Injectable hydrogels, as a class of highly hydrated soft materials, are of interest for biomedicine due to their precise implantation and minimally invasive local drug delivery at the implantation site. The combination of in situ gelation ability and versatile therapeutic agent/cell loading capabilities makes injectable hydrogels ideal materials for drug delivery, tissue engineering, wound dressing and tumor treatment. In particular, the stimuli-responsive injectable hydrogels that can respond to different stimuli in and out of the body (e.g., temperature, pH, redox conditions, light, magnetic fields, etc.) have significant advantages in biomedicine. Here, we summarize the design strategies, advantages, and recent developments of stimuli-responsive injectable hydrogels in different biomedical fields. Challenges and future perspectives of stimuli-responsive injectable hydrogels are also discussed and the future steps necessary to fulfill the potential of these promising materials are highlighted.

Therapeutic nanoparticles (NPs) have shown their potential for biomedical applications (e.g., drug delivery). In this study, we report the synthesis of a bottlebrush block copolymer by ring opening metathesis polymerization (ROMP) and fabrication of pH-responsive NPs (denoted as BNPs) by self-assembly of an innovative bortezomib (BTZ) prodrug. The cleavage of borate ester bonds at acidic pH results in the release of BTZ from BNPs. Moreover, BNPs can inhibit cell and tumor growth without significant side effects.