Experimental and numerical investigation on particle–particle interaction of multi-particle separation in an alternating and repetitive microchannel

Inertial focusing plays a major role in size-based cell separation or enrichment for microfluidic applications in many medical areas such as diagnostics and treatment. These applications often deal with suspensions of different particles which cause interactions between particles with different diameters such as particle–particle collision. In this study, particle–particle interaction in a laminar flow through a low aspect ratio alternating and repetitive microchannel is investigated both numerically and experimentally. It is revealed that particle–particle collision affects high quality particle focusing. computational fluid dynamics simulations are conducted for demonstrating the effect of the flow field in the transverse cross-section on the focusing quality and position. The experiments and simulations both revealed that if the flow is seeded with a mixture of particles of 3.3 and 9.9 µm diameters, the quality of focusing intensity is degenerated compared to the focusing features obtained by particles with a diameter of 9.9 µm solely. The results clearly show that particle–particle collision between the 3.3 and 9.9 µm particles has a negative effect on particle focusing behavior of the 9.9 µm particles.

     

High-throughput,single-stream microparticle focusing using a microchannel with asymmetric sharp corners

A new microfluidic device for fast and high-throughput particle focusing is reported. The particle focusing is based on the combination of inertial lift force effect and centrifugal force effect generated in a microchannel with a series of repeated asymmetric sharp corners on one side of the channel wall. The inertial lift force induces two focused particle streams in the microchannel, and the centrifugal force generated at the sharp corner structures tends to drive the particles laterally away from the corner. With the use of a series of repeated asymmetric sharp corner structures, a single and highly focused particle stream was achieved near the straight channel wall at a wide range of flow rate. In comparison with other hydrodynamic particle focusing methods, this method is less sensitive to the flow rate and can work at a higher flow rate (up to 700 μL/min) and Reynolds number (Re = 129.5). With its simple structure and operation, and high throughput, this method can be potentially used in particle focusing processes in a variety of lab-on-a-chip applications.     

Improving particle detection sensitivity of a microfluidic resistive pulse sensor by a novel electrokinetic flow focusing method

A novel and simple method of improving the particle detection sensitivity of a microfluidic resistive pulse sensor was presented in this paper. This novel electrokinetic flow focusing method utilizes a focusing solution (with high resistivity) flowing from the upstream focusing channel to the downstream focusing channel. The focusing solution in the sensing gate works like a virtual insulation wall that greatly narrows the gate and thus improves the detection sensitivity. An equation was derived to relate the magnitude of the output signal to the resistivity and the width of the focusing solution. The width of the focused particle solution under different voltages was numerically predicted. The results show that the magnitude of output signal increases with the decrease in the width of the focused particle stream. More importantly, the detection sensitivity can be improved by decreasing the space occupied by the focusing solution in the upstream and downstream channels as much as possible. Detection of 1 μm particle with a sensing gate of 30 × 40 × 10 μm (width × length × height) was successfully achieved. The proposed method is simple and advantageous in detecting smaller particles without fabricating a small sensing gate.     

Particle focusing in microfluidic devices

Focusing particles (both biological and synthetic) into a tight stream is usually a necessary step prior to counting, detecting, and sorting them. The various particle focusing approaches in microfluidic devices may be conveniently classified as sheath flow focusing and sheathless focusing. Sheath flow focusers use one or more sheath fluids to pinch the particle suspension and thus focus the suspended particles. Sheathless focusers typically rely on a force to manipulate particles laterally to their equilibrium positions. This force can be either externally applied or internally induced by channel topology. Therefore, the sheathless particle focusing methods may be further classified as active or passive by the nature of the forces involved. The aim of this article is to introduce and discuss the recent developments in both sheath flow and sheathless particle focusing approaches in microfluidic devices.     

Particle inertial focusing and its mechanism in a serpentine microchannel

Particle inertial focusing in a curved channel promises a big potential for lab-on-a-chip applications. This focusing concept is usually based on the balance of inertial lift force and the drag of secondary flow. This paper proposes a new focusing concept independent of inertial lift force, relying solely on secondary flow drag and particle centrifugal force. Firstly, a focusing mechanism in a serpentine channel is introduced, and some design considerations are described in order to make the proposed focusing concept valid. Then, numerical modelling based on the proposed focusing mechanism is conducted, and the numerical results agree well with the experimental ones, which verify the rationality of proposed mechanism. Thirdly, the effects of flow condition and particle size on the focusing performance are studied. The effect of particle centrifugal force on particle focusing in a serpentine microchannel is carefully evaluated. Finally, the speed of focussed particles at the outlet is measured by a micro-PIV, which further certifies the focusing positions of particles within the cross section. Our study provides insights into the role of centrifugal force on inertial focusing. This paper demonstrates for the first time that a single focusing streak can be achieved in a symmetric serpentine channel. The simple serpentine microchannel can easily be implemented in a single-layer microfluidic device. No sheath flow or external force field is needed allowing a simple operation in a more complex lab-on-a-chip system.     

