Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D5: Biofluids: Red Blood Cells |
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Chair: Michael Plesniak, George Washington University Room: 3008 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D5.00001: Quantitative imaging of RBC suspensions in bifurcating microchannels Joseph Sherwood, David Holmes, Efstathios Kaliviotis, Stavroula Balabani The local velocity and concentration characteristics of both red blood cells (RBCs) and suspending medium flowing in a bifurcating microchannel were measured simultaneously. An imaging technique involving alternate bright field and laser light illumination was employed to capture both RBC and fluorescent PIV images of human healthy blood, flowing through a sequentially bifurcating 50 micrometer square PDMS microchannel. The acquired images were further processed using PIV algorithms to yield the velocity distribution of RBCs and suspending medium while the brightfield images also provided data on hematocrit distribution and cell-depleted layer. Various flow rates, aggregation states and proportions of flow entering each branch were considered. Asymmetric hematocrit distributions were quantified around the bifurcations and found to be enhanced by aggregation. The data were compared with computational fluid dynamics studies of continuous Newtonian and Non-Newtonian fluids in order to elucidate the impact of the two-phase nature of the flow, particularly RBC aggregation. The work is currently being extended to examine the role of RBC properties on microhemodynamics and the implications for disease. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D5.00002: Red blood cell dynamics under high shear rates: in vitro experimental investigations Luca Lanotte, Cyrille Claudet, Jean-Marc Fromental, Manouk Abkarian The full understanding of red blood cell (RBC) dynamics is an intriguing challenge that involves transversal branches of science. Despite the potential impact that it could have on medical research and industrial applications, a systematic study of RBCs response under significant shear rates (200$<$$\dot{\gamma}$$<$3000 s$^{-1}$) is still lacking in scientific literature. In this work, in vitro experiments of microfluidics and rheometric measurements are combined to investigate mechanical properties of highly sheared RBCs. By high-speed microscopy, we investigated RBCs flow through rectangular channels in unconfined conditions. In parallel, RBCs suspensions of different hematocrits have been processed by a cone-plate rheometer and subsequently observed by optical microscopy to ensure reliability to the experimental results. The outcomes of both microfluidics and rheological approaches clearly show the presence of strongly deformed shapes, in addition to the expected elongated ellipsoids. Plausible explanations for formation and stability of these striking highly deformed shapes are here proposed. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D5.00003: Influence of red blood cell clustering on phase separation in capillary networks Thomas Podgorski, Celine Boucly, Gwennou Coupier We investigate the flow of red blood cell suspensions in microfluidic bifurcations and capillary networks. At strong degrees of confinement, such as those encountered in the microcirculation, phase separation takes place at bifurcations of the network, leading to strong heterogeneities and fluctuations of the hematocrit (blood cell concentration). We highlight the influence of the mechanical properties of cells : an increase of membrane or cytoplasm rigidity, as can happen in pathologies such as sickle cell disease tends to reduce the phase separation. The influence of the attractive interaction between cells, that leads to clustering (rouleau formation) was also investigated by varying the concentration of macromolecules in the solution (dextran or fibrinogen). We show that hydrodynamic stresses in bifurcations can lead to rupture of clusters at a critical speed which increases with interaction energy. Overall, the clustering phenomenon tends to increase phase separation and hematocrit heterogeneities. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D5.00004: Effect of viscoelasticity and RBC migration phenomena in stenotic microvessels Yiannis Dimakopoulos, Alexandros Syrakos, Georgios Georgiou, John Tsamopoulos This study deals with the numerical simulation of the hemodynamics in stenotic microvessels. The blood flow in microvessels differs significantly from that in large arteries and veins, because the Red Blood Cells (RBCs) are comparable in size with the radius of the microvessels and, consequently, local effects such as cell interaction and migration are more pronounced. In terms of complexity of the flow, viscoelasticity along with stress-gradient induced migration effects have a more dominant role, which exceeds the viscous, inertial and transient effects. Recently, a non-homogeneous viscoelastic model has been proposed by Moyers-Gonzalez et al. (2008), which can accurately predict the Fahraeus effects. We developed a numerical algorithm for the time-integration of the set of differential equations that arise from the coupling of momentum, mass, and population balances for RBCs and aggregates with the constitutive laws for both species. The simulations show that a cell-depleted layer develops along the vessel wall with an almost constant thickness. Along this layer, the shear stresses are almost Newtonian because of the plasma, but the normal stresses that are exerted on the wall are high due to the contribution of the individual RBCs and rouleaux. