Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H19: Biofluids: Cellular III - Computational Studies on Mechanical Properties of Cellular Flows |
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Chair: Jonathan Freund, University of Illinois Room: 310/311 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H19.00001: Lipid tubule growth by osmotic pressure Padmini Rangamani, Di Zhang, George Orster, Amy Shen We present here a procedure for growing lipid tubules in vitro. This method allows us to grow tubules of consistent shape and structure and thus can be a useful tool for nano-engineering applications. There are three stages during the tubule growth process: initiation, elongation and termination. Balancing the forces that act on the tubule head shows that the growth of tubules during the elongation phase depends on the balance between osmotic pressure and the viscous drag exerted on the membrane from the substrate and the external fluid. Using a combination of mathematical modeling and experiment, we identify the key forces that control tubule growth during the elongation phase. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H19.00002: Lattice Boltzmann simulations of leukocyte rolling and deformation in a three-dimensional shear flow Ye Luo, Dewei Qi, Guowei He Lattice Boltzmann simulation is used to simulate the motion of a leukocyte in fluid. The cell membrane is built by lattice spring model. The interaction between the fluid flow and the solid surface is treated by immersed boundary method. Stochastic Monte Carlo method is used to deal with receptor/ligand interaction. It is shown that the model can correctly predict the characteristic ``stop-and-g'' motion of rolling leukocytes. Effects of cell deformation, shear rates, bonding force, microvilli distribution on rolling are studied and compared with experiments. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H19.00003: Effect of asymmetric deformation on capsule lateral migration Stephanie Nix, Yohsuke Imai, Daiki Matsunaga, Takuji Ishikawa, Takami Yamaguchi In a Stokes flow, lateral migration is the movement of a particle perpendicular to the flow direction due to the presence of a wall and/or shear gradient. Lateral migration has an effect on microscale flows in a number of fields. For example, in the cardiovascular system, the presence of a cell-free layer in blood vessels near the vessel wall is caused by the lateral migration away from the wall. In this study, we use the boundary integral method to investigate the wall-induced lateral migration of a capsule, which consists of a hyperelastic membrane enclosing an inner fluid. The boundary integral equation can be separated into two terms that represent contributions due to the capsule shape and wall. We find that the extent of the asymmetrical deformation of the capsule works to decrease the rate of migration perpendicular to the wall by up to 30\% compared to the far-field analytical solution. Additionally, the effect of the asymmetrical deformation persists for distances up to ten times the capsule radius. Since the effect of asymmetrical deformation is only weakly dependent on the membrane properties, this type of analysis could be useful towards the understanding of lateral migration of other particles, such as drops and vesicles. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H19.00004: Relaxation of deformed drops, vesicles, and cells Miao Yu, Jia Zhang, Hao Lin, Jeffrey Zahn, Wenchang Tan The deformation of drops, vesicles, and cells constitutes an important class of problems in chemical and biomedical engineering, and is often explored as a means to study interfacial dynamics and mechanical properties of the lipid membrane. Less attention has been paid to the relaxation process after the deforming mechanism is removed. In this work, analyses of such process are presented. A drop, vesicle or cell of spherical shape at rest is initially deformed into a spheroid. The relaxation process is then solved within the same theoretical framework in both small- and moderate-deformation limits. Different regimes are discovered. For sufficiently small initial deformations, the change in the membrane tension is a negligible higher-order effect for both vesicles and cells, and they behave identically to drops in the relaxation process. For moderate initial deformations, vesicle and cell relaxation is dominantly governed by the folding of undulations on the lipid membrane which differs from the behavior of a drop. Membrane properties, namely, membrane tension and bending rigidity, are the key parameters governing this dynamic process. A detailed comparison with experimental data for vesicles/cells is performed, and the results are presented and discussed. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H19.00005: Flow-induced segregation in confined multicomponent suspensions: Effects of particle size and rigidity Michael Graham, Amit Kumar The effects of particle size and rigidity on segregation in confined flow of binary suspensions of fluid-filled capsules are investigated in a model system resembling whole blood. We study this problem using a boundary integral method as well as with a master equation model that incorporates wall-induced migration and hydrodynamic pair collisions. Boundary integral results indicate that, in a mixture of large and small particles, the small particles marginate, while the large particles antimarginate. Here margination refers to localization of particles near walls, while antimargination refers to the opposite. In a mixture of particles with equal size and unequal stiffness, the stiffer particles marginate while the flexible ones antimarginate. The master equation model traces the origins of these behaviors to the size and rigidity dependence of the wall-induced migration velocity and of the cross-stream particle displacements in various types of collisions. Finally, a set of coupled non-local drift-diffusion equations is derived, providing further insights in terms of the drift and diffusion of various species. