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 A14: Biofluids: Cellular I: Transport of Blood Cells |
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Chair: Prosenjit Bagchi, Rutgers University Room: 317 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A14.00001: Red blood cell damage by shear stress for different blood types Gilad Arwatz, Katherine Bedkowski, Alexander Smits In surgical practice, blood damage caused by medical devices is often a limiting factor in the duration of an acute procedure or in chronic exposures such as hemodialysis. In order to establish guidelines for designing medical devices, a study was conducted to determine the relationship between shear stress and damage to red blood cells using a concentric Couette device. By measuring the hemolysis level for various shear stresses and exposure times, a non-dimensional relationship between shear stress and blood damage for different blood types was established. [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A14.00002: Transition to Non-Newtonian behavior of blood suspensions flowing in small tubes Bruce Caswell, Huan Lei, Dmitry Fedosov, George Karniadakis Blood flow in tubes is widely considered to be Newtonian down to diameters of about 200 microns. We have employed a multi-scale, Dissipative Particle Dynamics (DPD) model of the red blood cell (RBC) to investigate suspensions driven through small tubes (\textbf{diameters 20-150 microns).} The cross-stream stress gradient induces radial migration of the suspended RBCs resulting in the formation of a hematocrit (H) peak at the centerline, and at the wall a cell-free layer (CFL) whose edge is the point of maximum RBC distortion. This suggests that hard- sphere suspension theories will not capture well blood flow in tubes. For the larger tubes the velocity profiles beyond the CFL are essentially parabolic even though the core H is non-uniform. As the diameter decreases: (1) the CFL moves inward and the central H peak grows, but for the smallest (20 microns) the H peak is shifted off-center, (2) the bulk velocity profiles become similar to those of a shear-thinning non-Newtonian fluid. However, accurate modeling of the velocity field of the bulk flow in small tubes as a homogeneous non-Newtonian fluid can only be achieved if model parameters are taken to depend on tube diameter and pressure drop. [Preview Abstract] |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A14.00003: Hydrodynamic forces on a wall-bound leukocyte due to interactions with flowing red cells Amir H. G. Isfahani, Jonathan B. Freund As part of both healthy and pathologically physiological mechanisms sphere-like white blood cells (leukocytes) adhere to the walls of small blood vessels. We use quantitative numerical simulations to compare the forces from flowing red blood cells on a wall-adhered leukocyte to a homogenized model of blood at the same flow conditions. We model the highly flexible red blood cells using a fast $O(N \log N)$ boundary integral formulation. These elastic membranes deform substantially but strongly resist surface dilatation. They enclose a higher than plasma viscosity hemoglobin solution. The no-slip condition is enforced on the stationary leukocyte as well as the vessel walls. Vessel diameters of 10 to 20 microns are studied. Different hematocrits, leukocyte shapes, and flow conditions are examined. In vessels comparable to the size of the cells, we show that the particulate character of blood significantly affects the magnitude of the forces that the leukocyte experiences, transiently increasing it well above the homogenized-blood prediction: for example, for a tube hematocrit of $25\%$ and a spherical protrusion with a diameter 0.75 that of the tube, the average forces are increased by about $40\%$ and the local forces by more than $100\%$ relative to those expected for a blood model homogenized by its effective viscosity. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A14.00004: Dynamics of Microcapsules and Red Blood Cells in Oscillating Shear Flow Mengye Zhao, Prosenjit Bagchi In a recent experimental work, Dupire et al [PRL, \textbf{104}, 168101 (2010)] reported a nonperiodic behavior of the red blood cells suspended in a sinusoidally oscillating shear flow. The nonperiodic motion was characterized by intermittent cell swinging and tumbling. A theoretical model based upon the work of Keller and Skalak [JFM, \textbf{120}, 27 (1982)] for shape- preserving cells was shown to predict the nonperiodic motion that was highly sensitive to the initial conditions. In this talk, we present a three-dimensional numerical study of deformable capsules in sinusoidally oscillating shear flow in order to address if similar nonperiodic motion is observed when deformation is present. For initially oblate capsules, we observe two types of dynamics: a swinging motion in response to the altering flow direction that occurs at both high and low values of shear rate amplitudes, and a continuous/unidirectional tumbling motion that occurs at intermediate values. We obtain phase diagram that shows existence of two critical shear rates and two oscillation frequencies. Unlike Dupire et al, we do not find nonperiodic motion, but we find that the swinging/tumbling dynamics is sensitive to the initial condition. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A14.00005: Modeling of Red Blood Cells and Related Spleen Function Zhangli Peng, Igor Pivkin, Ming Dao A key function of the spleen is to clear red blood cells (RBCs) with abnormal mechanical properties from the circulation. These abnormal mechanical properties may be due to RBC aging or RBC diseases, e.g., malaria and sickle cell anemia. Specifically, 10\% of RBCs passing through the spleen are forced to squeeze into the narrow slits between the endothelial cells, and stiffer cells which get stuck are killed and digested by macrophages. To investigate this important physiological process, we employ three different approaches to study RBCs passage through these small slits, including analytical theory, Dissipative Particle Dynamics (DPD) simulation and Multiscale Finite Element Method (MS-FEM). By applying the analytical theory, we estimate the critical limiting geometries RBCs can pass. By using the DPD method, we study the full fluid-structure interaction problem, and compute RBC deformation under different pressure gradients. By employing the MS-FEM approach, we model the lipid bilayer and the cytoskeleton as two distinct layers, and focus on the cytoskeleton deformation and the bilayer-skeleton interaction