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D5.00005: Red Blood Cell Hematocrit Influences Platelet Adhesion Rate in a Microchannel Andrew Spann, James Campbell, Sean Fitzgibbon, Armando Rodriguez, Eric Shaqfeh The creation of a blood clot to stop bleeding involves platelets forming a plug at the site of injury. Red blood cells indirectly play a role in ensuring that the distribution of platelets across the height of the channel is not uniform -- the contrast in deformability and size between platelets and red blood cells allows the platelets to preferentially marginate close to the walls. We perform 3D boundary integral simulations of a suspension of platelets and red blood cells in a periodic channel with a model that allows for platelet binding at the walls. The relative rate of platelet activity with varying hematocrit (volume fraction of red blood cells) is compared to experiments in which red blood cells and platelets flow through a channel coated with von Willebrand factor. In the simulations as well as the experiments, a decrease in hematocrit of red blood cells is found to reduce the rate at which platelets adhere to the channel wall in a manner that is both qualitatively and quantitatively similar. We conclude with a discussion of the tumbling and wobbling motions of platelets in 3D leading up to the time at which the platelets bind to the wall. [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D5.00006: Twisting of Red Blood Cells Entering a Constriction Nancy Zeng, William Ristenpart Most work on the dynamic response of red blood cells (RBCs) to hydrodynamic stress has focused on linear velocity profiles. Relatively little experimental work has examined how individual RBCs respond to pressure driven flow in more complex geometries, such as the flow at the entrance of a capillary. Here, we establish the mechanical behaviors of healthy RBCs undergoing a sudden increase in shear stress at the entrance of a narrow constriction. We pumped RBCs through a constriction in an ex vivo microfluidic device and used high speed video to visualize and track the flow behavior of more than 4,400 RBCs. We show that approximately 85\% of RBCs undergo one of four distinct modes of motion: stretching, twisting, tumbling, or rolling. Intriguingly, a plurality of cells ($\sim$30\%) exhibited twisting (rotation around the major axis parallel to the flow direction), a mechanical behavior that is not typically observed in linear velocity profiles. We examine the mechanical origin of twisting using, as a limiting case, the equations of motion for rigid ellipsoids, and we demonstrate that the observed rotation is qualitatively consistent with rigid body theory. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D5.00007: Intermittency and Synchronized Tumbling and Tank-treading in Red Blood Cell Dynamics in Steady and Oscillatory Shear Flows Prosenjit Bagchi, Daniel Cordasco Red blood cells are known to exhibit a variety of rich and complex dynamics when subjected to a shear flow. Of particular interest is the intermittent behavior that is characterized by coexistence of the tumbling motion, and the tank-treading motion. Several reduced-order theoretical models assuming fixed cell shape emerged that either supported or rejected the possibility of such dynamics, although no full-scale computer simulation of deformable cells has conclusively observed such dynamics. Here we present the first computational evidence of intermittent dynamics of red blood cells in steady and oscillatory shear flows. Our model fully resolves the cell deformation taking in to consideration all essential properties of the cell membrane and internal fluid, and hence, contradicts the notion that intermittency is suppressed in deformable cells. For the intermittent dynamics, we observe sequences of tumbling interrupted by swinging, as well as sequences of swinging interrupted by tumbling. In the synchronized dynamics, the tumbling and membrane rotation occur simultaneously with integer ratio of rotational frequencies. These dynamics are shown to be dependent on the stress-free state of the cytoskeleton, and are explained based on the cell membrane energy landscape. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D5.00008: Effect of Strain Rate on the Mechanical Behavior of Red Blood Cells Entering a Constriction Jordan Mancuso, William Ristenpart Most work on the effect of hydrodynamic stress on red blood cells (RBCs) has focused on linear velocity profiles. Microfluidic devices have provided a means to examine the mechanical behavior of RBCs undergoing a sudden increase in shear stress at the entrance of a constriction, with previous work primarily focused on a fixed constriction taper angle and corresponding hydrodynamic strain rate. Here we investigate the effect of strain rate on the stretching dynamics exhibited by RBCs as they enter a microfluidic constriction. Systematic variations in the constriction taper angle allow the strain rate to be precisely tuned, and high speed video yields precise measurements of the corresponding RBC deformations. We demonstrate that maximal RBC stretching occurs at an intermediate constriction taper angle, despite the lower magnitude of the strain rate. We interpret the results in terms of the time integral of the elongational strain rate, and we discuss the implications for shear-induced mechanotransduction. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D5.00009: Red Blood Cell Dispersion in Morphologically-Inspired Microfluidic Models of Alveolar Capillary Networks Hagit Stauber, Rami Fishler, Dan Waisman, Josue Sznitman Microfluidics is frequently used to study blood flow characteristics in microcapillary networks and investigate transport properties of red blood cells (RBC). To date, most of microfluidic studies have not focused on the specific morphology of alveolar capillary networks (ACN), with characteristic length scales of $\sim$ 5 $\mu$m, known to give rise to organ-specific blood flow characteristics. To better understand flow characteristics and dispersion of RBCs in ACNs, we have designed morphologically-inspired microfluidic models of alveolar capillary beds at a real scale. We fabricate lab-on-chip devices featuring confined staggered pillar arrays with diameters of $\sim$ 10 $\mu$m, representative of the dense ACN capillary meshes. Devices are supplied by an external reservoir containing whole blood at various hematocrit levels, to mimic RBC perfusion (Re\textless 0.01) within alveolar capillaries. Whole-field velocity patterns are imaged (PIV) and RBC motion is tracked using particle tracking velocimetry (PTV) from which dispersion coefficients are extracted. Our efforts are aimed at delivering a real-scale quantitative description of the pulmonary ACN microcirculation. [Preview Abstract] |
Sunday, November 23, 2014 4:12PM - 4:25PM |
D5.00010: ABSTRACT WITHDRAWN |
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