The whole blood clot
Human skin, when injured, is capable of carrying out self-repair to restore tissue integrity. Wound healing involves 4 overlapping processes, beginning immediately at the onset of injury with hemostasis and transitioning to inflammation, proliferation, and remodeling.
In an open wound, the healing process is initiated with the activation of the coagulation cascade, resulting in the formation of a fibrin blood clot that plugs severed blood vessels and fills in tissue discontinuity at the wound site.
The blood clot, having reestablished hemostasis, is also essential to inflammation, with its fibrin scaffold that serves as a protective, provisional extracelluar matrix (ECM) that harbors the cytokines and growth factors (interleukin, transforming growth factor-β, platelet-derived growth factor, and vascular endothelial growth factor, among others) released by the degranulation of activated platelets. The clot also recruits endothelial cells and fibroblasts, which begin to synthesize a permanent ECM at the wound bed, in addition to inducing the migration of neutrophils, and wound macrophages.
As the clot dries out and becomes a protective scab, under which tissue remodeling takes place undisturbed, the fibrin is replaced by fibronectin and hyaluronan, and the scab falls off to reveal a collagenous scar.