Hydrodynamic Focusing Of Particles Research Articles

Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

Microfluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

Sheath-assisted hydrodynamic particle focusing in higher Reynolds number flows

Focusing of sample cells or particles to a single-particle stream in miniature flow cytometers is achieved using pressure-driven hydrodynamic focusing in microfluidic channels. Hydrodynamic focusing models predict the focused sample stream width in the low Reynolds number regime (Re 1) of the Navier–Stokes equations, wherein the viscous forces dominate the inertial forces. Nonetheless, operating in the viscous regime of the laminar microfluidic flow results in high relative focused stream width, and also limits the efficiency of microfluidic flow cytometers as sample throughput is low due to extremely low flow rates. Hence, to enhance the power of microfluidic cell focusing, study of the hydrodynamic focusing mechanism at high Re, and thus, the effect of inertial forces in sheath-assisted flows is required. This work presents a comparative analysis of sheath-assisted hydrodynamic particle focusing in both the viscous and inertial regimes. Experimental results for pressure-driven hydrodynamic focusing inside microchannels in the higher Re (60 < Re < 130) laminar regime are presented along with particle trajectory simulations. Furthermore, we present a comparison of the focusing performance of sheath-assisted hydrodynamic focusing at lower and higher Re. These studies underline the conditions for single-particle focusing for a range of flow parameters and relative particle sizes, particularly for microfluidic flow cytometry. Such analyses constitute an essential aspect of engineering miniature flow cytometers or other cell manipulation techniques.

A three-dimensional quantitative study on the hydrodynamic focusing of particles with the immersed boundary – Lattice Boltzmann method

Hydrodynamic focusing of particles is numerically studied by the immersed boundary – lattice Boltzmann method. Particle focusing entropy is proposed to quantitatively characterize processing performance and final results of hydrodynamic focusing. Simulations of hydrodynamic focusing in several straight microchannels are carried out to evaluate versatility of the focusing entropy. Time evolutions of focusing entropies and particle trajectories are analyzed contrastively. The results demonstrate that the focusing entropy is an effective scale to measure particles ordering degree and hydrodynamic focusing performance. Higher ordering degree determines lower focusing entropy, which indicates better focusing performance. Channel cross section, particle rigidness and channel Reynolds number are three major factors influencing focusing dynamics and final results. Rectangular microchannel is more advantageous than circular and square ones in hydrodynamic focusing. Particles of different rigidness in rectangular microchannel can be separated significantly with the flow mediation. Increasing channel Reynolds numbers can lead to higher efficiency and better focusing performance.

GS54 2層マイクロ流路を用いた3次元粒子集束法の開発

Particle focusing into a specific area in a microchannel is especially important for precise particle detection, separation and sorting in various microfluidic devices for biomedical diagnostics and cell biology. In recent years, although various particle focusing approaches in microchip have been reported, they have some problems such as complicated fabrication and peripherals. This study suggests an innovative three-dimensional (3D) hydrodynamic particle focusing technique applicable in wide Re with only two inlets. The performances of the particle focusing m under different flow rates and channel shapes were evaluated by numerical simulation. In addition, experimental evaluation of the focusing was performed by particle speed measurement. As a result, we confirmed the validity of the proposed particle focusing technique.

Numerical simulation of hydrodynamic focusing of particles in straight channel flows with the immersed boundary-lattice Boltzmann method

Abstract Hydrodynamic focusing of particles instraight channel flows is studied by a hybrid immersed boundary (IB)-lattice Boltzmann (LB) method. In this method, the multi relaxation time (MRT)-LB equation with a force term is utilized to model the incompressible fluid flow over a regular Eulerian grid, and the IB method is employed to couple the finite element method based membrane model which represents the particle dynamics in fluid flow. The present method was validated by studying the three-dimensional top-lid-driven flow and the transient deformation of an initially spherical capsule under shear flow, and there were good agreements with previous theoretical and numerical results. Simulations of hydrodynamic dynamics in straight channels were performed to demonstrate the versatility of the hybrid method. The results show that Reynolds number and particle size are the important factors influencing focusing dynamics. The particles are focused onto their equilibrium positions at suitable Reynolds numbers of the channel flow. The higher the Reynolds number is, the more outward the equilibrium positions will be. The capability of the present method in studying the hydrodynamic separation of particles with different sizes and the transition of multi equilibrium positions were also discussed. This work also demonstrates the potential usefulness of IB-LBM in studying particle focusing, separation and sorting in confined flows.

