Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session GL: Bio-Fluids: Rheology and Transport |
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Chair: Dennis Siginer, Petroleum Institute Room: 103A |
Monday, November 24, 2008 8:00AM - 8:13AM |
GL.00001: An Improved Comprehensive Model for the Apparent Viscosity of Blood Frank Jacobitz, Spencer Anderson An improved comprehensive model for the apparent viscosity of blood is developed and used in simulations of the microcirculation in capillary bundles of rat spinotrapezius muscle fascia. In the microcirculation, the apparent viscosity of blood depends on the local vessel diameter, hematocrit, and shear rate. The proposed comprehensive model extends the apparent viscosity model developed by Pries, Secomb, Gaehtgens, and Gross (Circulation Research, 67, 826-834, 1990), which describes the effect of vessel diameter and hematocrit on the apparent viscosity. A shear thinning term is developed using the experimental data of Lipowsky, Usami, and Chien (Microvascular Research, 19, 297-319, 1980). Curve fits of this data can be combined with equations given in the Pries et al. work to create a system of equations that can be used to find the shear thinning factor. The simulations based on the improved apparent viscosity model use realistic vessel topology for the microvasculature, reconstructed from microscope images of tissue samples, and consider passive and active vessel properties. The numerical method is based on a Hagen-Poiseuille balance in the microvessels and a sparse matrix solver is used to obtain the solution. It was found that the inclusion of the shear factor decreases the overall flowrate in the capillary bundle. Many vessel connections in the fascia are characterized by relatively low shear rates and therefore increased apparent viscosity. [Preview Abstract] |
Monday, November 24, 2008 8:13AM - 8:26AM |
GL.00002: Grow with the Flow: A Dynamic Tale of Blood Clot Formation Karin Leiderman, Aaron Fogelson The body heals injured blood vessels and prevents bleeding by clotting the blood. Clots are primarily made of blood-borne cells and a fibrous material that is assembled at the site of injury in flowing blood. Clot composition and structure change with local chemistry and fluid dynamics, which in turn alter the flow. To better understand this fluid-structure coupling, we have created a mathematical model to simulate the formation of a blood clot in a dynamic fluid environment. The growing clot is represented as a mixed porous medium whose permeability is dependent on the coagulation chemistry within it. The flow field resulting from a clot with specific calculated permeability and size can then be recovered by solving the Navier-Stokes equations with an added friction term. We report on how this complex fluid-structure interaction affects the limiting factor(s) of blood clot growth. [Preview Abstract] |
Monday, November 24, 2008 8:26AM - 8:39AM |
GL.00003: Adhesion, Deformation, Rolling, and Detachment of a Liquid Capsule on An Adhesive Surface In Shear Flow Vijay Pappu, Prosenjit Bagchi 3D computational modeling and simulation are presented on adhesion, deformation, rolling and detachment of a liquid capsule on adhesive surfaces in shear flow with an objective to understand the adhesive rolling motion of biological cells, such as leukocyte and cancel cells, and the coupling between cell deformation and biophysics of the adhesive bonds. The computational model is based on an immersed boundary method for deformable capsules, and a finite difference-Fourier transform technique for solving the complete Navier-Stokes equations. The flow solver is coupled with a Monte Carlo simulation representing random process for bond formation and breakage between the capsule and the adhesive surface. Becuase of the stochastic process of bond formation and breakage, the roling motion is comprised of intermittent ``stops-and-runs'' which is well-known for biological cells such as leukocytes, which is reproduced in our simulations. The major objective of this talk is to present phase diagrams for cell adhesion which are obtained in terms of the critical bond strength as a function of cell deformability and biophysical parameters of the adhesion bonds. Through these phase diagrams, we elucidate the role of the hydrodynamic lift force, that exists on an wall- bounded deformable particle in shear flow, in the process of cell capture. Funded by NSF (BES-0603035 and CTS-0625936). [Preview Abstract] |
Monday, November 24, 2008 8:39AM - 8:52AM |
GL.00004: Multi-scale Simulation of Receptor-Ligand-Mediated Adhesion of Two (PMN) Leukocytes Vijay Gupta, Kostas Konstantopoulos, Charles Eggleton Leukocytes are recruited from the bloodstream to the site of inflammation through interactions between cell surface receptors and complementary ligands expressed on the surface of the endothelium. PMNs rolling on activated endothelium can mediate secondary capture of PMNs flowing in the free stream through homotypic interactions. This interaction is mediated by L-selectin binding to PSGL-1 between the free-stream and adherent PMNs. Both L-selectin and PSGL-1 molecules are concentrated on the tips of PMN microvilli. It has been demonstrated that steady application of a threshold level of shear rate is necessary to support PMN homotypic aggregation in bulk suspension. A reduction of shear rate below a threshold value diminishes the probability of cell adhesion. Cell aggregation is a complex phenomenon involving the interplay of bond kinetics and hydrodynamics. We simulate PSGL-1--L-selectin-mediated homotypic leukocyte adhesion-dissociation under an externally applied force field using the Immersed Boundary Method. We investigate the influence of membrane elasticity and kinetic parameters on contact area, bond dynamics, average number of bonds formed and their respective life time. A Hookean spring model is used to characterize receptor-ligand bonds and their stochastic nature is simulated using the Monte Carlo technique. [Preview Abstract] |
Monday, November 24, 2008 8:52AM - 9:05AM |
