Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E14: Biofluids: Cellular II: Blood Transport |
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Chair: Jonathan Freund, University of Illinois at Urbana Champaign Room: 317 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E14.00001: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E14.00002: Quantifying the glycocalyx effects in blood flow in capillaries Mingge Deng, Huan Lei, Bruce Caswell, George Karniadakis We employ Dissipative Particle Dynamics (DPD) to simulate blood flow in small capillaries with the glycocalyx attached to the endothelial surface. The effects of the glycocalyx on hematocrit and resistance to blood flow are analyzed by comparing with and without glycocalyx attached to the surface. Of particular interest is the quantification of the slip boundary condition at the edge of glycocalyx and also of the glycocalyx deformation at different grafting densities, stiffness and height of the glycocalyx. In addition to the physical insight gained for this important but relatively unexplored bio-flow, simple models for the slip velocity will be proposed that can be used in continuum simulations of blood flow in micro-vessels. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E14.00003: Mechanism of flow induced segregation in suspensions of binary mixtures of deformable capsules based on rigidity in confined geometries Amit Kumar, Michael Graham Flow induced segregation in mixtures of deformable particles based on rigidity is relevant in many biological and technological applications. For example, this property can be employed in the detection or separation of stiffened RBCs in various diseased states like malaria in a point of care microfluidic device. We numerically study here neo-Hookean capsule suspensions subjected to pressure driven flows in a slit geometry using an accelerated implementation of the boundary integral method. The effect of a wide variety of parameters like volume fraction, capillary number, confinement ratio, number fraction of the floppy particle (X), and the rigidity ratio between the two components of the mixture were explored. In pure suspensions, the mean wall normal position of the stiff and the floppy particles were comparable; however, in mixtures, the stiff particles were found to be increasingly displaced towards the walls with increasing X. Simple model studies involving pair collisions between stiff and floppy particles qualitatively explain the above behavior. Numerical results are further incorporated in the Fokker-Planck equation, which is found to correctly model the particle motion and predict the segregation behavior. The drift and diffusion terms in the Fokker-Planck equation are consistent with the results of pair collision. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E14.00004: Simulation of neutrophil motion and deformation: Influence of rheology and flow configuration Melanie Le Roux, Jacques Magnaudet We report on preliminary computations of neutrophils (white cells) flowing and deforming in capillary vessels in different flow configurations. We crudely consider that the cell is made of a solid core and a viscoelastic cytoplasm surrounded by an elastic membrane and moves within a Newtonian plasma. A Volume Of Fluid approach is employed to follow the displacement of the cell while the Immersed Boundary Method is used to take into account the presence of a solid core; the viscoelastic behavior of the cytoplasm is mimicked using the Oldroyd-B model. We discuss the behavior of the cell when placed in 3 different flow configurations, namely a four roll-mill device allowing all types of linear flow fields to be generated in the central region where the cell stands, a contraction followed by an expansion in a straight channel, and a periodic network of prismatic blocks. The dimensions of the last two systems are such that the cell experiences large deformations while moving. We discuss the influence of the physical parameters of the system, especially the Capillary and Deborah numbers and the ratio of the inner and outer Newtonian viscosities, on the flow and cell evolution. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E14.00005: Multiscale modeling of sickle anemia blood blow by Dissipative Partice Dynamics Huan Lei, Bruce Caswell, George Karniadakis A multi-scale model for sickle red blood cell is developed based on Dissipative Particle Dynamics (DPD). Different cell morphologies (sickle, granular, elongated shapes) typically observed in \textit{in vitro} and \textit{in vivo} are constructed and the deviations from the biconcave shape is quantified by the Asphericity and Elliptical shape factors. The rheology of sickle blood is studied in both shear and pipe flow systems. The flow resistance obtained from both systems exhibits a larger value than the healthy blood flow due to the abnormal cell properties. However, the vaso-occulusion phenomenon, reported in a recent microfluid experiment, is not observed in the pipe flow system unless the adhesive interactions between sickle blood cells and endothelium properly introduced into the model. [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E14.00006: Tracer-incorporated X-ray imaging of biofluid flow phenomena Sung Yong Jung, Sungsook Ahn, Sang Joon Lee Particle-traced X-ray imaging technologies have been developed by combining the merits of the X-ray radiography and particle image velocimetry (PIV) technique. The developed X-ray imaging technology has strong potential in the noninvasive analysis of various flows such as non-transparent fluid flows or fluids flowing in opaque conduits. In this study, tracer-incorporated X-ray imaging technology was developed. In addition, new- concepted tracer particles were designed for in vitro and in vivo X-ray imaging analysis of various biofluids. As tracer particles in X-ray image, X-ray contrast enhancer Iopamidol was encapsulated into bio-compatible polymeric chitosan microparticles and gold nanoparticles with high X-ray absorption efficiency were directly incorporated into cells. The Iopamidol-incorporated polymeric microparticles