Bioinspired Printable Tough Adhesives with In Situ Benignly Triggered Mechanical Enhancements

Abstract Adhesives can intimately connect humans to machines, seamlessly bond diverse tissues in the human body, and manage various diseases. However, the precise spatial control of wet and tough adhesion of biocompatible hydrogels on biological tissues remains a major challenge. Inspired by the bioglue secreted by sandcastle worms, the design of printable tough adhesives (PTAs) is proposed, a supramolecular hydrogel that can be printed into defined structures, in situ mechanically reinforced into a tough matrix with physiologically relevant benign triggers, and strongly adhere to diverse substrates. With carefully selected polymer components and ratios, it is discovered that the 3D printed PTAs can achieve a marked increase in toughness, tensile strength, and stiffness after being immersed in water/saline solution or attached to biological tissues. To assess the robust toughening mechanism triggered by the supramolecular interactions, the effects of polymer content and pH on the mechanical performance of PTAs and the kinetics of their triggered reinforcement are thoroughly investigated. The potential of PTAs is further demonstrated for manufacturing tough connective tissue mimetics, controlling patterned bioadhesion, and designing programmable 4D soft robotics. The bioinspired, printable, benignly triggerable, and adhesive supramolecular PTAs are expected to find broad applications in engineering and medicine.