Fibrin binding isotherms in the presence and absence of ultrasound. Equilibrium binding to fibrin of t-PA at a single concentration was determined from individual perfusion experiments as in Fig 1. One perfusion experiment generated a single point for binding in either the absence (▵, ○, □; -----) or presence (▴, •, ▪; _____) of ultrasound. (A) Surface-immobilized fibrin. (B) Non-crosslinked fibrin. (C) Crosslinked fibrin.