Stabilization of Platelet Aggregates in High Shear Rate Flows by Von Willebrand Factor*

Arterial blood vessels vary widely in geometry and flow properties. Even in high shear rate environments, when an injury occurs to the vessel wall, platelets must be recruited to prevent the loss of blood. Stenotic arteries can also give rise to structures where platelet aggregation can occur deleteriously. In both cases, the mechanically sensitive polymeric protein Von Willebrand Factor (vWF) mediates the initial deposition of platelets to the growing aggregate. We present a dynamical systems model to study the average mechanical and chemical structure of an aggregate. We consider the aggregate as a porous media whose porosity and height change as platelets deposit. The drag force imparted on the aggregate is felt by all bound platelets, affecting the rate at which platelet-platelet crosslinks break. We find that as shear rate varies, inclusion of platelet-vWF-platelet crosslinking stabilizes the aggregate not only by increasing the total number of crosslinks, but also by changing the overall structure of the aggregate to reduce the drag force per platelet. These results have implications for aggregation in stenotic regions as well as in diseases such as Von Willebrand's Disease.