(162e) Red Blood Cell Suspensions With Polymer Additives: Orientation, Migration and Margination Dynamics

In recent experimental studies, it has been shown that introducing drag reducing polymers (DRPs) to blood in nanomolar concentration has many beneficial physiological effects, including the prevention of lethality from hemorrhagic shock in animals. In micro-channel experiments with suspensions of red blood cells (RBCs), DRPs have been shown to reduce cell free layer thickness and affect the orientation of the cells. The underlying mechanisms for these phenomena are not understood. In the present study, we investigate the dynamics of RBCs in Newtonian fluids and in dilute solutions of DRPs in microcirculation. Cell membranes are modeled with the Yeoh strain energy function and an energy penalty for bending. Polymer molecules are modeled as bead-spring chains with finitely extensible nonlinearly elastic springs. Three dimensional simulations are performed with a Stokes flow formulation of the immersed boundary method for the RBCs, combined with Brownian dynamics for the polymer molecules. We find that the cell-free layer thickness is substantially reduced near wall with addition of polymer, while elongation of RBCs and their alignment with flow direction is significantly enhanced. The wall shear stress decreases with increase in capillary number and is reduced in presence of polymers. The wall normal migration velocity of single RBC is found to decrease by adding polymer. The combined effect of reduced migration velocity and increased alignment with flow can explain the paradoxical behaviour of reduced flow resistance even with reduction in cell free layer as observed in experimental work. These predictions are in qualitative agreement with experiments.