Shear-induced platelet activation. Platelets in diluted PRP or whole blood subjected to fluid shear in a cone-plate viscometer abruptly undergo activation above a critical wall shear stress of 8-10 Pa (arrow). Inset shows that this activation is a strong function of the mechanical force applied on the platelet GP Ibα by the VWF that is bound to it. Here, doubling media viscosity more than doubles the extent of cell activation (adapted from Shankaran et al⁷¹ ).