“Two-Dimensional Computational Models of Red Blood Cell Motion through Microvessel Bifurcations and the Effects of Flexibility”

ABSTRACT
The motions of isolated red blood cells through diverging microvessel bifurcations are simulated using two-dimensional computational models. Two cases are considered: a rigid disk, and a flexible particle that incorporates the viscoelasticity, volume preservation, and structural rigidity of the red blood cell membrane and cytoskeleton. In each case, a symmetric bifurcation with constant flow rates in the branches is considered.  Both models show that the trajectories of cell centers of mass may deviate significantly from the background flow streamlines. The largest deviations occur for cells that start close to the wall of the parent vessel on the side opposite to the branch with higher flow. In such cases, the cell may enter the low-flow branch even when the background flow streamline corresponding to the initial position of the cell center of mass enters the highflow branch. For the rigid disk model, this behavior arises from the perturbation to the flow caused by the particle obstructing the entrance to the low-flow branch. The behavior is weaker for the flexible particles because of two effects: flexible particles migrate towards the center of the flow upstream of the bifurcation, and flexible particles tend to cause less of a perturbation to the flow near the entrance to the low-flow branch because they obstruct the entrance less. These results, when combined with information about the upstream distribution of red blood cells approaching a bifurcation, can be used to predict the partition of hematocrit as a function of flow partition in diverging bifurcations.