On-chip manipulation and trapping of microorganisms using a patterned magnetic pathway

We demonstrate on-chip manipulation and trapping of individual microorganisms at designated positions on a silicon surface within a microfluidic channel. Superparamagnetic beads acted as microorganism carriers. Cyanobacterium Synechocystis sp. PCC 6803 microorganisms were immobilized on amine-functionalized magnetic beads (Dynabead^® M-270 Amine) by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)–N-hydroxysulfosuccinimide coupling chemistry. The magnetic pathway was patterned lithographically such that half-disk Ni₈₀Fe₂₀ (permalloy) 5 μm elements were arranged sequentially for a length of 400 micrometers. An external rotating magnetic field of 10 mT was used to drive a translational force (maximum 70 pN) on the magnetic bead carriers proportional to the product of the field strength and its gradient along the patterned edge. Individual microorganisms immobilized on the magnetic beads (transporting objects) were directionally manipulated using a magnetic rail track, which was able to manipulate particles as a result of asymmetric forces from the curved and flat edges of the pattern on the disk. Transporting objects were then successfully trapped in a magnetic trapping station pathway. The transporting object moves two half-disk lengths in one field rotation, resulting in movement at ~24 μm s^?1 for 1 Hz rotational frequency with 5 μm pattern elements spaced with a 1 μm gap between elements.     

Magnetic concentration of particles and cells in ferrofluid flow through a straight microchannel using attracting magnets

Concentrating particles to a detectable level is often necessary in many applications. Although magnetic force has long been used to enrich magnetic (or magnetically tagged) particles in suspensions, magnetic concentration of diamagnetic particles is relatively new and little reported. We demonstrate in this work a simple magnetic technique to concentrate polystyrene particles and live yeast cells in ferrofluid flow through a straight rectangular microchannel using negative magnetophoresis. The magnetic field gradient is created by two attracting permanent magnets that are placed on the top and bottom of the planar microfluidic device and held in position by their natural attractive force. The magnet–magnet distance is mainly controlled by the thickness of the device substrate and can be made small, allowing for the use of a dilute ferrofluid in the developed magnetic concentration technique. This advantage not only enables a magnetic/fluorescent label-free handling of diamagnetic particles, but also renders such handling biocompatible.     

Fabrication and integration of microscale permanent magnets for particle separation in microfluidics

Microfluidic magnetophoresis is an effective technique to separate magnetically labeled bioconjugates in lab-on-a-chip applications. However, it is challenging and expensive to fabricate and integrate microscale permanent magnets into microfluidic devices with conventional methods that use thin-film deposition and lithography. Here, we propose and demonstrate a simple and low-cost technique to fabricate microscale permanent magnetic microstructures and integrate them into microfluidic devices. In this method, microstructure channels were fabricated next to a microfluidic channel and were injected with a liquid mixture of neodymium (NdFeB) powders and polydimethylsiloxane (PDMS). After the mixture was cured, the resulted solid NdFeB–PDMS microstructure was permanently magnetized to form microscale magnets. The microscale magnets generate strong magnetic forces capable of separating magnetic particles in microfluidic channels. Systematic experiments and numerical simulations were conducted to study the geometric effects of the microscale magnets. It was found that rectangular microscale magnets generate larger \(({\mathbf {H}}\cdot \nabla ) {\mathbf {H}}\) which is proportional to magnetic force and have a wider range of influence than the semicircle or triangle magnets. For multiple connected rectangular microscale magnet, additional geometric parameters, including separation distance, height and width of the individual elements, further influence the particle separation and were characterized experimentally. With an optimal size combination, complete separation of yeast cells and magnetic microparticles of similar sizes (\(4\;\upmu \hbox {m}\)) was demonstrated with the multi-rectangular magnet microfluidic device.     

