<P> Myofibroblasts are attracted by fibronectin and growth factors and they move along fibronectin linked to fibrin in the provisional ECM in order to reach the wound edges . They form connections to the ECM at the wound edges, and they attach to each other and to the wound edges by desmosomes . Also, at an adhesion called the fibronexus, actin in the myofibroblast is linked across the cell membrane to molecules in the extracellular matrix like fibronectin and collagen . Myofibroblasts have many such adhesions, which allow them to pull the ECM when they contract, reducing the wound size . In this part of contraction, closure occurs more quickly than in the first, myofibroblast - independent part . </P> <P> As the actin in myofibroblasts contracts, the wound edges are pulled together . Fibroblasts lay down collagen to reinforce the wound as myofibroblasts contract . The contraction stage in proliferation ends as myofibroblasts stop contracting and commit apoptosis . The breakdown of the provisional matrix leads to a decrease in hyaluronic acid and an increase in chondroitin sulfate, which gradually triggers fibroblasts to stop migrating and proliferating . These events signal the onset of the maturation stage of wound healing . </P> <P> When the levels of collagen production and degradation equalize, the maturation phase of tissue repair is said to have begun . During maturation, type III collagen, which is prevalent during proliferation, is replaced by type I collagen . Originally disorganized collagen fibers are rearranged, cross-linked, and aligned along tension lines . The onset of the maturation phase may vary extensively, depending on the size of the wound and whether it was initially closed or left open, ranging from approximately 3 days to 3 weeks . The maturation phase can last for a year or longer, similarly depending on wound type . </P> <P> As the phase progresses, the tensile strength of the wound increases . Collagen will reach approximately 20% of its tensile strength after 3 weeks, increasing to 80% by 12th week . The maximum scar strength is 80% of that of unwounded skin . Since activity at the wound site is reduced, the scar loses its red appearance as blood vessels that are no longer needed are removed by apoptosis . </P>

Which phase of healing begins about 3 weeks after injury