Diamagnetic particle focusing using ferromicrofluidics with a single magnet

Focusing particles into a tight stream is critical to many applications such as microfluidic flow cytometry and particle sorting. Current magnetic field-induced particle focusing techniques rely on the use of a pair of repulsive magnets, which makes the device integration and operation difficult. We develop herein a new approach to focusing nonmagnetic particles in ferrofluid flow through a T-microchannel using a single permanent magnet. Particles are deflected across the suspending ferrofluid by negative magnetophoresis and confined by a water flow to the center plane of the microchannel, leading to a focused particle stream flowing near the bottom channel wall. Such three-dimensional diamagnetic particle focusing is demonstrated in a sufficiently diluted ferrofluid through both the top and side views of the microchannel. As the suspended particles can be visualized in bright field, this magnetic focusing method is expected to find applications to label-free (i.e., no magnetic or fluorescent labeling) cellular focusing in lab-on-a-chip devices.     

Intra-droplet acoustic particle focusing: simulations and experimental observations

The aim of this paper is to study resonance conditions for acoustic particle focusing inside droplets in two-phase microfluidic systems. A bulk acoustic wave microfluidic chip was designed and fabricated for focusing microparticles inside aqueous droplets (plugs) surrounded by a continuous oil phase in a 380-μm-wide channel. The quality of the acoustic particle focusing was investigated by considering the influence of the acoustic properties of the continuous phase in relation to the dispersed phase. To simulate the system and study the acoustic radiation force on the particles inside droplets, a simplified 3D model was used. The resonance conditions and focusing quality were studied for two different cases: (1) the dispersed and continuous phases were acoustically mismatched (water droplets in fluorinated oil) and (2) the dispersed and continuous phases were acoustically matched (water droplets in olive oil). Experimentally, we observed poor acoustic particle focusing inside droplets surrounded by fluorinated oil while good focusing was observed in droplets surrounded by olive oil. The experimental results are supported qualitatively by our simulations. These show that the acoustic properties (density and compressibility) of the dispersed and continuous phases must be matched to generate a strong and homogeneous acoustic field inside the droplet that is suitable for high-quality intra-droplet acoustic particle focusing.     

Viscosity-difference-induced asymmetric selective focusing for large stroke particle separation

We developed a new approach for particle separation by introducing viscosity difference of the sheath flows to form an asymmetric focusing of sample particle flow. This approach relies on the high-velocity gradient in the asymmetric focusing of the particle flow to generate a lift force, which plays a dominated role in the particle separation. The larger particles migrate away from the original streamline to the side of the higher relative velocity, while the smaller particles remain close to the streamline. Under high-viscosity (glycerol–water solution) and low-viscosity (PBS) sheath flows, a significant large stroke separation between the smaller (1.0 μm) and larger (9.9 μm) particles was achieved in a sample microfluidic device. We demonstrate that the flow rate and the viscosity difference of the sheath flows have an impact on the interval distance of the particle separation that affects the collected purity and on the focusing distribution of the smaller particles that affects the collected concentration. The interval distance of 293 μm (relative to the channel width: 0.281) and the focusing distribution of 112 μm (relative to the channel width: 0.107) were obtained in the 1042-μm-width separation area of the device. This separation method proposed in our work can potentially be applied to biological and medical applications due to the wide interval distance and the narrow focusing distribution of the particle separation, by easy manufacturing in a simple device.     

Three-dimensional hydrodynamic flow focusing of dye,particles and cells in a microfluidic device by employing two bends of opposite curvature

This work relates to three-dimensional (3D) hydrodynamic flow focusing, wherein sample is encapsulated by sheath fluid in all the directions, making it a preferred method for particle focusing. Given the complex phenomenon involved in achieving 3D hydrodynamic focusing, we have been able to demonstrate a relatively simple microdevice for achieving this objective. In this work, a novel approach for 3D focusing utilizing two bends of opposite curvature in microchannel is proposed and demonstrated through experiments and numerical simulations. The proposed microdevice is fabricated on a single layer of polydimethylsiloxane and a single sheath inlet is used, thereby simplifying the 3D focusing mechanism and reducing the requirements of cost enhancing accessories. The mechanism underlying particle focusing is examined in detail. This microdevice provides several distinct advantages over other designs mentioned in the literature.     

