Metal-free antioxidant nanozyme incorporating bioactive hydrogel as an antioxidant scaffold for accelerating bone reconstruction

Oxidative stress at bone defect sites mediates inflammation and even osteoblast apoptosis, severely hindering the repair process. While current antioxidant bone tissue engineering (BTE) scaffolds lack broad-spectrum reactive oxygen species (ROS) scavenging capability and structure-activity elucidation. Herein, we report a threedimensional nitrogen-doped carbon antioxidant nanozyme (ZIFC) derived from metal-organic frameworks, which exhibits cascading superoxide dismutase- and catalase-like activities, along with the ability to scavenge other harmful free radicals. Through the experimental studies and theoretical calculations, we reveal that the catalase-like activity arises from the synergistic catalytic interaction between graphitized pyridinic nitrogen and its adjacent carbon atom. Moreover, hybrid double network hydrogel integrated with ZIFC is utilized to construct composite scaffold (Gel/ZIFC) by 3D printing. In vivo transcriptome analysis confirms that Gel/ZIFC can rapidly activate antioxidant defense system and suppress local inflammation under oxidative stress microenvironment, thereby protecting cells from oxidative damage. Subsequently, owing to the unique osteoinductive property of carbon nanomaterials and the osteoconductive property of 3D-printed scaffold, Gel/ZIFC composite scaffold exhibits desirable bone repair efficacy. The elucidation of structure-activity relationship and therapeutic mechanism provides new insights and guidance for devising antioxidant BTE scaffolds, and demonstrates their feasibility for clinical application.