An injectable, self-healing hyaluronic acid-based hydrogel as a dual-responsive depot for extracellular vesicle delivery.

Extracellular vesicles (EVs) are promising therapeutic agents for regenerative medicine, but their clinical translation is hampered by poor retention at the target site. Hydrogels offer a promising strategy for localized EV delivery; however, achieving controlled release and cytocompatibility remains challenging. Here, an injectable, self-healing hyaluronic acid (HA)/poly(ethylene glycol) (PEG) composite hydrogel was developed under mild aqueous conditions via hydrazone crosslinking between adipic dihydrazide-modified HA (HA-ADH) and aldehyde-terminated PEG (PEG-ALD) through Schiff-base chemistry. The resulting dynamic network exhibited dual responsiveness, with accelerated degradation under mildly acidic conditions (pH 5.5) and rapid enzymatic disassembly in the presence of hyaluronidase. Hydrogel properties were tuned by varying the final polymer concentration and the aldehyde-to-hydrazide (CHO/NH2) molar ratio (0.15, 0.25, and 0.50), enabling control over swelling behavior, stability, and post-shear network recovery. The intermediate formulation was selected for EV release studies. Human dermal mesenchymal stromal cell-derived EVs (MSC-EVs) were retained within the hydrogel network, with release occurring only following hydrogel hydrolysis. In contrast, enzymatic degradation triggered rapid EV release within 3 days. Preservation of EV integrity following release was supported by the detection of the surface marker CD81, atomic force microscopy (AFM) imaging, and the presence of soluble protein cargo such as VEGF-A. Overall, the HA/PEG system may function as an EV-protective depot responsive to microenvironmental changes for localized therapeutic delivery.