Injectable chondroitin sulfate-grafted self-antioxidant hydrogels ameliorate nucleus pulposus degeneration against overactive inflammation

Overactive inflammatory cascade accompanied by oxidative stress in the nucleus pulposus exacerbates intervertebral disc degeneration (IVDD). Hydrogels have been demonstrated to be promising in treating IVDD, yet they remain less efficacious in the case of anti-inflammation associated with antioxidation. In this study, we designed an injectable self-antioxidant hydrogel (HA/CS) with enhanced inflammation inhibitory performance for delivering chondroitin sulfate (CS) with well-documented anti-inflammatory property to treat IVDD. The hydrogel was rapidly formed via dynamic boronate ester bonding between furan/phenylboronic acid and furan/dopamine-modified hyaluronic acid (HA), and mechanically enhanced by Diels-Alder reaction-induced secondary crosslinking, partial dopamine groups of which contribute to grafting phenylboronic acid-modified CS (CS-PBA). This hydrogel exhibits favorable injectability, mechanical property, and pH-responsive delivery behavior. The dopamine moiety endows the hydrogel with efficient antioxidative property. By sustained delivery of CS, the HA/CS hydrogel is well competent to inhibit inflammatory cytokine expression and maintain anabolic/catabolic balance in an inflammation-simulated environment. Most importantly, the HA/CS hydrogel significantly ameliorates degeneration in a puncture-induced IVDD rat model. The self-antioxidant HA/CS hydrogel designed in this work may serve as a novel and promising therapeutic platform for IVDD.