Fig. 1: Optical system used to follow and quantify thrombin-induced formation and contraction of a fibrin clot and kinetics of platelet-driven fibrin clot contraction.

a A PRP sample pre-activated by thrombin (80 μl) was placed into a plastic cuvette pre-lubricated with a detergent to prevent sticking to the walls and allowed to clot and contract, followed by the photographic registration of the dynamic clot size (left). The serial clot images were converted to a kinetic curve, which shows the extent of clot contraction as a function of time (right). The clot contraction kinetics were characterized by the slope of the kinetic curve (reflecting the rate of clot contraction) and the final extent of contraction at 20 min after addition of thrombin. b Experimental kinetic curves of thrombin-induced clot contraction in platelet-rich plasma containing normal (blue, 450,000/µl), reduced (black, 100,000/µl), and elevated (red, 1,000,000/µl) platelet counts. c, d Comparative averaged numbers for the final extent of clot contraction (c) and the slope of the kinetic curves reflecting the rate of clot contraction (d) at various platelet counts. Results are presented as mean ± SEM (\(n=\) 3). e, f Representative scanning electron micrographs of clots from the same PRP sample (450,000 platelets/µl) showing a fibrin-platelet meshwork before (e) and after (f) contraction. Scale bars are 15 µm.