Enhancing Tribo-Rehydration in Hydrogel by Brush-Like Surface and Its Modulation

Abstract

Synovial exudation, creeping, and lubrication failure in natural cartilage under a long-term normal loading can be counteracted by a tribo-rehydration (sliding-induced rehydration) phenomenon. Hydrogels, as porous materials, can also restore interfacial lubrication and overcome creep through this strategy. At appropriate sliding velocities, water molecules at the interface contact inlet are driven by hydrodynamic pressures into the porous network to resist creep extrusion. In this work, polyelectrolyte brushes were grafted onto the hydrogel surface to construct a loose, large-pore network structure and improve the interface hydration, enhancing the tribo-rehydration. Compared to the gel without grafted brushes, the grafted surface facilitated the water molecules flowing into the gel network, and the hydrated brushes effectively anchor water at the interface and increase their enrichment at the contact surface for enhancing the rehydration. Finally, the structure of the polymer brush was modulated by multivalent ions to explore the relationship between the rehydration and structure. These results indicate that constructing a loose, hydrated polymer brush layer on the gel surface significantly enhances its tribo-rehydration capability. This strategy can not only improve the load-bearing capacity and resistance to creep of the hydrogel but also effectively restore and maintain long-term lubrication.