiments has been developed. It has been coupled with an image analysis program to facilitate real-time monitoring of the experiments. The set-up and experimental protocol are described in detail. Results are presented for ’active’ magnetic bead separators, where on-chip microfabricated electromagnets supply the magnetic field and field gradients necessary for magnetic bead separation. It is shown conceptually how such a system can be applied for parallel biochemical processing in a microfluidic system. ’Passive’ magnetic separators are presented, where on-chip soft magnetic elements are magnetized by an external magnetic field and create strong magnetic fields and gradients inside a microfluidic channel. Systems with the elements placed beside the microfluidic channel is combined with hydrodynamic focusing to demonstrate a magnetic bead microarray inside a microfluidic channel. Systems where the on-chip magnetic material is placed underneath the microfluidic channel are also presented. One of these designs feature multiple magnetic length scales, and it is shown that this enhances bead capture ability. A ’hybrid’ magnetic separator design, where the magnetic field from on-chip current lines couples with an externally applied homogenous field to create strong fields and gradients is demonstrated. This gives extra magnetic bead manipulation possibilities compared to the passive designs. It is demonstrated how this can be used for magnetic bead microarrays. Finally, it is discussed, based on the research presented in this thesis, how to further develop magnetic separation systems in microfluidic systems, and recommendations are given for the choice of magnetic design based on the desired application.
  • Magnetic size effects in iron nanoparticles and nanoparticle arrays, Y. Ijiri et al. (2002)
    TitleMagnetic size effects in iron nanoparticles and nanoparticle arrays
    AuthorsY. Ijiri, D. F. Farrell, S. Yamamuro, S. A. Majetich
    PublicationAPS Meeting Abstracts
    DateMarch 1, 2002
    AbstractIn order to probe magnetic size effects on the nanometer length scale, we have investigated a series of different size-selected iron nanoparticles which self-assemble into ordered arrays. The particles were synthesized in solution from the decomposition of iron pentacarbonyl and coated with surfactant molecules. Concentrations, reaction rates, and surfactants were varied to produce particles with mean diameters from 5 to 10 nm and tight size distributions of 5-10%. Magnetization measurements reveal unusual features in the dependencies of the blocking temperature and the time-dependent decay of the magnetization as a function of particle size. The results are interpreted by considering the expected changes to the magnitude of the relevant dipolar and exchange interactions.
  • Magnetic susceptibility of strongly magnetic ores at different magnetic field intensities, Rychkov et al. (1978)
    TitleMagnetic susceptibility of strongly magnetic ores at different magnetic field intensities
    Authors Rychkov, Lomovtsev
    PublicationJournal of Mining Science
    DateNovember 11, 1978
    AbstractConclusions 1. At a given intensity, the magnetic susceptibility of strongly magnetic ores is directly proportional to the maximum susceptibility, proportional to the fourth root of the magnetic field intensity corresponding to the susceptibility maximum, and inversely proportional to the fourth root of the given magnetic field intensity. 2. The proposed procedure for determining the specific force of magnetic attraction (5) of strongly magnetic particles to the separator poles, which takes account of the dependence of the susceptibility on the field intensity, the textural-structural chracteristics of the ore, and the ferromagnetic phase content of the intergrowth can be used to calculate the operating conditions of the separator and of apparatus for dry magnetic beneficiation of crushed strongly magnetic ores.
  • Magnetic susceptibility studies of single-crystalline zinc ferrites under pressure, A. Wiechec et al. (2005)
    TitleMagnetic susceptibility studies of single-crystalline zinc ferrites under pressure
    AuthorsA. Wiechec, R. Zach, Z. Ka[cedilla]kol, Z. Tarnawski, A. Kozlowski, J.M. Honig
    PublicationPhysica B: Condensed Matter
    DateApril 30, 2005
    AbstractMagnetic susceptibility measurements of magnetite and zinc ferrite (Fe3-xZnxO4, x=0.0174, 0.049) single-crystal samples were performed under pressure up to 1.2 GPa in the temperature range close to the Verwey transition TV. The application of pressure p decreases TV linearly. The [chi]AC signal is not affected above TV, but rises below TV with p; this was explained by increasing domain wall movement. Finally, the isotropy point TIP increases with pressure indicating that magnetism does not actively participate in the Verwey transition.
  • Magnetism and microfluidics, Nicole Pamme (2006)
    TitleMagnetism and microfluidics
    AuthorNicole Pamme
    PublicationLab on a Chip
    AbstractMagnetic forces are now being utilised in an amazing variety of microfluidic applications. Magnetohydrodynamic flow has been applied to the pumping of fluids through microchannels. Magnetic materials such as ferrofluids or magnetically doped PDMS have been used as valves. Magnetic microparticles have been employed for mixing of fluid streams. Magnetic particles have also been used as solid supports for bioreactions in microchannels. Trapping and transport of single cells are being investigated and recently, advances have been made towards the detection of magnetic material on-chip. The aim of this review is to introduce and discuss the various developments within the field of magnetism and microfluidics.
  • Magnetism & Magnetic Materials; 3S100 course syllabus 2007-2008, H.M. Swagten (2007)
    TitleMagnetism & Magnetic Materials; 3S100 course syllabus 2007-2008
    AuthorH.M. Swagten
    PublisherEindhoven University of Technology
  • Magnetism of nanometer-scale iron particles arrays (invited), S. Wirth et al. (1999)
    TitleMagnetism of nanometer-scale iron particles arrays (invited)
    AuthorsS. Wirth, S. von Molnar, M. Field, D. D. Awschalom
    DateApril 15, 1999
    Proceedings TitleJ. Appl. Phys.
  • Magnetization and actuation of polymeric microstructures containing dispersed magnetic nano-particles., Francis Fahrni et al. (2008)
    TitleMagnetization and actuation of polymeric microstructures containing dispersed magnetic nano-particles.
    AuthorsFrancis Fahrni, Leo J. van Ijzendoorn, Menno W. J. Prins
    PlaceEindhoven University of Technology
  • Magnetization Curling, A. Aharoni (1966)
    TitleMagnetization Curling
    AuthorA. Aharoni
    Publicationphysica status solidi (b)
  • Magnetization curling in a sphere, I. Eisenstein et al. (1976)
    TitleMagnetization curling in a sphere
    AuthorsI. Eisenstein, A. Aharoni
    PublicationJournal of Applied Physics
    DateJanuary 00, 1976
    AbstractUsing simplifying assumptions, solutions for the magnetization distribution in the curling mode are obtained for a ferromagnetic sphere with a uniaxial anisotropy. These are used to obtain a magnetization curve for a vanishing anisotropy constant and the remanent domain configuration in a cobalt sphere. In the latter case it is shown that as the radius of the sphere increases, two cylindrically symmetric coaxial domains are being formed. Some features of this configuration are discussed and a comparison is made with previous literature.
  • Magnetization processes in magnetotactic bacteria systems, Tatyana Polyakova et al. (2005)
    TitleMagnetization processes in magnetotactic bacteria systems
    AuthorsTatyana Polyakova, Vitalii Zablotskii
    PublicationJournal of Magnetism and Magnetic Materials
    DateMay 2005
    AbstractIn low fields, the magnetization of magnetotactic bacteria (MTB) culture is affected by chemotaxis and can be described by the Langevin function which depends on magnetic field strength and chemotaxis energy. In moderate fields, bacteria magnetization switching occurs as the second-order phase transition induced by increasing the field applied opposite the MTB magnetic moments. For bacteria containing one or two chains of magnetosomes we calculated the switching field as a function of the gap between magnetic particles.
  • Magnetization Reversal of Almost Perfect Whiskers, F. E. Luborsky et al. (1964)
    TitleMagnetization Reversal of Almost Perfect Whiskers
    AuthorsF. E. Luborsky, C. R. Morelock
    PublicationJournal of Applied Physics
    DateJuly 00, 1964
  • Magnet levitation at your fingertips, A. K. Geim et al. (1999)
    TitleMagnet levitation at your fingertips
    AuthorsA. K. Geim, M. D. Simon, M. I. Boamfa, L. O. Heflinger
    DateJuly 22, 1999
  • Magnetocrystalline Anisotropy of Low Temperature Phase of Magnetite, K. Abe et al. (1976)
    TitleMagnetocrystalline Anisotropy of Low Temperature Phase of Magnetite
    AuthorsK. Abe, Y. Miyamoto, S. Chikazumi
    PublicationJournal of the Physical Society of Japan
    DateDecember, 1976
    AbstractThe magnetocrystalline anisotropy of low temperature phase of magnetite (Fe3O4) was measured for a monoclinic single phase specimen by using computerized fully-automatic torque magnetometer. The anisotropy is expressed by Ea=Kaα2a+Kbα2b+Kaaα4a+Kbbα4b+Kabα2aα2b-Kuα2111, where αa, αb and α111 are direction cosines of the magnetization with respect to the monoclinic a-, b- and cubic [111] axes, respectively, the last of which coincides with the longest cube diagonal. The values of the anisotropy constants at 4.2 K are: Ka=25.5, Kb=3.7, Ku=2.1, Kaa=1.8, Kbb=2.4 and Kab=7.0 in 105 erg/cm3. It was found that Ka, Kb and Ku exhibit the temperature dependence of an activation type with the activation energy of about 0.02 eV. It was also found that the constants Kaa, Kbb and Kab are well expressed in terms of cubic K1. The mechanism of the anisotropy is also discussed.
  • Magnetroviscoelastic behavior of composite gels, Tohru Shiga et al. (1995)
    TitleMagnetroviscoelastic behavior of composite gels
    AuthorsTohru Shiga, Akane Okada, Toshio Kurauchi
    PublicationJournal of Applied Polymer Science
    AbstractDynamic viscoelasticity of silicone gels having many lines of dispersed iron particles under the influence of external magnetic fields was studied. The particulate composite enhanced its elastic modulus by action of magnetic fields. The magnetroviscoelastic behavior was caused by the cohesive forces between magnetically polarized particles and was analyzed using a simple model of induced dipole-induced dipole interactions. The presented results provide insight into the relationship between macroscopic viscoelastic behavior of the composite gels and the microscopic bondings between dispersed particles. � 1995 John Wiley & Sons, Inc
  • ma-N 400 and ma-N 1400 - Negative Tone Photoresists, Micro Resist Technology GmbH (2008)
    Titlema-N 400 and ma-N 1400 - Negative Tone Photoresists
    AuthorMicro Resist Technology GmbH
  • ma-N 400 and ma-N 1400 Photoresists - technology for Lift-Off Process, Micro Resist Technology GmbH (2004)
    Titlema-N 400 and ma-N 1400 Photoresists - technology for Lift-Off Process
    AuthorMicro Resist Technology GmbH
    Date2 july 2004
    AbstractThe ma-N 400 and ma-N 1400 are an innovation in negative tone photoresists for flexible use for proximity and contact exposure. Full application compatibility with processing of conventional positive tone photoresists is guaranteed. Adjustable negative sidewalls can be created by a simple lithographic process. The generation of more than 1000 nm metal structures by the lift-off process is achievable.
  • Manipulation of Self-Assembled Structures of Magnetic Beads for Microfluidic Mixing and Assaying, A. Rida et al. (2004)
    TitleManipulation of Self-Assembled Structures of Magnetic Beads for Microfluidic Mixing and Assaying
    AuthorsA. Rida, M.A.M. Gijs
    PublicationAnalytical Chemistry
    DateNovember 1, 2004
    AbstractWe present an original concept of manipulation of magnetic microbeads in a microchannel. It is based on the dynamic motion of a self-assembled structure of ferrimagnetic beads that are retained within a microfluidic flow using a local alternating magnetic field. The latter induces a rotational motion of the magnetic particles, thereby strongly enhancing the fluid perfusion through the magnetic structure that behaves as a dynamic random porous medium. The result is a very strong particle-liquid interaction that can be controlled by adjusting the magnetic field frequency and amplitude, as well as the liquid flow rate, and is at the basis of very efficient liquid mixing. The principle is demonstrated using a microfluidic chip made of poly(methyl methacrylate) with integrated soft ferromagnetic plate structures. The latter are part of an electromagnetic circuit and serve to locally apply a magnetic field over the section of the microchannel. Starting from a laminar flow pattern of parallel fluorescein dye and nonfluorescent liquid streams, we demonstrate a 95% mixing efficiency using a mixing length of only 400 m and at liquid flows of the order of 0.5 cm/s. We anticipate that the intense interaction between the fluid and magnetic particles with functionalized surfaces holds large potential for the development of future bead-based assays.
  • Manufacture of high-aspect-ratio micro-hair sensor arrays, G. J. Schmitz et al. (2005)
    TitleManufacture of high-aspect-ratio micro-hair sensor arrays
    AuthorsG. J. Schmitz, Ch Brücker, P. Jacobs
    PublicationJournal of Micromechanics and Microengineering
    AbstractArrays of microposts or micropillars find a variety of applications and one of their key properties is the aspect ratio (AR) of the individual posts. This parameter, for example, determines the sensitivity of micropost force field sensors. A concept for the manufacture of arrays of micro-hairs is presented allowing us to create extremely high AR of the filiform micro-hairs. The concept is based on a 'lost mould process' allowing for frictionless de-moulding of the sensor array by melting respectively dissolution of a mould. Such a 'lost mould process' requires an inexpensive manufacture of the moulds. Moulds were thus prepared by laser drilling of wax foils. The concept has been applied to the manufacture of micro-hairs from poly(dimethylsiloxane) (PDMS) elastomers and aspect ratios close to 20 have been achieved. The basic concept is not restricted to elastomers but can be adapted to other types of materials.
  • Measuring the exchange-stiffness constant of nanocrystalline solids by elastic small-angle neutron scattering, A. Michels et al. (2000)
    TitleMeasuring the exchange-stiffness constant of nanocrystalline solids by elastic small-angle neutron scattering
    Authors A. Michels, J. Weissmüller, A. Wiedenmann, J. S. Pedersen, J. G. Barker
    PublicationPhilosophical Magazine
    DateDecember 2000
    AbstractIn ferromagnets with a non-uniform magnetocrystalline and/or magnetoelastic anisotropy, such as nanocrystalline or cold-worked polycrystalline materials, the static magnetic microstructure gives rise to elastic magnetic small-angle neutron scattering (SANS). The paper explores a method for determining the exchange-stiffness constant A by analysis of the dependence of the elastic SANS cross-section on the applied magnetic field. Experimental results for A and for the spin-wave stiffness constant D in cold-worked or nanocrystalline Ni and Co are found to agree with literature data obtained by inelastic neutron scattering on single-crystal specimens.
