Abstract Body: Background
Extracellular vesicles (EVs) are essential mediators of intercellular communication. EVs secreted by cardiosphere-derived cells (CDC-EVs) hold promise as vectors in the context of cardiac repair and remodeling through modulation of cardiomyocyte apoptosis and the immune response following injury. Cardiac retention of CDC-EVs is a critical factor influencing their therapeutic efficacy as first-pass uptake and washout from the myocardium remains a variable. We hypothesized that loading CDC-EVs in a shear-thinning, hybrid hydrogel would provide sustained myocardial delivery and reduced EV extraction by the lungs.

Methods
The hydrogel system was constructed via a two-step approach utilizing Michael-addition reaction and host-guest complexation. This system incorporates four components: (1) an adamantane-functionalized multi-arm polyethylene glycol, (2) monosubstituted β-cyclodextrin-maleimide, (3) a thiolated hyaluronic acid, and (4) a heparin molecule containing thiol moieties. Following LAD ligation, intramyocardial injections of DiR-labeled EVs or hydrogel-encapsulated DiR-labeled EVs were performed on mice. Animals were euthanized after 24 hours and organs harvested. Whole organ biofluorescence was performed using IVIS Spectrum imaging.

Results
Hydrogel-encapsulated EVs exhibited enhanced cardiac retention 24 hours post-MI when compared with EVs without hydrogel (17 ± 4.4 vs. 3.4 ± 0.9, mean radiant efficiency as a % of dose ± SEM, p<0.01 using unpaired two-tailed t-test). Mice treated with hydrogel encapsulated EVs showed reduced EV retention in the lungs compared to controls treated with EVs alone (5.7 ± 0.9 vs. 10.6 ± 1.4, mean radiant efficiency as a % of dose ± SEM, p<0.05 using unpaired two-tailed t-test).

Conclusion
Usage of shear-thinning hydrogel as an EV delivery vehicle enhances EV retention in the heart and decreases off-target uptake of EVs following acute MI. This finding suggests that hydrogel delivery may be a promising strategy to improve the therapeutic efficacy of CDC-EVs for cardiac repair.