Light Scattering Studies of Fibrin Clots1

Hemostasis depends largely on the conversion of fibrinogen to fibrin, catalyzed by the enzyme thrombin. In recent years, there has been considerable advance of knowledge of the formation of thrombin from its various precursors. However, a comparatively small amount of effort has been directed toward studies of the physical nature of the fibrin clot as a possible guide in the better understanding of hemostatic mechanisms in health and disease. In 1947 Ferry and Morrison (1, 2) converted purified human fibrinogen to fibrin under various conditions of pH, ionic strength, and fibrinogen concentration, and they measured such properties of the clot as opacity, rigidity, friability, and so forth and proposed two general structures: "The fine and the coarse clot." The fine clot showed small deviation from Rayleigh's law which states that the opacity is inversely proportional to the fourth power of the wavelength, but the coarse clot showed considerable departure from this proportion. They stated: "In a solid structure, such as fibrin clot, it is impossible to calculate explicitly the size and shape of structural units from opacity measurements." The larger strands have been studied by direct microscopic observation (3, 4) but the average size strand is too narrow for the limits of optical resolution. The diameter of the fibrin strands has also been measured by the electron microscope (5-8). This instrument, however, has the inherent objection of drying the clot with collapse of the three dimensional network. In the studies to be reported herein, light scatter-