  • Mechanical Properties and Consequences of Stereocilia and Extracellular Links in Vestibular Hair Bundles, Jong-Hoon Nam et al. (2006)
    TitleMechanical Properties and Consequences of Stereocilia and Extracellular Links in Vestibular Hair Bundles
    AuthorsJong-Hoon Nam, John R. Cotton, Ellengene H. Peterson, Wally Grant
    PublicationBiophysical Journal
    DateApril 15, 2006
    AbstractAlthough knowledge of the fine structure of vestibular hair bundles is increasing, the mechanical properties and functional significance of those structures remain unclear. In 2004, Bashtanov and colleagues reported the contribution of different extracellular links to bundle stiffness. We simulated Bashtanov's experimental protocol using a three-dimensional finite element bundle model with geometry measured from a typical striolar hair cell. Unlike any previous models, we separately consider two types of horizontal links: shaft links and upper lateral links. Our most important results are as follows. First, we identified the material properties required to match Bashtanov's experiment: stereocilia Young's modulus of 0.74 GPa, tip link assembly (gating spring) stiffness of 5300 pN/microm, and the combined stiffness of shaft links binding two adjacent stereocilia of 750 [~] 2250 pN/microm. Second, we conclude that upper lateral links are likely to have nonlinear mechanical properties: they have minimal stiffness during small bundle deformations but stiffen as the bundle deflects further. Third, we estimated the stiffness of the gating spring based on our realistic three-dimensional bundle model rather than a conventional model relying on the parallel arrangement assumption. Our predicted stiffness of the gating spring was greater than the previous estimation.
  • Mechanical stability and adhesion of microstructures under capillary forces. I. Basic theory, C.H. Mastrangelo et al. (1993)
    TitleMechanical stability and adhesion of microstructures under capillary forces. I. Basic theory
    AuthorsC.H. Mastrangelo, C.H. Hsu
    PublicationJournal of Microelectromechanical Systems
    AbstractStrong capillary forces are developed in the fabrication process of surface micromachined structures during the wet etch of sacrificial layers. The magnitude of these forces is in some cases sufficient to deform and pin these structures to the substrate resulting in device failure. The deflection, mechanical stability, and adhesion of thin micromechanical structure under capillary forces are examined. These phenomena are divided into two separate stages of mechanical collapse and adhesion to the underlying substrate. The basic theory of collapse is described. Approximate conditions are computed to prevent contact to the substrate
  • Mechanics of Motor Proteins and the Cytoskeleton, J Howard (2002)
    TitleMechanics of Motor Proteins and the Cytoskeleton
    AuthorJ Howard
    PublicationApplied Mechanics Reviews
    DateMarch, 2002
  • Mechanosensory Transduction in "Sensory" and "Motile" Cilia, Michael L. Wiederhold (2003)
    TitleMechanosensory Transduction in "Sensory" and "Motile" Cilia
    AuthorMichael L. Wiederhold
    PublicationAnnual Review of Biophysics and Bioengineering
  • MEMS-based fabrication and microfluidic analysis of three-dimensional perfusion systems, Choi et al. (2008)
    TitleMEMS-based fabrication and microfluidic analysis of three-dimensional perfusion systems
    Authors Choi, Vukasinovic, Glezer, Allen
    PublicationBiomedical Microdevices
    AbstractThis paper describes fabrication and fluidic characterization of 3D microperfusion systems that could extend the viability of high-density 3D cultures in vitro. High-aspect ratio towers serve as 3D scaffolds to support the cultures and contain injection sites for interstitial delivery of nutrients, drugs, and other reagents. Hollow and solid-top tower arrays with laser ablated side-ports were fabricated using SU-8. Appropriate sizing of fluidic ports improves the control of agent delivery. Microfluidic perfusion can be used to continuously deliver equal amount of nutrients through all ports, or more media can be delivered at some ports than the others, thus allowing spatial control of steady concentration gradients throughout the culture thickness. The induced 3D flow around towers was validated using micro particle image velocimetry. Based on experimental data, the flow rates from the characteristic ports were found to follow the analytical predictions.
  • Method of images and electrostatic screening by a polarized dielectric sphere, Clinton DeW. Van Siclen (1988)
    TitleMethod of images and electrostatic screening by a polarized dielectric sphere
    AuthorClinton DeW. Van Siclen
    PublicationAmerican Journal of Physics
    DateDecember 00, 1988
  • Microcoils for transport of magnetic beads, Qasem Ramadan et al. (2006)
    TitleMicrocoils for transport of magnetic beads
    AuthorsQasem Ramadan, Chen Yu, Victor Samper, Daniel Puiu Poenar
    PublicationApplied Physics Letters
    DateJanuary 16, 2006
  • Microelectromagnets for the control of magnetic nanoparticles, C. S. Lee et al. (2001)
    TitleMicroelectromagnets for the control of magnetic nanoparticles
    AuthorsC. S. Lee, H. Lee, R. M. Westervelt
    PublicationApplied Physics Letters
    DateNovember 12, 2001
  • Microfabricated solenoids and Helmholtz coils for NMR spectroscopy of mammalian cells, Klaus Ehrmann et al. (2007)
    TitleMicrofabricated solenoids and Helmholtz coils for NMR spectroscopy of mammalian cells
    AuthorsKlaus Ehrmann, Nicolas Saillen, Franck Vincent, Matthieu Stettler, Martin Jordan, Florian Maria Wurm, Pierre-Andre Besse, Radivoje Popovic
    PublicationLab on a Chip
    AbstractNMR-microprobes based on solenoids and Helmholtz coils have been microfabricated and NMR-spectra of mammalian cells have successfully been taken. The microfabrication technology developed for these probes consists of three electroplated copper levels for low resistance coils and three SU-8 layers for the integration of microchannels. This technology allows fabricating solenoids, Helmholtz and planar coils on the same wafer. The coils have inner diameters in the range of 160 to 400 [micro sign]m and detection volumes of 5 to 22 nL. The solenoid and Helmholtz coils show improved RF-field characteristics compared to a planar coil fabricated with the same process. The fabricated solenoid has a particularly low resistance of only 0.46 [capital Omega] at 300 MHz. Moreover, it is very sensitive and has a very uniform RF-field, but shows large line width. The Helmholtz coils are slightly less sensitive, but display a far narrower line width, and are therefore a good compromise. With a Helmholtz coil, a SNR of 620 has been measured after one scan on 9 nL pure water. An NMR-microprobe based on a Helmholtz coil has also been used to take spectra of CHO cells that have been concentrated in the sensitive region of the coil with a mechanical filter integrated into the channel.
  • Microfabrication of cavities in polydimethylsiloxane using DRIE silicon molds, Ut-Binh T. Giang et al. (2007)
    TitleMicrofabrication of cavities in polydimethylsiloxane using DRIE silicon molds
    AuthorsUt-Binh T. Giang, Dooyoung Lee, Michael R. King, Lisa A. DeLouise
    PublicationLab on a Chip
    AbstractWe present a novel method to create cavities in PDMS that is simple and exhibits wide process latitude allowing control over the radius of curvature to form shallow concave pits or deep spherical cavities.
  • `Microfluidic' chips may accelerate biomedical research, David Orenstein (2006)
    Title`Microfluidic' chips may accelerate biomedical research
    AuthorDavid Orenstein
    PublicationStanford Report
    DateJanuary 18, 2006
  • Microfluidic Device for Single-Cell Analysis, A. R Wheeler et al. (2003)
    TitleMicrofluidic Device for Single-Cell Analysis
    AuthorsA. R Wheeler, W. R Throndset, R. J Whelan, A. M Leach, R. N Zare, Y. H Liao, K. Farrell, I. D Manger, A. Daridon
    PublicationAnalytical Chemistry
    AbstractWe have developed a novel microfluidic device constructed from poly(dimethylsiloxane) using multilayer soft lithography technology for the analysis of single cells. The microfluidic network enables the passive and gentle separation of a single cell from the bulk cell suspension, and integrated valves and pumps enable the precise delivery of nanoliter volumes of reagents to that cell. Various applications are demonstrated, including cell viability assays, ionophore-mediated intracellular Ca2+ flux measurements, and multistep receptor-mediated Ca2+ measurements. These assays, and others, are achieved with significant improvements in reagent consumption, analysis time, and temporal resolution over macroscale alternatives.
  • Microfluidic logic gates and timers, Michael W. Toepke et al. (2007)
    TitleMicrofluidic logic gates and timers
    AuthorsMichael W. Toepke, Vinay V. Abhyankar, David J. Beebe
    PublicationLab on a Chip
    AbstractWe use surface tension-based passive pumping and fluidic resistance to create a number of microfluidic analogs to electronic circuit components. Three classes of components are demonstrated: (1) OR/AND, NOR/NAND, and XNOR digital microfluidic logic gates; (2) programmable, autonomous timers; and (3) slow, perfusive flow rheostats. The components can be implemented with standard pipettes and provide a means of non-electronic and autonomous preprogrammed control with potential utility in cell studies and high throughput screening applications.
  • Microfluidic mixers: from microfabricated to self-assembling devices, C. J Campbell et al. (2004)
    TitleMicrofluidic mixers: from microfabricated to self-assembling devices
    AuthorsC. J Campbell, B. A Grzybowski
    PublicationPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
    AbstractThis paper begins with a survey of both passive and active microfluidic mixers that have been implemented in recent years. It then describes a micromixing device based on dynamic self-assembly. This device is easy to fabricate and has excellent working characteristics in the continuous-flow mode. The paper concludes with a brief discussion of possible applications of self-assembly in microfluidics.
  • Microfluidic platforms for lab-on-a-chip applications, Stefan Haeberle et al. (2007)
    TitleMicrofluidic platforms for lab-on-a-chip applications
    AuthorsStefan Haeberle, Roland Zengerle
    PublicationLab on a Chip
    AbstractWe review microfluidic platforms that enable the miniaturization, integration and automation of biochemical assays. Nowadays nearly an unmanageable variety of alternative approaches exists that can do this in principle. Here we focus on those kinds of platforms only that allow performance of a set of microfluidic functions-defined as microfluidic unit operations-which can be easily combined within a well defined and consistent fabrication technology to implement application specific biochemical assays in an easy, flexible and ideally monolithically way. The microfluidic platforms discussed in the following are capillary test strips, also known as lateral flow assays, the "microfluidic large scale integration" approach, centrifugal microfluidics, the electrokinetic platform, pressure driven droplet based microfluidics, electrowetting based microfluidics, SAW driven microfluidics and, last but not least, "free scalable non-contact dispensing". The microfluidic unit operations discussed within those platforms are fluid transport, metering, mixing, switching, incubation, separation, droplet formation, droplet splitting, nL and pL dispensing, and detection.
  • Microfluidics: Fluid physics at the nanoliter scale, Todd M. Squires et al. (2005)
    TitleMicrofluidics: Fluid physics at the nanoliter scale
    AuthorsTodd M. Squires, Stephen R. Quake
    PublicationReviews of Modern Physics
    AbstractMicrofabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Péclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.
  • Microfluidic technologies in clinical diagnostics, Thomas H. Schulte et al. (2002)
    TitleMicrofluidic technologies in clinical diagnostics
    AuthorsThomas H. Schulte, Ron L. Bardell, Bernhard H. Weigl
    PublicationClinica Chimica Acta
    DateJuly 2002
    AbstractBackground: Laboratory instrumentation and analytical devices are becoming smaller, simpler, and smarter. This trend to miniaturization extends to fluid handling and fluid analysis. However, fluid behavior undergoes significant changes as geometric scale decreases. The laminar flow behavior of fluids in microfluidic devices must be accommodated in the design and development of clinical and bio-clinical miniaturized systems. Conclusion: The scale of chemical and clinical analysis systems will continue to decrease. The capability to manufacture smaller fluidic devices and to quantitatively monitor smaller volumes of liquids bring this process of miniaturization into the domain of laminar flow. New and enabling technologies are being developed using the unique diffusion-based characteristics of the laminar flow domain for sample preparation and analysis. These new analytical systems will have a significant impact on the future of clinical diagnostics.
  • Micromagnetic energy barriers, R. Skomski et al. (2006)
    TitleMicromagnetic energy barriers
    AuthorsR. Skomski, J. Zhou, R. D. Kirby, D. J. Sellmyer
    DateApril 15, 2006
    Proceedings Title50th Annual Conference on Magnetism and Magnetic Materials
    Conference Name50th Annual Conference on Magnetism and Magnetic Materials
    PlaceSan Jose, California (USA)
    AbstractThe structure of micromagnetic energy barriers responsible for slow magnetization processes is investigated. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy. This restricts the range of physically meaningful energy barriers. An analysis of the underlying micromagnetic free energy yields power-law dependences with exponents of 3/2 or 2 for physically reasonable models. This must be contrasted to other power laws, such as linear laws, and to 1/H-type dependences. In the limit of small energy barriers, corrections to the Arrhenius law become important. In this regime, there is no simple expression for the relaxation behavior, but two requirements help to judge models and approximations. First, at low temperatures, the Arrhenius-type power laws must be reproduced. Second, as in the Arrhenius limit, the approaches must correspond to well-defined energy landscapes.
  • Micro magnetic silicone elastomer membrane actuator, Melvin Khoo et al. (2001)
    TitleMicro magnetic silicone elastomer membrane actuator
    AuthorsMelvin Khoo, Chang Liu
    PublicationSensors and Actuators A: Physical
    DateApril 15, 2001
    AbstractWe present results of the design, fabrication, and testing of a microfabricated, membrane-type magnetic actuator. Magnetic pieces made of electroplated Permalloy (Ni80Fe20) are embedded in a thin flexible membrane made of silicone elastomer. When an external magnetic field is applied, a torque generated on the magnetic pieces produces membrane displacement. Permalloy pieces that are 100-[mu]m-wide, 870-[mu]m-long, and 22-[mu]m-thick are strategically positioned in a 2-mm-square, 40-[mu]m-thick polydimethylsiloxane (PDMS) membrane (Sylgard 184). This design, produced through numerical simulations, is optimized to realize large membrane displacements. Tests performed on this membrane actuator showed displacements >80 [mu]m in the presence of a 2.85x105 A/m external magnetic field. Larger displacements are possible with greater magnetization fields. This type of membrane actuator can be applied to the fabrication of tetherless micropumps for use in microfluidic systems.
  • Micromagnetic simulation of ferromagnetic part-spherical particles, Richard P. Boardman et al. (2004)
    TitleMicromagnetic simulation of ferromagnetic part-spherical particles
    AuthorsRichard P. Boardman, Hans Fangohr, Simon J. Cox, Alexander V. Goncharov, Alexander A. Zhukov, Peter A. J. de Groot
    DateJune 01, 2004
  • Micro magnetic stir-bar mixer integrated with parylene microfluidic channels, Kee Suk Ryu et al. (2004)
    TitleMicro magnetic stir-bar mixer integrated with parylene microfluidic channels
    AuthorsKee Suk Ryu, Kashan Shaikh, Edgar Goluch, Zhifang Fan, Chang Liu
    PublicationLab on a Chip
    AbstractPreviously, we reported a micro magnetic stir-bar mixer driven by an external rotating magnetic field and its rapid mixing performance in polydimethyl-siloxane (PDMS) channels. The PDMS piece with embedded fluid channels were manually aligned to a glass substrate and assembled. In this paper, we report the fabrication and testing results of a micro magnetic stir-bar monolithically integrated in parylene surface-micromachined channels with improved design features, including small tolerance of the stir-bar to channel wall (10 [micro sign]m). Using of parylene based microchannels with improved design not only provides improved mixing, but also eliminates certain problems associated with PDMS-based channels. For example, porosity of PDMS causes evaporation and absorption of chemicals and thus channels made of PDMS are prone to cross-contamination. We have also demonstrated that the magnetic stir-bar can be used to pump liquid in micro channels.