were successfully applied for in vivo blood flow measurement in a rat. The gold nanoparticles were selectively incorporated into cancer cells, by which cancer cells can be detected in situ. The developed X-ray imaging technology would have a great potential in biomedical applications such as in situ analysis of blood flow and cancer detection. [Preview Abstract] |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E14.00007: Transport of magnetic nanobeads in a small blood vessel Jonathan Freund Numerical simulations are used to study the transport of sub-micron spherical magnetic beads in a model microvessel, particularly how transport is affected by physiologically realistic concentrations of flowing red cells. (Such beads are candidate vehicles for targeted drug delivery.) A previously validated high-fidelity boundary integral algorithm is used to solve the flow equations in the viscous limit in a $\sim 15\mu$m vessel. As expected, the red cells suppress transport toward the vessel wall when a magnetic field is applied normal to the flow direction. A more subtle mechanism is important when a magnetic field has a component parallel to the vessel. A homogeneous fluid model would be insensitive to forces applied in this direction, but tendency of blood cells to tilt away from the wall on their upstream side breaks the streamwise symmetry. These tilted cells act as viscous-flow variants of turning vanes, guiding magnets toward the wall if they are slowed by the magnetic field and toward the vessel center if they are accelerated by the magnetic field. This affects dispersion in the vessel and can also alter wall-ward magnetic field driven transport. [Preview Abstract] |
Sunday, November 20, 2011 6:11PM - 6:24PM |
E14.00008: White blood cell deformation and firm adhesion Alex Szatmary, Charles Eggleton For a white blood cell (WBC) to arrive at infection sites, it forms chemical attachments with activated endothelial cells. First, it bonds with P-selectin, which holds it to the wall, but weakly; this allows the WBC to roll under the shear flow of the blood around it. Later, the WBCs bond with the stronger intracellular adhesion molecule-1 (ICAM-1); it is these ICAM bonds that allow the WBCs to fully resist the flow and stop rolling, allowing them to crawl through the endothelial wall. We model this numerically. Our model uses the immersed boundary method to represent the interaction of the shear flow with the deformable cell membrane. Receptors are on the tips of microvilli-little fingers sticking off of the cell membrane. The microvilli also deform. The receptors stochastically form and break bonds with molecules on the wall. Using this method, the history of each microvillus and its bonds can be found, as well as the distribution of the adhesion traction forces and how all of these vary with the deformability of the white blood cell. At higher shear rates, the white blood cell membrane deforms more, increasing its contact area with the surface; this effect is larger for softer membranes. We investigate how the deformability of the WBC affects the ease with which it forms firm adhesion. [Preview Abstract] |
Sunday, November 20, 2011 6:24PM - 6:37PM |
E14.00009: Modification of Platelet Margination Rate via Reduction of Viscosity Ratio Daniel Reasor, Marmar Mehrabadi, David Ku, Cyrus Aidun Experimental investigations of platelet margination have primarily been limited to effects of hematocrit (Ht.) and shear rate. The suspending fluids used commonly have viscosities greater than plasma which can modify the transition in dynamical regimes from tumbling to tank-treading for isolated RBCs. This work focuses on the effects of $\lambda$, the ratio of internal to suspending fluid viscosity of RBCs, on the rate of platelet margination in a rigid 41.3 $\mu$m diameter vessel. Simulations are performed with a lattice-Boltzmann fluid solver using the standard bounce-back boundary condition coupled with a coarse-grained spectrin-link RBC membrane model and a Newtonian dynamics solver for rigid platelets. Our results are consistent with observations that an increase in Ht.~increases the rate of platelet margination for Ht.=20-40\%, but we focus on the modification of $\lambda$ at Ht.=20\%. Our results show that rigid RBCs inhibit margination, but modifying $\lambda$ with deformable RBCs show significant increases in margination rate. Our observations demonstrate an increase in platelet wall-normal velocity fluctuations, enhanced margination rate, and an increase in the wall-normal diffusivity as $\lambda$ is reduced from the physiological value of five. [Preview Abstract] |
Sunday, November 20, 2011 6:37PM - 6:50PM |
E14.00010: The Effect of Discoid Shape on Platelet Margination in a Microvessel Marmar Mehrabadi, Daniel Reasor, David Ku, Cyrus Aidun Margination of platelets to the skimming layer only occurs above a threshold hematocrit (Ht.). Platelet size and concentration in blood is much smaller compared to red blood cells (RBCs). We study the hypothesis that platelets are passively convected to vessel walls and that their morphology can effect margination rate and dynamics. To examine this, we study the influence of particle shape on margination rate through changing the aspect ratio (AR) of rigid particles at fixed volume. We use a coarse-grained spectrin-link method for RBC membranes and Newtonian dynamics for rigid particles coupled with a 3D lattice-Boltzmann fluid solver using standard bounce-back boundary conditions. Simulations are performed at Ht.=20\% in a 41.$\bar{3}$ $\mu$m vessel. Our results show that AR has a significant effect on margination rate: Lower AR particles marginate more rapidly. We also show that the higher AR particles ``flip'' and ``slide'' between RBCs as they migrate to the skimming layer. The final location of particles in the skimming layer is also influenced by their shape. Thin disk-shaped particles interact with the RBCs at the edge of the skimming layer more frequently than with the vessel wall while spherical particles interact with both simultaneously. [Preview Abstract] |
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