Superspreading and ultra-infiltrative coacervate mediates strong underwater adhesion on hydrated and lipidic substrates.

Developing adhesives with robust underwater adhesion to diverse substrates, particularly highly hydrated and lipidic substrates, remains a major challenge. Inspired by the tough adhesion of barnacles on marine creatures, here we report a dilution-resistant and superspreading coacervate to mediate robust underwater adhesion by enabling interfacial infiltration and intertwining. Conjugation of terminal butyl groups to poly(propylene glycol) (PPG) triggers liquid-liquid phase separation of the aqueous solution and formation of PPG coacervate driven by the hydrogen bonding and hydrophobic interactions. The simple coacervate shows distinctive superspreading properties to facilitate interfacial wetting, infiltration and formation of intertwined interfaces on both the hydrated and lipidic substrates and concentrates the loaded hydrophilic curing agents to form a robust underwater adhesive by rapid in situ photocuring. The coacervate-based adhesive demonstrates strong underwater adhesion to diverse substrates, including highly hydrated and lipidic substrates with multiscale porosity and in complex aqueous environments. Potential applications of this adhesive are validated by robust adhesion-mediated hydrogel and/or organogel assemblies and effective sealing of underwater leakages and tissue perforations.