A multifunctional injectable hydrogel co-delivering GDF6 and MnO₂ nanozymes alleviates intervertebral disc...

Intervertebral disc degeneration (IDD) is a primary cause of low back pain, characterized by cell loss, extracellular matrix (ECM) degradation, and a harsh microenvironment with excessive oxidative stress, creating an urgent need for regenerative therapies. This study aimed to develop and evaluate a multifunctional injectable hydrogel (Gel@MnO₂/GDF6) co-delivering growth differentiation factor 6 (GDF6) for anabolic stimulation and manganese dioxide (MnO₂) nanozymes for reactive oxygen species (ROS) scavenging to treat IDD. The MnO₂ nanorods and the chitosan-arginine/oxidized dextran-based hydrogel were synthesized and characterized, demonstrating sustained GDF6 release and pH-responsive degradation. In vitro, Gel@MnO₂/GDF6 protected nucleus pulposus (NP) cells from H₂O₂-induced oxidative stress by reducing ROS, upregulating antioxidant enzymes, promoting anabolic ECM metabolism (increasing Aggrecan and Collagen II while decreasing ADAMTS-4 and MMP-13), reducing key inflammatory cytokine expression (TNF-α and IL-6), and activating the Smad pathway. In vivo, intra-discal injection of Gel@MnO₂/GDF6 into a rat IDD model significantly attenuated disc degeneration over 12 weeks, as evidenced by improved histological scores, preserved disc height and hydration on radiological and MRI assessments, restoration of ECM protein homeostasis, reduced cellular apoptosis, mitigated inflammatory marker expression, and activated Smad pathway, with these therapeutic effects being superior to those achieved with hydrogels containing only MnO₂ or GDF6. Importantly, all tested hydrogel formulations, including Gel@MnO₂/GDF6, demonstrated good systemic biocompatibility. These findings collectively demonstrate that the multifunctional Gel@MnO₂/GDF6 hydrogel effectively promotes intervertebral disc regeneration by concurrently mitigating oxidative stress and fostering an anabolic, anti-inflammatory microenvironment, validating its potential as a promising therapeutic method for IDD.