  • Micromagnetism and the Microstructure of Ferromagnetic Solids, H. Kronmüller et al. (2003)
    TitleMicromagnetism and the Microstructure of Ferromagnetic Solids
    AuthorsH. Kronmüller, M. Fähnle
    PublisherCambridge University Press
    AbstractThe main theme of this book is micromagnetism and microstructure as well as the analysis of the relations between characteristic properties of the hysteresis loop and microstructure. Also presented is an analysis of the role of microstructure in the fundamental magnetic properties (for example magnetorestriction or critical behaviour) of crystalline and amorphous alloys. The authors apply the theory of micromagnetism to all aspects of advanced magnetic materials including domain patterns and magnetization processes under the influence of defect structures. Coverage includes modern developments in computational micromagnetism and its application to spin structures of small particles and platelets. It will be of interest to researchers and graduate students in condensed matter, physics, electrical engineering and materials science, as well as to industrial researchers working in the electrotechnical and recording industry. * The first book to deal with the relations between magnetic properties and microstructure * Includes micromagnetism of advanced metallic materials * Describes computational micromagnetism of magnetization processes as well as the magnetic structures of small particles and thin films Contents 1. Introduction 2. Magnetic Gibbs free energy 3. Basic micromagnetic equilibrium conditions 4. Domain walls in crystalline and amorphous solids 5. Interaction of domain walls with defects 6. Coercivity of modern magnetic materials 7. Statistical theory of domain wall pinning 8. Law of approach to ferromagnetic saturation and high-field susceptibility 9. Microstructure and domain patterns 10. Magnetic after-effects in amorphous alloys 11. Magnetorestriction in amorphous and polycrystalline ferromagnets 12. Micromagnetic theory of phase transitions in spatially disordered spin systems 13. Computational micromagnetism of thin platelets and small particles 14. Computational micromagnetism of dynamic magnetization processes.
  • Micromixing with Linked Chains of Paramagnetic Particles, S.L. Biswal et al. (2004)
    TitleMicromixing with Linked Chains of Paramagnetic Particles
    AuthorsS.L. Biswal, A.P. Gast
    PublicationAnalytical Chemistry
    DateNovember 1, 2004
    AbstractParamagnetic colloidal particles aggregate into linear chains under an applied external magnetic field. These particles can be chemically linked to create chains that can be magnetically actuated to manipulate microscopic fluid flow. The flexibility of the chain can be adjusted by varying the length of the linker molecule. In this paper, we describe the use of a suspension of linked paramagnetic chains in a rotating magnetic field to perform microscale mixing. The effect of chain rotation and flexibility on the diffusion of molecules is studied by observing the mixing of an acid and base in a microchannel. We show that, as the chain rotation frequency increases, there is marked increase in the effective mixing between fluid streams; however, a maximum frequency exists and above this frequency the chains are no longer effective in mixing. More flexible chains are more effective at mixing over a larger range of frequencies.
  • Micropump based on PZT unimorph and one-way parylene valves, Guo-Hua Feng et al. (2004)
    TitleMicropump based on PZT unimorph and one-way parylene valves
    AuthorsGuo-Hua Feng, Eun Sok Kim
    PublicationJournal of Micromechanics and Microengineering
    AbstractThis paper describes a micropump composed of a piezoelectric PZT unimorph and one-way parylene valves. Two different designs of the valves (cantilever- and bridge-type) are studied, fabricated and tested. The micropump (13 × 13 × 1.2 mm3 in size) is capable of pumping liquid up to 700 mL min[?]1 with its pumping speed being insensitive to a backpressure up to 2.5 kPa. The flow rate of 700 mL min[?]1 is obtained when the micropump is driven with square pulses at 6 kHz with 50% duty cycle and 100 V peak-to-peak. The maximum static pumping pressure is measured to be 4 kPa.
  • Model of magnetorheological elastomers, L. C. Davis (1999)
    TitleModel of magnetorheological elastomers
    AuthorL. C. Davis
    PublicationJournal of Applied Physics
    DateMarch 15, 1999
  • Monolithic Microfabricated Valves and Pumps by Multilayer Soft Lithography, Marc A. Unger et al. (2000)
    TitleMonolithic Microfabricated Valves and Pumps by Multilayer Soft Lithography
    AuthorsMarc A. Unger, Hou-Pu Chou, Todd Thorsen, Axel Scherer, Stephen R. Quake
    DateApril 7, 2000
  • Multiple Actions of Propofol on alphabetagamma and alphabetadelta GABAA Receptors, Hua-Jun Feng et al. (2004)
    TitleMultiple Actions of Propofol on alphabetagamma and alphabetadelta GABAA Receptors
    AuthorsHua-Jun Feng, Robert L. Macdonald
    PublicationMol Pharmacol
    DateDecember 1, 2004
    AbstractGABAA receptors are predominantly composed of alphabetagamma and alphabetadelta isoforms in the brain. It has been proposed that alphabetagamma receptors mediate phasic inhibition, whereas alphabetadelta receptors mediate tonic inhibition. Propofol (2,6-di-isopropylphenol), a widely used anesthetic drug, exerts its effect primarily by modulating GABAA receptors; however, the effects of propofol on the kinetic properties of alphabetagamma and alphabetadelta receptors are uncertain. We transfected human embryonic kidney (HEK293T) cells with cDNAs encoding rat alpha1, alpha6, beta3, gamma2L, or delta subunits and performed whole-cell patch-clamp recordings to explore this issue. Propofol (3 microM) increased GABA concentration-response curve maximal currents similarly for both alpha1beta3gamma2L and alpha6beta3gamma2L receptors, but propofol increased those for alpha1beta3delta and alpha6beta3delta receptors differently, the increase being greater for alpha1beta3delta than for alpha6beta3delta receptors. Propofol (10 microM) produced similar alterations in alpha1beta3gamma2L and alpha6beta3gamma2L receptor currents when using a preapplication protocol; peak currents were not altered, desensitization was reduced, and deactivation was prolonged. Propofol enhanced peak currents for both alpha1beta3delta and alpha6beta3delta receptors, but the enhancement was greater for alpha1beta3delta receptors. Desensitization of these two isoforms was not modified by propofol. Propofol did not alter the deactivation rate of alpha1beta3delta receptor currents but did slow deactivation of alpha6beta3delta receptor currents. The findings that propofol reduced desensitization and prolonged deactivation of gamma2L subunit-containing receptors and enhanced peak currents or prolonged deactivation of delta subunit-containing receptors suggest that propofol enhancement of both phasic and tonic inhibition may contribute to its anesthetic effect in the brain.
  • Nanoimprinting of conductive tracks using metal nanopowders, Seok-min Kim et al. (2007)
    TitleNanoimprinting of conductive tracks using metal nanopowders
    AuthorsSeok-min Kim, Jinsu Kim, Jiseok Lim, Minseok Choi, Shinill Kang, Sukwon Lee, Hyuk Kim
    PublicationApplied Physics Letters
    DateOctober 01, 2007
  • Nanoparticles probe biosystems, Paula Gould (2004)
    TitleNanoparticles probe biosystems
    AuthorPaula Gould
    PublicationMaterials Today
    DateFebruary 2004
  • Negative Tone Photoresist Series ma-N 1400 - processing guidelines, Micro Resist Technology GmbH (2005)
    TitleNegative Tone Photoresist Series ma-N 1400 - processing guidelines
    AuthorMicro Resist Technology GmbH
  • New Magnetic Anisotropy, W. H. Meiklejohn et al. (1957)
    TitleNew Magnetic Anisotropy
    AuthorsW. H. Meiklejohn, C. P. Bean
    PublicationPhysical Review
    DateFebruary 01, 1957
    AbstractA new type of magnetic anisotropy has been discovered which is best described as an exchange anisotropy. This anisotropy is the result of an interaction between an antiferromagnetic material and a ferromagnetic material. The material that exhibits this exchange anisotropy is a compact of fine particles of cobalt with a cobaltous oxide shell. The effect occurs only below the Néel temperature of the antiferromagnetic material, which is essentially room temperature for the cobaltous oxide. An exchange torque is inferred to exist between the metal and oxide which has a maximum value at 77°K of ∼2 dyne-cm/cm2 of interface.
  • Novel highly elastic magnetic materials for dampers and seals: part II. Material behavior in a magnetic field, S. Abramchuk et al. (2007)
    TitleNovel highly elastic magnetic materials for dampers and seals: part II. Material behavior in a magnetic field
    AuthorsS. Abramchuk, E. Kramarenko, D. Grishin, G. Stepanov, L. V. Nikitin, G. Filipcsei, A. R. Khokhlov, M. Zr�nyi
    PublicationPolymers for Advanced Technologies
    AbstractThe combination of polymers with magnetic particles displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic field sensitive elastomers represent a new type of composites consisting of small particles, usually from nanometer range to micron range, dispersed in a highly elastic polymeric matrix. In this paper, we show that in the presence of built-in magnetic particles it is possible to tune the elastic modulus by an external magnetic field. We propose a phenomenological equation to describe the effect of the external magnetic field on the elastic modulus. We demonstrate the engineering potential of new materials on the examples of two devices. The first one is a new type of seals fundamentally different from those used before. In the simplest case, the sealing assembly includes a magnetoelastic strip and a permanent magnet. They attract due to the magnetic forces. This ensures that due to high elasticity of the proposed composites and good adhesion properties, the strip of magnetoelastic will adopt the shape of the surface to be sealed, this fact leading to an excellent sealing. Another straightforward application of the magnetic composites is based on their magnetic field dependent elastic modulus. Namely, we demonstrate in this paper the possible application of these materials as adjustable vibration dampers. Copyright � 2007 John Wiley & Sons, Ltd
  • Observation of ferrotoroidic domains, Bas B. Van Aken et al. (2007)
    TitleObservation of ferrotoroidic domains
    AuthorsBas B. Van Aken, Jean-Pierre Rivera, Hans Schmid, Manfred Fiebig
    DateOctober 11, 2007
  • On-chip micro-electromagnets for magnetic-based bio-molecules separation, Qasem Ramadan et al. (2004)
    TitleOn-chip micro-electromagnets for magnetic-based bio-molecules separation
    AuthorsQasem Ramadan, Victor Samper, Daniel Poenar, Chen Yu
    PublicationJournal of Magnetism and Magnetic Materials
    AbstractThis paper reports a comprehensive theoretical, finite element and measurement analysis of different designs of planar micro-electromagnets for bio-molecular manipulation. The magnetic field due to current flowing in complex shapes of current-carrying conductors have been calculated analytically, simulated using finite-element analysis (FEA), and measured using the superconducting quantum interference device technique (SQUID). A comparison of the theoretical and measured magnetic field strength and patterns is presented. The planar electromagnets have been fabricated using patterned Al 2 [mu]m thick. The aim of the study is to explore and optimize the geometrical and structural parameters of planar electromagnets that give rise to the highest magnetic fields and forces for magnetic micro-beads manipulation. Magnetic beads are often used in biochemical assays for separation of bio-molecules. Typical beads are 0.2-10 [mu]m in diameter and have superparamagnetic properties. Increasing the intensity of the magnetic field generated by a coil by injection a larger current is not the most suitable solution as the maximum current is limited by Joule heating. Consequently, in order to maximize the field for a given current, one should optimize the geometry of the coil, as this is an extremely significant factor in determining the magnetic field intensity in 2D planar designs. The theoretical and measured results of this work show that the meander micro-electromagnet with mesh-shaped winding profile produces the strongest magnetic field (about 2.7 [mu]T for a current intensity of 6 mA) compared with other meander designs, such as the serpentine and rosette-shaped ones. The magnetic fields of these three types of meander-shaped micro-electromagnets were compared theoretically with that produced by a spiral micro-electromagnet whose technological realization is more complicated and costly due to the fact that it requires an additional insulation layer with a contact window and a second patterned metal layer as a via. Nevertheless, the spiral design produces a much stronger magnetic field up to five times larger than that of the mesh-shaped micro-electromagnet for the same current and electromagnet area. The measured results strongly agree with these conclusions resulted from the theoretical analysis. The results presented in this paper provide a solid and useful basis for the design of a micro-fluidic bio-molecule separation and detection system using magnetic fields and magnetic beads.
  • On the electromagnetic force on a polarizable body, A. Engel et al. (2002)
    TitleOn the electromagnetic force on a polarizable body
    AuthorsA. Engel, R. Friedrichs
    PublicationAmerican Journal of Physics
    DateApril 2002
  • Organic polymer: Ferromagnetism or antiferromagnetism, Daping Chu et al. (1990)
    TitleOrganic polymer: Ferromagnetism or antiferromagnetism
    AuthorsDaping Chu, Sen Liu, Zhong-can Ou-Yang
    PublicationPhysics Letters A
    DateNovember 5, 1990
    AbstractHere we propose a structure model of quasi-one-dimensional polymers with antiferromagnetic exchange interaction between radicals, which will show ferromagnetic behavior in an applied field. Break down units are suggested for easy calculation. Some analytical and numerical results are given.
  • Permanent Magnetism, R. Skomski et al. (1999)
    TitlePermanent Magnetism
    AuthorsR. Skomski, J.M.D Coey
    PublisherTaylor & Francis
  • Permanent Magnets, J.M.D. Coey (1999)
    TitlePermanent Magnets
    AuthorJ.M.D. Coey
    PublicationWiley Encyclopedia of Electrical and Electronics Engineering
    AbstractThe sections in this article are: Magnetic Properties, Magnet Processing, Magnet Materials, Magnet Applications, Prospects
  • Photodefinable polydimethylsiloxane (PDMS) for rapid lab-on-a-chip prototyping, Ali Asgar S. Bhagat et al. (2007)
    TitlePhotodefinable polydimethylsiloxane (PDMS) for rapid lab-on-a-chip prototyping
    AuthorsAli Asgar S. Bhagat, Preetha Jothimuthu, Ian Papautsky
    PublicationLab on a Chip
    DateSep, 2007
    AbstractIn this paper, we introduce a new and simple method of patterning polydimethylsiloxane (PDMS) directly using benzophenone as a photoinitiator. The photodefinable PDMS mixture (photoPDMS) is positive-acting and only sensitive to light below 365 nm, permitting processing under normal ambient light. Features of the order of 100 [micro sign]m, which are sufficiently small for most microfluidic applications, were successfully fabricated using this novel process. A parametric study of process parameters was performed to optimize the fabrication. As a demonstration, microfluidic channels of varying dimensions were successfully fabricated using this process and experimentally characterized using fluorescence microscopy. To further demonstrate photoPDMS potential, thin (<30 [micro sign]m) free-standing films with through patterns were fabricated and successfully used as shadow masks. The photoPDMS process completely eliminates the need for a master, permits processing under normal ambient light conditions, and makes fabrication fast and simple. This process for rapid prototyping of low-cost, disposable LOCs can be accomplished without cleanroom facilities and thus can be employed for a wide range of applications.
