Numerical study on effects of liposome-encapsulated hemoglobin on blood flows at microvascular bifurcation with considering erythrocyte aggregation

Flow analysis at microvascular bifurcation after partial replacement of red blood cell (RBC) with liposome-encapsulated hemoglobin (LEH) was performed. A two-dimensional bifurcation model with a parent vessel and two daughter branches was considered. Here, we adopted the lattice Boltzmann method (LBM) for the computation of blood flow. Moreover, the immersed boundary method was employed to incorporate the fluid-membrane interaction between the flow field and deformable RBCs. The cell membrane is treated as a neo-Hookean viscoelastic material. We used Oseen approximation and calculated the force acting on LEH particles. A Morse potential was adopted to model the intercorpuscular interaction (LEH-LEH and LEH-RBC). Assuming these corpuscles distributions in the parent vessel obtained by the Poiseuille flow simulation, we conducted simulations of RBC and LEH behavior in the bifurcation flow model. When only RBCs flowed into the daughter branches with unevenly distributed flows, plasma separation occurred and the RBC flow to the lower-flow branch was disproportionately decreased. On the other hand, when the half of RBCs was replaced by isovolumic LEH particles, the biasing of RBC flow was enhanced. However, LEH particles flowed favorably into the lower-flow branch because many LEH particles within the parent vessel were suspended in the plasma layer that is impenetrable to RBCs. The biasing of the RBC flux was enhanced when the RBC aggregation was taken into account in the model. Additionally, it was clarified that the RBC aggregation-induced change of the plasma layer thickness has a marked influence on the fractional LEH flux at the microvascular bifurcation.