Design and Application of Strong and Tough Low-Friction Hydrogels.

Hydrogels, with their high water content, tissue-like softness, and excellent biocompatibility, are prime candidates for dynamic load-bearing interfaces such as cartilage replacement and implant coatings. However, the toughening structures introduced to enhance damage resistance often compromise surface lubrication: highly dissipative networks, while suppressing bulk crack propagation, frequently increase interfacial friction and accelerate wear. This toughness-lubrication trade-off constitutes a central bottleneck limiting the long-term service of hydrogels under dynamic contact conditions. This review examines the friction and wear behavior of various hydrogel systems and, from the dual perspectives of bulk mechanical reinforcement and surface lubrication regulation, summarizes the core design mechanisms of toughening and hydration lubrication strategies, respectively. Based on this analysis, this review proposes a functional decoupling design principle: hierarchical structures-ranging from homogeneous to heterogeneous-in which the bulk dissipates mechanical load while the surface maintains hydration lubrication, thereby reconciling mechanical toughness with lubrication. Finally, this review surveys cutting-edge applications of such materials in tissue engineering, device coatings, drug delivery, electronic energy-harvesting and storage devices, and soft actuators, providing a reference for the development of hydrogels that integrate excellent mechanical properties with lubrication functionality.