Boundary-Lubricated Hydrogels with Load-Bearing Capacity via Microphase Separation Strategy

Lubricating hydrogels show promise as cartilage substitutes but face mechanical fragility (elastic modulus <100 kPa) and fluid-dependent lubrication failure under physiological loads. hydrogels are presented with nanoconfined water via microphase-separated structures, combining hydrogen-bond-stabilized polymer-dense domains and hydrated regions. By tuning hydrated nanopore size (≈10 nm) and enhancing bound water content, these hydrogels achieve boundary lubrication with ultralow friction (coefficient of friction, COF≈0.01) under extreme conditions: contact pressures >10 MPa, velocities spanning 1-100 mm s^-1. Additionally, hydrogels demonstrate effective lubrication under sub-zero temperatures. The hydrogen bond-reinforced network balances exceptional mechanical properties-compression modulus of 53.8 MPa and fracture energy of 54462.6 J m^{- 2}-surpassing conventional hydrogels. Their uniform heterogeneous structure enables self-renewal post-wear, sustaining long-term lubrication. This design decouples mechanical robustness from lubrication sustainability, overcoming the traditional interdependency where mechanical degradation accelerates lubrication failure. By optimizing polymer network topology to regulate water states, load-bearing boundary lubrication is enabled, addressing critical limitations in cartilage-mimetic materials. The strategy offers a pathway for durable hydrogels in biomedical applications requiring simultaneous pressure resistance, velocity adaptability, and environmental resilience.