  Blood flow in sickle cell disease (SCD) can substantially differ from normal
blood flow due to significant alterations in the physical properties of the red
blood cells (RBCs). Chronic complications, such as inflammation of the
endothelial cells lining blood vessel walls, are associated with SCD, for
reasons that are unclear. Here, detailed boundary integral simulations are
performed to investigate an idealized model flow flow in SCD, a binary
suspension of flexible biconcave discoidal fluid-filled capsules and stiff
curved prolate capsules that represent healthy and sickle RBCs, respectively,
subjected to pressure-driven flow in a planar slit. The key observation is
that, unlike healthy RBCs that concentrate around the center of the channel and
form an RBC-depleted layer (i.e. cell-free layer) next to the walls, sickle
cells are largely drained from the bulk of the suspension and aggregate inside
the cell-free layer, displaying strong margination. These cells are found to
undergo a rigid-body-like rolling orbit near the walls. Furthermore, the
additional shear stress on the walls induced by the presence of marginated
cells is computed. Compared to the small fluctuations in wall shear stress for
a suspension of healthy RBCs, large local peaks in wall shear stress are
observed for the binary suspensions, due to the proximity of the marginated
stiff cells to the walls. As endothelial cells are known to mechanotransduce
physical forces such as aberrations in shear stress and convert them to
physiological processes such as activation of inflammatory signals, these
results may aid in understanding mechanisms for endothelial dysfunction
associated with SCD.
