(498b) The Effects of Suspending Fluid Viscoelasticity on Red Blood Cell Dynamics

Intravenous infusions of solutions of drag-reducing polymers (DRPs) in minute quantities has been found to have beneficial effects in a number of acute and chronic animal disease models. While the addition of DRPs to blood flows in vitro has been observed to induce significant hemodynamic effects, the exact mechanism of their effects is unknown. Previous hemodynamic studies have found that the dynamics of red blood cells (RBCs) in blood flows is strongly associated with the shape changes the RBCs undergo, which in turn depends on the stresses exerted on the RBCs by the flow. Past simulations of blood flows have modeled RBCs as capsules in Newtonian fluid flows, with predictions of RBC shape changes and dynamics in good agreement with experiment observations. However, the presence of DRPs makes the suspending fluid exhibit non-Newtonian behavior, which might affect the stresses experienced by RBCs in the flow, and the resultant RBC shapes and dynamics. In this study, we perform direct numerical simulations of red blood cells (RBCs) suspended in non-Newtonian fluids. An immersed boundary algorithm known as the Immersed Finite Element Method (IFEM) is used to accurately determine the internal forces in the solid domain. This scheme does not require costly re-meshing and is able to incorporate non-linear viscoelasticity in the fluid domain. The internal force calculation in the solid domain in the IFEM is coupled with a finite volume based incompressible fluid solver, both of which are massively parallelized for distributed memory architectures. We investigate the effects of viscoelasticity of the suspending fluid on single-RBC dynamics in shear flow, and the effects of viscoelasticity and channel confinement on the deformation and velocity of RBCs in pressure-driven channel flow. We observe fluid elasticity leads to decreased deformation of RBCs in shear flow but increased deformation in the pressure–driven flow, and investigate the resultant distribution of principal stresses in the membrane and polymer stresses in the flow fields. We also investigate the effects of fluid elasticity on the collective dynamics of a suspension of multiple red blood cells in duct flow as a model for the effect of intravenous infusions of DRPs on flow in blood vessels.