Geometrical optimization of microstripe arrays for microbead magnetophoresis

Manipulation of magnetic beads plays an increasingly important role in molecular diagnostics. Magnetophoresis is a promising technique for selective transportation of magnetic beads in lab-on-a-chip systems. We investigate periodic arrays of exchange-biased permalloy microstripes fabricated using a single lithography step. Magnetic beads can be continuously moved across such arrays by combining the spatially periodic magnetic field from microstripes with a rotating external magnetic field. By measuring and modeling the magnetophoresis properties of thirteen different stripe designs, we study the effect of the stripe geometry on the magnetophoretic transport properties of the magnetic microbeads between the stripes. We show that a symmetric geometry with equal width of and spacing between the microstripes facilitates faster transportation and that the optimal period of the periodic stripe array is approximately three times the height of the bead center over the microstripes.     

无级调速脉冲感应电动机原理分析

设计了一种新型电动机.它是利用暂态电流通电、断电自感与互感形成大小变化的脉冲和一定相位差的多次这类脉冲,产生跳跃式的旋转磁场,使得铝芯转子转动.     

Construction and operation of a microrobot based on magnetotactic bacteria in a microfluidic chip

Magnetotactic bacteria (MTB) are capable of swimming along magnetic field lines. This unique feature renders them suitable in the development of magnetic-guided, auto-propelled microrobots to serve in target molecule separation and detection, drug delivery, or target cell screening in a microfluidic chip. The biotechnology to couple these bacteria with functional loads to form microrobots is the critical point in its application. Although an immunoreaction approach to attach functional loads to intact MTB was suggested, details on its realization were hardly mentioned. In the current paper, MTB-microrobots were constructed by attaching 2 μm diameter microbeads to marine magnetotactic ovoid MO-1 cells through immunoreactions. These microrobots were controlled using a special control and tracking system. Experimental results prove that the attachment efficiency can be improved to ∼30% via an immunoreaction. The motility of the bacteria attached with different number of loads was also assessed. The results show that MTB can transport one load at a velocity of ∼21 μm/s and still move and survive for over 30 min. The control and tracking system is fully capable of directing and monitoring the movement of the MTB-microrobots. The rotating magnetic fields can stop the microrobots by trapping them as they swim within a circular field with a controllable size. The system has potential use in chemical analyses and medical diagnoses using biochips as well as in nano/microscale transport.     

Cell rotation using optoelectronic tweezers

A cell rotation method by using optoelectronic tweezers (OET) is reported. The binary image of a typical OET device, whose light and dark sides act as two sets of parallel plates with different ac voltages, was used to create a rotating electric field. Its feasibility for application to electrorotation of cells was demonstrated by rotating Ramos and yeast cells in their pitch axes. The electrorotation by using OET devices is dependent on the medium and cells' electrical properties, the cells' positions, and the OET device's geometrical dimension, as well as the frequency of the electric field.     

Model studies of electric and magnetic fields of the heart

The first magnetocardiogram was published one decade ago. Subsequent development of magnetocardiography is discussed. A general expression is developed for the quasi-static magnetic field outside a nonmagnetic volume conductor containing internal electromotive forces. The multipole expansion for the magnetic field is derived and an expression is obtained for the magnetic field of a dipole current source in a sphere. The heart is modelled by 20 current dipoles in a homogeneous conducting sphere. Electric and magnetic scalar potentials at the surface of the sphere are calculated. These data, perturbed by noise, are used to solve the inverse problem, i.e. to determine the moments of the multiple dipole array which would generate the external potentials. The accuracy of the inverse solution is improved when a combination of electric and magnetic data is used rather than electric data alone.     

Droplet-based microfluidic washing module for magnetic particle-based assays

In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The droplet-based washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets. To realize the droplet-based washing function, the following four procedures were sequentially carried in a droplet-based microfluidic device: parallel synchronization of two trains of droplets by using a ladder-like channel network; lateral electrocoalescence by an electric field; magnetic particle manipulation by a magnetic field; and asymmetrical splitting of merged droplets. For the stable droplet synchronization and electrocoalescence, we optimized droplet generation conditions by varying the flow rate ratio (or droplet size). Image analysis was carried out to determine the fluorescent intensity of reagents before and after the washing step. As a result, the unbound reagents in sample droplets were significantly removed by more than a factor of 25 in the single washing step, while the magnetic particles were successfully extracted into washing buffer droplets. As a proof-of-principle, we demonstrate a magnetic particle-based immunoassay with streptavidin-coated magnetic particles and fluorescently labelled biotin in the proposed continuous flow droplet-based microfluidic platform.     

