Sandcastle Worm Cement‐Mimicking Underwater Adhesives via Liquid–Liquid Phase Separation and Auto‐Catalyzed Network Strengthening

Achieving robust underwater adhesion remains challenging due to the interference of interfacial water and insufficient cohesion within conventional adhesives. Inspired by the sandcastle worm's cement forming via liquid-liquid phase separation (LLPS), we developed a novel class of tannic acid/polyethylene glycol/Laponite (TA/PEG/Lap, TPL) composite adhesives to effectively enhance interfacial water repulsion and underwater adhesion. TA and PEG self-assembled into a dynamic adhesive coacervate matrix via LLPS, while Laponite nanoclays were subsequently introduced as reinforcement fillers and catalysts to trigger polyphenol oxidation, thereby transforming TPL from dynamic soft gel to mechanically robust solid. Specifically, the initially self-healing TPL can adapt to the irregular surface topography by repelling interfacial water and forming adhesion, thereafter self-cure to strengthen the mechanical interlocking with irregular substrate surfaces, and eventually realize robust underwater adhesion. Leveraging the transient network reversibility and self-driven crosslinking stability, the TPL formulations can be processed into injectable, sprayable, coatable, or scaffold forms, offering robust adhesion, fault tolerance, eco-compatibility, long-term stability, fire resistance, and antibacterial activity. Overall, this work establishes a paradigm shift in bioinspired design of robust underwater adhesives and highlights the potential of TPL systems for multi-scenario and multi-functional applications, including acute hemostasis, soil fixation, infrastructure crack repair, and other underwater sealing tasks.