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Journal ArticleDOI

Hydrodynamic resistance and mobility of deformable objects in microfluidic channels.

06 Oct 2014-Biomicrofluidics (AIP Publishing)-Vol. 8, Iss: 5, pp 054112-054112
TL;DR: This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel, and provides a mathematical formula that correlates induced hydrod dynamic resistance of a single droplet with the droplet size and viscosity.
Abstract: This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio ρ and droplet-to-medium viscosity ratio λ. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet ΔRd with the droplet size ρ and viscosity λ. A simple theoretical model is developed to obtain closed form expressions for droplet mobility ϕ and ΔRd. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility ϕ and induced hydrodynamic resistance ΔRd. Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio ρ and viscosity ratio λ, which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance ΔR of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance ΔR is related to the cell concentration and apparent viscosity of the cells.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, a theoretical and experimental investigation of flow through compliant microchannels in which one of the walls is a thin PDMS membrane is reported. And the authors derived a theoretical model that provides an insight into the physics of the coupled fluid-structure interaction.
Abstract: We report theoretical and experimental investigations of flow through compliant microchannels in which one of the walls is a thin PDMS membrane. A theoretical model is derived that provides an insight into the physics of the coupled fluid–structure interaction. For a fixed channel size, flow rate and fluid viscosity, a compliance parameter $$f_{\text{p}}$$ is identified, which controls the pressure–flow characteristics. The pressure and deflection profiles and pressure–flow characteristics of the compliant microchannels are predicted using the model and compared with experimental data, which show good agreement. The pressure–flow characteristics of the compliant microchannel are compared with that obtained for an identical conventional (rigid) microchannel. For a fixed channel size and flow rate, the effect of fluid viscosity and compliance parameter $$f_{\text{p}}$$ on the pressure drop is predicted using the theoretical model, which successfully confront experimental data. The pressure–flow characteristics of a non-Newtonian fluid (0.1 % polyethylene oxide solution) through the compliant and conventional (rigid) microchannels are experimentally measured and compared. The results reveal that for a given change in the flow rate, the corresponding modification in the viscosity due to the shear thinning effect determines the change in the pressure drop in such microchannels.

58 citations

Journal ArticleDOI
TL;DR: A review of state-of-the-art numerical techniques employed in the literature for modeling slug flow in microchannels is presented in this paper, where the proposed solutions in literature for overcoming some of the drawbacks of the numerical methods are presented.

48 citations

Journal ArticleDOI
TL;DR: A combined experimental and theoretical technique that enables the characterization of various mechanical properties of biological cells and leads to a new paradigm for mechanophenotyping of biological Cells.
Abstract: We report a combined experimental and theoretical technique that enables the characterization of various mechanical properties of biological cells. The cells were infused into a microfluidic device that comprises multiple parallel micro-constrictions to eliminate device clogging and facilitate characterization of cells of different sizes and types on a single device. The extension ratio λ and transit velocity Uc of the cells were measured using high-speed and high-resolution imaging which were then used in a theoretical model to predict the Young's modulus Ec = f(λ, Uc) of the cells. The predicted Young's modulus Ec values for three different cell lines (182 ± 34.74 Pa for MDA MB 231, 360 ± 75 Pa for MCF 10A and, 763 ± 93 Pa for HeLa) compare well with those reported in the literature from micropipette measurements and atomic force microscopy measurement within 10% and 15%, respectively. Also, the Young's modulus of MDA-MB-231 cells treated with 50 μM 4-hyrdroxyacetophenone (for localization of myosin II) for 30 min was found out to be 260 ± 52 Pa. The entry time te of cells into the micro-constrictions was predicted using the model and validated using experimentally measured data. The entry and transit behaviors of cells in the micro-constriction including cell deformation (extension ratio λ) and velocity Uc were experimentally measured and used to predict various cell properties such as the Young's modulus, cytoplasmic viscosity and induced hydrodynamic resistance of different types of cells. The proposed combined experimental and theoretical approach leads to a new paradigm for mechanophenotyping of biological cells.

38 citations

Journal ArticleDOI
TL;DR: In this paper, the internal flow field of droplets traveling in a rectangular microchannel by means of microparticle image velocimetry is studied. And the effects of capillary number, viscosity ratio and interfacial tension on the flow topology are investigated.
Abstract: This paper discusses the studies on the internal flow field of droplets traveling in a rectangular microchannel by means of microparticle image velocimetry, specifically concentrating on the effects of capillary number, viscosity ratio and interfacial tension. The flow topology is predominantly dependent on the capillary number. It shows that the evident transitions from three pairs of recirculation zones at lower capillary numbers to one pair of recirculation zones near the sidewalls with low velocity in the central area at intermediate capillary numbers, then to a pair of recirculation zones closest to the axial centerline with high velocity in the central area at higher capillary numbers. There are two critical capillary numbers increasing with viscosity ratio in the evolution of flow features. Droplet size only influences two velocity components values other than the flow topology within intervals separated by the critical values. The equilibrium mechanism of viscous friction force and Marangoni stress dominate the internal topological transition in a surfactant added system. The obtained internal fluid phenomena inside droplets are beneficial to provide a guideline for screening of biochemical reaction conditions in the device.

