Back to Departmental Colloquium: Spring 2015
Departmental Colloquium
Date: Thursday, Mar 26, 2015
Time: 4:00PM
Location: LCB 219
Michael Graham
University of Wisconsin-Madison
Title |
Collide and conquer: flow-induced segregation phenomena in blood and other multicomponent suspensions |
Abstract |
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 that is critical for the physiological responses of inflammation and hemostasis. Potential beneficial effects on hemodynamics arise from addition of high molecular weight long-chain polymer molecules known as drag-reducing additives (DRAs) to blood; one effect of these additives is the reduction of the cell- free-layer thickness. 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 flow- induced segregation phenomena in blood and other complex mixtures, using a combination of theory and direct simulations of flowing suspensions. Two specific issues are addressed here: (1) the origin of the margination phenomenon and its dependence on the relative properties of the different types of suspended particles in a mixture and (2) the effect of DRAs on the formation of the cell-free layer. A kinetic theory model based on pair collisions and wall-induced hydrodynamic migration can capture the key effects observed in direct simulations, including a “drainage transition” in which one component is completely depleted from the bulk of the flow. In the case of polymer additives, the experimentally observed thinning of the cell-free layer is reproduced in simulations and the mechanism underlying it is described. 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. |
Computational Mathematics
Applied Mathematics