Tough Adhesives
for Wet Surfaces

Design and function of tough adhesives. (A) The tough adhesive (TA) consists of a dissipative matrix (light blue square) made of a hydrogel of hybrid ionic and covalent bonds (blue and black lines), and an adhesive surface (light green region) that contains bridging polymers with positively charged primary amines (green lines). Physical penetration of the bridging polymer may occur between the adhesive and the substrate (light green region). (B) As an interfacial crack approaches, a large process zone (pink area) dissipates significant energy as ionic bonds between alginate chains and calcium ions are broken. (C) Material property chart of these new tough adhesives (red) and existing adhesives in terms of adhesion energy and matrix toughness, including hydrogel-based adhesives (fibrin glues, PEG-based adhesive like COSEAL, mussel-inspired adhesives), adhesive bandages, cyanoacrylate and cartilage. These data demonstrates the TA has superior adhesive performance over all existing adhesives, and even forms adhesion comparable to that between cartilage and bone in the body.