High glucose-primed HUVEC-derived extracellular vesicles encapsulated in microgels boost diabetic ischaemic flap regeneration via HIF-1α/VEGF pathway

Diabetic wound healing poses a major clinical challenge. One of the promising therapy, the flap transplantation surgery exhibited unsatisfactorily low flap survival due to the intertwined pathological barriers: impaired angiogenesis, excessive oxidative stress, and persistent inflammation, leading to poor tissue repair. While the therapeutic platforms based on extracellular vesicles (EVs) emerges as a promising treatment, its efficacy is often limited by the inadequate yield and rapid in vivo clearance. To address this challenge, this study developed a strategy centered on preconditioning human umbilical vein endothelial cells (HUVECs) with high glucose (HG) stress to produce HG-preconditioned extracellular vesicles (hEVs), which significantly improve production, enrich regenerative cargoes (e.g., HIF-1α, VEGF), and enhance homologous cellular internalization. The hEVs derived from HUVECs were encapsulated by microfluidically fabricated gelatin methacryloyl (GelMA) microgels to create GelMA@hEVs. The biodegradable and biocompatible GelMA microgels enabled a sustained hEVs release profile. Therefore, GelMA@hEVs exhibited significant efficacy improvement in promoting endothelial cell proliferation, migration, and tube formation critical for vascularization, mitigating reactive oxygen species, and modulating macrophage polarization toward a pro-reparative phenotype. Mechanistically, these therapeutic effects relied on activating the HIF-1α/VEGF pathway, a core axis for angiogenesis dysregulated in diabetes. In diabetic ischaemic flap models, GelMA@hEVs significantly improved flap survival, restored vascular perfusion, and facilitated tissue regeneration without systemic toxicity. Altogether, this work provides a generalizable strategy for diabetic ischaemic flap repair by combining engineered EVs as bioactive cargo with a microgel scaffold for sustained delivery, offering a promising in situ tissue engineering solution.