  • Photosensitive poly(dimethylsiloxane) materials for microfluidic applications, Katerina Tsougeni et al. (2007)
    TitlePhotosensitive poly(dimethylsiloxane) materials for microfluidic applications
    AuthorsKaterina Tsougeni, Angeliki Tserepi, Evangelos Gogolides
    PublicationMicroelectron. Eng
    AbstractPoly(dimethylsiloxane) (PDMS) is used as a thermally crosslinked material in microfluidics and Bio-MEMS. Recently photo-patternable materials show increasing interest, as the demand for easy alignment arises for multilayered structures. We present a photopatterning process for PDMS in microfluidics, for two main uses: (a) as a thin (approximately 10@mm) structural layer, and (b) as a very thin (approximately 1@mm) hard mask for oxygen plasma etching of microfluidic polymeric substrates down to several tens of microns. We study the deep-UV and I-line photocrosslinking properties of siloxane copolymers containing vinyl-methyl-siloxane groups as polymerizable units. These materials are sensitive to DUV and can be sensitized to 300-400nm using free radical initiators. We prove that even thermally curable PDMS (Sylgard 184, base) can become photosensitive in DUV, although its practical use is limited to very thin films, due to its small molecular weight.
  • Photosensitive Poly(Dimethylsiloxane) (Photopdms) for Rapid and Simple Polymer Fabrication, Ali Asgar S. Bhagat et al. (2007)
    TitlePhotosensitive Poly(Dimethylsiloxane) (Photopdms) for Rapid and Simple Polymer Fabrication
    AuthorsAli Asgar S. Bhagat, Preetha Jothimuthu, Ian Papautsky
    DateJune 2007
    Conference NameSolid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International
    AbstractIn this paper, we report a new and simple method of patterning polydimethylsiloxane (PDMS) directly under normal ambient light for rapid prototyping of disposable microfluidic lab-on-a-chips (LOCs). The photodefinable PDMS (photoPDMS) is positive-acting and only sensitive to light below 365 nm, which permits processing outside a gold room. A parametric study was conducted to optimize this novel fabrication technique. Features as small as 100 ¿m were successfully fabricated using photoPDMS. To further demonstrate the potential of this novel technique, thin (< 30 ¿m) free-standing patterned PDMS films. Successful demonstration of this novel process presents a feasibly simpler alternative approach for rapid prototyping of disposable microfluidic biochips for lab-on-a-chip applications.
  • Physical Theory of Ferromagnetic Domains, Charles Kittel (1949)
    TitlePhysical Theory of Ferromagnetic Domains
    AuthorCharles Kittel
    PublicationReviews of Modern Physics
    DateOctober 1949
  • Plastic micropumps using ferrofluid and magnetic membrane actuation, C. Yamahata et al. (2004)
    TitlePlastic micropumps using ferrofluid and magnetic membrane actuation
    AuthorsC. Yamahata, M.A.M. Gijs
    Conference Name17th IEEE International Conference on Micro Electro Mechanical Systems, 2004
    AbstractThis paper presents a simple and low-cost prototyping technology for the realization of integrated micropumps in polymethylmethacrylate (PMMA). The three-dimensional (3D) micropumps consist of stacks of structured PMMA layers, which are either realised with precision milling tools for the more complex parts, or fabricated using the powder blasting technique for channel-type structures. We integrate silicone membranes into the chip to realize check-valves or use dynamic diffuser valves. We use two different types of magnetic actuation external to the micropump: (i) an external magnet displaces a ferrofluid liquid plug that plays the role of a piston in a channel; (ii) an external coil actuates an integrated magnetic membrane, consisting of NdFeB magnetic powder in a polydimethylsiloxane (PDMS) matrix.
  • Pneumatically actuated elastomeric device for nanoscale surface patterning, Shifeng Li et al. (2007)
    TitlePneumatically actuated elastomeric device for nanoscale surface patterning
    AuthorsShifeng Li, Timothy M. Dellinger, Qin Wang, Sandra Szegedi, Chang Liu
    PublicationApplied Physics Letters
    DateJuly 09, 2007
  • Polydimethylsiloxane, a photocurable rubberelastic polymer used as spring material in micromechanical sensors, Joost Conrad Lötters et al. (1997)
    TitlePolydimethylsiloxane, a photocurable rubberelastic polymer used as spring material in micromechanical sensors
    AuthorsJoost Conrad Lötters, Wouter Olthuis, Peter H. Veltink, Piet Bergveld
    PublicationMicrosystem Technologies
    DateFebruary 22, 1997
    AbstractPolydimethylsiloxane (PDMS) is a commercially available physically and chemically stable photocurable silicone rubber which has a unique flexibility (G곚rkPa) at room temperature. Further properties of PDMS are a low elasticity change versus temperature (1.1 kPa/°C), no elasticity change versus frequency and a high compressibility. PDMS is an interesting polymer to be used as spring material in micromechanical sensors such as accelerometers. The spring constant of the PDMS structures was theoretically calculated and measurements were done on accelerometers with PDMS springs to validate the theory. The measured and calculated spring constants showed a good correspondence, so the measurement results showed that the PDMS structures can successfully be used as mechanical springs.
  • Polydimethylsiloxane as an elastic material applied in a capacitive accelerometer, Joost Conrad Lötters et al. (1996)
    TitlePolydimethylsiloxane as an elastic material applied in a capacitive accelerometer
    AuthorsJoost Conrad Lötters, Wouter Olthuis, Peter H. Veltink, Piet Bergveld
    PublicationJournal of Micromechanics and Microengineering
    DateMarch 1996
    AbstractPolydimethylsiloxane is a silicone rubber. It has a unique flexibility, resulting in one of the lowest glass-transition temperatures of any polymer. Furthermore, it shows a low elasticity change versus temperature, a high thermal stability, chemical inertness, dielectric stability, shear stability and high compressibility. Because of its high flexibility and the very low drift of its properties with time and temperature, polydimethylsiloxane could be well suited for mechanical sensors, such as accelerometers. A novel capacitive accelerometer with polydimethylsiloxane layers as springs has been realized. The obtained measurement results are promising and show a good correspondence with the theoretical values.
  • Polydimethylsiloxane-magnetite nanoparticle complexes and dispersions in polysiloxane carrier fluids, K.S. Wilson et al. (2005)
    TitlePolydimethylsiloxane-magnetite nanoparticle complexes and dispersions in polysiloxane carrier fluids
    Authors K.S. Wilson, J.D. Goff, J.S. Riffle, L.A. Harris, T.G. St.Pierre
    PublicationPolymers for Advanced Technologies
    AbstractDispersions of sterically stabilized magnetite nanoparticles in polydimethylsiloxane (PDMS) carrier fluids have been prepared for potential biomedical applications. Trivinylsiloxy-terminated PDMS was functionalized with mercaptoacetic acid or mercaptosuccinic acid to afford PDMS stabilizers containing either three or six carboxylic acid groups, respectively, at one chain-end. Magnetite nanoparticles were synthesized by a chemical co-precipitation reaction of FeCl2 and FeCl3 with hydroxide at pH 9-10. Subsequently, the PDMS stabilizers were adsorbed onto the magnetite nanoparticle surfaces via the carboxylate groups in an interfacial reaction at an acidic pH. The complexes were characterized with transmission electron microscopy to establish an average particle diameter of 7.4 ± SD 1.7 nm and approximately spherical shape. Complexes containing up to 67 wt% magnetite were prepared using these PDMS stabilizers, resulting in maximum saturation specific magnetizations of ?50 emu g-1. The polymer-magnetite nanoparticle complexes could be dispersed in PDMS oligomers to afford polysiloxane ferrofluids. Copyright © 2005 John Wiley & Sons, Ltd.
  • Polymethylhydrosiloxane (PMHS) as a functional material for microfluidic chips, S. J. Lee et al. (2008)
    TitlePolymethylhydrosiloxane (PMHS) as a functional material for microfluidic chips
    AuthorsS. J. Lee, M. Goedert, M. T. Matyska, E. M. Ghandehari, M. Vijay, J. J. Pesek
    PublicationJournal of Micromechanics and Microengineering
    AbstractPolymethylhydrosiloxane (PMHS) has been investigated as a candidate material for microfluidic chips. The ability to modify the surface of PMHS by hydrosilation is particularly advantageous for separation processes. The chemical modification of PMHS is verified by diffuse reflectance infrared Fourier transform (DRIFT) analysis, and the modified PMHS is shown to be stable when exposed to extreme pH conditions between 2 and 9. Spectrophotometer measurements show that PMHS exhibits over 40% transmittance for ultraviolet (UV) wavelength as low as 220 nm, indicating viability for sensor applications based on UV absorption. The UV transmittance is furthermore observed to be insensitive to thickness for specimens tested between 1.6 mm and 6.4 mm thick. Full curing of PMHS liquid resin occurs between 48 and 72 h at 110 °C with no secondary additives. Casting of microscale features is achieved by using soft lithography methods similar to established techniques for fabrication based on polydimethylsiloxane (PDMS). Microchannels approximately 100 µm wide and 50 µm deep are also demonstrated by carbon dioxide laser ablation, with uniform channels produced using an energy dose of 0.2 mJ mm[?]1 with respect to line length. Other basic functional requirements for microfluidic chips are discussed, including the ability to bond PMHS substrates by plasma treatment.
  • Poly(vinyl alcohol) as a structure release layer for the microfabrication of polymer composite structures, Kweku A. Addae-Mensah et al. (2007)
    TitlePoly(vinyl alcohol) as a structure release layer for the microfabrication of polymer composite structures
    AuthorsKweku A. Addae-Mensah, Ronald S. Reiserer, John P. Wikswo
    PublicationJournal of Micromechanics and Microengineering
    AbstractWhile lift-off techniques are common in the fabrication of hard, silicon-based microelectromechanical systems (MEMS), these techniques are not yet in widespread use in soft lithography, where polymer materials are used to fabricate MEMS devices for biological applications (bioMEMS). We present fabrication steps that allow us to make use of poly(vinyl alcohol) as a structure release agent in bioMEMS microfabrication. The release method offers a simple, cost effective and reliable way to release microfabricated structures that need to be bonded to other structures or are already bonded to them. We use this technique to release discs made of SU-8 that are attached to a vertical cylindrical microcantilever array that is replica molded using polydimethylsiloxane (PDMS). This approach may be used to release structures made from a variety of materials that are not compatible with typical lift-off chemistries, although we address only SU-8 and PDMS in this technical note.
  • Primary cilia: new perspectives, Denys Wheatley (2004)
    TitlePrimary cilia: new perspectives
    AuthorDenys Wheatley
    PublicationCell Biology International
  • Process and formulation variables in the preparation of injectable and biodegradable magnetic microspheres, Hong Zhao et al. (2007)
    TitleProcess and formulation variables in the preparation of injectable and biodegradable magnetic microspheres
    AuthorsHong Zhao, Jeffrey Gagnon, Urs Hafeli
    PublicationBioMagnetic Research and Technology
    AbstractThe aim of this study was to prepare biodegradable sustained release magnetite microspheres sized between 1 to 2 mum. The microspheres with or without magnetic materials were prepared by a W/O/W double emulsion solvent evaporation technique using poly(lactide-co-glycolide) (PLGA) as the biodegradable matrix forming polymer. Effects of manufacturing and formulation variables on particle size were investigated with non-magnetic microspheres. Microsphere size could be controlled by modification of homogenization speed, PLGA concentration in the oil phase, oil phase volume, solvent composition, and polyvinyl alcohol (PVA) concentration in the outer water phase. Most influential were the agitation velocity and all parameters that influence the kinematic viscosity of oil and outer water phase, specifically the type and concentration of the oil phase. The magnetic component yielding homogeneous magnetic microspheres consisted of magnetite nanoparticles of 8 nm diameter stabilized with a polyethylene glycole/polyacrylic acid (PEG/PAA) coating and a saturation magnetization of 47.8 emu/g. Non-magnetic and magnetic microspheres had very similar size, morphology, and size distribution, as shown by scanning electron microscopy. The optimized conditions yielded microspheres with 13.7 weight% of magnetite and an average diameter of 1.37 mum. Such biodegradable magnetic microspheres seem appropriate for vascular administration followed by magnetic drug targeting.
  • Quantification of chaotic strength and mixing in a micro fluidic system, Ho Jun Kim et al. (2007)
    TitleQuantification of chaotic strength and mixing in a micro fluidic system
    AuthorsHo Jun Kim, Ali Beskok
    PublicationJournal of Micromechanics and Microengineering
    AbstractComparative studies of five different techniques commonly employed to identify the chaotic strength and mixing efficiency in micro fluidic systems are presented to demonstrate the competitive advantages and shortcomings of each method. The 'chaotic electroosmotic stirrer' of Qian and Bau (2002 Anal. Chem. 74 3616-25) is utilized as the benchmark case due to its well-defined flow kinematics. Lagrangian particle tracking methods are utilized to study particle dispersion in the conceptual device using spectral element and fourth-order Runge-Kutta discretizations in space and time, respectively. Stirring efficiency is predicted using the stirring index based on the box counting method, and Poincaré sections are utilized to identify the chaotic and regular regions under various actuation conditions. Finite time Lyapunov exponents are calculated to quantify the chaotic strength, while the probability density function of the stretching field is utilized as an alternative method to demonstrate the statistical analysis of chaotic and partially chaotic cases. Mixing index inverse, based on the standard deviation of scalar species distribution, is utilized as a metric to quantify the mixing efficiency. Series of numerical simulations are performed by varying the Peclet number (Pe) at fixed kinematic conditions. The mixing time (tm) is characterized as a function of the Pe number, and tm [?] ln(Pe) scaling is demonstrated for fully chaotic cases, while tm [?] Pea scaling with a [?] 0.33 and a = 0.5 are observed for partially chaotic and regular cases, respectively. Employing the aforementioned techniques, optimum kinematic conditions and the actuation frequency of the stirrer that result in the highest mixing/stirring efficiency are identified.