基于嵌入式MPP系统的数据操作策略研究

针对一种完全国产化的嵌入式MPP系统,通过抽象出系统的数据空间划分、确定系统的数据访问方式以及建立系统的数据映射机制,提出了与体系结构相适应的、与存储方式无关的数据操作策略。实验结果表明,该数据操作策略能够实现异构系统间高效、正确地数据交换。     

Magnetohydrodynamics modelling of a permanent magnets activated MRF clutch–brake

Microsystem Technologies - Chattering due to vibrations on the machine tool shaft and control of the transmitted torque are both a concern in precision machining. Hence, a magnetorheological fluid...     

On-chip separation of Lactobacillus bacteria from yeasts using dielectrophoresis

Dielectrophoresis, the induced motion of dielectric particles in non-uniform electric fields, enables the separation of suspended bio-particles based on their dimensions or dielectric properties. This work presents a microfluidic system, which utilises a combination of dielectrophoretic (DEP) and hydrodynamic drag forces to separate Lactobacillus bacteria from a background of yeasts. The performance of the system is demonstrated at two operating frequencies of 10?MHz and 100?kHz. At 10?MHz, we are able to trap the yeasts and bacteria at different locations of the microelectrodes as they experience different magnitudes of DEP force. Alternatively, at 100?kHz we are able to trap the bacteria along the microelectrodes, while repelling the yeasts from the microelectrodes and washing them away by the drag force. These separation mechanisms might be applicable to automated lab-on-a-chip systems for the rapid and label-free separation of target bio-particles.     

Design of a yield stress characterizing platform for magnetorheological fluid magnetized by permanent magnets

In this paper we proposed a platform for measuring shear force of magnetorheological (MR) fluid by which the relationship of yield stress and magnetic flux density of specific materials can be determined. The device consisted of a rotatable center tube placed in a frame body and the magnetic field was provided by two blocks of permanent magnets placed oppositely outside the frame body. The magnitude and direction of the magnetic flux were manipulated by changing the distance of the two permanent magnets from the frame body and rotating the center tube, respectively. For determining the magnetic field of the device, we adopted an effective method by fitting the finite element method result to the measured one and then rebuilt the absent components to approximate the magnetic field, which was hardly to be measured as different device setup were required. With the proposed platform and analytical methods, the drawing shear force and the corresponding yield stress contributed by MR fluid in respect to the magnitude and direction of given magnetic flux density could be evaluated effectively for specific designing purposes without the requirement of a large, complex, and expensive instrument.

     

Microfluidic devices in superconducting magnets: on-chip free-flow diamagnetophoresis of polymer particles and bubbles

Superconducting magnets enable the study of high magnetic fields on materials and objects, for example in material synthesis, self-assembly or levitation experiments. The setups employed often lack in precise spatial control of the object of interest within the bore of the magnet. Microfluidic technology enables accurate manipulation of fluidic surroundings and we have investigated the integration of microfluidic devices into superconducting magnets to enable controlled studies of objects in high magnetic fields. Polymeric microparticles similar in size to biological cells were manipulated via diamagnetic repulsion. The particles were suspended in an aqueous paramagnetic medium of manganese (II) chloride and pumped into a microfluidic chip, where they were repelled in continuous flow by the high magnetic field. The extent of deflection was studied as a function of increasing (1) particle size, (2) paramagnetic salt concentration, and (3) magnetic field strength. Optimizing these parameters allowed for the spatial separation of two particle populations via on-chip free-flow diamagnetophoresis. Finally, preliminary findings on the repulsion of air bubbles are shown.     

Rectilinear oscillations of two spherical particles embedded in an unbounded viscous fluid

Microsystem Technologies - The problem of the rectilinear oscillations of two spherical particles along the line through their centers in an axi-symmetric, viscous, incompressible flow at low...     

