Melatonin@Exosome hydrogel composed of chitosan and hyaluronic acid: A promising dressing for wound healing based on exosome therapy.

Wounds pose a significant challenge to both healthcare and the economy, as current therapies often fail to address the complex biology of healing. Exosomes derived from fetal tissue, enriched with regenerative microRNAs and proteins, have demonstrated strong potential in promoting wound repair. Melatonin is an indoleamine with multiple effects, including antioxidant and immunomodulatory activities. It has been shown to promote tissue regeneration; however, it degrades rapidly and has low bioavailability. This study investigates the potential of melatonin-loaded fetal tissue-derived exosomes (MEL@EXO) combined with a pH-responsive, biocompatible hydrogel composed of chitosan, polyvinylpyrrolidone (PVP), hyaluronic acid (HA), and glycerin to accelerate full-thickness wound healing. Fetal tissue-derived exosomes were isolated from Wistar rat fetal tissues using differential centrifugation and PEG-induced extraction. Melatonin was encapsulated by electroporation. Exosomes had the expected size, globular shape, stability, and high melatonin-loading efficiency. The hydrogel was prepared by gradually adding PVP to chitosan dissolved in citric acid under constant stirring, followed by the incorporation of HA and glycerin. The hydrogel showed a pH-responsive sol-gel transition and porous architecture, enabling sustained exosome release. Cytotoxicity evaluation on Human Dermal Fibroblast (HDF cell line) confirmed that the MEL@EXO hydrogel and its components exhibited no cytotoxic effects. Furthermore, the hemolysis test revealed no significant hemolysis, confirming the biocompatibility of the composite. In vivo, MEL@EXO hydrogel accelerated wound closure compared to the control and single-component groups. Histological studies revealed that wounds treated with MEL@EXO were undergoing re-epithelialization, thick collagen deposition, and angiogenesis. These findings support the potential of the MEL@EXO hydrogel as a robust and versatile platform for full-thickness wound healing.