  • Rapid prototyping of active microfluidic components based on magnetically modified elastomeric materials, William C. Jackson et al. (2001)
    TitleRapid prototyping of active microfluidic components based on magnetically modified elastomeric materials
    AuthorsWilliam C. Jackson, Hy D. Tran, Michael J. O'Brien, Emmanuil Rabinovich, Gabriel P. Lopez
    PublicationJournal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures
    AbstractReplica molding of elastomeric materials has proven to be an extremely useful new technology for the formation of complex microfluidic systems. Recent demonstrations of convenient methods for production of such systems by simple, rapid methods that do not require expensive fabrication facilities have enabled the extensive use of microsystems in research and development into a host of new application fields. This report describes a simple new method for fabricating active elastomeric components in microfluidic systems that is based on deformation of elastic materials that have been impregnated or coated with magnetic materials. Computer controlled miniature electromagnets are used to activate switching valves within microfluidics systems. Similar fabrication techniques can be easily extended to construct complex, and potentially completely integrated, microfluidic systems containing active valves, pumps, injectors, mixers, and flow controllers. Preliminary results indicate fabrication of channels approximately 200 µm in width, with valves approximately 5 mm in size (including both valve chamber and valve actuator). The fabrication cycle time is on the order of one day using readily available benchtop equipment, and the valves seal hermetically against a 1.5 kPa back pressure. ©2001 American Vacuum Society.
  • Rapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane), D.C. Duffy et al. (1998)
    TitleRapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane)
    AuthorsD.C. Duffy, J.C. McDonald, O.J.A. Schueller, G.M. Whitesides
    PublicationAnalytical Chemistry
    DateDecember 1, 1998
    AbstractThis paper describes a procedure that makes it possible to design and fabricate (including sealing) microfluidic systems in an elastomeric material-poly(dimethylsiloxane) (PDMS)-in less than 24 h. A network of microfluidic channels (with width >20 m) is designed in a CAD program. This design is converted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relief photoresist. PDMS cast against the master yields a polymeric replica containing a network of channels. The surface of this replica, and that of a flat slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic systems, such as glass, silicon, silicon oxide, and oxidized polystyrene; a number of substrates for devices are, therefore, practical options. Oxidation of the PDMS has the additional advantage that it yields channels whose walls are negatively charged when in contact with neutral and basic aqueous solutions; these channels support electroosmotic pumping and can be filled easily with liquids with high surface energies (especially water). The performance of microfluidic systems prepared using this rapid prototyping technique has been evaluated by fabricating a miniaturized capillary electrophoresis system. Amino acids, charge ladders of positively and negatively charged proteins, and DNA fragments were separated in aqueous solutions with this system with resolution comparable to that obtained using fused silica capillaries.
  • Rapid replication of polymeric and metallic high aspect ratio microstructures using PDMS and LIGA technology, K. Kim et al. (2002)
    TitleRapid replication of polymeric and metallic high aspect ratio microstructures using PDMS and LIGA technology
    AuthorsK. Kim, S. Park, J.-B. Lee, H. Manohara, Y. Desta, M. Murphy, C. H. Ahn
    PublicationMicrosystem Technologies
    DateNovember 04, 2002
    Abstract This paper present a method of rapid replication of polymeric high aspect ratio microstructures (HARMs) and a method of rapid reproduction of metallic micromold inserts for HARMs using polydimethylsiloxane (PDMS) casting and standard LIGA processes. A high aspect ratio (HAR) metallic micromold insert, featuring a variety of test microstructures made of electroplated nickel with 15:1 height-to-width ratio for 300 μm microstructures, was fabricated by the standard LIGA process using deep X-ray lithography (DXRL). A 10:1 mixture of pre-polymer PDMS and a curing agent were cast onto the HAR metallic micromold insert, cured and peeled off to create reverse images of the HAR metallic micromold insert in PDMS. In addition to the replication of polymeric HARMs, replicated PDMS HARMS were coated with a metallic sacrificial layer and electroplated in nickel to reproduce another metallic micromold insert. This method can be used to rapidly and massively reproduce HAR metallic micromold inserts in low cost mass production manner without further using DXRL.
  • Recent advances in microscale pumping technologies: a review and evaluation, Iverson et al. (2008)
    TitleRecent advances in microscale pumping technologies: a review and evaluation
    Authors Iverson, Garimella
    PublicationMicrofluidics and Nanofluidics
    AbstractMicropumping has emerged as a critical research area for many electronics and biological applications. A significant driving force underlying this research has been the integration of pumping mechanisms in micro total analysis systems and other multi-functional analysis techniques. Uses in electronics packaging and micromixing and microdosing systems have also capitalized on novel pumping concepts. The present work builds upon a number of existing reviews of micropumping strategies by focusing on the large body of micropump advances reported in the very recent literature. Critical selection criteria are included for pumps and valves to aid in determining the pumping mechanism that is most appropriate for a given application. Important limitations or incompatibilities are also addressed. Quantitative comparisons are provided in graphical and tabular forms.
  • Recent developments in single-cell analysis, Xin Lu et al. (2004)
    TitleRecent developments in single-cell analysis
    AuthorsXin Lu, Wei-Hua Huang, Zong-Li Wang, Jie-Ke Cheng
    PublicationAnalytica Chimica Acta
    DateMay 17, 2004
    AbstractCells play a significant role in life activities such as metabolism and signal transduction and so on. The development of cellular research puts forward a severe challenge to analyst, and the study of single-cell has already become the focus of the frontiers in analytical chemistry. Combining capillary electrophoresis (CE) with detection methods such as laser-induced fluorescence (LIF) and electrochemical detection (ED), and mass spectrometry (MS) have particular description for single-cell analysis. Due to extensive research on objects and complex characteristic in the single-cell, scientists have developed more methods and technologies for application in single-cell analysis. Here we reviewed the current approach of technologies of single-cell analysis in manipulation, injection and lysis of single-cell, capillary electrophoresis, imaging analysis, temporal and spatial monitoring on dynamics of single-cells, and the application.
  • Re-configurable fluid circuits by PDMS elastomer micromachining, D. Armani et al. (1999)
    TitleRe-configurable fluid circuits by PDMS elastomer micromachining
    AuthorsD. Armani, C. Liu, N. Aluru
    Conference NameTwelfth IEEE International Conference on Micro Electro Mechanical Systems, 1999
    PlaceOrlando, FL, USA
    AbstractWe report on a microfabrication technique for realizing re-configurable micro fluidics devices using polymethylsiloxane material (PDMS). The mechanical characteristics of the material, including the Young's modulus and the adhesion energy have been determined experimentally. The magnitude of Young's modulus ranges from 8.7×105 Pa to 3.6×105 Pa. The adhesion energy is a function of the PDMS composition as well as chemical treatment. A method for efficiently developing flow interconnects has been demonstrated
  • Replication and Compression of Surface Structures with Polydimethylsiloxane Elastomer, D. Campbell et al. (1999)
    TitleReplication and Compression of Surface Structures with Polydimethylsiloxane Elastomer
    AuthorsD. Campbell, K.J. Beckman, C.E. Calderon, P.W. Doolan, R.H. Moore, A.B. Ellis, G.C. Lisensky
    PublicationJournal of Chemical Education
    DateApril, 1999
    AbstractThis paper describes simple classroom demonstrations and laboratory experiments based on properties of polydimethylsiloxane (PDMS). PDMS is a colorless, transparent elastomer. Spheres cast from PDMS can be cross-linked to varying extents to affect their rigidity, as seen in their ability to bounce when dropped. PDMS recently has been used by Whitesides et al. to replicate submicron-scale patterns by casting a negative relief image from a master template, and to progressively reduce the dimensions of these patterns through cycles based on mechanical compression. Curing PDMS in contact with features pressed into aluminum foil transfers the foil features to the elastomer. The raised surface features of the resulting cured PDMS block can transfer ink images to paper in a fashion that is similar to microcontact printing processes. Stretching or compressing the block will alter the dimensions of the transferred image. Curing PDMS in contact with the microscopic features on optical transform slides can transfer the slide features to the elastomer. The feature spacings, altered by stretching or compressing the elastomer, can be determined through the optical transform experiment. Moreover, when the elastomer is suitably compressed, the features, now with reduced dimensions, can be transferred first to an epoxy resin and then to a new sample of PDMS, representing a cycle that can lead to progressively reduced feature spacings.
  • Saturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-γFe2O3, and their relationship to structure, Goss (1988)
    TitleSaturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-γFe2O3, and their relationship to structure
    Author Goss
    PublicationPhysics and Chemistry of Minerals
    DateNovember 01, 1988
    AbstractThis study has characterised the oxidation products of a fine-grained single domain magnetite which was made synthetically by a colloidal method. Changes in the intrinsic magnetic properties (saturation magnetisation, saturation remanence, and coercive force) during progressive oxidation are correlated with lattice parameter changes and an oxidation mechanism. It is proposed that magnetite oxidises to hematite via at least two metastable maghemites. The first of these, formed on low temperature oxidation by the formation of a magnetite/maghemite solid solution, is a face centered maghemite with lattice parameter a= 8.3419±0.0006 Å. A second maghemite, produced on oxidation at higher temperatures, has a primitive cubic structure and a lattice parameter a = 8.3505±0.0005 Å. Maghemite cation distributions are derived to explain the reduced saturation magnetisations of between 56 and 74 Am2 kg-1 observed, and a maghemite structure containing an increase in tetrahedral Fe3+ ions and up to 3 octahedral vacancies per 32 oxygen unit cell is proposed.
  • Series of AZ-compatible negative photoresists, Anya Voigt et al. (1995)
    TitleSeries of AZ-compatible negative photoresists
    AuthorsAnya Voigt, Gabi Gruetzner, E. Sauer, S. Helm, T. Harder, Simone Fehlberg, Juergen Bendig
    DateJune 09, 1995
    Conference NameAdvances in Resist Technology and Processing XII
    PlaceSanta Clara, CA, USA
  • Shaped Ceramics with Tunable Magnetic Properties from Metal-Containing Polymers, Mark J. MacLachlan et al. (2000)
    TitleShaped Ceramics with Tunable Magnetic Properties from Metal-Containing Polymers
    AuthorsMark J. MacLachlan, Madlen Ginzburg, Neil Coombs, Thomas W. Coyle, Nandyala P. Raju, John E. Greedan, Geoffrey A. Ozin, Ian Manners
    DateFebruary 25, 2000
  • Shrinkage ratio of PDMS and its alignment method for the wafer level process, Seok Lee et al. (2008)
    TitleShrinkage ratio of PDMS and its alignment method for the wafer level process
    AuthorsSeok Lee, Seung Lee
    PublicationMicrosystem Technologies
    DateFebruary 05, 2008
    AbstractIn the research area known as Lab-on-a-Chip, poly-dimethylsiloane (PDMS) is a popular material whose fabrication method is the replication of patterns by curing on a mold. Shrinkage of PDMS occurs when it is cured; this is a problem related to the alignment between the PDMS layer and the rigid substrate during the wafer-level processing. In this paper, the 2D shrinkage ratio of PDMS is measured experimentally for various curing conditions including the temperature, thickness, and mixing ratio of the curing agent and dilutant. In order to measure this, scale marks were patterned onto a 4 in. wafer and replicated onto a PDMS substrate. When the patterned Si wafer and PDMS substrate were aligned, the difference of each scale mark was observed. A cross-shaped groove was patterned with a scale mark as a align key for the easy alignment of substrates. For a general recipe, the measured shrinkage ratios of PDMS were 1.06, 1.52 and 1.94% for curing temperature of 65, 80 and 100�C, respectively. Considering the shrinkage ratio of PDMS, the design offset applied in a photomask is 1.07, 1.54 and 1.98% for curing temperature of 65, 80 and 100�C, respectively.
  • Shrinky-Dink microfluidics: 3D polystyrene chips, C. Chen et al. (2008)
    TitleShrinky-Dink microfluidics: 3D polystyrene chips
    Authors C. Chen, D.N. Breslauer, J.I. Luna, A. Grimes, W. Chin, L.P. Lee, M. Khine
    PublicationLab on a Chip
    AbstractWe present a novel approach for the ultra-rapid direct patterning of complex three-dimensional, stacked polystyrene (PS) microfluidic chips. By leveraging the inherent shrinkage properties of biaxially pre-stressed thermoplastic sheets, microfluidic channels become thinner and deeper upon heating. Design conception to fully functional chips can thus be completed within minutes.
  • Siloxane Polymers for High-Resolution, High-Accuracy Soft Lithography, H. Schmid et al. (2000)
    TitleSiloxane Polymers for High-Resolution, High-Accuracy Soft Lithography
    AuthorsH. Schmid, B. Michel
    DateApril 18, 2000
    AbstractWe report the formulation of siloxane polymers for high-resolution, high-accuracy stamps for soft lithography. With this technique, a molecular, polymeric, or liquid ink is applied to the surface of a stamp and then transferred by conformal contact to a substrate. Stamps for this technique are usually made of a commercial siloxane elastomer with appropriate mechanical properties to achieve conformal contact but are incapable of printing accurate, submicrometer patterns. To formulate better stamp polymers, we used models of rubber-like elasticity as guidelines. Poly(dimethylsiloxane) networks were prepared from vinyl and hydrosilane end-linked polymers and vinyl and hydrosilane copolymers, with varying mass between cross-links and junction functionality. The polymer formulations were characterized by strain at break as well as compression modulus and surface hardness measurements. This resulted in the identification of bimodal polymer networks having mechanical properties that allow the replication of high-density patterns at the 100 nm scale and that withstand the mechanical constraints during use as a stamp material. We also demonstrate advantageous implementations of the formulated polymers in hybrid stamps that achieve submicrometer-dimensional accuracy over large areas.
  • Similarity rules of magnetic minor hysteresis loops in Fe and Ni metals, S. Takahashi et al. (2008)
    TitleSimilarity rules of magnetic minor hysteresis loops in Fe and Ni metals
    AuthorsS. Takahashi, S. Kobayashi, Y. Kamada, T. Shishido
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Corrected Proof
    Date16 March 2008
    AbstractWe have studied similarity rules of quasistatic minor hysteresis loops for Fe and Ni single crystals in the wide temperature range from 10 to 600�K. Two similarity rules of MR*/Ma*~3/4 and WR*/WF*~1/6, were found in a medium field range where irreversible movement of Bloch walls plays a crucial role for magnetization; Ma*, MR*, WF*, and WR* are magnetization, remanence, hysteresis loss, and remanence work of a minor hysteresis loop. The similarity rules hold true, being almost independent of kinds of ferromagnets, applied stress, and temperature. The origin was discussed from the viewpoint of pinning effects due to dislocations as well as eddy current effects which become predominant at low temperatures for samples with low dislocation density.
