Efficient Wet Adhesion through Mussel-Inspired Proto-Coacervates

Adhesion underwater is a major challenge. Mussel-inspired complex coacervates functionalized with L-3,4-dihydroxyphenylalanine (L-DOPA) are proposed for underwater adhesives through versatile chemistry of DOPA, however, simple, efficient, controllable, and nontoxic procedures to harness them are still under investigation. In this study, inspired from the mussel byssus formation process, coacervate adhesives are formed underwater by simple injection of an acidic proto-coacervate of DOPA functionalized polyelectrolytes on underwater surfaces. The proto-coacervate is initially an acidic liquid, it increased in pH due to water diffusion, resulting in coacervation driven by electrostatic interaction, without the requirement for pH adjustment or organic solvents. Additionally, the pH of liquid–liquid phase separation is tuned by substituting polyelectrolytes with different pK_a, which satisfied different pH requirement in real life. The coacervate-based adhesives on glass substrates exhibit strengths comparable to commercial glues when dry and to mussel glue when wet, showing high biocompatibility in human epidermis in vitro.