Injectable, photoresponsive hydrogels for delivering neuroprotective proteins enabled by metal-directed protein...

Axon regeneration constitutes a fundamental challenge for regenerative neurobiology, which necessitates the use of tailor-made biomaterials for controllable delivery of cells and biomolecules. An increasingly popular approach for creating these materials is to directly assemble engineered proteins into high-order structures, a process that often relies on sophisticated protein chemistry. Here, we present a simple approach for creating injectable, photoresponsive hydrogels via metal-directed assembly of His6-tagged proteins. The B₁₂-dependent photoreceptor protein CarH_C can complex with transition metal ions through an amino-terminal His6-tag, which can further undergo a sol-gel transition upon addition of AdoB₁₂, leading to the formation of hydrogels with marked injectability and photodegradability. The inducible phase transitions further enabled facile encapsulation and release of cells and proteins. Injecting the Zn²⁺-coordinated gels decorated with leukemia inhibitory factor into injured mouse optic nerves led to prolonged cellular signaling and enhanced axon regeneration. This study illustrates a powerful strategy for designing injectable biomaterials.