How does the motion of oblate spheroid and red blood cells impact platelet margination and thrombosis - a dynamical system perspective

Under arterial blood flow conditions, red blood cells (RBCs) migrate away from the walls and platelets marginate to the RBC-free layer formed near the walls. Platelet margination increases the near-wall platelet concentration contributing to high-shear thrombus growth leading to myocardial infarction and stroke. Here we show that a dynamical view of particle motion in shear flow provides a deeper understanding of the mechanism underlying platelet margination or segregation of any hard particle suspended in a concentration of soft deformable capsules, such as RBCs. In the special case of zero particle Reynolds number (Re_p =0) neutrally buoyant rigid particles rotate along a well-defined closed orbit (Jeffery, 1922), and deformable capsules, such as RBCs, tumble in a periodic state. However, in the presence of inertia, the particle motion can be more complex. In case of nonspherical rigid particles (such as platelets), several rotational (periodic) states and a steady state have been identified in previous studies. We note that the final equilibrium state of a rigid nonspherical particle with increasing the fluid inertia is the steady state through a saddle-node bifurcation we identified long ago (Aidun et al., 1998, 2000). RBCs also reach a steady state with tank treading motion. The tumbling periodic motion of the RBC at low shear, the steady tank-treading motion at higher shear and interaction of rigid platelet motion are explored to gain insight in the mechanism of platelet margination.