  Little is known about mechanics underlying the interaction among platelets
during activation and aggregation. Although the strength of a blood thrombus
has likely major biological importance, no previous study has measured directly
the adhesion forces of single platelet-platelet interaction at different
activation states. Here, we filled this void first, by minimizing surface
mediated platelet activation and second, by generating a strong adhesion force
between a single platelet and an AFM cantilever, preventing early platelet
detachment. We applied our setup to measure rupture forces between two
platelets using different platelet activation states, and blockade of platelet
receptors. The rupture force was found to increase proportionally to the degree
of platelet activation, but reduced with blockade of specific platelet
receptors. Quantification of single platelet-platelet interaction provides
major perspectives for testing and improving biocompatibility of new materials;
quantifying the effect of drugs on platelet function; and assessing the
mechanical characteristics of acquired/inherited platelet defects.
