Recent advances in wet adhesives: Adhesion mechanism, design principle and applications

Achieving strong adhesion between the interfaces of similar and dissimilar materials is highly desirable in various fields. However, the adhesion of common adhesives is diminished and even eliminated upon contact with water, because it prevents direct contact between the adhesive and adherend substrate and competes with the substrate surface groups to interact with the adhesive functional groups. So far, numerous mussel-inspired catechol-based wet adhesives have been reported, opening a pathway for the development of wet adhesives. However, catechol is sensitive to pH, oxidation, and temperature, which limit its adhesion capability and application convenience. To overcome these limitations, many non-catechol-based adhesives have been explored and prepared in recent years. This review systematically summarizes and discusses several types of wet adhesives starting with the most extensively investigated catechol-based wet adhesives, followed by a focus on non-catechol-based wet adhesives that adhere though hydrogen bonding, electrostatic interactions, dynamic covalent bonding, topological entanglement, and dry polymer crosslinking, as well as by mimicking adhesion in organisms. Finally, wet adhesives that can debond on demand are discussed. This review describes the opportunities and challenges encountered in the design and development of wet adhesives with more advanced adhesion performances and application prospects.