Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L16: Biofluids: Blood Transport |
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Chair: Jonathan Freund, University of Illinois at Urbana-Champaign Room: 28B |
Monday, November 19, 2012 3:35PM - 3:48PM |
L16.00001: The flow of red cells through spleen-like filtering slits Jonathan Freund It is widely understood that the spleen is the principal site in the body for removal of old red blood cells. As they age during their approximately 120 day lifetimes, red blood cells have increasingly slow relaxation times. This mechanical change is potentially the identifying characteristic for filtering in the spleen, which is thought to occur in particularly narrows slit-like passages ($< 1\mu$m$\; \times \sim 7 \mu$m). The mechanism of the filtering, however, is unclear. Most simply, increasing cell viscosity with age would slow, rather than stop, cell passage. Similarly, `testing' the cells via significant strains during each passage through the spleen might be expected to accelerate aging through fatigue-like mechanisms. Our detailed simulations of red cells passing trough a model slit geometry suggest that increasing cell viscosity can fundamentally change its passage. The results are suggestive of a bifurcation, such as in the onset of instability, with increasing cell interior viscosity. Higher viscosities (or elastic capillary numbers) are seen in cases to lead to a fingering-like instability, which might be expected to severely damage aged cells, leading to their removal, while leaving younger low viscosity cells relatively unstressed. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L16.00002: Dynamics of monocytes flowing in a model pulmonary capillary bed Annie Viallat, Jules Dupire The dynamics of blood cells in the pulmonary bed is an issue for tissue perfusion and host defense. The capillary segments in the lungs are smaller than the size of leukocytes so that most of them change their shape to enter and travel through a capillary pathway. During inflammation, changes in the cytoskeleton of leukocytes may stiffen them, resulting in their massive stop and sequestration within lung capillaries. However, due to difficulties of in vivo studies, little is known about the dynamics of leukocytes in the microcirculation and about the coupling between cellular rheology, capillary geometry and flow. We report the dynamics of monocytes (THP-1 cell line) flowing under constant pressure drop in a periodic network of capillaries that mimics the capillary bed. The analysis of cell entrance in the first segment allows the estimation of effective cellular elasticity, viscosity and cortical tension. Cells then present an unsteady regime, with a non-periodic trajectory, a stretching of their average shape and an increase of their velocity. This regime is interpreted from a parameter equivalent to the Deborah number of the system. Finally, a periodic regime is reached with alternatively left and right turns at capillary bifurcations. The reduced cell velocity is governed by an effective friction coefficient between the cell and the capillary walls. Both transient and final regimes depend on cell deformability, as shown by modifying the cortical actin of the cytoskeleton. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L16.00003: The effect of polymer additives on flowing cells through capillaries Lailai Zhu, Luca Brandt It has been suggested that low concentration of long-chain polymer potentially cause benefit in hemodynamics. The effect of polymer additives on blood flow at low Reynolds number is not well studied, albeit well-known for drag reduction in turbulent flow. We adopt a novel general geometry Ewald-like method (GGEM) recently developed\footnote{P. Pranay, \textit{et al}. Physics of Fluids, 22, 123103, 2010} to study the fluid-structure interaction. GGEM method can be regarded as an accelerated implementation of boundary integral method, or a variant of immersed boundary method in the Stokesian regime. We perform three dimensional simulations to study the effect of polymer additives on the dynamics of a periodic file of red blood cells (RBCs) through a capillary tube. Fluid motion is solved by spectral element method and solid mechanics of cell membrane by spectral method based on spherical harmonics. Brownian dynamics is used for the polymer molecules. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L16.00004: Transport of diseased red blood cells in the spleen Zhangli Peng, Igor Pivkin, Ming Dao A major function of the spleen is to remove old and diseased red blood cells (RBCs) with abnormal mechanical properties. We investigated this mechanical filtering mechanism by combining experiments and computational modeling, especially for red blood cells in malaria and sickle cell disease (SCD). First, utilizing a transgenic line for 3D confocal live imaging, in vitro capillary assays and 3D finite element modeling, we extracted the mechanical properties of both the RBC membrane and malaria parasites for different asexual malaria stages. Secondly, using a non-invasive laser interferometric technique, we optically measured the dynamic membrane fluctuations of SCD RBCs. By simulating the membrane fluctuation experiment using the dissipative particle dynamics (DPD) model, we retrieved mechanical properties of SCD RBCs with different shapes. Finally, based on the mechanical properties obtained from these experiments, we simulated the full fluid-structure interaction problem of diseased RBCs passing through endothelial slits in the spleen under different fluid pressure gradients using the DPD model. The effects of the mechanical properties of the lipid bilayer, the cytoskeleton and the parasite on the critical pressure of splenic passage of RBCs were investigated separately. