Synergy of noncovalent interlink and covalent toughener for tough hydrogel adhesion

Tough adhesion between soft and wet materials is important to many applications in medicine and engineering. Examples include implants, wound dressing, and soft machines. Recent work has highlighted a general principle: tough adhesion can be realized through the synergy of interlink and toughener. Here we develop an adhesive double-network hydrogel to achieve tough adhesion through noncovalent interlinks and covalent tougheners. We show that the noncovalent interlinks can be strong enough to unzip many covalent tougheners. Adhesion energy above 500 J/m(2) is achieved. Interplay between noncovalent interlinks and covalent tougheners provides new possibilities for toughening mechanism. This work will guide material designs for tough adhesion, as well as contribute to fundamental mechanics of adhesion. (C) 2020 Published by Elsevier Ltd.