Orbital Drift, Stress-Free Configuration, and Shape Memory of Red Blood Cells in Shear Flo

Three-dimensional numerical simulations using an immersed boundary/front-tracking method are utilized to study some novel dynamics of red blood cells (RBCs) in shear flow beyond the well-known rigid-body-like tumbling (TB) and fluid-like tank-treading (TT). These computational simulations are the first to address the following problems: (a) Orbital drift. It is shown that red blood cells may exhibit a precessing motion around the vorticity axis or a kayaking motion about the shear plane. Unlike rigid ellipsoids in Stokes flow, it is observed that deformable cells reorient their axis toward the vorticity axis or toward the shear plane depending on the initial shape, shear rate, and viscosity ratio. (b) Stress-free configuration. We consider the possibility that the resting biconcave membrane of the RBC may not be stress-free. It is shown that the assumption of stress-free shape can have a profound effect on the cell deformation and dynamics at low viscosity ratios representative of many in vitro studies. (c) Intermittency. We present the first evidence of intermittent sequences of TB and TT for deformable cells. The intermittent dynamics occur in an irregular sequence while in the synchronized dynamics TB and TT occur simultaneously with integer ratio of rotational frequencies. (d) Dynamics in oscillating shear. A comprehensive analysis of RBC motion in oscillating shear flow is performed and the existence of a chaotic motion is shown. (e) Shape memory. Lastly, we present the first 3D computational study to resolve the shape memory of RBCs in which membrane elements return to their original locations as well as global recovery of the biconcave shape after flow cessation. The timescale of recovery is orders of magnitude longer than that The timescale of recovery is orders of magnitude longer than that observed in simple stretch-relaxation experiments and is also strongly dependent on RBC stress-free configuration. The shape memory is shown to exist even when the membrane is displaced normal to the plane of shear flow.