Cross-Stream Distribution and Dynamics of Red Blood Cells in Sickle Cell Disease

Diseased red blood cells (RBCs) in patients suffering from sickle cell disease (SCD) display substantially different physical properties than do healthy RBCs. Direct numerical simulations are performed for pressure-driven flow in a planar slit containing a binary mixture of deformable biconcave discoids and stiff curved prolate spheroids that represent healthy and sickle RBCs, respectively. The key observation in such suspensions is that the sickles exhibit a strong margination towards the walls. The deformable biconcave discoids tend to undergo a so-called tank-treading motion, while the stiff sickles behave like rigid bodies and undergo a Jeffery-like tumbling or kayaking motion. A systematic investigation of the dynamics of single sickles in free and confined shear flows further reveals that the steady-state motion of the sickles is independent of their initial orientations. The margination behavior coupled with the Jeffery-like motions of the sickles near the walls may help substantiate a recently proposed hypothesis of a mechanism for chronic complications of sickle cell disease.