GL.00005: Mesoscale Model for Blood Cell Adhesion and Transport using Ellipsoidal Particles Jennifer Chesnutt, Jeffrey Marshall A novel discrete-element computational model for efficient transport, collision, and adhesion of ellipsoidal particles is applied to blood cells adhering through receptor-ligand binding in three-dimensional flow. The model has been used for simulation of over 13,000 adhesive cells through approximation of blood cells as elastic particles and other physically-justifiable approximations. The computational model is validated against experimental data of red blood cell (RBC) aggregation in shear and channel flows. The structure of aggregates formed by RBCs is analyzed by various measures that relate RBCs which are in contact with each other and that characterize an aggregate by fitting an ellipse to the projection of cells contained in the aggregate. Factors such as shear rate and adhesive surface energy density between cells are examined for their effects on the size and structure of RBC aggregates in both two- and three-dimensional computations. The effect of RBC aggregation on migration of blood elements (RBCs, leukocytes, platelets) in channel flow is also investigated. [Preview Abstract] |
Monday, November 24, 2008 9:05AM - 9:18AM |
GL.00006: Migration of Connexin in the Membranes of Living Cells Daharsh Rana, Matthew Bledsoe, Karl May, Jennifer Kreft The cell membrane has been traditionally represented using the fluid mosaic model consisting of phospholipids with proteins diffusing freely in them. But studies of the diffusion of proteins indicate interactions with other proteins in or near the cell membrane are important in determining the motion of membrane proteins. We have studied connexin, a gap-junction protein, to investigate the mechanism by which proteins move in the cellular membrane. Green fluorescence protein marker was used to label connexin. The motion of the protein as it migrated to the point of contact between cells was recorded in experiment. In addition, a lattice Boltzmann simulation has been developed to simulate the movement of connexin in a cellular environment. This computational data is validated by matching quantitatively experimental results and used to gain further insight into the mechanism of migration of connexin. [Preview Abstract] |
Monday, November 24, 2008 9:18AM - 9:31AM |
GL.00007: Nutrient Transport and Acquisition by Diatom Chains in a Moving Fluid Magdalena Musielak The role of fluid motion in the transport of solutes to and away from cells and aggregates is a fundamental question in biological and chemical oceanography. However, little is known about behavior of phytoplankton cells in well-defined flow fields. Experimental data to test the contribution of advection to nutrient acquisition by phytoplankton are scarce, mainly because of the inability to imitate fluid motions in the vicinities of cells in natural flows, and difficulty to detect nutrient fluxes on the scale of interest. Thus, computational experiments are needed to analyze the contribution of advection to mass transfer and nutrient acquisition by phytoplankton. We present in this talk a mathematical model based on the immersed boundary method, that couples the interaction of non-motile diatom chains with the moving fluid and the nutrient. We apply our model to investigate the impact of shape, length, and flexibility of chains on nutrient uptakes in various flow regimes. Our numerical results obtained thus far confirm intuitive predictions, and open the door to possible experimental work. [Preview Abstract] |
Monday, November 24, 2008 9:31AM - 9:44AM |
GL.00008: Coating flow of non-Newtonian anti-HIV microbicide vehicles Su Chan Park, Andrew Szeri, St\'ephane Verguet, David Katz, Aaron Weiss Elastohydrodynamic lubrication over soft substrates is of importance for the drug delivery functions of vehicles for anti-HIV topical microbicides. These are intended to inhibit transmission into vulnerable mucosa, e.g. in the vagina. First generation prototype microbicides have gel vehicles, which spread after insertion and coat luminal surfaces. Effectiveness derives from potency of the active ingredients and completeness and durability of coating. Delivery vehicle rheology, luminal biomechanical properties and the force due to gravity influence the coating mechanics. We develop a framework for understanding the relative importance of boundary squeezing and body forces on the extent and speed of the coating that results. In the case of a shear-thinning fluid, the Carreau number also plays a role. Numerical solutions are developed for a range of conditions and materials. Results are interpreted with respect to tradeoffs between wall elasticity, longitudinal forces, bolus viscosity and bolus volume. These provide initial insights of practical value for formulators of non-Newtonian gel delivery vehicles for anti-HIV microbicidal formulations. [Preview Abstract] |
Monday, November 24, 2008 9:44AM - 9:57AM |
GL.00009: Rheology of suspensions of vesicles and red blood cells. Thomas Podgorski, Victoria Vitkova, Maud-Alix Mader, Benoit Polack, Chaouqi Misbah We investigate the rheology of dilute suspensions of lipid vesicles and red blood cells (RBC) as a function of the viscosity ratio between the internal and external fluids. Experiments on RBC and vesicles, as well as the result of theoretical investigations on vesicles exhibit a minimum of the intrinsic viscosity when the viscosity ratio is close to the value at which at the miscoscopic scale, a transition from tank-treading to tumbling occurs for individual objects in simple shear flow. This reveals a qualitative change due to the link between microscopic and macroscopic dynamics. [Preview Abstract] |
Monday, November 24, 2008 9:57AM - 10:10AM |
GL.00010: Numerical Study on Flows of Red Blood Cells with Liposome-Encapsulated Hemoglobin at Microvascular Bifurcation Toru Hyakutake, Shigeki Tani, Takeshi Matsumoto, Shinichiro Yanase Flow analysis at microvascular bifurcation after partial replacement of red blood cell (RBC) with liposome-encapsulated hemoglobin (LEH) was performed using the lattice Boltzmann method. A two-dimensional bifurcation model with a parent vessel and daughter branch was considered, and the distributions of the RBC, LEH, and oxygen fluxes were calculated. When only RBCs flow into the daughter branches with unevenly distributed flows, plasma separation occurred and the RBC flow to the lower-flow branch was disproportionately decreased. On the other hand, when the half of RBC are replaced by LEH, the biasing of RBC flow was enhanced whereas LEH flowed favorably into the lower-flow branch, because many LEH within the parent vessel are suspended in the plasma layer, where no RBCs exist. Consequently, the branched oxygen fluxes became nearly proportional to flows. These results indicate that LEH facilitates oxygen supply to branches that are inaccessible to RBCs. [Preview Abstract] |
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