Fibrin gel structure and clotting time.

Liquid permeation studies of fibrin gels, which were formed in the presence of thrombin (Fibrin II) and in the presence of Batroxobin (Fibrin I), showed that those gels have distinctly different flow properties. For both gels the permeability coefficient (Ks) and average pore size varied depending on the conditions for gel formation. Low pH and ionic strength favour high Ks and large pore sizes, whereas high pH and ionic strength produce gels with low Ks and small pore sizes. Parallel turbidity studies showed correlations between the optical properties of the gels and permeation data. Of particular importance was the finding that the clotting time (Ct) is directly related to Ks of the final gels. Thus events preceding gel formation determine the gel structure. It is proposed that the average lengths of polymers formed prior to gelatin varies directly with Ct. Shorter polymers give infinite net works (gels) which are tight and longer polymers provide for formation of infinite net works which are more porous. At the same Ct, the net work formed with thrombin is, over a wide range of Ct, tighter than that formed with Batroxobin. It was also found that Ks is inversely related to the fibrin concentration (C) in the gels. The ratio Ct/C (permeability index) is thus an important determinant for the gel structure. The applicability of the permeability index to whole blood as a predictive test for thromboembolic and bleeding conditions is discussed.