Injectable Hydrogels for Programmable Nanoparticle Release.

Injectable hydrogels represent a promising strategy for the extended release of biological molecules, thereby reducing the frequency of injections. This study introduces a novel system based on Michael addition of dextran and polyethylene glycol (PEG) polymers functionalized with oxanorbornadiene (OND) and thiol groups, respectively. Reliable control over gelation speed allows administration by injection using a simple syringe-to-syringe mixing protocol that entrains more than 95% of virus-like particle (VLP) cargo. A combination of retro-Diels-Alder and hydrolytic ester bond cleavage gives rise to programmable release of the VLPs. Different release profiles, including burst, linear, and delayed release over a two-week period, are engineered using different OND linkages, and rheological characterization shows the hydrogels to be well within the desired range of stiffness for subcutaneous use. The modular nature of this system offers a generalizable platform for developing degradable materials aimed at sustained release biomedical applications.