A Two-phase mixture model of platelet aggregation.

We present a two-phase model of platelet aggregation in coronary-artery-sized blood vessels. The model tracks the number densities of three platelet populations as well as the concentration of a platelet activating chemical. Through the formation of elastic bonds, activated platelets can cohere with one another to form a platelet thrombus. Bound platelets in a thrombus move in a velocity field different from that of the bulk fluid. Stresses produced by the elastic bonds act on the bound platelet material. Movement of the bound platelet material and that of the background fluid are coupled through an interphase drag and an incompressibility constraint. The relative motion between bound platelets and the background fluid permits intraclot transport of individual platelets and activating chemical, allows the bound platelet density to reach levels much higher than the platelet density in the bulk blood, and allows thrombus formation to occur on a physiological timescale, all of which were precluded by our earlier single phase model. Computational results from the two-phase model indicate that through complicated fluid-structure interactions, the platelet thrombus can develop significant spatial inhomogeneities and that the amount of intraclot flow may greatly affect the growth, density, and stability of a thrombus.