Chemical Reaction-Powered Self-Assembly and Dehydration of Supramolecular Hydrogels for Phase-Transitional Robots

Phase-transitional robots have long intrigued the scientists from multidisciplinary fields, yet their realization remains a formidable task due to the lack of soft materials that seamlessly integrate phase transition with actuation functionality. Here, we report phase-transitional hydrogel robots enabled by chemical reaction-powered supramolecular gelation of a peptide solution followed by a dehydration process. The peptide contains a carboxyl group which can be converted into hydrophobic oxazolone moiety upon addition of carbodiimide. This chemical transformation neutralizes the negative charge of the peptide, thereby activating its self-assembly into a hydrogel. Interestingly, over time, the hydrogel network becomes more hydrophobic because of the progressive formation of hydrophobic oxazolone species, which in turn leads to dehydration-induced macroscopic contraction of the hydrogel. The contraction degree can be regulated by changing the concentrations of carbodiimide. This sol-to-gel transition followed by actuation behavior enables phase-transitional robots that can flow into complex terrains to catch and transport cargoes, showing extraordinary morphological adaptivity. As an application, we show that the robot can adaptively enter a narrow channel to regulate an electrical circuit. This work unlocks the potential of chemically fueled supramolecular self-assembly for the development of phase-transitional robots that show unparalleled morphological adaptivity and functionalities.