Schematic representation of the consecutive steps of fibrin polymerization. The figure shows the following steps: (1) the enzymatic release of fibrinopeptides from fibrinogen, the formation of monomeric fibrin-containing exposed knobs, and the partial dissociation of the αC regions; (2) the self-assembly of monomeric fibrin via knob-hole interactions and the formation of half-staggered 2-stranded fibrin oligomers; (3) the lateral aggregation of protofibrils (fibrin oligomers made of 20 to 25 monomers) promoted by homophilic αC-αC-interactions within and between protofibrils, including the formation of αC-polymers; (4) the packing of protofibrils into a fiber with a 22.5-nm periodic cross-striation due to the half-staggered molecular structure and regular paracrystalline arrangement; and (5) the fibrin network formation due to the branching of fibers by either of 2 mechanisms.