I will talk about platelet margination in tubular blood flow with a special emphasis on the effects of the red blood cell capillary number Ca (i.e. the ratio of viscous fluid to elastic membrane forces). Platelet margination is important for blood clotting: the healing process of damaged blood vessel walls is initiated by nearby platelets. Platelets should therefore be located close to the vessel wall, ideally within the layer that is free of red blood cells (cell-free layer). The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods.
It turns out that a non-diffusive radial platelet transport facilitates margination. This non-diffusive effect is important near the edge of the cell-free layer, but only for Ca > 0.2, when red blood cells are tank-treading. Platelets at Ca > 0.2 eventually reach the cell-free layer where they are effectively captured. However, platelets can escape again for Ca < 0.2.