Gelatin Methacryloyl Hydrogel Encapsulating CiMECs-Derived Extracellular Vesicles Ameliorates Lactation Function via Alleviating Mammary Oxidative Stress.

Background: Postpartum hypogalactia is a prevalent obstetric complication worldwide, closely associated with excessive oxidative stress and impaired antioxidant defense in mammary tissue. Current hormone-based therapies carry endocrine disruption risks, while natural antioxidant bioactive agents such as extracellular vesicles (EVs) are largely limited by rapid in vivo clearance and poor tissue retention. Methods: We constructed an injectable gelatin methacryloyl (GelMA) hydrogel system to encapsulate chemically induced mammary epithelial cell-derived EVs (CiMECs-EVs) and systematically evaluated their antioxidant and lactogenic activities via multi-omics analysis, cellular functional assays and a bromocriptine-induced murine hypogalactia model. Results: CiMECs-EVs induced a functional mammary epithelial-like phenotype in fibroblasts in a dose-dependent manner with functional cargo enriched in glutathione metabolism and redox-regulatory miRNAs. The GelMA matrix protected EV integrity and enabled sustained release, and the composite system significantly ameliorated mammary duct structure and lactation function in vivo with specific mammary tropism and no systemic toxicity, outperforming free EV treatment. Conclusions: This study presents a safe protein biomacromolecule-based antioxidant delivery platform that effectively restores mammary redox balance and antioxidant defenses, providing a promising non-hormonal therapeutic strategy for postpartum hypogalactia.