Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session R11: Microfluidics: Particles |
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Chair: Alexander Alexeev, Georgia Institute of Technology Room: 26A |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R11.00001: Three dimensional open cavity flow for the continuous separation of suspended particles Jorge A. Bernate, Colin Paul, Chengxun Liu, Liesbet Lagae, Konstantinos Konstantopoulos, Zachary Gagnon, German Drazer We present a microfluidic platform for the continuous separation of suspended particles based on their size and settling velocity, which relies on the reorientation of the flow field created by applying a pressure gradient across and along a periodic array of open cavities. The flow along the open cavities deflects different particles to a different degree depending on the extent to which they penetrate into the open cavities. Two regimes can be distinguished depending on the ratio $r$ between the settling velocity of the particles and their velocity across the cavities. When $r \approx 1$, heavier particles settle deeper into the open cavities and deflect more than lighter ones. When $r \ll 1$, smaller particles are advected deeper into the cavities by the flow and deflect more than larger ones. We probe these regimes by separating spherical particles of different size and density at different flow rates. We show the potential of this platform to be used as a microfluidic \emph{centrifuge} depleting RBCs and enriching spiked MCF-7 cancer cells. This platform can be easily integrated with external fields resulting in a potentially versatile technique. In particular, we use dielectrophoretic forces for the high-throughput separation of particles of the same size. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R11.00002: Microfluidic separation of motile sperm with millilitre-scale sample capacity Reza Nosrati, Marion Vollmer, Lise Eamer, Krista Zeidan, Maria C. San Gabriel, Armand Zini, David Sinton Isolating motile from non-motile spermatozoa has been a challenge since the establishment of \textit{in vitro} fertilization. Microfluidic approaches have been employed for this purpose, but current devices are limited by low sample volume. Here, we present a high-throughput microfluidic device that separates spermatozoa from one millilitre of raw semen sample based on the hydrodynamic characteristics of swimming sperm in a confined geometry. The device consists of two layers: an outer injection ring on top aligned with a network of radial microchannels at the bottom guiding motile sperm into an inner collection chamber. This approach (1) maximizes exposure of the sperm to the fluid channels, (2) maximizes surface area density (3) prevents fluid flow bias, and (4) employs a non-Newtonian viscoelastic medium consistent with the \textit{in vivo} environment. Tests with human and bull spermatozoa indicate an increase in motile sperm concentration from 62.2{\%} in raw semen to 99.2{\%} in separated sample combined with a higher incidence of normal morphology. DNA integrity testing is currently underway. In conclusion, we present an effective one-step procedure to perform semen purification and separation on a millilitre-scale with clinically relevant numbers. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R11.00003: Single-stream inertial focusing of microparticles across laminar streamlines through geometry-induced secondary flows Aram Chung, Dianne Pulido, Justin Oka, Mahdokht Masaeli, Hamed Amini, Dino Di Carlo The ability to continuously control microparticle position in a confined microchannel is remarkably useful for a wide range of biomedical studies Current state-of-the-art systems to achieve particle focusing require either complex external setups accompanying complicated fabrication steps or logistically burdensome sheath fluid. Using the fluid inertia acting on particles in microchannels has been introduced to address these limitations since inertia can position particles precisely in a predictable manner. Previous work has predominantly demonstrated multiple focusing streams however here we present a novel method that initially randomly distributed microparticles can be focused into a single-stream by (1) introducing a series of cylindrical pillars in a microchannel or (2) locally modifying channel geometry Briefly, the combination of inertial focusing upstream and a pair of local helical secondary flows induced by the obstacles or steps in channel height allows for migration of microparticles to a single position in a high-throughput manner We present comprehensive numerical and experimental studies and results of the particle-fluid interaction and focusing mechanism, characterize the role of flow deformation, determine focusing accuracy and discuss potential applications. [Preview Abstract] |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R11.00004: Size-based dielectrophoretic particle sorting in a microfluidic device with thermal effects Barukyah Shaparenko, Han-Sheng Chuang, Howard Hu, Haim Bau Dielectric particles in a dielectric medium experience a force known as dielectrophoresis~(DEP) when subjected to a nonuniform electric field. Since this DEP force is proportional to the particle volume, it is well-suited for size-based particle sorting. Additionally, we use the geometric constraints of a narrow segment of microchannel to aid sorting by means of pinched flow fractionation~(PFF). We found that in microfluidic devices, thermal effects due to Joule heating may be important. Temperature variations of the electrical material properties give rise to additional forces, including electrothermal flow in the medium and a thermal DEP force acting on the particles. We combine PFF and DEP in series to create a microfluidic sorting device, with an interdigitated array of five L\mbox{-}shaped electrodes and five outlet channels permitting the sorting of up to five different particle sizes. The sorting process is regulated by on-chip voltage control, so that the same device is easily adaptable to different particle sizes. We compare computed particle trajectories from an analytical solution with experimental sorting results. