Deformation and clustering of red blood cells in microcapillary flows

Abstract

The shape changes and clustering of red blood cells (RBCs) under flow in cylindrical microcapillaries are studied using a triangulated surface model for the membrane and a particle-based mesoscopic simulation technique for the embedding fluid. As the flow velocity increases, the RBCs make a transition from a discocyte shape at low velocities to a parachute shape at high velocities; close to the critical flow velocity, the RBC can also be found in a transient slipper shape. The transition and critical flow velocity are examined for various capillary diameters and RBC volume fractions (hematocrit H_T). At high flow velocities and low hematocrits, the parachute-shaped RBCs can be found in clusters which are hydrodynamically stabilized. Here, the formation of a fluid vortex between neighboring cells, called bolus, develops which keeps the cells at a preferred distance. Decreasing the flow velocity towards the critical velocity, we observe an increasing frequency of drastic RBC shape fluctuations to slipper-shaped RBCs that can result in cluster breakup. These clusters resemble those seen in experiments using optical microscopy.