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L16.00005: Analysis of Red Blood Cell Behavior in a Narrow Tube Haruki Hosaka, Toshihiro Omori, Yohsuke Imai, Takami Yamaguchi, Takuji Ishikawa Red Blood Cell (RBC) is a main component of blood accounting for 40 percent in volume, and enclosed by a twodimensional hyper elastic membrane. RBCs strongly influence rheological properties and mass transport of blood. The deformation of RBCs in capillary and at narrowing is also important in considering mechano-transduction of RBCs and hemolysis, though it has not been clarified in detail. Thus, in this study, we investigated the behavior of a RBC flowing in a narrow tube. To carry out the fluid-structure interaction analysis, we coupled a boundary element method to analyze the velocity of the internal and external fluid with a finite element method to analyze the deformation of the membrane. The boundary element method has good calculation accuracy and its computational cost is low because three-dimensional flow filed can be calculated by a two-dimensional computational mesh. The background flow in a tube is pressure-driven Poiseuille flow. Additionally, to reduce the computational time, we implemented massive parallel computation by using GPUs. The results show that the deformation of a RBC is strongly affected by the Capillary number, which is the ratio of viscous force to the elastic force, radius of the tube, and the initial orientation. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L16.00006: Mechanistic insights into flow induced segregation in blood and other multicomponent suspensions Amit Kumar, Michael Graham Blood is a multicomponent suspension comprising mostly of red-blood-cells (RBCs) along with trace amounts of leukocytes and platelets. Under normal flow conditions both the leukocytes and the platelets segregate near the vessel walls, a phenomenon commonly known as margination. The key physical differences between RBCs, leukocytes, and platelets are their relative size and rigidity: leukocytes are larger than RBCs and platelets smaller, but both are considerably stiffer than RBCs. In this work we study the blood flow problem using a model system of fluid-filled elastic capsule mixtures. Using boundary integral (BI) simulations we delineate the effect of size and rigidity on the segregation behavior, and relate these to the observations of leukocyte and platelet margination in blood. Further, we introduce a novel Monte Carlo simulation technique, which incorporates two of the key transport mechanisms in confined suspensions: the wall-induced migration and hydrodynamic pair collisions. The model accurately reproduces the results of BI simulations and provides a mechanistic understanding of the margination phenomena. In particular, it clarifies the important role of heterogeneous pair collisions (collisions between two different species) on the observed margination behavior. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L16.00007: ABSTRACT WITHDRAWN |
Monday, November 19, 2012 5:06PM - 5:19PM |
L16.00008: Depletion induced clustering of red blood cells in microchannels Christian Wagner, Mathias Brust, Thomas Podgorski, Gwennou Coupier The flow properties of blood are determined by the physical properties of its main constituents, the red blood cells (RBC's). At low shear rates RBC's form aggregates, so called rouleaux. Higher shear rates can break them up and the viscosity of blood shows a shear thinning behavior. The physical origin of the rouleaux formation is not yet fully resolved and there are two competing models available. One predicts that the adhesion is induced by bridging of the plasma (macromolecular) proteins in-between two RBC's. The other is based on the depletion effect and thus predicts the absence of macromolecules in-between the cells of a rouleaux. Recent single cell force measurements by use of an AFM support strongly the depletion model. By varying the concentration of Dextran at different molecular weights we can control the adhesions strength. Measurements at low hematocrit in a microfluidic channel show that the number of size of clusters is determined by the depletion induced adhesion strength. [Preview Abstract] |
Monday, November 19, 2012 5:19PM - 5:32PM |
L16.00009: Off-plane motion of a non-spherical capsule in simple shear flow Toshihiro Omori, Takuji Ishikawa, Yohsuke Imai, Takami Yamaguchi Dynamics of a capsule and a biological cell in fluid flow is now of great interest in chemical engineering and bioengineering. In this study, we numerically investigated the motion of a spheroid capsule in simple shear flow including a red blood cell type biconcave disk. The membrane of a capsule was modeled by a two-dimensional hyperelastic material, and its large deformation was solved by a finite element method. The motion of internal and external liquids was estimated as a Stokes flow and solved by a boundary element method. The results showed that the orientation of a spheroid capsule is variant under time reversal, though that of a rigid spheroid is invariant. The final orientation of a spheroid capsule over a long time duration tends to converge to a certain direction depending on the shear rate despite initial placement with random orientation. These results can be utilized for a particle alignment technique and form a fundamental basis of the suspension mechanics of capsules and biological cells. [Preview Abstract] |
Monday, November 19, 2012 5:32PM - 5:45PM |
L16.00010: Shear induced diffusion in a red blood cell suspension Thomas Podgorski, Xavier Grandchamp, Aparna Srivastav, Gwennou Coupier In the microcirculation, blood exhibits an inhomogeneous structure which results in the well know Fahraeus-Lindqvist effect : the apparent viscosity decreases when the diameter of the capillary decreases due to the formation of a marginal cell depletion layer (known as plasma skimming). This structure is a consequence of several phenomena, which include i) the migration of cells aways from walls due to lift forces and gradients of shear and ii) shear induced diffusion due to collisions and interactions among cells. We investigated these phenomena through experiments in simple shear and microchannel flows, with dilute suspensions of vesicles and blood cells. Pairwise interactions between suspended objects result in non-linear and flow-dependent diffusion, whose properties have been measured in different experiments for vesicles and blood cells. The injection of a sheet of concentrated blood cell suspension in a microchannel with a rectangular cross-section allows, through the measurement of its widening along the channel, to measure the diffusivity of blood cells, both in the local plane of shear and in the vorticity direction. [Preview Abstract] |
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