Combined AC electroosmosis and dielectrophoresis for controlled rotation of microparticles

Electrorotation is widely used for characterization of biological cells and materials using a rotating electric field. Generally, multiphase AC electric fields and quadrupolar electrode configuration are needed to create a rotating electric field for electrorotation. In this study, we demonstrate a simple method to rotate dielectrophoretically trapped microparticles using a stationary AC electric field. Coplanar interdigitated electrodes are used to create a linearly polarized nonuniform AC electric field. This nonuniform electric field is employed for dielectrophoretic trapping of microparticles as well as for generating electroosmotic flow in the vicinity of the electrodes resulting in rotation of microparticles in a microfluidic device. The rotation of barium titanate microparticles is observed in 2-propanol and methanol solvent at a frequency below 1 kHz. A particle rotation rate as high as 240 revolutions per minute is observed. It is demonstrated that precise manipulation (both rotation rate and equilibrium position) of the particles is possible by controlling the frequency of the applied electric field. At low frequency range, the equilibrium positions of the microparticles are observed between the electrode edge and electrode center. This method of particle manipulation is different from electrorotation as it uses induced AC electroosmosis instead of electric torque as in the case of electrorotation. Moreover, it has been shown that a microparticle can be rotated along its own axis without any translational motion.     

Resistive pulse sensing of magnetic beads and supraparticle structures using tunable pores

Tunable pores (TPs) have been used for resistive pulse sensing of 1 μm superparamagnetic beads, both dispersed and within a magnetic field. Upon application of this field, magnetic supraparticle structures (SPSs) were observed. Onset of aggregation was most effectively indicated by an increase in the mean event magnitude, with data collected using an automated thresholding method. Simulations enabled discrimination between resistive pulses caused by dimers and individual particles. Distinct but time-correlated peaks were often observed, suggesting that SPSs became separated in pressure-driven flow focused at the pore constriction. The distinct properties of magnetophoretic and pressure-driven transport mechanisms can explain variations in the event rate when particles move through an asymmetric pore in either direction, with or without a magnetic field applied. Use of TPs for resistive pulse sensing holds potential for efficient, versatile analysis and measurement of nano- and microparticles, while magnetic beads and particle aggregation play important roles in many prospective biosensing applications.     

Refillable and magnetically actuated drug delivery system using pear-shaped viscoelastic membrane

We report a refillable and valveless drug delivery device actuated by an external magnetic field for on-demand drug release to treat localized diseases. The device features a pear-shaped viscoelastic magnetic membrane inducing asymmetrical deflection and consecutive touchdown motion to the bottom of the dome-shaped drug reservoir in response to a magnetic field, thus achieving controlled discharge of the drug. Maximum drug release with 18 ± 1.5 μg per actuation was achieved under a 500 mT magnetic flux density, and various controlled drug doses were investigated with the combination of the number of accumulated actuations and the strength of the magnetic field.     

Closed plane curves described by finite and infinite sums of rotating vectors

A large group of closed plane curves may be classified as roulettes, including epicycloids, hypocycloids, and related epitrochoids and hypotrochoids. The equation for the roulette in complex polar form shows that any roulette may be described by the vector sum of two vectors of specified constant magnitudes rotating with constant angular velocities. Methods for plotting, and for electronic display of roulettes are described. An equation is derived for a roulette approximation for an N-sided regular polygon. In particular, an application to two-dimensional potential theory is described and illustrated by consideration of the roulette approximation for a square as an equipotential curve, with derivation of equations for equipotential curves in the field surrounding the square. General equations are derived for given closed plane curves with points whose x and y coordinates may separately be expanded in Fourier series as functions of the polar angle, assuming these expansions are valid. It is shown that, in general, a closed plane curve may be considered as being described by an infinite sum of vectors, each rotating in a circle. Simplifying effects of symmetry about a polar axis and/or about the origin are discussed, and methods for harmonic analysis of a given closed plane curve with aid of an electronic calculator are described.     

微波和脉冲磁场复合作用下鲜切哈密瓜杀菌实验研究

本文进行了微波和脉冲磁场复合作用下鲜切哈密瓜的杀菌实验研究,考察了微波预处理,磁场强度,脉冲次数及初始茵落总数对杀菌效果的影响。研究结果表明：微波和脉冲磁场的复合处理可以有效杀死鲜切哈密瓜中的细菌,茵落总数的最大杀菌率可以达到99．9％;12s的微波预处理可以起到物料升温与一定的杀菌作用,为脉冲磁场下鲜切哈密瓜的杀菌创造了有利条件;当磁场强度为0．6T时,随着脉冲作用次数的增加,菌落总数先下降,后有所增加,其转折点为20;当脉冲数为10时,随着磁场强度的增加,茵落总数总体上呈下降的趋势;初始菌落总数的增加有利于微波杀菌效果的提高,但对脉冲磁场的杀菌效果影响较小。     

磁场分析在基于GMM的微动夹钳结构设计中的应用

本文阐述了在微动夹钳结构设计中,磁场分析的应用过程。首先提出微动夹钳的几种合理结构,然后利用磁场分析软件分析这几种结构的微动夹钳的磁场分布情况,提出一种最佳的结构方案。     

