Effect of RBCs on the generation of contractile force. (A) Whole blood samples were incubated with 200 μM blebbistatin or vehicle control, and the contractile stress generated by the platelet-fibrin meshwork was measured as normal (perpendicular) stress between the rheometer plates. (B) Samples were reconstituted to the same platelet concentration (∼200 000/µL) in the absence or following the addition of RBCs to attain volume fraction of 40%. (C) The dynamics of contractile stresses generated by the clots formed in whole blood and PRP. Because the samples in panel (B) differ in platelet concentrations, the contractile stress generated in the whole blood and PRP clots was normalized to the platelet count obtained by a complete blood count (ie, presented as normal stress per platelet).