Schematic of the optical analyzer system. (A) Blood samples were added to the cuvette and allowed to clot. The cuvette was placed in the thermostat and exposed to light every 15 seconds, and images were recorded using a charge-coupled device (CCD) camera. (B) Images of blood clots during the process of contraction. (C) Data on clot size were compiled into a time course (kinetic) curve (solid line) with the following parameters extracted: lag time – time to 95% relative clot size (a), AUC (b), and final degree of contraction (c). The original curve of kinetics is segregated to the 3 parts (phase 1, phase 2, and phase 3) determined by assessing the local maximum and minimum of the instantaneous first derivative (dashed). Phase 1 shows the initial exponential phase of contraction; k₁ is the rate constant associated with this phase of contraction. Phase 2 shows the middle linear region of contraction; k₂ corresponds to the slope or rate of contraction in this region. Phase 3 shows the final phase of contraction, an exponential phase, and k₃ corresponds to rate constant at which this decay occurs. Scanning electron microscopy was used to visually compare the ultrastructures of contracted blood clots in platelet-rich plasma (PRP) (D) and whole blood (E). Note that in PRP (D) fibrin fibers radiate from platelet aggregates and form bundles that likely propagate tension produced by the contracting platelets. In whole blood (E), the regular platelet-fibrin meshwork is partially impaired by RBCs that change the ability of fibrin to propagate the contractile force generated by platelets.