Effect of fibrin(ogen) concentration on clot contraction. (A) The kinetics of clot contraction in washed platelets (∼400 000/µL) resuspended buffer containing purified fibrinogen at a final concentration of 0.5, 1.0, 2.5, and 5.0 mg/mL and clotted with 1 U/mL thrombin and 2 mM CaCl₂. (B) The extent of contraction normalized to the paired 0.5 mg/mL sample performed with the same source of platelets and fibrinogen. (C) The final extent of clot contraction observed under conditions described in (A) at 1 hour. *P < .05; **P < .01; ***P < .001.