(142dc) Mechanism of Flow Induced Segregation in Blood and Other Multicomponent Suspensions

Blood is a multicomponent mixture comprising mostly of red-blood-cells (RBCs) along with trace amounts of other components like leukocytes, platelets, and circulating tumor cells (in the case of cancer). Under physiological flow conditions both the leukocytes and the platelets segregate near the walls of the blood vessel, a phenomenon commonly known as margination, while the RBCs tend to migrate away from the walls. The key physical differences between RBCs, leukocytes, and platelets are their relative size and rigidity: the leukocytes are larger than RBCs, while the platelets are smaller; both are considerably stiffer than RBCs. However, how these differences in properties lead to the observed segregation behavior is poorly understood. In this work we focus on the model system of a fluid-filled elastic capsule mixture in which individual components differ in size and rigidity. Using detailed boundary integral simulations we delineate the effect of both of these key properties on the flow induced segregation behavior and relate these to the observations of leukocyte and platelet margination in blood flow. To gain a mechanistic understanding of these results, we introduce a novel hydrodynamic-Monte Carlo simulation technique, which incorporates two of the main ingredients of flow dynamics in confined suspensions: the wall induced migration and pair collisions. In particular, the model clarifies the important role played by heterogeneous collisions, i.e. collisions between two different species in a mixture,  in the observed segregation behavior. The model is also shown to reproduce the results of the detailed boundary integral simulations, while requiring only a fraction of the latter's computational cost.  The insights and tools presented in this poster will be helpful, e.g., in designing drug delivery particles for optimal vascular targeting and for designing microfluidic devices for separating/enriching trace components of blood.