Extracellular vesicles (EVs) derived from mesenchymal stromal cells (MSCs) have emerged as promising agents for tissue engineering and regenerative medicine strategies, offering cell-free paracrine effects to promote tissue repair e.g. myocardial infarction (MI). However, conventional EV administration and controlled deliver methods – specifically for cardiac therapies such as intra-myocardial or intravenous injection – are limited by low cardiac retention, potential tissue injury, and clinical translation challenges [1,2].
We developed a in situ crosslinkable, visible-light gelatin methacryloyl (GelMA) and poly-vinyl alcohol-tyramine (PVA-Tyr) hydrogel platform using ruthenium/sodium persulfate (Ru/SPS) photoinitiator system [1,3,4,5] for minimally invasive delivery of EVs and/or covalently bound growth factors (e.g. VEGF) [2]. This hydrogel system physically entrapped EVs, allowing controlled release via diffusion and enzymatic degradation in GelMA or hydrolytic degradation in PVA-Tyr hydrogels [3,5]. MSC-derived EV characterization, in vitro release kinetics, and bioactivity were assessed, followed by in vivo evaluation for retention, tissue penetration, and cardiac repair efficacy in an MI mouse model. Injection-free sprayable GelMA containing EVs was in situ crosslinked with visible light to form a cardiac patch directly on infarcted heart surface.
Incorporation of EVs did not alter GelMA crosslinking efficiency, mechanical properties, or degradation. Over 70% of EVs were released from hydrogels within 72 hours, demonstrating initial burst and sustained release profiles. Released EVs promoted cardiomyocyte proliferation, reduced apoptosis, and stimulated angiogenesis in vitro. In vivo imaging showed significantly improved cardiac retention and deep myocardial penetration of EVs using the GelMA delivery system, compared to EVs alone. Mice treated with EV-laden GelMA demonstrated markedly reduced scar size, increased viable myocardium, enhanced cellular proliferation and angio-myogenesis four weeks post-MI.
Our hydrogel delivery strategy enables localized, injection-free administration of EVs in situ, enhancing therapeutic retention and efficacy without secondary tissue damage. This in-situ light-crosslinkable approach provides a practical and translatable platform for tissue repair, with significant potential to advance EV-based therapies into clinical practice.