ULTRASOUND REVERSIBLY DISAGGREGATES FIBRIN FIBERS

Ultrasound accelerates fibrinolysis in vitro and in vivo, primarily th rough non-thermal mechanisms including cavitation. We have previously observed that ultrasound reversibly increases flow through fibrin gels , a property primarily determined by the structure of the fibrin matri x. Therefore, the effect of ultrasound on the ultrastructure of fibrin gels was examined using scanning electron microscopy. Non-crosslinked fibrin gels were fixed and prepared for microscopy before, during and after exposure to 1 MHz ultrasound, and quantitative analysis of fibe r population density and diameter was performed, Gels exposed and fixe d in the presence of ultrasound exhibited an increase in density of 65 +/- 26% (mean +/- SD) at 4 W/cm(2) (p < 0.000001) accompanied by a de crease in fiber diameter of 27 +/- 9% (p < 0.000001). Gels fixed 15 mi n following ultrasound exposure showed no significant change in either density or diameter compared to unexposed gels, indicating that the u ltrasound-induced change in fiber structure was reversible. Factor XII I-crosslinked fibrin gels exhibited no change in population density or diameter when exposed to ultrasound. These results indicate that ultr asound exposure causes reversible disaggregation of uncrosslinked fibr in fibers into smaller fibers, an effect that may alter flow resistanc e and create additional binding sites for fibrinolytic components, imp roving fibrinolytic efficacy.