Answer:
Fibronectins are matrix molecules that are involved in wound contraction, cell-cell and cell-matrix interaction, cell migration, collagen matrix deposition, and epithelialization. They act as a scaffold for collagen deposition. They are produced by fibroblasts, epithelial cells, and macrophages and are found in the tissue stroma and basal lamina. They are among the first proteins laid down in the fresh wound. They bind a variety of molecules including collagen, actin, fibrin and hyaluronic acid. They become cross-linked to fibrin during wound healing and facilitate fibroblast attachment.
The ground substance or stroma is another component of the wound matrix, consisting of glycosaminoglycans (GAGS) and proteoglycans. There are four types of GAGS involved in tissue structure and wound healing - chondroitin sulfate, heparin sulfate, keratat sulfate, and hyaluronic acid. The proteoglycans appear to create a charged environment that facilitates cell mobility.
Collagen provides strength and integrity for all tissues and is a key component in all phases of wound healing. Immediately after injury, collagen comes into contact with blood and promotes platelet aggregation and activation of chemotactic factors. Later, it becomes the foundation of the wound extracellular matrix. It is synthesized by fibroblasts beginning with procollagen alpha chains. The alpha chains form a triple helical molecule, with hydroxylation of proline and lysine being important for the helix formation. Cross-linking between the chains by disulfide bonding also occurs within the cell. The procollagen is cleaved into collagen at the cell membrane.
Collagen synthesis begins at 5-7 days after wounding, and increases linearly for 2-3 weeks when it reaches a steady-state. Skin wound tensile strength peaks at 60 days, reaching 80% of the tensile strength of normal skin.