  The multi-cellular hydrodynamic interactions play a critical role in the
phenomenology of blood flow in the microcirculation. A fast algorithm has been
developed to simulate large numbers of cells modeled as elastic thin membranes.
For red blood cells, which are the dominant component in blood, the membrane
has strong resistance to surface dilatation but is flexible in bending. Our
numerical method solves the boundary integral equations built upon Green's
functions for Stokes flow in periodic domains. This fluid dynamics video is an
example of the capabilities of this model in handling complex geometries with a
multitude of different cells. The capillary branch geometries have been modeled
based upon observed capillary networks. The diameter of the branches varies
between 10-20 mum. A constant mean pressure gradient drives the flow. For the
purpose of this fluid dynamics video, the red blood cells are initiated as
biconcave discs and white blood cells and platelets are initiated as spheres
and ellipsoids respectively. The hematocrit as well as the average velocity
vary in the different branches due to the nonlinear interactions of the cells.
Physiologically, red blood cells enclose a concentrated solution of hemoglobin
which is about five times more viscous than plasma but for this simulation the
viscosity of the fluid inside and outside of red blood cells have been taken to
be the same.
