SEM images of fibrin clots formed using high and low thrombin concentrations before and during lysis using tPA. (A-B) The structure of fibrin₅ and fibrin₁₀₀ formed at 5 and 100nM thrombin, respectively. Insets are areas from panels A and B at higher magnification to show more detail of the fibrin fiber structure present in each clot. (C-D) The same kind of fibrin but after 10 minutes of lysis after the addition of tPA to the surface of the clot. (C) Characteristic fibrin aggregate structures in fibrin₅ that are not formed in fibrin₁₀₀.