Injectable melatonin-loaded carboxymethyl chitosan (CMCS)-based hydrogel accelerates wound healing by reducing inflammation and promoting angiogenesis and collagen deposition

Carboxymethyl chitosan (CMCS)-based hydrogels have antibacterial activity, and have shown the abilities of preventing wound infection, promoting cell proliferation, accelerating collagen deposition, and stimulating hyaluronic acid formation during wound healing. As a hormone produced by the pineal gland in humans and animals, melatonin promotes skin wound healing by regulating the release of inflammatory mediators and accelerating the proliferation and migration of cells, angiogenesis, and collagen deposition. However, the combined effects of CMCS and melatonin on wound healing remain unclear. Injectable CMCS-based hydrogels containing melatonin were prepared, and their healing effects were evaluated using a full-thickness cutaneous wound model in rats. Compared with the control and the hydrogel with no melatonin groups, the melatonin-loaded hydrogel significantly increased the percentage of wound closure, promoted the proliferation of granulation tissue and re-epithelialization, and accelerated collagen deposition. Additionally, the melatonin-loaded hydrogel promoted angiogenesis and vascular endothelial growth factor receptor protein expression and increased the expression of cyclooxygenase-2 and inducible nitric oxide synthase. The melatonin-loaded hydrogel also markedly increased the expression of collagen III, α-smooth muscle actin, and transforming growth factor-β1 proteins and reduced collagen I expression. These results suggest that the melatonin-loaded hydrogel promoted granulation tissue formation and accelerated wound healing by reducing inflammation and promoting angiogenesis and collagen deposition.