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.