Flow rate-insensitive microparticle separation and filtration using a microchannel with arc-shaped groove arrays

Inertial microfluidics can separate microparticles in a continuous and high-throughput manner, and is very promising for a wide range of industrial, biomedical and clinical applications. However, most of the proposed inertial microfluidic devices only work effectively at a limited and narrow flow rate range because the performance of inertial particle focusing and separation is normally very sensitive to the flow rate (Reynolds number). In this work, an innovative particle separation method is proposed and developed by taking advantage of the secondary flow and particle inertial lift force in a straight channel (AR = 0.2) with arc-shaped groove arrays patterned on the channel top surface. Through the simulation results achieved, it can be found that a secondary flow is induced within the cross section of the microchannel and guides different-size particles to the corresponding equilibrium positions. On the other hand, the effects of the particle size, flow rate and particle concentration on particle focusing and separation quality were experimentally investigated. In the experiments, the performance of particle focusing, however, was found relatively insensitive to the variation of flow rate. According to this, a separation of 4.8 and 13 µm particle suspensions was designed and successfully achieved in the proposed microchannel, and the results show that a qualified particle separation can be achieved at a wide range of flow rate. This flow rate-insensitive microfluidic separation (filtration) method is able to potentially serve as a reliable biosample preparation processing step for downstream bioassays.     

Quantitative characterization of the focusing process and dynamic behavior of differently sized microparticles in a spiral microchannel

In this paper, a spiral microchannel was fabricated to systematically investigate particle dynamics. The focusing process or migration behavior of different-sized particles in the outlet region was presented. Specifically, for focused microparticles, quantitative characterization and analysis of how particles migrate towards the equilibrium positions with the increase in flow rate (De = 0.31–3.36) were performed. For unfocused microparticles, the particle migration behavior and the particle-free region’s formation process were characterized over a wide range of flow rates (De = 0.31–4.58), and the emergence of double particle-free regions was observed at De ≥ 3.36. These results provide insights into the design and operation of high-throughput particle/cell filtration and separation. Furthermore, using the location markers pre-fabricated along with the microchannel structures, the focusing or migration dynamics of different-sized particles along the spiral microchannel was systematically explored. The particle migration length effects on focusing degree and particle-free region width were analyzed. These analyses may be valuable for the optimization of microchannel structures. In addition, this device was successfully used to efficiently filter rare particles from a large-volume sample and separate particles of two different sizes according to their focusing states.     

Inertially focused diamagnetic particle separation in ferrofluids

Continuous flow separation of target particles from a mixture is essential to many chemical and biomedical applications. There has recently been an increasing interest in the integration of active and passive particle separation techniques for enhanced sensitivity and flexibility. We demonstrate herein the proof-of-concept of a ferrofluid-based hybrid microfluidic technique that combines passive inertial focusing with active magnetic deflection to separate diamagnetic particles by size. The two operations take place in series in a continuous flow through a straight rectangular microchannel with a nearby permanent magnet. We also develop a three-dimensional numerical model to simulate the transport of diamagnetic particles during their inertial focusing and magnetic separation processes in the entire microchannel. The predicted particle trajectories are found to be approximately consistent with the experimental observations at different ferrofluid flow rates and ferrofluid concentrations.     

一种基于引导策略的自适应粒子群算法

为解决粒子群算法前期搜索“盲目”,后期搜索速度慢且易陷入局部极值的问题,对算法中粒子更新方式和惯性权重进行了改进,提出了一种基于引导策略的自适应粒子群算法。该算法在种群中引入4种粒子,即主体粒子、双中心粒子、协同粒子和混沌粒子对粒子位置更新进行引导,克服算法的随机性,从而提高搜索效率;为进一步克服粒子群优化算法进化后期易陷入早熟收敛的缺点,引入聚焦距离变化率的概念,通过聚焦距离变化率的大小动态调整惯性权重,以提高算法的收敛速度和精度,两者结合极大地提高了搜索到全局最优解的有效性。对4个标准测试函数进行仿真,实验结果表明IPSO算法在收敛速度、收敛精度以及成功率上都明显优于LDWPSO和WPSO算法。     

Multisizer 3库尔特计数仪在墨粉检测过程中重复性的试验

本文简单综述了粒度、粒度分布的定义以及粒度测试的基本方法,介绍了静电显影用墨粉中粒度测试方法,重点介绍了库尔特计数仪在墨粉检测中重复性问题,对选够墨粉粒度测试仪器具有一定的指导意义。     

