Tensile destruction test as an estimation of partial proteolysis in fibrin clots

We report a technique devised to evaluate the effects of partial proteolysis on the mechanical characteristics of acellular non-cross-linked fibrin clots. The destruction technique applies coaxial tension on mechanically preconditioned cylindrical molded clots and measures the number of mechanical failures vs the total number of samples at a given load (2, 3, and 4 grams force). We used different plasmin concentrations (0, 0.01, 0.02, 0.04, and 0.08 U/mL) in the bathing medium to cause partial proteolysis. We monitored the fibrinolysis process by measuring the amount of protein released in the bathing medium. Our results showed no difference in the creep function in all the groups studied. We compare our technique with compaction, a commonly used mechanical technique that compresses the sample by centrifugation, and found that our technique is capable of detecting minor changes of fibrinolysis (the results of the least square fit for the destruction test at 2 grams force, as a function of plasmin concentration, has a coefficient of determination of R(2) = 0.55), while compaction did not show a statistically significant difference in the same conditions, suggesting that each individual fibrin fiber bears load only under tension. Our findings suggest that when the fibers are cleaved their capacity to withstand stress is seriously challenged; thus, in principle, tensile destruction test can detect a minimal degree of proteolysis.