The first step in the inflammatory phase is the formation of a blood clot, which controls bleeding and forms a thin fibrin network, bridging the wound margins. Simultaneously, an intense inflammatory reaction develops, with the arrival of a large number of leukocytes that remove bacteria, necrotic tissue, and other debris from the wound. Additionally, macrophages secrete growth factors important for the chemotaxis of fibroblasts, smooth muscle, and endothelial cells. Almost immediately after injury, fibroblasts begin to mobilize from the deeper dermal structures and migrate toward the wound edges. Simultaneously, the cut epithelial edges begin to proliferate, with new epithelial cells accumulating at the cut edges.
The proliferation phase begins 3 to 5 days after injury. Epithelialization of an incised wound starts immediately afterward with the epithelial cells at the edges loosening their connections to each other and the basement membrane. Epithelial cells are typically able to bridge an incised and approximated wound (≤1 mm) within 48 hours. New capillaries form, bringing oxygen and nutrients to the proliferating cells and a characteristic red color to the tissue. After approximately 5 days, the fibroblasts are synthesizing collagen precursors as well as mucopolysaccharides and other glycoproteins to form the wound matrix. Collagen is secreted into this matrix and quickly polymerizes to begin to add tensile strength to the wound. The production of collagen continues for 2 to 4 weeks. During this time, there is further fibroblastic proliferation into the depth of the wound.
The third phase of healing of an incised wound is the maturation phase, which begins about 3 weeks after injury and lasts as long as 9 months after injury. During this phase, the tensile strength of the wound continues to increase, owing to the further crosslinking of collagen fibers combined with the remodeling of collagen fibers along the lines of mechanical stress, producing a stronger and more durable matrix. Typically, the maximum tensile strength of the wound is achieved at approximately 60 days and is roughly 80% of the nonincised skin.
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