The effect of the endothelial surface layer on cell–cell interactions in microvessel bifurcations

Red blood cells (RBCs) carry oxygen and make up 40–45% of blood by volume in large vessels down to 10% or less in smaller capillaries. Because of their finite size and large volume fraction, they are heterogeneously distributed throughout the body. This is partially because RBCs are distributed or partitioned nonuniformly at diverging vessel bifurcations where blood flows from one vessel into two. Despite its increased recognition as an important player in the microvasculature, few studies have explored how the endothelial surface layer (ESL; a vessel wall coating) may affect partitioning and RBC dynamics at diverging vessel bifurcations. Here, we use a mathematical and computational model to consider how altering ESL properties, as can occur in pathological scenarios, change RBC partitioning, deformation, and penetration of the ESL. The two-dimensional finite element model considers pairs of cells, represented by interconnected viscoelastic elements, passing through an ESL-lined diverging vessel bifurcation. The properties of the ESL include the hydraulic resistivity and an osmotic pressure difference modeling how easily fluid flows through the ESL and how easily the ESL is structurally compressed, respectively. We find that cell–cell interaction leads to more uniform partitioning and greatly enhances the effects of ESL properties, especially for deformation and penetration. This includes the trend that increased hydraulic resistivity leads to more uniform partitioning, increased deformation, and decreased penetration. It also includes the trend that decreased osmotic pressure increases penetration.