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H19.00006: The wall traction induced by flowing red blood cells in model microvessels and its potential mechanotransduction Jonathan Freund, Julien Vermot There is evidence in early embryonic development, even well before advective oxygen transport is important, that the presence of red bloods cells \textit{per se} trigger essential steps of normal vascular development. For example, Lucitti {\it et al.}\ [{\it Development} {\bf 134}, 3317 (2007)] showed that sequestration of blood cells early in the development of a mouse, such that the hematocrit is reduced, suppresses normal vascular network development. Vascular development also provides a model for remodeling and angiogenesis. We consider the transient stresses associated with blood cells flowing in model microvessels of comparable diameter to those at early stages of development ($6\mu$m to $12\mu$m). A detailed simulation tool is used to show that passing blood cells present a significant fluctuating traction signature on the vessel wall, well above the mean stresses. This is particularly pronounced for slow flows ($\la 50\mu$m/s) or small diameters ($\la 7\mu$m), for which root-mean-square wall traction fluctuations can exceed their mean. These events potentially present mechanotranduction triggers that direct development or remodeling. Attenuation of such fluctuating tractions by a viscoelastic endothelial glycocalyx layer is also considered. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H19.00007: Capturing mechanical properties of biological cells using coarse-grained modeling Wenbin Mao, Monique Chang, Alexander Alexeev Understanding cell mechanics is important for a variety of biomedical applications. Our goal is to develop a coarse-grained computational model that can properly capture the micromechanics of biological cells. The coarse-grained cell model includes an elastic shell enclosing a cross-linked polymer network and a viscous fluid representing, respectively, cell membrane, cytoskeleton, and cytoplasm. We use this model to investigate the mechanical response of cells to external forces and compare the results with the experimental AFM measurements. We systematically vary the properties and structure of the internal polymer network and the outer membrane to assess their influence on the cell mechanical responses. This model not only reveals interesting insights into the cell mechanics, but also provides a promising tool for investigation of motile and multicellular systems. [Preview Abstract] |
Monday, November 25, 2013 12:01PM - 12:14PM |
H19.00008: Effect of cytoskeleton stress-free state on red blood cell responses in low shear rate flows Qiang Zhu, Zhangli Peng, Adel Mashayekh Inspired by the recent experiment on erythrocytes (red blood cells, or RBCs) in weak shear flows (Dupire et al. 2012), we conduct a numerical investigation to study the dynamics of RBCs in low shear rate flows by applying a multiscale fluid-structure interaction model. By employing a spheroidal stress-free state in the cytoskeleton we are able to numerically predict an important feature that the cell maintains its biconcave shape during tank treading motions. This has not been achieved by any existing models. Furthermore, we numerically confirm the hypothesis that as the stress-free state approaches a sphere, the threshold shear rates corresponding to the establishment of tank treading decrease. By comparing with the experimental measurements, our study suggests that the stress-free state of RBCs is a spheroid which is close to a sphere, rather than a biconcave shape applied in existing models (the implication is that the RBC skeleton is prestressed in its natural biconcave state). It also suggests that the response of RBCs in low shear rate flows may provide a measure to quantitatively determine the distribution of shear stress in RBC cytoskeleton at the natural state. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H19.00009: Nonlinear Response of Bio-Polymers Subject to Stretching Flow with Thermal Noise Mingge Deng, Leopold Grinberg, Bruce Caswell, George Karniadakis The dynamics of elastic filaments subject to hydrodynamic forces exhibits complex nonlinear dynamics in the neighborhood of stagnation points in the flow. Here, the motion of a single in-extensible bio-polymer with an-isotropic friction tensor subjected to a stretching flow is modeled with stochastic differential equations as well as dissipative particle dynamics simulations. Our results show that the negative tension induces a stretch-coil transition beyond a critical value, where the noise is amplificated due to the interaction between thermal noise and nonlinear effects. [Preview Abstract] |
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