A case-study in algebraic manipulation using mechanized reasoning tools

In this article, two different mechanized reasoning tools (Coq and Isabelle/HOL) are used in order to prove some basic but significant properties extracted from a symbolic computation system called Kenzo. In particular, we focused on a property called ‘cancellation theorem’, which can be applied to the proof of the idempotence property of a differential morphism. This result is used as a case-study to compare the capabilities and styles of the two proof assistants. The conclusion of our comparison is that both tools are adequate to solve the case-study presented in this article in a rather similar way but depending on their specific styles. This research is part of a more general project devoted to increase the reliability of computer algebra systems for calculations in algebraic topology.     

Optical manipulation of microobjects using binary diffractive elements

The paper describes the computation of binary diffractive optical elements (DOE) producing specific complex light patterns. The approach is based on amplitude and phase coding methods. The experimental complex light distributions are shown to agree with the computer simulation results. Due to the phase gradient this kind of light beams can be used for moving microscopic particles along a particular path. The light fields like that have been used successfully to trap and move tiny transparent polystyrol spheres 5 micrometer in diameter.     

Induction heating of dual magnetic particles embedded PDMS molds for roller embossing applications

Microsystem Technologies - Roller embossing is an effective manufacturing process for replicating microstructures onto polymeric substrates, featuring high-volume production, rapid manufacturing,...     

支持多属性决策的嵌入式系统软硬件划分

针对硬件面积、价格成本、功耗、实时性和可靠性多目标优化的一类嵌入式系统软硬件划分问题,提出了一种采用多属性决策技术的求解方法。首先对可靠性指标进行了转换,通过改进的最短路径算法获得满足约束的Pareto方案集合;然后,采用基于组合权重的TOPSIS算法对多个划分方案进行评价排序,得到最优的多目标划分解;最后,通过一个实例验证了本方法的有效性和可行性。     

Direct manipulation of FFD: efficient explicit solutions and decomposible multiple point constraints

Published online: 25 July 2001     

Symbolic manipulation CAD of control engineering by using REDUCE

Computer aided design (CAD) is an indispensable tool for control engineering. Recently various CAD systems have been developed by using numerical computation languages, but these are not capable of treating symbolic computation. However, control theories provide many symbolic computation algorithms. This study develops a new CAD system which can perform symbolic manipulation, based on REDUCE 3.2. It is shown that this CAD system can be applied to wider problems than the conventional ones, by means of two examples.     

对于氧化锌棒状结构的介电泳操控研究

主要研究电极形貌,频率,浓度,电压对于微粒介电泳操控影响的情况。我们采用溶液法制备ZnO棒状结构,长度在10μm左右,然后用微滴管定量地滴在自行制作的微米间隙电极间进行介电泳操控,通过控制不同条件,实现了ZnO棒按电场有明显分布的情况。并通过SEM图像了解电极,频率,电压,浓度对于ZnO介电泳操控的影响,掌握介电操控的主要影响因素。     

A control-theoretic study on iterative solutions to nonlinear equations for applications in embedded systems

In this paper, the fixed point iteration and Newton’s methods for iteratively solving nonlinear equations are studied in the control theoretical framework. This work is motivated by the ever increasing demands for integrating iterative solutions of nonlinear functions into embedded control systems. The use of the well-established control theoretical methods for our application purpose is inspired by the recent control-theoretical study on numerical analysis. Our study consists of two parts. In the first part, the existing fixed point iteration and Newton’s methods are analysed using the stability theory for the sector-bounded Lure’s systems. The second part is devoted to the modified iteration methods and the integration of sensor signals into the iterative computations. The major results achieved in our study are, besides some academic examples, applied to the iterative computation of the air path model embedded in the engine control systems.     

Task scheduling in hard real-time embedded systems using hardware co-processors

This paper describes the development of hardware-based techniques for scheduling in high-performance real-time systems. The focus of attention is hard real-time applications, scheduling being implemented within a co-processor unit. Two experimental co-processor structures are described, one based on programmable logic devices, the other being a microprocessor-based one. The relative merits of the two approaches are discussed and major conclusions are highlighted.