Wide-range controllable stick-to-slip hydrogels by synergistic effects of wettability and surface morphology

Materials with the ability to swiftly transition into a lubricated state hold significant importance across various applications, including human-machine interfaces, crawling robots, and medical dressings. Achieving a rapid and reversible shift from high adhesion to low friction over a broad range has posed a considerable challenge, as most reversible transitions in adhesive hydrogels typically occur only at the microscopic level. In this study, this challenge has been addressed by leveraging the synergistic interplay between dynamic macroscopic contact and microscopic group changes to engineer a switchable adhesion-to-lubrication hydrogel (denoted as the PVA/PAA hydrogel). Upon the application of borax to the PVA/PAA hydrogels (denoted as the B-PVA/PAA hydrogel), alterations in surface morphology and hydrophilicity ensue due to the cross-linking of hydroxyl and boron atoms and the subsequent dissociation of carboxyl groups induced by borax. These transformations caused by synergistic effects give rise to changes in the adhesive and lubrication characteristics of the hydrogels. Consequently, the hydrogel can readily transition between an adhesive state (adhesion strength ~ 26 kPa) and a lubrication state (μ ~ 0.028), driven by shifts in surface topography and hydrophilicity. This mechanism provides a versatile and efficient approach for the creation of a fast-switchable adhesive gel with stick-slip properties, offering promising prospects for a wide array of practical applications.