Friction-adaptive hydrogel coating for mechanical-immune synergy in ligament-to-bone integration

The long-term success of anterior cruciate ligament (ACL) reconstruction depends on the stable integration between artificial grafts and host bone. Despite their favorable mechanical strength, polyethylene terephthalate (PET) artificial ligaments often suffer from micromotion-induced fibrosis and persistent foreign body reactions (FBR), which together hinder osteointegration. Here, we develop a dual-network hydrogel coating with time-staged local immunomodulatory capability, enabling functional "mechano-immune" synergy at the graft-bone interface. Catechol-functionalized hyaluronic acid (HAMA-DOP) forms strong adhesive interactions with PET through π-π stacking, hydrogen bonding, and reversible covalent bonds. Subsequent oxidative crosslinking into a dense quinone-based secondary network enhances shear resistance and fatigue durability, while supporting self-healing. Pluronic F127 diacrylate (PF127-DA) introduces a thermoresponsive structure allowing the hydrogel to transition from injectable fluid at 4 °C to a stable gel at 37 °C, enabling localized and phase-specific release of celecoxib (CXB). This facilitates early suppression of inflammation and sustained promotion of regeneration. In vivo studies reveal a dose-dependent regulatory effect of CXB, where low-dose delivery promotes M2 macrophage polarization, H-type vessel formation, and bone bridging, while high doses impair immune homeostasis and osteointegration. This work establishes a robust, biologically responsive interface strategy, advancing the design of innovative coatings for enhanced outcomes in artificial ligament integration.