Mesenchymal stem cell-derived small extracellular vesicles-loaded GelMA microspheres enhance diabetic wound healing by promoting M2 macrophage polarization through p38 MAPK inhibition

Diabetic foot ulcers (DFUs) represent a serious complication of diabetes, typically exhibiting persistent inflammation and impaired tissue repair. Although small extracellular vesicles derived from mesenchymal stem cells (MSC-sEVs) possess therapeutic potential for diabetic wound repair by modulating inflammatory responses, their regulatory mechanisms and limited <i>in vivo</i> retention remain challenges. Here, we developed MSC-sEVs-loaded gelatin methacryloyl (GelMA) microspheres (sEVs@MS) as a therapeutic dressing for diabetic wounds. MSC-sEVs were characterized and found to induce M1-to-M2 polarization in lipopolysaccharide (LPS)-treated bone marrow-derived macrophages (BMDMs), significantly downregulating iNOS and TNF-α while upregulating CD206 and IL-10 <i>in vitro</i>. RNA sequencing analysis identified <i>Mapk14</i> and <i>Nfkbia</i> as key regulators within the p38 MAPK signaling pathway, with their expression levels significantly decreased following MSC-sEVs treatment. Consistent with these findings, western blot confirmed that MSC-sEVs effectively inhibit the p38 MAPK pathway with decreased phosphorylation of p38 and MAPKAPK2. To achieve sustained delivery of MSC-sEVs, we fabricated lyophilized GelMA microspheres and loaded the vesicles using a rehydration-induced swelling strategy. <i>In vivo</i> experiments demonstrated that both sEVs and sEVs@MS treatments enhanced M2 macrophage polarization and reduced inflammation, whereas sEVs@MS prolonged MSC-sEVs retention at the wound site for 7 days, thereby promoting wound closure by day 28. Histological analysis further confirmed that sEVs@MS improved epidermal regeneration and collagen deposition, ultimately accelerating wound repair in diabetic rats. Collectively, these findings establish sEVs@MS as an effective therapeutic strategy for diabetic wounds treatment.