force at the molecular level. Finally the results of these three approaches are compared to each other and correlated to the experimental observations. [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A14.00006: Phase Diagram and Breathing Dynamics of Red Blood Cell Motion in Shear Flow Prosenjit Bagchi, Alireza Yazdani We present phase diagrams of red blood cell dynamics in shear flow using three-dimensional numerical simulations. By considering a wide range of shear rate and interior-to-exterior fluid viscosity ratio, it is shown that the cell dynamics is often more complex than the well-known tank-treading, tumbling and swinging motion, and is characterized by an extreme variation of the cell shape. We identify such complex shape dynamics as `breathing' dynamics. During the breathing motion, the cell either completely aligns with the flow direction and the membrane folds inward forming two cusps, or, it undergoes large swinging motion while deep, crater-like dimples periodically emerge and disappear. At lower bending rigidity, the breathing motion occurs over a wider range of shear rates, and is often characterized by the emergence of a quad-concave shape. The effect of the breathing dynamics on the tank-treading-to-tumbling transition is illustrated by detailed phase diagrams which appear to be more complex and richer than those of vesicles. In a remarkable departure from classical theory of nondeformable cells, we find that there exists a critical viscosity ratio below which the transition is dependent on shear rate only. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A14.00007: Red blood cell clusters in Poiseuille flow Giovanni Ghigliotti, Hassib Selmi, Chaouqi Misbah, Lassaad Elasmi We present 2D numerical simulations of sets of vesicles (closed bags of a lipid bilayer membrane) in a parabolic flow, a setup that mimics red blood cells (RBCs) in the microvasculature. Vesicles, submitted to sole hydrodynamical interactions, are found to form aggregates (clusters) of finite size. The existence of a maximal cluster size is pointed out and characterized as a function of the flow intensity and the swelling ratio of the vesicles. Moreover bigger clusters move at lower velocity, a fact that may prove of physiological interest. These results quantify previous observations of the inhomogeneous distribution of RBCs in vivo (Gaehtgens et al., Blood Cells 6 - 1980). An interpretation of the phenomenon is put forward based on the presence of boli (vortices) between vesicles. Both the results and the explanation can be transposed to the three-dimensional case. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A14.00008: Microfluidic investigation of the effects of oxidative stress on mechanotransduction in red blood cells N.F. Zeng, W.D. Ristenpart Recent work has suggested that RBCs are able to sense and respond to small changes in their environment through post translational modifications (PTMs) in membrane proteins. Because oxidative stress is an important driving force to induce PTMs, the effects of oxidative stress on membrane deformability, lipid peroxidation, and cytoskeletal/hemoglobin crosslinking have been studied extensively. However, experimental work to date on the effects of oxidative stress on RBC mechanotransduction has been limited to applied forces dissimilar to those experienced by RBCs in vivo. Here we investigate the dynamics of shear-induced mechanotransduction in RBCs subjected to varying degrees of oxidative stress by using hydrogen peroxide as a generator of oxidizing radicals. We use a microfluidic platform to impose precisely defined fluid flows that mimic in vivo conditions. The RBCs are visualized passing through a narrow constriction using high speed video at 15,000 frames per second, and quantitative hematological information including cell elongation, rotation and velocity are extracted via custom image analysis algorithms. We demonstrate that oxidative stress significantly alters the dynamic behavior of the RBCs under flow conditions, and we discuss the implications for the consequent effects on mechanotransductive vasodilatory signaling. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A14.00009: Stability of red cells flowing in a narrow tube Natalie Beams, Jonathan Freund Red blood cells are well known to line up in an orderly arrangement when forced to flow through a narrow capillary-scale round tube (diameter $\leq 8\mu$m). However, in slightly larger tubes this order can break down, resulting in apparently chaotic flow. We investigate this breakdown using a high-fidelity boundary integral solver for flowing blood cells. This solver has been validated for both the flow of organized and highly deformed cells in narrow tubes and for more random flow in larger tubes. Our studies focus on a family of cases with 8 red cells, each discretized with spherical harmonics. The cells are modeled as elastic shells enclosing a viscous fluid. Studying the development of instabilities using ad hoc perturbation techniques as well as non-normal modal analysis, we show a strong increase in instability for larger tube diameters. Increasing the cell interior viscosity is also observed to increase the amplification of perturbations. [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A14.00010: 2-D Model for Normal and Sickle Cell Blood Microcirculation Yonatan Tekleab, Wesley Harris Sickle cell disease (SCD) is a genetic disorder that alters the red blood cell (RBC) structure and function such that hemoglobin (Hb) cannot effectively bind and release oxygen. Previous computational models have been designed to study the microcirculation for insight into blood disorders such as SCD. Our novel 2-D computational model represents a fast, time efficient method developed to analyze flow dynamics, O$_2$ diffusion, and cell deformation in the microcirculation. The model uses a finite difference, Crank-Nicholson scheme to compute the flow and O$_2$ concentration, and the level set computational method to advect the RBC membrane on a staggered grid. Several sets of initial and boundary conditions were tested. Simulation data indicate a few parameters to be significant in the perturbation of the blood flow and O$_2$ concentration profiles. Specifically, the Hill coefficient, arterial O$_2$ partial pressure, O$_2$ partial pressure at 50\% Hb saturation, and cell membrane stiffness are significant factors. Results were found to be consistent with those of Le Floch [2010] and Secomb [2006]. [Preview Abstract] |
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