  • Single-Domain Circular Nanomagnets, R. P. Cowburn et al. (1999)
    TitleSingle-Domain Circular Nanomagnets
    AuthorsR. P. Cowburn, D. K. Koltsov, A. O. Adeyeye, M. E. Welland, D. M. Tricker
    PublicationPhysical Review Letters
  • Size dependence of specific power absorption of Fe3O4 particles in AC magnetic field, Ming Ma et al. (2004)
    TitleSize dependence of specific power absorption of Fe3O4 particles in AC magnetic field
    AuthorsMing Ma, Ya Wu, Jie Zhou, Yongkang Sun, Yu Zhang, Ning Gu
    PublicationJournal of Magnetism and Magnetic Materials
    DateJanuary 2004
    AbstractThe specific absorption rate (SAR) values of aqueous suspensions of magnetite particles with different diameters varying from 7.5 to 416 nm were investigated by measuring the time-dependent temperature curves in an external alternating magnetic field (80 kHz, 32.5 kA/m). Results indicate that the SAR values of magnetite particles are strongly size dependent. For magnetite particles larger than 46 nm, the SAR values increase as the particle size decreases where hysteresis loss is the main contribution mechanism. For magnetite particles of 7.5 and 13 nm which are superparamagnetic, hysteresis loss decreases to zero and, instead, relaxation losses (Neel loss and Brownian rotation loss) dominate, but Brown and Neel relaxation losses of the two samples are all relatively small in the applied frequency of 80 kHz.
  • Small Domain Structures in Magnetization Reversal Process of Write Head in Hard Disk Drives Observed by Strain Imaging, K. Takata (2006)
    TitleSmall Domain Structures in Magnetization Reversal Process of Write Head in Hard Disk Drives Observed by Strain Imaging
    AuthorK. Takata
    PublicationJapanese Journal of Applied Physics
    DateMarch, 2006
    AbstractDetection and imaging of magnetic-field-induced strains using scanning probe microscopy enable us to observe magnetic domain structures. Using strain imaging, domain structures in a magnetization reversal process of a thin film write head in a hard disk drive were investigated by scanning the air-bearing surface of the head. An external magnetic field was applied by the head coil. In the process, a characteristic small domain structure appeared in several portions in the bottom pole of the write head. The domain structure was hemispherical with a diameter of around 0.6 µm, consisting of two opposite magnetizations in the direction of the applied magnetic field. The domain structures appeared under a head coil current of less than 10 mA but vanished at larger currents. The portions where the domain structures were created should impede smooth magnetization reversal.
  • Small inexpensive diamagnetic levitation apparatus, Charles A. Sawicki (2001)
    TitleSmall inexpensive diamagnetic levitation apparatus
    AuthorCharles A. Sawicki
    PublicationThe Physics Teacher
    DateDecember 00, 2001
    AbstractA small, inexpensive (5 x 5 x 9 cm and $17) diamagnetic levitation apparatus is described in which a cubic NdFeB magnet 0.476 cm on a side is suspended in a potential energy well created using small ceramic disk magnets and two graphite plates.
  • Smart nanocomposite polymer gels, Zsolt Varga et al. (2003)
    TitleSmart nanocomposite polymer gels
    AuthorsZsolt Varga, J�zsef Feh�r, Genov�va Filipcsei, Mikl�s Zr�nyi
    PublicationMacromolecular Symposia
    AbstractThe combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic polymer gel represents a new type of composites consisting of small magnetic particles, usually from the nanometer range to the micron range, dispersed in a highly elastic polymeric gel matrix. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic fields. Giant deformational effects, high elasticity, anisotropic properties, temporary reinforcement and quick response to magnetic field open new opportunities for using such materials for various applications.
  • Sm–Co hard magnetic nanoparticles prepared by surfactant-assisted ball milling, Yiping Wang et al. (2007)
    TitleSm–Co hard magnetic nanoparticles prepared by surfactant-assisted ball milling
    AuthorsYiping Wang, Yang Li, Chuanbing Rong, J. Ping Liu
    AbstractHard magnetic nanoparticles based on the Sm2Co17 and SmCo5 systems have been successfully produced using a surfactant-assisted ball milling technique. A size-selection process has been developed to obtain nanoparticles of different sizes with narrow size distribution. Significant room-temperature coercivity up to 3.1 kOe has been achieved with the Sm2Co17-based nanoparticles of an average size of 23 nm. It has been found that surfactants play multifold roles in the processing.
  • Solid-state physics: Response with a twist, Karin M. Rabe (2007)
    TitleSolid-state physics: Response with a twist
    AuthorKarin M. Rabe
    DateOctober 11, 2007
  • Solvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices, J.N. Lee et al. (2003)
    TitleSolvent Compatibility of Poly(dimethylsiloxane)-Based Microfluidic Devices
    AuthorsJ.N. Lee, C. Park, G.M. Whitesides
    PublicationAnalytical Chemistry
    DateDecember 1, 2003
    AbstractThis paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels-Alder reaction in a microchannel.
  • Solvent-resistant elastomeric microfluidic devices and applications, R. van Dam (2005)
    TitleSolvent-resistant elastomeric microfluidic devices and applications
    AuthorR. van Dam
    AbstractMicrofluidics is increasingly being used in many areas of biotechnology and chemistry to achieve reduced reagent volumes, improved performance, integration, and parallelism, among other advantages. Though early devices were based on rigid materials such as glass and silicon, elastomeric materials such as polydimethylsiloxane (PDMS) are rapidly emerging as a ubiquitous platform for applications in biotechnology. This is due, in part, to simpler fabrication procedures and to the ability to integrate mechanical microvalves at vastly greater densities. For many applications in the areas of chemical synthesis and analysis, however, PDMS cannot replace glass and silicon due to its incompatibility with many solvents and reagents. Such areas could benefit tremendously from the development of an elastomeric microfluidic device technology that combines the advantages of PDMS with the property of solvent resistance. Simplified fabrication could increase the accessibility of microfluidics, and the possibility of dense valve integration could lead to significant advances in device sophistication. Applications could be more rapidly developed by design re-use due to the independence of mechanical valves on fluid properties (unlike electrokinetic pumping), and the property of permeability could enable novel fluidic functions for accessing a broader range of reactions than is possible in glass and silicon. The first half of this thesis describes our strategies and efforts to develop this new enabling technology. Several approaches are presented in Chapter 3, and two particularly successful ones, based on new elastomers (FNB and PFPE), are described in Chapters 4 and 5. Chapter 6 describes a novel method of fabricating devices from 3D molds that could expand the range of useful elastomers. The second half of this thesis discusses microfluidic combinatorial synthesis and high throughput screening—applications that take particular advantage of the ability to integrate thousands of individual valves and reaction chambers. Chapter 7 introduces several scalable device architectures and presents results of preliminary steps toward the synthesis of combinatorial DNA and peptide arrays. A novel method of performing universal gene expression analysis with combinatorial DNA arrays is described in Chapter 8 and an algorithm for predicting relationships among genes from gene expression array data is presented in Chapter 9.
  • Some Applications of the Method of Images-I., Jakob Kunz et al. (1921)
    TitleSome Applications of the Method of Images-I.
    AuthorsJakob Kunz, P. L. Bayley
    PublicationPhysical Review
    DateFebruary 1921
  • Spatio-temporally-complex concentration profiles using a tunable chaotic micromixer, Chia-Hsien Hsu et al. (2006)
    TitleSpatio-temporally-complex concentration profiles using a tunable chaotic micromixer
    AuthorsChia-Hsien Hsu, Albert Folch
    PublicationApplied Physics Letters
    DateOctober 02, 2006
  • Special Issue: Magnetoelectronics, Gary Prinz et al. (1995)
    TitleSpecial Issue: Magnetoelectronics
    AuthorsGary Prinz, Kristl Hathaway
    PublicationPhysics Today
    DateApril 1, 1995
  • Spin Coater Theory, Cost Effective Equipment (2000)
    TitleSpin Coater Theory
    AuthorCost Effective Equipment
    Date17 Oct 2000
    PublisherBrewer Science
    AbstractSpin coating has been used for several decades for the application of thin films. A typical process involves depositing a small puddle of a fluid resin onto the center of a substrate and then spinning the substrate at high speed (typically around 3000 rpm). Centripetal acceleration will cause most of the resin to spread to, and eventually off, the edge of the substrate, leaving a thin film of resin on the surface. Final film thickness and other properties will depend on the nature of the resin (viscosity, drying rate, percent solids, surface tension, etc.) and the parameters chosen for the spin process. Factors such as final rotational speed, acceleration, and fume exhaust contribute to how the properties of coated films are defined. One of the most important factors in spin coating is repeatability. Subtle variations in the parameters that define the spin process can result in drastic variations in the coated film. The following is an explanation of some of the effects of these variations.
  • Spin-Flopping in MnF[sub 2] by High Magnetic Fields, I. S. Jacobs (1961)
    TitleSpin-Flopping in MnF[sub 2] by High Magnetic Fields
    AuthorI. S. Jacobs
    PublicationJournal of Applied Physics
    DateMarch 00, 1961
    AbstractObservations of spin-flopping, or decoupling between the direction of antiferromagnetism and the easyaxis of the crystal, are presented for MnF2 in single crystal and powder form at low temperatures. Magnetizationmeasurements in pulsed fields to 140 koe are employed to explore the critical interaction energy inthis antiferromagnet, as an alternative tool to microwave resonance. The orientation dependence predictedby Néel in 1936 is confirmed. The critical field for spin-flopping given by the combination of anisotropy andexchange, (2HEHA)<sup>(1/2)</sup> is found to be 93±2 koe in excellent agreement with resonance results of S. Foner[(a) Phys. Rev. 107, 683 (1957); (b) J. phys. radium 20, 336 (1959)], and F. M. Johnson and A. H.Nethercot [Phys. Rev. 104, 847 (1956); 114, 705 (1959)]
  • Spin wave stiffness constants in some ferrimagnetics, C. M. Srivastava et al. (1987)
    TitleSpin wave stiffness constants in some ferrimagnetics
    AuthorsC. M. Srivastava, R. Aiyar
    PublicationJournal of Physics C: Solid State Physics
    AbstractThe magnitude of the spin wave stiffness parameter. D and its dependence on temperature in YIG, Fe3O4 and Li-Zn ferrite has been examined and compared with theory. It is shown that values of D obtained using the exchange constants that satisfactorily explain the equilibrium magnetic properties of these systems yield results in agreement with experiment for YIG and Fe3O4 but are inappropriate for the Li-Zn ferrite. The temperature dependence of D in YIG and Fe3O4 is satisfactorily explained on the basis of the interaction of acoustic magnons with optic magnons.
  • Stability of Microfabricated High Aspect Ratio Structures in Poly(dimethylsiloxane), P. Roca-Cusachs et al. (2005)
    TitleStability of Microfabricated High Aspect Ratio Structures in Poly(dimethylsiloxane)
    AuthorsP. Roca-Cusachs, F. Rico, E. Martinez, J. Toset, R. Farre, D. Navajas
    DateJune 7, 2005
    AbstractThe stability of structures microfabricated in soft elastomeric polymers is an important concern in most applications that use these structures. Although relevant for several applications, the collapse to the ground of high aspect ratio structures (ground collapse) is still poorly understood. The stability of soft microfabricated high aspect ratio structures versus ground collapse was experimentally assessed, and a new model of ground collapse involving adhesion was developed. Sets of posts with diameters from 0.36 to 2.29 m were fabricated in poly(dimethylsiloxane) and tested in air or immersed in water and ethanol to change the work of adhesion. The critical aspect ratio (the highest length-to-width ratio for which a post is not at risk of collapsing) was determined as a function of the diameter. The critical aspect ratio in air ranged from 2 to 4 and increased with the diameter. Work of adhesion was found to be determinant for and inversely correlated to stability. These results highlight the role played by adhesion and offer the possibility of improving stability by reducing the work of adhesion. The ground collapse model developed accounted for the main features of structure stability. The results indicate that ground collapse can be a limiting factor in the design of soft polymer structures.
  • Static and dynamic magnetic properties of spherical magnetite nanoparticles, G. F. Goya et al. (2003)
    TitleStatic and dynamic magnetic properties of spherical magnetite nanoparticles
    AuthorsG. F. Goya, T. S. Berquo, F. C. Fonseca, M. P. Morales
    PublicationJournal of Applied Physics
    AbstractWe present a detailed study of static and dynamic magnetic behavior of Fe3O4 nanoparticles with average particle sizes <d> ranging from 5 to 150 nm. Bulk-like properties such as saturation magnetization, hyperfine parameters, coercive field, and Verwey transition are observed in 150 nm particles. For decreasing particle size, the Verwey temperature, TV, shifts down to ~20 K for <d> = 50 nm and is no longer observable for smaller particles. The smallest particles (<d> = 5 nm) display superparamagnetic behavior at room temperature, with transition to a blocked state at TB~45 K, which depends on the applied field. The existence of surface spin disorder can be inferred from the decrease of saturation magnetization MS at low temperatures, as the average particle size is reduced. This disordered surface did not show effects of exchange coupling to the particle core, as observed from hysteresis loops after field cooling in a 7 T magnetic field. For particles with <d> = 5 nm, dynamic ac susceptibility measurements show a thermally activated Arrhenius–Néel dependence of the blocking temperature with applied frequency. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy. From the calculus of the magnetic anisotropy, it is inferred that there is no structural transition from cubic to triclinic symmetry for <d> = 5 nm, in agreement with the absence of the Verwey transition. A value K1 = 4.68×105 erg/cm3 is obtained for the magnetocrystalline anisotropy constant of the cubic phase.
  • Statistical inference for particle size distribution of magnetic nanoparticles, Gang Lei et al. (2008)
    TitleStatistical inference for particle size distribution of magnetic nanoparticles
    AuthorsGang Lei, K.R. Shao, G.Y. Yang
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
  • Stiffness of sensory-cell hair bundles in the isolated guinea pig cochlea, David Strelioff et al. (1984)
    TitleStiffness of sensory-cell hair bundles in the isolated guinea pig cochlea
    AuthorsDavid Strelioff, Åke Flock
    PublicationHearing Research
    DateJuly 1984
    AbstractStiffness of hair bundles on cochlear hair cells was measured in turns 2, 3 and 4 of isolated preparations of the guinea-pig organ of Corti maintained in tissue culture medium. Defined as the force required to produce a linear 1.0 [mu]m deflection of the hair-bundle tip, stiffness is greater for deflection in the excitatory than in the inhibitory direction. The excitatory-to-inhibitory ratio for inner hair cells (IHC) is significantly lower than the ratio for outer hair cells (OHC). Hair-bundle stiffness decreases radially from the first to third rows of OHC. Over the measurement range of 9.0-18.0 mm from the stapes hair-bundle stiffness decreases much more for OHC (88-97%) than for IHC (50%). Although an increase in hair-bundle length with distance from the stapes accounts for some of the observed stiffness decrease, the major decrease is due to an increase in compliance of the sensory-hair attachment to the hair-cell surface.
