Tough bonding of hydrogels to diverse non-porous surfaces

A hydrogel-design strategy achieves transparent and conductive bonding of synthetic hydrogels to a variety of non-porous surfaces, with interfacial toughness values over 1,000 J m−2. In many animals, the bonding of tendon and cartilage to bone is extremely tough (for example, interfacial toughness ∼800 J m−2; refs 1,2), yet such tough interfaces have not been achieved between synthetic hydrogels and non-porous surfaces of engineered solids3,4,5,6,7,8,9. Here, we report a strategy to design tough transparent and conductive bonding of synthetic hydrogels containing 90% water to non-porous surfaces of diverse solids, including glass, silicon, ceramics, titanium and aluminium. The design strategy is to anchor the long-chain polymer networks of tough hydrogels covalently to non-porous solid surfaces, which can be achieved by the silanation of such surfaces. Compared with physical interactions, the chemical anchorage results in a higher intrinsic work of adhesion and in significant energy dissipation of bulk hydrogel during detachment, which lead to interfacial toughness values over 1,000 J m−2. We also demonstrate applications of robust hydrogel–solid hybrids, including hydrogel superglues, mechanically protective hydrogel coatings, hydrogel joints for robotic structures and robust hydrogel–metal conductors.