基于图像序列的油质颗粒检测系统研究与实现

研究以设计实现一套能对油质颗粒进行便捷、快速和稳定检测的系统为基本目标;首先,给出系统的基本构成和实现的基本原理;然后,在现有数字图像处理技术基础上,重点针对油质颗粒图像处理和颗粒识别提出了适合系统需求的分块阈值处理算法和隔行隔列杂质颗粒识别算法;实验表明,采用分块阈值处理算法不仅能够提高系统处理速度,而且能够很好地消除油质颗粒受光照的影响,提高颗粒的检测精度;隔行隔列颗粒识别算法同样可以提高系统的检测速度。     

Electrical measurement of cross-sectional position of particles flowing through a microchannel

The first high-throughput system for the electrical detection of cross-sectional position and velocity of individual particles flowing through a rectangular microchannel is presented. Lateral position (along channel width) and vertical position (along channel height) are measured using two different sets of coplanar electrodes. In particular, the ratio of travel times measured with electrodes generating a current flow transverse or oblique with respect to particle trajectory yields lateral position. The relative prominence and transit time of a bipolar double-Gaussian signal obtained with a suited electrode configuration, respectively, supply vertical position and velocity. The operating principle is presented by means of finite element numerical simulations. The method is experimentally validated by comparing the electrical estimates of position and velocity of polystyrene beads with optical estimates obtained by processing high-speed images. The system is used to observe bead focusing at different particle Reynolds numbers. This system, providing a fully electrical characterization of single-particle motion, represents a powerful tool, e.g. to understand fluid motion at the microscale, in particle separation studies, or to assess the performance of particle focusing devices. Moreover, it can be simultaneously used to perform single-cell impedance spectroscopy, thus achieving an unprecedented multiparamteric characterization.     

Analysis of particle interaction in particle swarm optimization

In this paper, we analyze the behavior of particle swarm optimization (PSO) on the facet of particle interaction. We firstly propose a statistical interpretation of particle swarm optimization in order to capture the stochastic behavior of the entire swarm. Based on the statistical interpretation, we investigate the effect of particle interaction by focusing on the social-only model and derive the upper and lower bounds of the expected particle norm. Accordingly, the lower and upper bounds of the expected progress rate on the sphere function are also obtained. Furthermore, the sufficient and necessary condition for the swarm to converge is derived to demonstrate the PSO convergence caused by the effect of particle interaction.     

Optimal Matching Control of a Low Energy Charged Particle Beam in Particle Accelerators

Particle accelerators are devices used for research in scientific problems such as high energy and nuclear physics. In a particle accelerator, the shape of particle beam envelope is changed dynamically along the forward direction. Thus, this reference direction can be considered as an auxiliary "time" beam axis. In this paper, the optimal beam matching control problem for a low energy transport system in a charged particle accelerator is considered. The beam matching procedure is formulated as a finite "time" dynamic optimization problem, in which the Kapchinsky-Vladimirsky (K-V) coupled envelope equations model beam dynamics. The aim is to drive any arbitrary initial beam state to a prescribed target state, as well as to track reference trajectory as closely as possible, through the control of the lens focusing strengths in the beam matching channel. We first apply the control parameterization method to optimize lens focusing strengths, and then combine this with the time-scaling transformation technique to further optimize the drift and lens length in the beam matching channel. The exact gradients of the cost function with respect to the decision parameters are computed explicitly through the state sensitivity-based analysis method. Finally, numerical simulations are illustrated to verify the effectiveness of the proposed approach.      

Inertial migration of single particle in a square microchannel over wide ranges of <Emphasis Type="Italic">Re</Emphasis> and particle sizes

Inertial migration of particles has been widely used in inertial microfluidic systems to passively manipulate cells/particles. However, the migration behaviors and the underlying mechanisms, especially in a square microchannel, are still not very clear. In this paper, the immersed boundary-lattice Boltzmann method (IB-LBM) was introduced and validated to explore the migration characteristics and the underlying mechanisms of an inertial focusing single particle in a square microchannel. The grid-independence analysis was made first to highlight that the grid number across the thin liquid film (between a particle and its neighboring channel wall) was of significant importance in accurately capturing the migrating particle’s dynamics. Then, the inertial migration of a single particle was numerically investigated over wide ranges of Reynolds number (Re, from 10 to 500) and particle sizes (diameter-to-height ratio a/H, from 0.16 to 0.5). It was interesting to find that as Re increased, the channel face equilibrium (CFE) position moved outward to channel walls at first, and then inflected inwards to the channel center at high Re (Re?>?200). To account for the physical mechanisms behind this behavior, the secondary flow induced by the inertial focusing single particle was further investigated. It was found that as Re increased, two vortices appeared around the particle and grew gradually, which pushed the particle away from the channel wall at high Re. Finally, a correlation was proposed based on the numerical data to predict the critical length L_c (defined to describe the size of fluid domain that was strongly influenced by the particle) according to the particle size a/H and Re.