Mechanically Robust Lubricating Hydrogels Employing Surface Host‐Guest Regenerating Polymer Brushes

ABSTRACT In biomimetic articular cartilage, the incorporation of hydrophilic polymer brushes onto the surface of hydrogels with ultrahigh mechanical strength can significantly enhance surface water content and create structural features similar to natural cartilage. However, under extreme loads, the grafted polymer brushes are particularly vulnerable to damage from mechanical shearing, which can result in lubrication failure. Herein, we developed mechanically robust lubricating hydrogels (MRLH) using a host‐guest mediated surface‐initiated atom transfer radical polymerization (SI‐ATRP) strategy. The MRLH is composed of a high‐strength cyclodextrin‐based hydrogel that achieves directional anchoring of an adamantane‐functionalized ATRP initiator through specific supramolecular host‐guest recognition. This is followed by the graft polymerization of sulfopropyl methacrylate (SPMA), resulting in a stable polyelectrolyte brush layer that provides an ultra‐low coefficient of friction (COF < 0.02) under simulated physiological loads. Importantly, the supramolecular anchoring allows the lubricating brush layer to regenerate multiple times after experiencing wear damage, maintaining a low‐friction state through a simple SI‐ATRP re‐initiation reaction. Furthermore, this method shows significant potential for expansion; by modulating the properties of the grafted polymer brush, we achieved reversible friction modulation controlled by temperature and light. Overall, this study is paving the way for the design of next‐generation smart biolubricating materials.