In this work, we developed novel stimuli-responsive injectable hydrogels composed of a highly biocompatible cartilage acellularized matrix (CAM) and a water-soluble cross-linker containing a diselenide bridge by using ultrafast norbornene (Nb)-tetrazine (Tz) click chemistry. The cross-linking reaction between the Nb groups of the CAM and Tz groups of the cross-linker evolved nitrogen gas and resulted in injectable hydrogels with highly porous structures. The synthesized hydrogels demonstrated high drug loading efficiencies (up to 93%), good swelling ratios, and useful mechanical properties. The doxorubicin (DOX)-loaded hydrogels released minimal amounts of DOX in the simulated physiological medium; however, sustained release of DOX was detected under reducing conditions, revealing more than 90% DOX release after 96 h. Interestingly, the indocyanine green (ICG)-incorporated hydrogels produced reactive oxygen species upon exposure to NIR light and exhibited burst release (>50% DOX release) of DOX during the first 4 h, followed by a sustained release phase. In vitro cytocompatibility tests showed that the synthesized CAM-Nb and hydrogels are essentially nontoxic to HFF-1 fibroblast cells and human colorectal adenocarcinoma cells (HT-29), indicating their excellent bioorthogonality and biocompatibility. Furthermore, DOX-loaded and DOX + ICG-loaded hydrogels inhibited the metabolic activities of HT-29 cells after GSH or NIR exposure and induced antitumor effects similar to those of free DOX. Therefore, these biocompatible and reduction-responsive injectable hydrogels, which exhibited on-demand drug release after NIR exposure, could be promising candidates for minimally invasive local delivery of cancer therapeutics.
