Engineering and Monitoring the Sustained Release of Extracellular Vesicles from Hydrogels for In Vivo Therapeutic Applications

Extracellular vesicles (EVs) are gaining interest in regenerative medicine and biomaterials have been shown to extend EV bioavailability following delivery. Herein, the labeling of both hydrogels and EVs is reported to better understand hydrogel design for sustained EV release into tissues. Shear-thinning hydrogels are engineered using guest–host (i.e., adamantane–cyclodextrin) modifications to hyaluronic acid (GH), as well as GH hydrogels with the addition of gelatin crosslinked via transglutaminase (GH+Gel) to temporally control hydrogel properties. When labeled with a near-IR dye and injected into rat myocardial tissue, the GH+Gel hydrogel is retained (>14 days) longer than the GH hydrogel alone (≈7 days), likely due to the added gelatin network. To overcome challenges associated with common EV labeling methods, a highly versatile metabolic labeling methodology is utilized via the incorporation of N-azidoacetylmannosamine-tetraacylated during EV synthesis to introduce azide groups that can then be reacted with DBCO dyes. When injected in saline, EVs are cleared within 24 h in hearts; however, hydrogels enhance EV retention, with levels based on hydrogel degradation behavior, namely, >14 days for GH+Gel hydrogel and ≈7 days for GH hydrogel alone. These findings support the use of hydrogels in EV therapies.