三线摆测量刚体转动惯量及其误差分析

本文研究了三线摆法测量刚体转动惯量的误差影响因素并对误差的来源和原因进行了分析,在此基础上对实验操作提出了一些改进的方法,以提高实验的精度。     

磁法勘探大别山区探矿中的应用

本论文介绍了安徽省大别山区铁矿磁异常数据的处理及解释。论文首先对网格化的野外原始磁异常数据进行滤波处理,以消除测量的偶然误差和近地表不均匀磁性体的干扰。然后,对上述预处理后的磁异常数据进行解析延拓,本论文作了三个不同高度的向上延拓及两个不同高度的向下延拓。通过上述数据处理,结果表明,利用这种滤波和解析延拓方法对确定地下异常体与预测成矿区是很有成效的。     

Interaction between cells in dielectrophoresis and electrorotation experiments

Progress in microelectrode-based technologies has facilitated the development of sophisticated methods for manipulating and separating cells, bacteria, and other bioparticles. For many of these various applications, the theoretical modeling of the electrical response of compartmentalized particles to an external field is important. In this paper we address the analysis of the interaction between cells immersed in rf fields. We use an integral formulation of the problem derived from a consideration of the charge densities induced at the interfaces of the particle compartments. The numerical solution by a boundary element technique allows characterization of their dielectric properties. Experimental validation of this theoretical model is obtained by investigating two effects: (1) The influence that dipolar “pearl chaining” has on the dielectrophoretic behavior of human T lymphocytes and (2) the frequency variation of the spin and orbital torques of approaching insulinoma β-cells in a rotating field.     

On the Computation of Functionals Over Sample Paths of a Randomly Rotating Rigid Body

This paper deals with the computation of the values of two functionals which are defined over the sample paths of a randomly rotating rigid body. It is assumed that the body is subjected to two different kinds of perturbation. The first kind of perturbation is represented by the standard Wiener process and the second kind by a homogeneous process with independent increments, finite second-order moments, mean zero and no continuous sample functions. In order to measure quantitatively the stochastic stability of the body's motion, two functionals are defined over its sample paths. It is shown that each of these functionals is a solution to a corresponding partial integro-differential equation. A numerical procedure for the solution of these equations is suggested, and its efficiency and applicability are demonstrated with examples.     

Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase

We present dual-mode, on-demand droplet routing in a multiple-outlet microfluidic device using an oil-based magnetic fluid. Magnetite (Fe₃O₄) nanoparticle-contained oleic acid (MNOA) was used as a carrier phase for droplet generation and manipulation. The water-in-MNOA droplets were selectively distributed in a curved microchannel with three branches by utilizing both a hydrodynamic laminar flow pattern and an external magnetic field. Without the applied magnetic field, the droplets travelled along a hydrodynamic centerline that was displaced at each bifurcating junction. However, in the presence of a permanent magnet, they were repelled from the centerline and diverted into the desired channel when the repelled distance exceeded the minimum offset allocated to the channel. The repelled distance, which is proportional to the magnetic field gradient, was manipulated by controlling the magnet''s distance from the device. To evaluate routing performance, three different sizes of droplets with diameters of 63, 88, and 102 μm were directed into designated outlets with the magnet positioned at varying distances. The result demonstrated that the 102-μm droplets were sorted with an accuracy of ∼93%. Our technique enables on-demand droplet routing in multiple outlet channels by simply manipulating magnet positions (active mode) as well as size-based droplet separation with a fixed magnet position (passive mode).     

基于Wiimote的手术仿真硬件接口设计

虚拟手术是虚拟现实技术在医学领域的一个重要应用,人机交互水平是决定仿真系统好坏的关键部分。介绍了手术仿真系统的硬件接口设计,该系统采用Wiimote控制器作为硬件接口,利用其陀螺仪数据捕获其在三维空间的旋转信息,其加速度感应器追踪其三维平移运动轨迹。结合二者的数据完整地实现手术器械6个自由度,可以为使用者提供较好的手术仿真体验。     

核磁共振永磁体无源匀场的神经网络方法

针对核磁共振永磁体的磁场传统匀场方法难度大，经验依赖程度高的情况，提出了人工神经网络应用于磁场匀场的手段。通过基于Matlab的神经网络设计，建立了一个匀场的BP网络模型。由于在磁体的不同的均匀度条件下匀场的方法不同，所以该网络由两个子网络组成----粗调网络和精调网络，并分别对其进行训练。该模型建立之后，可以快速、准确地匀场，使无源匀场不再盲目得进行多次尝试，一次就能使判断准确。通过人工神经网络方法匀场的磁体，均匀度高，满足了核磁共振岩心分析仪的匀场环境。     

浅谈正弦型函数曲线的加工方法

数控车床是机械制造系统中一种具有高效率、高精度与高柔性的自动化机床。可以有效解决复杂、精密、小批多变零件的加工问题。而对于轴类零件上一些高精度的非圆曲线,如椭圆、双曲线、正弦线、余弦线、抛物线等构成的回转体表面,通常采用直线逼近法来加工,本文结合自己多年的实习操作经验,现以华中世纪星HNC-21T系统数控车床为例,对加工正弦曲线的宏程序的编程方法进行探讨。