A study of fibrin clot structure under various ionic conditions using stereoscopic IVEM images

Abstract

Fibrin clots are formed by the conversion of fibrinogen into fibrin monomers which assemble to produce two-stranded protofibrils that aggregate to form fibers. These fibers may also aggregate laterally with other fibers to form larger fiber bundles. Investigations of fibrin clot structures under various ionic conditions using SEM showed dramatic differences in fiber morphology and clot structure. Fibrin clots formed under various ionic conditions were investigated by the examination of stereoscopic IVEM images. This technique provides greater depth discrimination and higher resolution images of clot ultrastructure. Details of fiber association and branching are of particular interest.Purified human fibrinogen was prepared at a concentration of 0.5 mg/ml in 0.4M, 0.2M, and 0.05M buffers (0.05M Tris-HCI, pH 7.4, with 2mM CaCl2). Fibrinogen solutions were mixed with thrombin to a final concentration of 0.3U/ml and aiiquots placed onto Formvar and carbon coated grids. After clotting for 1 hr. at room temperature, clots were fixed with 3% glutaraldehyde in 0.1 M Na-cacodylate buffer, pH 7.2, for 5 min. Grids were kept constantly moist to avoid collapse or syneresis.