Hydrogels with Dynamically Tunable Friction Engineered through Regrafting Polymer Brushes

The control of friction in soft materials is critically important for applications such as soft robotics. This work presents a supramolecular hydrogel designed with reforming polymer brushes to achieve dynamically tunable friction. The hydrogel network, based on PAM-<i>co</i>-PAA and integrated with β-cyclodextrin, allows for the reversible grafting of hydrophilic pSPMA brushes via host-guest interaction with adamantane-terminated polymers (Ad-SPMA). This design yields a remarkable reduction in the coefficient of friction (COF), from 0.334 for the pristine gel to 0.0609. Furthermore, because the polymer brushes can be detached and regrafted through the reversible CD-Ad bonds, the lubricating layer can be reloaded upon damage, allowing the friction to be switched between high and low states. This study demonstrates that host-guest chemistry provides a robust mechanism for dynamic friction control via a regrafting brush layer, establishing a new paradigm for tuning hydrogel lubricity.