(248f) Complex Dynamics of Vesicles and Red Blood Cells in Viscous Flows

Red blood cells in shear flow can tank-tread, tumble, or "swing" (tank-treading accompanied by oscillations in the inclination angle). I will present a model that quantitatively describes this behavior. The analysis accounts for the fact that the membrane is deformable, incompressible, and resistant to bending and shearing. In shear flows, the theory shows that a closed lipid membrane (vesicle or red cell) deforms into a prolate ellipsoid, which tumbles at low shear rates, and swings at higher shear rates. The amplitude of the oscillations decreases with shear rate. In quadratic flows, the theory predicts that red blood cells always migrate towards the flow centerline unlike drops, whose direction of migration depends on the viscosity ratio. These results improve understanding of blood rheology in the microcirculation.