Immunomodulatory hydrogel loaded with PD-L1-expressing exosomes reprograms macrophages and accelerates diabetic wound healing.

Diabetic foot ulcers (DFU), a severe complication of diabetes mellitus, present a global healthcare challenge due to high risks of limb amputation and mortality. This study developed a multifunctional hydrogel dressing, Gelatin Methacryloyl (GelMA) hydrogel loaded with interleukin-4 (IL-4)-engineered exosomes (Exos), designed to synergistically modulate immune responses and enhance angiogenesis for complete diabetic wound repair. The programmed death-ligand 1 (PD-L1)-enriched Exos were engineered via IL-4 overexpression in NIH3T3 fibroblasts. The GelMA hydrogel loaded NIH3T3 fibroblast-derived Exos with IL-4 overexpression (GelMA/ExosIL-4 hydrogel) exhibited favorable physicochemical characteristics, including a three-dimensional porous microstructure, injectability, tissue adhesion, self-healing properties, and sustained moisture retention. In vitro evaluation demonstrated biocompatibility, sustained exosome release, and enhanced viability, migration, and tube formation of human umbilical vein endothelial cells (HUVECs). In a diabetic wound model, the hydrogel significantly accelerated wound closure, promoted re-epithelialization and angiogenesis, and skewed macrophages toward anti-inflammatory M2 polarization while suppressing T-cell proliferation. These findings highlight the dual immunomodulatory and pro-angiogenic efficacy of GelMA/ExosIL-4 hydrogel, offering a promising therapeutic strategy for chronic wound management.