  • Stretched Polymer Nanohairs by Nanodrawing, H.E. Jeong et al. (2006)
    TitleStretched Polymer Nanohairs by Nanodrawing
    AuthorsH.E. Jeong, S.H. Lee, P. Kim, K.Y. Suh
    PublicationNano Letters
    DateJuly 12, 2006
    AbstractA simple, yet innovative, method is presented for fabricating high-aspect-ratio polymer nanohairs (aspect ratio >20) on a solid substrate by sequential application of molding and drawing of a thin polymer film. The polymer film was prepared by spin coating on a rigid or flexible substrate, and the temperature was raised above the polymer's glass transition while in conformal contact with a poly(urethane acrylate) mold having nanocavities. Consequently, capillary forces induced deformation of the polymer melt into the void spaces of the mold and the filled nanostructure was further elongated upon removal of the mold due to tailored adhesive force at the mold/polymer interface. The optimum value of the work of adhesion at the mold/polymer interface ranged from 0.9 to 1.1 times that at the substrate/polymer interface.
  • Structural and magnetic features of heterogeneously nucleated Fe-oxide nanoparticles, K. Simeonidis et al. (2008)
    TitleStructural and magnetic features of heterogeneously nucleated Fe-oxide nanoparticles
    AuthorsK. Simeonidis, S. Mourdikoudis, I. Tsiaoussis, M. Angelakeris, C. Dendrinou-Samara, O. Kalogirou
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
  • Structure and function of mammalian cilia, Peter Satir et al. (2008)
    TitleStructure and function of mammalian cilia
    AuthorsPeter Satir, Søren Christensen
    PublicationHistochemistry and Cell Biology
    DateJune 16, 2008
    AbstractIn the past half century, beginning with electron microscopic studies of 9 + 2 motile and 9 + 0 primary cilia, novel insights have been obtained regarding the structure and function of mammalian cilia. All cilia can now be viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation. This view has had unanticipated consequences for our understanding of developmental processes and human disease.
  • Studies of spin-coated polymer films, K. Norrman et al. (2005)
    TitleStudies of spin-coated polymer films
    AuthorsK. Norrman, A. Ghanbari-Siahkali, N. B. Larsen
    PublicationAnnual Reports Section "C" (Physical Chemistry)
    AbstractSpin-coating is widely employed for the highly reproducible fabrication of thin film coatings over large areas with high structural uniformity. Research in recent years has extended the scope of spin-coating by chemically engineering the interface of support and solution to obtain specific structural order in the resulting supported thin films. This review will discuss both the fundamental physical and chemical processes governing the conventional spin-coating process and describe methodologies for the preparation of spin-coated polymer thin films. Furthermore, a range of advanced applications and recent developments within this field will be reviewed with focus on engineering chemical and topological structure during the coating process.
  • Styrene-coated iron nanobeads for medical use, C.S. Kuroda et al. (2005)
    TitleStyrene-coated iron nanobeads for medical use
    AuthorsC.S. Kuroda, M. Maeda, H. Nishibiraki, N. Matsushita, H. Handa, M. Abe
    PublicationMagnetics, IEEE Transactions on
    AbstractSpherical iron nanoparticles with a diameter of 10 nm were synthesized using a water in oil reverse micelle systems. The particles were encapsulated in styrene polymer by an emulsion polymerization method. The resulting beads were 150/spl plusmn/50 nm in diameter, having a saturation magnetization of 23.5 emu/g. The styrene-coated iron particles exhibited superparamagnetism, as measured by Mo/spl uml/ssbauer spectroscopy, and dispersed well in water. The saturation magnetization was higher than reported for commercially available polymer-coated micron sized beads.
  • Supermagnetism in magnetic nanoparticle systems, S. Bedanta (2006)
    TitleSupermagnetism in magnetic nanoparticle systems
    AuthorS. Bedanta
    Date11 Dec, 2006
  • Surface oxidation of nickel thin films, Kumari et al. (1992)
    TitleSurface oxidation of nickel thin films
    Authors Kumari, Natarajan, Vaidyan, Koshy
    PublicationJournal of Materials Science Letters
    DateJanuary 01, 1992
  • Surfactant effects in magnetite nanoparticles of controlled size, P. Guardia et al. (2007)
    TitleSurfactant effects in magnetite nanoparticles of controlled size
    AuthorsP. Guardia, B. Batlle-Brugal, A.G. Roca, O. Iglesias, M.P. Morales, C.J. Serna, A. Labarta, X. Batlle
    PublicationJournal of Magnetism and Magnetic Materials
    DateSeptember 2007
    AbstractMagnetite Fe3O4 nanoparticles of controlled size within 6 and 20 nm in diameter were synthesised by thermal decomposition of an iron organic precursor in an organic medium. Particles were coated with oleic acid. For all samples studied, saturation magnetisation Ms is size-independent, and reaches a value close to that expected for bulk magnetite, in contrast to results in small particle systems for which Ms is usually much smaller due to surface spin disorder. The coercive field for the 6 nm particles is in agreement with coherent rotation, taking the bulk magnetocrystalline anisotropy into account. Both results suggest that the oleic acid molecules covalently bonded to the nanoparticle surface yield a strong reduction in the surface spin disorder. However, although the saturated state may be similar, the approach to saturation is different and, in particular, the high-field differential susceptibility is one order of magnitude larger than in bulk materials. The relevance of these results in biomedical applications is discussed.
  • Sylgard® 184 Silicone Elastomer, Solar Product Information, Dow Corning Corporation (2007)
    TitleSylgard® 184 Silicone Elastomer, Solar Product Information
    AuthorDow Corning Corporation
    AbstractTwo-part silicone that cures to a flexible elastomer for protection of electrical and electronic devices in solar applications
  • Synthesis and characterization of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids, R.Y. Hong et al. (2008)
    TitleSynthesis and characterization of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids
    AuthorsR.Y. Hong, J.H. Li, H.Z. Li, J. Ding, Y. Zheng, D.G. Wei
    PublicationJournal of Magnetism and Magnetic Materials
    VolumeIn Press, Accepted Manuscript
  • Synthesis of poly(methyl methacrylate) stabilized colloidal zero-valence metallic nanoparticles, Zhanhu Guo et al. (2006)
    TitleSynthesis of poly(methyl methacrylate) stabilized colloidal zero-valence metallic nanoparticles
    AuthorsZhanhu Guo, Laurence L. Henry, Vadim Palshin, Elizabeth J. Podlaha
    PublicationJournal of Materials Chemistry
    AbstractPoly(methyl methacrylate) (PMMA) stabilized colloidal metallic iron nanoparticles without additional surfactant or stabilizer were fabricated by a wet chemical reduction method. The synthesized colloidal iron nanoparticles were found to be stable in tetrahydrofuran (THF) solution and the dried PMMA-Fe nanocomposites were ferromagnetic even at room temperature as illustrated by magnetometer measurement. The particle size increased with the decrease of the initial PMMA concentration and the magnetic properties also depended on the initial PMMA concentration.
  • Synthesis of Y-Fe-O ultrafine particles using inductively coupled plasma, M. Sugasawa et al. (1998)
    TitleSynthesis of Y-Fe-O ultrafine particles using inductively coupled plasma
    AuthorsM. Sugasawa, N. Kikukawa, N. Ishikawa, N. Kayano, T. Kimura
    PublicationJournal of Aerosol Science
    DateJune 1, 1998
    AbstractIn a previous study, we synthesized ultrafine particles containing a new ferro- or ferri-magnetic compound in an Y-Fe-O system. This was done by supplying a co-precipitated powder, having an Y : Fe molar ratio of 1 : 1.9, to an argon-oxygen radio frequency (RF) plasma. The resultant new phase had an X-ray diffraction (XRD) pattern not registered in the JCPDS, the standard database of XRD patterns of known chemical compounds. To synthesize this new phase as a pure single-phase product, powder precursors prepared by the amorphous citric gel method and liquid precursors of mixed nitrate solutions with various Y : Fe ratios were supplied to the plasma. It was found that the new phase, which has good crystallinity and some magnetism, is synthesized as an almost pure single-phase product from a powder precursor with an Y : Fe ratio of 1 : 3.7. By observing the particle-size distributions and shapes (crystal habits) of the particles synthesized from powder and liquid precursors, and referring to previous studies, it was found that further experiments need to be conducted where the feed rates of powder or liquid precursors were varied systematically with all other conditions remaining constant.
  • Synthesis, Properties, and Applications of Iron Nanoparticles, Dale L. Huber (2005)
    TitleSynthesis, Properties, and Applications of Iron Nanoparticles
    AuthorDale L. Huber
    AbstractIron, the most ubiquitous of the transition metals and the fourth most plentiful element in the Earth?s crust, is the structural backbone of our modern infrastructure. It is therefore ironic that as a nanoparticle, iron has been somewhat neglected in favor of its own oxides, as well as other metals such as cobalt, nickel, gold, and platinum. This is unfortunate, but understandable. Iron?s reactivity is important in macroscopic applications (particularly rusting), but is a dominant concern at the nanoscale. Finely divided iron has long been known to be pyrophoric, which is a major reason that iron nanoparticles have not been more fully studied to date. This extreme reactivity has traditionally made iron nanoparticles difficult to study and inconvenient for practical applications. Iron however has a great deal to offer at the nanoscale, including very potent magnetic and catalytic properties. Recent work has begun to take advantage of iron?s potential, and work in this field appears to be blossoming
  • Temperature-Sensitive Hybrid Microgels with Magnetic Properties, A. Pich et al. (2004)
    TitleTemperature-Sensitive Hybrid Microgels with Magnetic Properties
    AuthorsA. Pich, S. Bhattacharya, Y. Lu, V. Boyko, H.-J.P. Adler
    DateNovember 23, 2004
    AbstractIn the present paper, we report the preparation of hybrid temperature-sensitive microgels which include magnetite nanoparticles in their structure. Polymeric microgels have been prepared by surfactant-free emulsion copolymerization of acetoacetoxyethyl methacrylate (AAEM) and N-vinylcaprolactam (VCL) in water with a water-soluble azo-initiator. The obtained microgels possess a low critical solution temperature (LCST) in water solutions, with a rapid decrease of the particle size being observed at elevated temperatures. Magnetite was deposited directly into microgels, leading to the formation of composite particles which combine both temperature-sensitive and magnetic properties. The influence of magnetite load on microgel size, morphology, swelling-deswelling behavior, and stability is discussed.
  • The breakdown of the fingerprinting of vortices by hysteresis loops in circular multilayer ring arrays, V. Rose et al. (2007)
    TitleThe breakdown of the fingerprinting of vortices by hysteresis loops in circular multilayer ring arrays
    AuthorsV. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, V. Metlushko
    PublicationApplied Physics Letters
  • The distribution, activity, and function of the cilia in the frog brain, Deborah J. Nelson et al. (1974)
    TitleThe distribution, activity, and function of the cilia in the frog brain
    AuthorsDeborah J. Nelson, Ernest M. Wright
    PublicationJ Physiol
    DateNovember 1, 1974
    Abstract1. The distribution, activity, and function of the cilia in the brain was studied using in vitro preparations of the frog choroid plexuses and ependyma. 2. Scanning electron microscopy revealed that twenty to forty cilia, about 20 microm long, project from the cells of the choroidal epithelium and ependyma into the ventricular system of the brain. 3. These cilia beat at a constant frequency which ranged from 5 to 20 c/s. Ciliary activity was enhanced by ATP, cyclic AMP, theophylline, and acetylcholine, and was depressed by DNP, IAA, Ni2+, La3+, and Co2+. 4. Ciliary motion produced a flow of c.s.f. over the surface of the cells lining the ventricles, and in the choroid plexus this flow reduced the effective thickness of the unstirred layer adjacent to the epithelium by about 100 microm. 5. These results are discussed in relation to the factors that control the frequency of ciliary beating, and the role of the cilia in the circulation of the c.s.f.
  • The Effect of Dislocations on Magnetization Near Saturation, William Fuller Brown (1941)
    TitleThe Effect of Dislocations on Magnetization Near Saturation
    AuthorWilliam Fuller Brown
    PublicationPhysical Review
    DateJuly 15, 1941
    AbstractThe effect of dislocations on the magnetization curve at high fields is calculated by direct use of dislocation theory. The deviation from saturation is assumed to be due to magnetostrictive forces, localized in the stress field about the dislocation rather than at the dislocation itself; their effect is more complicated than that of the simple "line concentrations of force" considered in an earlier article. Pairs of dislocations of opposite sign, separated by a short distance, contribute a term a / H to the deviation from saturation; in this respect they resemble line concentrations. Pairs separated by a long distance and surplus dislocations of one sign contribute a term b / H2, with b theoretically not a constant but a logarithmically varying function of H. From data on the variation of the empirical a and b with plastic strain, it is possible to calculate the density of dislocations and the "block" length if a value is assumed for the distance Y between the members of a dislocation pair. The orders of magnitude obtained agree with those obtained in the theory of hardening if Y is taken ≅2×10-6 cm. It appears that all but about 1 percent of the dislocations are members of such pairs.
  • The force acting on a superparamagnetic bead due to an applied magnetic field, Sergey S. Shevkoplyas et al. (2007)
    TitleThe force acting on a superparamagnetic bead due to an applied magnetic field
    AuthorsSergey S. Shevkoplyas, Adam C. Siegel, Robert M. Westervelt, Mara G. Prentiss, George M. Whitesides
    PublicationLab on a Chip
    AbstractThis paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.
  • The importance of being cilia, David Brinley (2005)
    TitleThe importance of being cilia
    AuthorDavid Brinley
    PublicationHHMI Bulletin
    DateSeptember 2005
    AbstractOn the surface of nearly every cell in the body is a slender protuberance called the primary cilium. Although ubiquitous, the primary cilium was long considered—with a few exceptions—to be a largely useless evolutionary vestige, destined to go the way of the tailbone and the wisdom tooth. But now we know that cilia are functioning organelles, essential to normal development and health.
  • The mechanical properties of the rubber elastic polymer polydimethylsiloxane for sensor applications, J. C. Lötters et al. (1997)
    TitleThe mechanical properties of the rubber elastic polymer polydimethylsiloxane for sensor applications
    AuthorsJ. C. Lötters, W. Olthuis, P. H. Veltink, P. Bergveld
    PublicationJournal of Micromechanics and Microengineering
    DateSept 1997
    AbstractPolydimethylsiloxane (PDMS) is a commercially available physically and chemically stable silicone rubber. It has a unique flexibility with a shear elastic modulus due to one of the lowest glass transition temperatures of any polymer . Further properties of PDMS are a low change in the shear elastic modulus versus temperature , virtually no change in G versus frequency and a high compressibility. Because of its clean room processability, its low curing temperature, its high flexibility, the possibility to change its functional groups and the very low drift of its properties with time and temperature, PDMS is very well suited for micromachined mechanical and chemical sensors, such as accelerometers (as the spring material) and ISFETs (as the ion selective membrane). It can also be used as an adhesive in wafer bonding, as a cover material in tactile sensors and as the mechanical decoupling zone in sensor packagings.