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.

Miniaturized flow cytometer with 3D hydrodynamic particle focusing and integrated optical elements applying silicon photodiodes

In this study, the design, realization and measurement results of a novel optofluidic system capable of performing absorbance-based flow cytometric analysis is presented. This miniaturized laboratory platform, fabricated using SU-8 on a silicon substrate, comprises integrated polymer-based waveguides for light guiding and a biconcave cylindrical lens for incident light focusing. The optical structures are detached from the microfluidic sample channel resulting in a significant increase in optical sensitivity. This allows the application of standard solid-state laser and standard silicon-based photodiodes operated by lock-in-amplification resulting in a highly practical and effective detection system. The easy-to-fabricate single-layer microfluidic structure enables independently adjustable 3D hydrodynamic sample focusing to an arbitrary position in the channel. To confirm the fluid dynamics and raytracing simulations and to characterize the system, different sets of microparticles and T-lymphocyte cells (Jurkat cell line) for vital staining were investigated by detecting the extinction (axial light loss) signal. The analytical classification via signal peak height/width demonstrates the high sensitivity and sample discrimination capability of this compact low-cost/low-power microflow cytometer.

Microfluidic structures for flow cytometric analysis of hydrodynamically focussed blood cells fabricated by ultraprecision micromachining

We present three-dimensional microfluidic structures with integrated optical fibers, mirrors and electrodes for flow cytometric analysis of blood cells. Ultraprecision milling technique was used to fabricate different flow cells featuring single-stage and two-stage cascaded hydrodynamic focusing of particles by a sheath flow. Two dimensional focussing of the sample fluid was proven by fluorescence imaging in horizontal and vertical directions and found to agree satisfactorily with finite element calculations. Focussing of the sample stream down to 5 microm at a particle velocity of 3 m s(-1) is accessible while maintaining stable operation for sample flow rates of up to 20 microL min(-1). In addition to fluorescence imaging, the micro-flow cells were characterised by measurements of pulse shapes and pulse height distributions of monodisperse microspheres. We demonstrated practical use of the microstructures for cell differentiation employing light scatter to distinguish platelets and red blood cells. Furthermore, T-helper lymphocytes labelled by monoclonal antibodies were identified by measuring side scatter and fluorescence.

Gravity-driven microfluidic particle sorting device with hydrodynamic separation amplification.

This paper describes a simple microfluidic sorting system that can perform size profiling and continuous mass-dependent separation of particles through combined use of gravity (1 g) and hydrodynamic flows capable of rapidly amplifying sedimentation-based separation between particles. Operation of the device relies on two microfluidic transport processes: (i) initial hydrodynamic focusing of particles in a microchannel oriented parallel to gravity and (ii) subsequent sample separation where positional difference between particles with different mass generated by sedimentation is further amplified by hydrodynamic flows whose streamlines gradually widen out due to the geometry of a widening microchannel oriented perpendicular to gravity. The microfluidic sorting device was fabricated in poly(dimethylsiloxane), and hydrodynamic flows in microchannels were driven by gravity without using external pumps. We conducted theoretical and experimental studies on fluid dynamic characteristics of laminar flows in widening microchannels and hydrodynamic amplification of particle separation. Direct trajectory monitoring, collection, and post-analysis of separated particles were performed using polystyrene microbeads with different sizes to demonstrate rapid (<1 min) and high-purity (>99.9%) separation. Finally, we demonstrated biomedical applications of our system by isolating small-sized (diameter <6 microm) perfluorocarbon liquid droplets from polydisperse droplet emulsions, which is crucial in preparing contrast agents for safe, reliable ultrasound medical imaging, tracers for magnetic resonance imaging, or transpulmonary droplets used in ultrasound-based occlusion therapy for cancer treatment. Our method enables straightforward, rapid, real-time size monitoring and continuous separation of particles in simple stand-alone microfabricated devices without the need for bulky and complex external power sources. We believe that this system will provide a useful tool to separate colloids and particles for various analytical and preparative applications and may hold potential for separation of cells or development of diagnostic tools requiring point-of-care sample preparation or testing.