Water-triggered self-healing and reversible underwater adhesion in metalorganic polymers

The strategies used by organisms living in water to adhere to surfaces have been a major source of inspiration to develop synthetic underwater adhesives. Amongst the mechanisms explored, byssus-inspired metalorganic chemistry offers a broad range of possibilities due to the breath of coordination bonds, salts and polymer backbones available. This has led to a significant amount of research on bio-inspired synthetic glue-type (liquid) and tape-type (solid) adhesives. However, reversibility under water, durability and universality of adhesion remains elusive. We demonstrate that the combination of Ni-metalorganic chemistry with a flexible hydrophobic polymer allows developing fully healable and recyclable polymers able to reversibly adhere (under water) to substrates with surface energies as diverse as Teflon and glass. Other metal ions such as Fe3+ and Zn2+ did not provide the desired adhesion in water. The underlying mechanism is attributed to local water-induced chain re-orientation and the use of strong but dynamic metalorganic coordination (Ni2+-2,5-thiophenedicarboxaldehyde). The results unveil a versatile route to develop solid-state underwater adhesives and water-triggered healing polymers using a one-pot synthesis strategy (Schiff-base with metal coordination) with an underlying mechanism that can be extrapolated to different application domains such as biomedical, energy and underwater soft robotics. Metallopolymer-based solid-adhesives able to reversibly adhere to hydrophobic and hydrophilic surfaces and to heal in water are presented. The role of Zn, Fe and Ni coordination and water on healing, recycling and underwater adhesion is discussed.