  • The origins and the future of microfluidics, George M. Whitesides (2006)
    TitleThe origins and the future of microfluidics
    AuthorGeorge M. Whitesides
    AbstractThe manipulation of fluids in channels with dimensions of tens of micrometres — microfluidics — has emerged as a distinct new field. Microfluidics has the potential to influence subject areas from chemical synthesis and biological analysis to optics and information technology. But the field is still at an early stage of development. Even as the basic science and technological demonstrations develop, other problems must be addressed: choosing and focusing on initial applications, and developing strategies to complete the cycle of development, including commercialization. The solutions to these problems will require imagination and ingenuity.
  • Theory of ferromagnetic hysteresis, D. C. Jiles et al. (1986)
    TitleTheory of ferromagnetic hysteresis
    AuthorsD. C. Jiles, D. L. Atherton
    PublicationJournal of Magnetism and Magnetic Materials
    DateSeptember 1986
    AbstractA mathematical model of the hysteresis mechanisms in ferromagnets is presented. This is based on existing ideas of domain wall motion including both bending and translation. The anhysteretic magnetization curve is derived using a mean field approach in which the magnetization of any domain is coupled to the magnetic field H and the bulk magnetization M. The anhysteretic emerges as the magnetization which would be achieved in the absence of domain wall pinning. Hysteresis is then included by considering the effects of pinning of magnetic domain walls on defect sites. This gives rise to a frictional force opposing the movement of domain walls. The impedance to motion is expressed via a single parameter k, leading to a simple model equation of state. This exhibits all of the main features of hysteresis such as the initial magnetization curve, saturation of magnetization, coercivity, remanence, and hysteresis loss.
  • Theory of the Approach to Magnetic Saturation, William Fuller Brown (1940)
    TitleTheory of the Approach to Magnetic Saturation
    AuthorWilliam Fuller Brown
    PublicationPhysical Review
    DateOctober 15, 1940
  • Theory of the Structure of Ferromagnetic Domains in Films and Small Particles, Charles Kittel (1946)
    TitleTheory of the Structure of Ferromagnetic Domains in Films and Small Particles
    AuthorCharles Kittel
    PublicationPhysical Review
    DateDecember 01, 1946
  • The physics of coercivity, Dominique Givord et al. (2003)
    TitleThe physics of coercivity
    AuthorsDominique Givord, Michel Rossignol, Vitoria M. T. S. Barthem
    PublicationJournal of Magnetism and Magnetic Materials
    DateMarch 2003
    AbstractIn hard magnets, coercivity is not a material intrinsic property. Magnetization reversal is constituted by a series of local processes, of which the first, termed as "true nucleation", takes place within a defect. An original analysis is proposed in this article which relates the coercive field Hc(T) to another experimental parameter, the activation volume. The obtained results exclude that coercivity is governed by true nucleation. Another process is necessarily involved before possible wall pinning in the bulk of the grains. It corresponds to the passage and expansion of the magnetic wall from the defect to the main hard phase. During passage/expansion, the wall energy increases progressively as the wall moves into regions with properties that approach those of the main hard phase and its surface area increases. At the same time, its behaviour tends to be governed by main phase properties. This scenario allows coercivity in hard magnets to be quantitatively interpreted.
  • Thermal Fluctuations of a Single-Domain Particle, W.F. Brown (1963)
    TitleThermal Fluctuations of a Single-Domain Particle
    AuthorW.F. Brown
    PublicationPhysical Review
    DateJune 01, 1963
    AbstractA sufficiently fine ferromagnetic particle has a uniform vector magnetization whose magnitude is essentially constant, but whose direction fluctuates because of thermal agitation. The fluctuations are important in superparamagnetism and in magnetic aftereffect. The problem is approached here by methods familiar in the theory of stochastic processes. The "Langevin equation" of the problem is assumed to be Gilbert's equation of motion augmented by a "random-field" term. Consideration of a statistical ensemble of such particles leads to a "Fokker-Planck" partial differential equation, which describes the evolution of the probability density of orientations. The random-field concept, though convenient, can be avoided by use of the fluctuation-dissipation theorem. The Fokker-Planck equation, in general, is complicated by the presence of gyroscopic terms. These drop out in the case of axial symmetry: then the problem of finding nonequilibrium solutions can be restated as a minimization problem, susceptible to approximate treatments. The case of energy barriers large in comparison with kT is treated both by approximate minimization and by an adaptation of Kramers' treatment of the escape of particles over barriers. The limits of validity of the discrete-orientation approximation are discussed.
  • The role of nucleation field of media in heat-assisted magnetic probe recording, Li Zhang (2007)
    TitleThe role of nucleation field of media in heat-assisted magnetic probe recording
    AuthorLi Zhang
    PublicationPhysica B: Condensed Matter
    DateMarch 1, 2007
    AbstractWe characterize a method of heat-assisted magnetic probe recording on perpendicular media. Heating source is field emission current from a scanning tunneling microscope (STM) tip. Recording media are three kinds of magnetic films, Co/Pt, CoNi/Pt, and Co/Pd multilayers with different nucleation fields. Pulses with amplitude of 5�V were applied between the STM tip and the recording medium. Experiments show that magnetic marks with an average size of 180�nm were formed on both Co/Pt and CoNi/Pt films whose nucleation fields are greater than their saturation magnetization. No marks were observed on the Co/Pd film whose nucleation field is smaller than its saturation magnetization. A model is built to simulate the dynamic process of domain formation in probe-based magnetic recording system. Simulation results agree with experiments and it explains the effect of the nucleation field of medium in perpendicular recording.
  • The Speed of a Protozoan, Ross Krupnik (2000)
    TitleThe Speed of a Protozoan
    AuthorRoss Krupnik
    AbstractThe Physics Factbook™ is an encyclopedia of scientific essays written by high school students that can be used by anybody. It is an exercise in library research methods in which students are sent out in search of a measurement with the intent of having them find more than just a number with a unit. It is an ongoing project with no foreseeable end date or limits.
  • The Stability and Oxidation Resistance of Iron- and Cobalt-Based Magnetic Nanoparticle Fluids Fabricated by Inert-Gas Condensation, N.H. Hai et al. (2004)
    TitleThe Stability and Oxidation Resistance of Iron- and Cobalt-Based Magnetic Nanoparticle Fluids Fabricated by Inert-Gas Condensation
    AuthorsN.H. Hai, R. Lemoine, S. Remboldt, M.A. Strand, S. Wignall, J.E. Shield, D. Leslie-Pelecky
    PlaceBoston, Massachusetts, U.S.A.
    PublisherMaterials Research Society
    AbstractMagnetic nanoparticle fluids have numerous biomedical applications, including magnetic imaging, drug delivery, and hyperthemia treatment for cancer. Ideal magnetic nanoparticle fluids have well-separated, biocompatible nanoparticles with a small size distribution that form a stable colloid. We have combined inert-gas condensation, which produces nanoparticles with low polydispersity, with deposition directly into a surfactant-laden fluid to prevent agglomeration. Iron, cobalt, and iron-nitride nanoparticle fluids fabricated using inert-gas condensation have with mean particle sizes from 5-50 nm and remain stable over long periods of time. Iron and cobalt nanoparticles oxidize on exposure to air, with oxidation rates dependent on surfactant type and concentration. Iron-nitride fluids are more oxidation and corrosion resistant, while retaining the same high degree of colloidal stability. Magnetic properties vary depending on the nanoparticle size and material, but can be varied from superparamagnetic to ferromagnetic with coercivities on the order of 1000 Oe. In addition to future biomedical applications, inertgas condensation into fluids offers the opportunity to study interparticle interactions over a broad range of intrinsic materials parameters and interparticle separations.
  • TITAN: a conducting polymer based microfluidic pump, Y. Wu et al. (2005)
    TitleTITAN: a conducting polymer based microfluidic pump
    AuthorsY. Wu, D. Zhou, G. M. Spinks, P. C. Innis, W. M. Megill, G. G. Wallace
    PublicationSmart Materials and Structures
    AbstractThe electromechanical actuation properties of polypyrrole have been utilized in the design and development of a low voltage fluid movement system for microfluidic channels. A confined concentric arrangement of polypyrrole actuators is used to induce fluid movement through an inner channel in a single unit. Series connection of these units and appropriate electrical connection/stimulation induces a novel peristaltic action that enables fluids to be pumped in a predetermined direction. Flow rates of up to 2.5 µl min[?]1 can be achieved against a back pressure of 50 mbar, which is sufficient to enable fluid movement in a glass capillary channel (diameter: 266 µm, length: 12.8 cm). The mechanism of fluid movement enables the use of low voltage devices (1 V) to drive fluid with an average power requirement of 8.7 mW.
  • Towards fluid manipulations in microfluidic channels by magnetic actuation of polymeric microstructures , Francis Fahrni (2007)
    TitleTowards fluid manipulations in microfluidic channels by magnetic actuation of polymeric microstructures
    AuthorFrancis Fahrni
  • Transient behaviour of magnetic micro-bead chains rotating in a fluid by external fields, Ioannis Petousis et al. (2007)
    TitleTransient behaviour of magnetic micro-bead chains rotating in a fluid by external fields
    AuthorsIoannis Petousis, Erik Homburg, Roy Derks, Andreas Dietzel
    PublicationLab on a Chip
    AbstractMagnetic micro-beads can facilitate many functions in lab-on-a-chip systems, such as bio-chemical labeling, selective transport, magnetic sensing and mixing. In order to investigate potential applications of magnetic micro-beads for mixing in micro fluidic systems, we developed a pin-jointed mechanism model that allows analysing the behaviour of rotating superparamagnetic bead chains. Our numerical model revealed the response of the chains on a rotating magnetic field over time. We could demonstrate that the governing parameters are the Mason number and number of beads in the chain. The results are in agreement with the simplified analytical model, assuming a straight chain, but also allow prediction of the transient chain shape. The modelled chains develop an anti-symmetric S-shape that is stable, if the Mason number for a given chain length does not surpass a critical value. Above that value, rupture occurs in the vicinity of the chain centre. However, variations in bead susceptibility can shift the location of rupture. Moreover, we performed experiments with superparamagnetic micro-beads in a small fluid volume exposed to a uniform rotating magnetic field. Our simulation could successfully predict the observed transient chain form and the time for chain rupture. The developed model can be used to design optimised bead based mixers in micro fluidic systems.
  • Tunable Poly(dimethylsiloxane) Topography in O2 or Ar Plasmas for Controlling Surface Wetting Properties and Their Ageing, K. Tsougeni et al. (2007)
    TitleTunable Poly(dimethylsiloxane) Topography in O2 or Ar Plasmas for Controlling Surface Wetting Properties and Their Ageing
    AuthorsK. Tsougeni, A. Tserepi, Vassilios Constantoudis, E. Gogolides
    PublicationJapanese Journal of Applied Physics
    DateFebruary 8, 2007
    AbstractA plasma-based methodology to fabricate ultraviolet (UV) curable poly(dimethylsiloxane) (PDMS) surfaces with controlled nano-texturing and wettability is described. The surface topography of photo-sensitive PDMS is modified in oxygen and argon plasmas. Plasma treatment of photo-crosslinked PDMS produces spontaneously-formed wavy structures with high nano-scale amplitude and with periodicity of a few 100's nm. With increasing plasma treatment duration, roughness increased while periodicity decreased, resulting in surfaces of enhanced surface area exploited for the enhancement and control of surface hydrophilicity and hydrophobicity. The mechanisms responsible for the plasma-induced PDMS surface nanotexturing are discussed. The beneficial effect of this nanotopography on retarding ageing of PDMS hydrophilicity is demonstrated. Possible applications in sensors and bio-microsystems are outlined.
  • Tuning the domain wall orientation in thin magnetic strips using induced anisotropy, S. Cherifi et al. (2007)
    TitleTuning the domain wall orientation in thin magnetic strips using induced anisotropy
    AuthorsS. Cherifi, R. Hertel, A. Locatelli, Y. Watanabe, G. Potdevin, A. Ballestrazzi, M. Balboni, S. Heun
    PublicationApplied Physics Letters
    AbstractThe authors report on a method to tune the orientation of in-plane magnetic domains and domain walls in thin ferromagnetic strips by manipulating the magnetic anisotropy of the system. Uniaxial in-plane anisotropy is induced in a controlled way by oblique evaporation of magnetic thin strips. A direct correlation between the magnetization direction and the domain wall orientation is found experimentally and confirmed by micromagnetic simulations. The domain walls in the strips are always oriented along the oblique evaporation-induced easy axis, irrespective of the shape anisotropy. The controlled manipulation of domain wall orientations could provide promising possibilities for recently proposed devices based on domain wall propagation
  • Two-Photon Three-Dimensional Microfabrication of Poly(Dimethylsiloxane) Elastomers, C. A Coenjarts et al. (2004)
    TitleTwo-Photon Three-Dimensional Microfabrication of Poly(Dimethylsiloxane) Elastomers
    AuthorsC. A Coenjarts, C. K Ober
    PublicationChem. Mater
  • Unconventional nanofabrication, B.D. Gates et al. (2004)
    TitleUnconventional nanofabrication
    AuthorsB.D. Gates, Q.B. Xu, J.C. Love, D.B. Wolfe, G.M. Whitesides
    PublicationAnnual review of materials research
    AbstractNanostructures are fabricated using either conventional or unconventional tools-that is, by techniques that are highly developed and widely used or by techniques that are relatively new and still being developed. This chapter reviews techniques of unconventional nanofabrication, and focuses on experimentally simple and inexpensive approaches to pattern features with dimensions < 100 nm. The techniques discussed include soft lithography, scanning probe lithography, and edge lithography. The chapter includes recent advances in fabricating nanostructures using each set of techniques, together with demonstrated advantages, limitations, and applications for each.
  • Using spherical magnetic particles for testing the intracellular viscosity, W. Stahlhofen et al. (1990)
    TitleUsing spherical magnetic particles for testing the intracellular viscosity
    AuthorsW. Stahlhofen, W. Moller
    PublicationJournal of Aerosol Science
    IssueSupplement 1
    AbstractSpherical magnetite-particles were used to measure the intracellular viscostiy and the cell-energy of macrophages in vivo. After strong-field magnetization and complete relaxation a weak magnetic field was applied in order to rotate the randomly oriented particles. From the increase of magnetization the viscosity was calculated and found to be 65.3 Pa[middle dot]s. The macrophage-activity was characterized as randomization process with an energy EZ = 6.7 [middle dot] 10-18 J.
  • Vector analysis; with applications to geometry and physics, M. Schwartz et al. (1964)
    TitleVector analysis; with applications to geometry and physics
    AuthorsM. Schwartz, S. Green, W. Rutledge
    PublisherJohn Weatherhill