Reusable and closed-loop recyclable underwater adhesives via printable multi-dynamic networks

Sustainable underwater adhesives have attracted wide attention in fields such as marine exploration and biomedicine. The development of recyclable underwater adhesives that can achieve strong and durable adhesion to various substrates is a daunting challenge. Herein, a series of recyclable underwater adhesives are developed through synergistic engineering of molecular design and multiple dynamic cross-linking networks. The selected well-designed adhesives exhibit excellent underwater adhesion on a variety of substrates, achieving a maximum adhesion strength up to 3.31 MPa. By integrating dynamic covalent and non-covalent cross-links, the adhesive demonstrates rapid self-healing, on-demand reversible adhesion/desorption, and consistent adhesion performance over more than 30 reuse cycles. Moreover, dynamic disulfide bonds impart dual closed-loop recyclability to the adhesive: chemical recycling achieves up to 89.6% monomer recovery, while physical recycling through melt reprocessing allows for effective reuse of adhesive waste. Furthermore, these adhesives exhibit 3D printability, thereby underscoring their great potential for creating customizable underwater adhesives. This study offers new insights into the development of recyclable underwater adhesives that combine strong, repeatable adhesion and desorption with 3D printing capabilities, paving the way for their broader adoption in practical applications.