Bioinspired design of hierarchical structured hydrogels with extraordinary lubrication and load-bearing capacity.

Conventional homogeneous hydrogels typically face an inherent trade-off between mechanical strength and lubrication performance. Achieving high load-bearing capacity requires dense crosslinking and tight chain entanglement, which inevitably restrict water uptake and suppress the formation of effective hydration layers. Herein, inspired by the anisotropic architecture of natural ligaments, we developed a robust lubricious hydrogel material (STOC-D) through synergistic spontaneous tensile orientation under confinement (STOC) processing and surface dissociation modification. The STOC process generates highly aligned polymer chains and densely packed microcrystalline domains that serve as robust physical crosslinks, effectively restricting chain slippage and crack propagation. This yields exceptional mechanical properties, including a tensile strength of 54.5 MPa, an elastic modulus of 62.7 MPa, and a tear energy of 25.7 kJ m-2. Subsequent surface dissociation creates a modulus gradient featuring a soft, highly hydrated outer layer rich in dangling chains, which enables rapid water infiltration and the formation of a stable hydration lubrication layer. As a result, the STOC-D hydrogel achieves ultralow coefficients of friction against both metallic and biological surfaces. Furthermore, in vitro cytotoxicity and in vivo subcutaneous implantation studies confirm its excellent biocompatibility. By successfully decoupling bulk mechanical reinforcement from surface hydration, this strategy overcomes the longstanding strength-lubrication trade-off in hydrogels, offering a promising method for load-bearing biomedical applications.