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R11.00005: Particle collision dynamics in periodic asymmetric microfluidic obstacle arrays for rare cell capture James Smith, Jason Gleghorn, Brian Kirby Particle--obstacle collision dynamics in periodic microfluidic obstacle arrays are presented in the context of microfluidic devices for the capture of rare cells, such as circulating tumor cells (CTCs). A coupled CFD--particle advection simulation was used to calculate particle trajectories for low Reynolds number, low Stokes number flows. A rich range of deterministic transport modes was identified as a function of array geometry, and the resulting particle size-dependent collision rate highlights the usefulness of these arrays for high-efficiency, high-purity rare cell capture. A reduced-order model, assuming unidirectional flow and infinitesimal obstacles, captures most of the details of transport in these systems with an $O(10^4)$ computational saving; this model is a useful tool for rapidly exploring a large design space and optimizing geometries for a specific rare cell capture application. Results of the CFD simulations, reduced-order ballistic models, and experiments with polystyrene particles and cancer cells indicate that array geometry is central to rare cell capture and that simple models can be used to inform the design of these microfluidic devices. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R11.00006: Size based separation of micro-particles using adhesive ciliated surfaces Anurag Tripathi, Amitabh Bhattacharya, Anna Balazs Separation of different size micro-particles in microfluidic devices is important for many biomedical applications. Various techniques ranging from active dielectrophoresis to passive separation using the concept of inertial microfluidics have been used previously. We propose a novel separation mechanism of micro-particles using active cilia arrays with adhesive tips. A near complete separation of micro-particles can be achieved for low Reynolds number (Re$\sim $0.1) regime where separation mechanisms based on inertial effects will be of little use. By means of Lattice Boltzmann simulations, we show that mixture of two different size particles with size ratio greater than or equal to two can be nearly completely separated by tuning adhesion strength, actuation frequency and cilia stiffness. [Preview Abstract] |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R11.00007: Size-dependent cell separation and enrichment using double spiral microchannels Guoqing Hu, Chao Liu, Jiashu Sun, Xingyu Jiang Much attention has been directed toward microfluidic technologies that can help improve circulating tumor cells (CTCs) separation from the blood sample. In the present work, we develop a double spiral microfluidic platform with one inlet and three outlets that allows for passive, label-free tumor cell enrichment with high throughput and efficiency, inspired by the single spiral cell sorter. The curved channel induces a Dean drag force acting on cells to compete with the inertial lift, resulting in large tumor cells to be focused and deflected into the middle outlet while small hematologic cells are removed from the inner outlet. We continuously isolated and enriched the rare tumor cells (MCF-7 and Hela cells) from diluted whole blood using the same geometry. At a spike ratio of 100 tumor cells per million hematologic cells, 92.28{\%} of blood cells and 96.77{\%} of tumor cells were collected at the inner and middle outlet, respectively, at the throughput of 33.3 million cells per minute. A numerical model is developed to simulate the Dean flows inside the curved geometry and to track the particle/cell trajectories, which is validated against the experimental observations and serves as a theoretical foundation in optimizing the operating conditions. [Preview Abstract] |
Tuesday, November 20, 2012 2:31PM - 2:44PM |
R11.00008: Thin films with self-assembled monolayers embedded on their surfaces Md. Shahadat Hossain, Bhavin Dalal, SathishKumar Gurupatham, Ian S. Fischer, Nadine Aubry, Pushpendra Singh We have recently shown that the capillarity-based process for self-assembling particle monolayers on fluid-liquid interfaces can be improved by applying an electric field in the direction normal to the interface. The electric field gives rise to repulsive dipole-dipole forces amongst the particles causing them to move apart, and thus allowing them to move freely without blocking one another. The latter is important in the formation of virtually defect-free monolayers with long-range order. In this talk, we present a technique for freezing these expanded monolayers onto the surface of a flexible thin film. The technique involves assembling the monolayer on the interface between a UV-curable resin and a fluid which can be air or another liquid, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film. [Preview Abstract] |
Tuesday, November 20, 2012 2:44PM - 2:57PM |
R11.00009: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2012 2:57PM - 3:10PM |
R11.00010: Using chiral structures to enhance particle deposition in microfluidic devices Yunji Gu, Zachary Mills, Alexander Alexeev We used three dimensional computer simulations to examine the deposition of nanoparticles suspended in a fluid flowing through a microchannel that encompasses a periodic array of chiral structures. The channel was filled with a viscous fluid and tracer particles were used to simulate the suspended nanoparticles. The structures induce secondary flows in the fluid, which enhance mixing and in turn induce more rapid deposition of nanoparticles on channel walls. To model the system, we employed a lattice Boltzmann model coupled with a Brownian dynamics model. To investigate how the chiral structures influence the deposition rate, we systematically varied three parameters in the system: the pitch and radius of the chirals, and the spacing between structures in the array. Our simulations revealed that structures enhance nanoparticle deposition and the effect is more pronounced at larger Peclet numbers. Furthermore, we established the optimal geometry of the structures leading to increased particle deposition on the microchannel walls. Our findings could be useful for improving microscale sensory devices. [Preview Abstract] |
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