34 citations

Journal ArticleDOI
TL;DR: The proposed microfluidic device has potential to be used as a lab on chip diagnostic tool for sorting of diseased cells from healthy cells based on stiffness contrast, which was found to depend on the stiffness contrast.
Abstract: This paper reports the characterization and sorting of cells based on stiffness contrast. Cell stiffness is characterized in terms of elastic modulus, deformability index and hydrodynamic resistance. For different cell types, elastic modulus is measured using nanoindentation experiments on AFM and deformability index of cells is measured by hydrodynamic stretching of the cells in a flow focusing microchannel device. Hydrodynamic resistance of cells is obtained by measuring the excess pressure drop across a segment of a microchannel and correlated with cell size ρc and elastic modulus using a large set of experimental data. The highly-invasive malignant breast cancer cells MDA MB 231, non-invasive malignant breast cancer cells MCF 7, human promyelocytic leukaemia cells HL60 and the cervical cancer cells HeLa are considered in the present study. A microfluidic device with focusing and spacing control for stiffness based sorting of cells was designed and fabricated. Experiments were performed to demonstrate cell sorting and characterize the device performance in terms of sorting efficiency, which was found to depend on the stiffness contrast. The proposed device has potential to be used as a lab on chip diagnostic tool for sorting of diseased cells from healthy cells based on stiffness contrast.

33 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a force density proportional to the surface curvature of constant color is defined at each point in the transition region; this force-density is normalized in such a way that the conventional description of surface tension on an interface is recovered when the ratio of local transition-reion thickness to local curvature radius approaches zero.

7,863 citations

Journal ArticleDOI
TL;DR: In this paper, a flow-focusing geometry is integrated into a microfluidic device and used to study drop formation in liquid-liquid systems, where both monodisperse and polydisperse emulsions can be produced.
Abstract: A flow-focusing geometry is integrated into a microfluidic device and used to study drop formation in liquid–liquid systems. A phase diagram illustrating the drop size as a function of flow rates and flow rate ratios of the two liquids includes one regime where drop size is comparable to orifice width and a second regime where drop size is dictated by the diameter of a thin “focused” thread, so drops much smaller than the orifice are formed. Both monodisperse and polydisperse emulsions can be produced.

2,264 citations

Journal ArticleDOI
TL;DR: The ability to differentially order particles of different sizes, continuously, at high rates, and without external forces in microchannels is expected to have a broad range of applications in continuous bioparticle separation, high-throughput cytometry, and large-scale filtration systems.
Abstract: Under laminar flow conditions, when no external forces are applied, particles are generally thought to follow fluid streamlines. Contrary to this perspective, we observe that flowing particles migrate across streamlines in a continuous, predictable, and accurate manner in microchannels experiencing laminar flows. The migration is attributed to lift forces on particles that are observed when inertial aspects of the flow become significant. We identified symmetric and asymmetric channel geometries that provide additional inertial forces that bias particular equilibrium positions to create continuous streams of ordered particles precisely positioned in three spatial dimensions. We were able to order particles laterally, within the transverse plane of the channel, with >80-nm accuracy, and longitudinally, in regular chains along the direction of flow. A fourth dimension of rotational alignment was observed for discoidal red blood cells. Unexpectedly, ordering appears to be independent of particle buoyant direction, suggesting only minor centrifugal contributions. Theoretical analysis indicates the physical principles are operational over a range of channel and particle length scales. The ability to differentially order particles of different sizes, continuously, at high rates, and without external forces in microchannels is expected to have a broad range of applications in continuous bioparticle separation, high-throughput cytometry, and large-scale filtration systems.

1,518 citations

Journal ArticleDOI
TL;DR: In this paper, a chip-like structure for capillary electrophoresis is presented, which is based on the photolithographic technique for structures in the micrometer range.

1,106 citations

Journal ArticleDOI
TL;DR: This critical review discusses the current understanding of the formation, transport, and merging of drops in microfluidics and focuses on the physical ingredients which determine the flow of Drops in microchannels.
Abstract: This critical review discusses the current understanding of the formation, transport, and merging of drops in microfluidics. We focus on the physical ingredients which determine the flow of drops in microchannels and recall classical results of fluid dynamics which help explain the observed behaviour. We begin by introducing the main physical ingredients that differentiate droplet microfluidics from single-phase microfluidics, namely the modifications to the flow and pressure fields that are introduced by the presence of interfacial tension. Then three practical aspects are studied in detail: (i) The formation of drops and the dominant interactions depending on the geometry in which they are formed. (ii) The transport of drops, namely the evaluation of drop velocity, the pressure-velocity relationships, and the flow field induced by the presence of the drop. (iii) The fusion of two drops, including different methods of bridging the liquid film between them which enables their merging.

900 citations