Surface-dependent differences in fibrin assembly visualized by atomic force microscopy

In this report, we present differences in the process of fibrin assembly on two model surfaces, hydrophobic graphite and negatively charged mica, visualized by atomic force microscopy (AFM) under aqueous conditions. Fibrinogen, thrombin, and soluble fibrin monomers, were added sequentially into the AFM fluid system, and the fibrin assembly process was followed and recorded as time-dependent changes in the features of the surface adsorbed proteins. On each surface, individual globular domains of fibrinogen were visualized which can be represented by three overlapping ellipsoids. Thrombin displayed a single globular domain which can be represented as a prolate ellipsoid regardless of the properties of the model surfaces. On graphite, the fibrin monomers interact with thrombin-treated fibrinogen to produce short fibrin strands, which is followed by propagation into long fibrin strands. The final product was an extensive fibrin network, in which a characteristic eyelet morphology was observed. On mica, the adsorbed protein molecules maintained their monomeric state, and fibrin network assembly was not observed. The differences in fibrin assembly are believed to be surface-dependent, in which different intermolecular interactions play a major role. In particular, electrostatic interaction and hydrophobic interaction are dominant in the fibrin/mica and fibrin/graphite system respectively. The results demonstrate that both material surface properties and the nature of intermolecular interactions affect fibrin assembly.