Simplified Models for Coarse-Grained Hemodynamics Simulations

Human blood can be approximated as a dense suspension of red blood cells in plasma. Here, we present two models we recently developed to investigate blood flow on different scales: in the first part of the paper we concentrate on describing individual cells or model systems such as vesicles with high resolution in order to understand the underlying fundamental properties of bulk hemodynamics. Here, we combine a lattice Boltzmann solver for the plasma with an immersed boundary algorithm to describe the cell or vesicle membranes. This method allows a detailed study of individual particles in complex hydrodynamic situations. Further, this model can be used to provide parameters for a more coarse-grained approach: in that second approach we simplify much further than existing particulate models. We find the essential ingredients for a minimalist description that still recovers hemorheology. These ingredients include again a lattice Boltzmann method describing hydrodynamic long range interactions mediated by the plasma between cells. The cells themselves are simplified as rigid ellipsoidal particles, where we describe the more complex short-range behavior by anisotropic model potentials. Recent results on the behaviour of single viscous red blood cells and vesicles in confined flow situations are shown alongside with results from the validation of our simplified model involving thousands or even millions of cells.