Breaking Through Hydration Layer Barrier: A Novel Ultra‐Strong Underwater Hydrogel Adhesive Toward Full‐Thickness Cartilage Repair

Abstract The absence of blood vessels and nerves in cartilage severely restricts its self‐healing capacity. Meanwhile, the inherent anti‐adhesive nature of articular cartilage matrix further complicates the integration of implanted scaffolds, leading to common issues such as scaffold displacement, reduced mechanical stability, impaired cell migration, and insufficient tissue regeneration. These challenges collectively render articular cartilage repair a formidable global issue. To address this, a groundbreaking ultra‐strong underwater hydrogel adhesive specifically designed for articular cartilage repair is introduced. This adhesive is formulated from a polyglycolic acid, tannic acid and tyrosine hydrogel system, significantly enhanced by the incorporation of anhydrous CaSO 4 and ZnSO 4 . Drawing inspiration from the “pinning” effect of nanoparticles in ceramics, the anhydrous CaSO 4 absorbs water, penetrates the hydration layer, and securely anchors polymer chains to the substrate. The coordination bonds between metal ions and polymer groups, combined with multiple bonding mechanisms, endow the adhesive with remarkable anti‐swelling and strong adhesion properties. This adhesive achieves an impressive underwater adhesion strength of 6.8 MPa on iron substrates, effectively overcoming the anti‐adhesive properties of cartilage. It successfully repairs full‐thickness cartilage defects without the need for exogenous factors or cells, offering a novel and promising approach for next‐generation underwater adhesives with extensive biomedical applications.