The effects of the endothelial surface layer's (ESL's) hydraulic resistivity and resistance to compression on red blood cell partitioning, deformation, and penetration of the ESL*

The heterogeneous red blood cell (RBC) distribution seen in the microvasculature has important consequences for transport of materials such as oxygen, nutrients, and drugs. Such heterogeneity is due, in part, to nonuniform partitioning of RBCs at microvascular bifurcations where higher flow downstream branches tend to claim a disproportionately high number of RBCs compared to the low flow branch. RBC distribution heterogeneity is also influenced by the presence of an endothelial surface layer (ESL), a layer on the order of 1 micron thick that coats the vessel wall. While many studies have considered RBC dynamics at bifurcations and many others have considered ESL effects on flow, none have considered both. To better understand how the ESL may affect partitioning, we constructed a computational model of RBCs passing one at a time through a bifurcation lined with an ESL. RBCs are modeled as viscoelastic networks immersed in Stokes flow while the ESL is modeled as a porous media that resists compression. We found that decreasing the ESL's hydraulic resistivity and/or its resistance to compression generated more nonuniform partitioning. In addition, because experiments have shown evidence that RBC deformation and adhesion may play important roles in various pathologies (e.g. cardiovascular disease and thrombosis), we also considered how ESL properties affected RBC deformation and penetration of the ESL. We found that decreasing the ESL's hydraulic resistivity and/or its resistance to compression increased RBC penetration of the ESL and, usually, decreased RBC deformation. We will also share preliminary results on how varying ESL properties affect RBC interactions with each other as they pass through a bifurcation. While all results are limited to very low hematocrits and a somewhat specific setting, they provide a strong start towards more fully characterizing ESL-RBC interactions.