2012 Young Researchers Workshop:
Kinetic Description of Multiscale Phenomena

Segregation phenomena in flowing suspensions of deformable particles: toward an understanding of cell and particle dynamics in blood flow

Michael Graham

University of Wisconsin, Madison

Blood is a suspension of particles of various shapes, sizes and mechanical properties and the distribution of these particles during blood flow is important in many contexts. Red blood cells (RBCs) tend to migrate toward the center of a blood vessel, leaving a so-called cell-free layer at the vessel wall, while white blood cells (WBCs) and platelets are preferentially found near the walls, a phenomenon called margination. This phenomenon is critical for the physiological responses of inflammation and hemostasis. Additionally, the segregation properties of WBCs, platelets, and RBCs can be employed for their separation or detection in microfluidic devices. Finally, drug delivery particles in the bloodstream will also undergo segregation phenomena – the influence of these phenomena on the efficacy of such particles is unknown. This talk describes efforts to gain a systematic understanding of margination. Direct hydrodynamic simulations of a binary suspension of stiff and flexible capsules are performed and a master equation model that incorporates the key particle transport mechanisms in suspensions -- wall-induced hydrodynamic migration and shear-induced pair collisions -- is proposed. Stochastic simulations of this model allow the relative importance of these two mechanisms to be directly evaluated and thereby reveal that, at least in the dilute case, margination is largely determined by the nature of pair collisions between different types of particles during flow. Having in hand an understanding of the mechanisms underlying these phenomena now allows more rational approaches to development of quantitative models of them and processes that exploit them. This knowledge will also lead to a better understanding of the consequences of these phenomena in physiology and medicine.