Mechanically Robust Lubricating Hydrogels Beyond the Natural Cartilage as Compliant Artificial Joint Coating

Natural cartilage exhibits superior lubricity as well as an ultra-long service lifetime, which is related to its surface hydration, load-bearing, and deformation recovery feature. Until now, it is of great challenge to develop reliable cartilage lubricating materials or coatings with persistent robustness. Inspired by the unique biochemical structure and mechanics of natural cartilage, the study reports a novel cartilage-hydrogel composed of top composite lubrication layer and bottom mechanical load-bearing layer, by covalently manufacturing thick polyelectrolyte brush phase through sub-surface of tough hydrogel matrix with multi-level crystallization phase. Due to multiple network dissipation mechanisms of matrix, this hydrogel can achieve a high compression modulus of 11.8 MPa, a reversible creep recovery (creep strain: ≈2%), along with excellent anti-swelling feature in physiological medium (v/v0 < 5%). Using low-viscosity PBS as lubricant, this hydrogel demonstrates persistent lubricity (average COF: ≈0.027) under a high contact pressure of 2.06 MPa with encountering 100k reciprocating sliding cycles, negligible wear and a deformation recovery of collapse pit in testing area. The extraordinary lubrication performance of this hydrogel is comparable to but beyond the natural animal cartilage, and can be used as compliant coating for implantable articular material of UHMWPE to present, offering more robust lubricity than current commercial system.

天然软骨具备优异的润滑性能与超长使用寿命，这与其表面水合作用、承载能力及形变恢复特性密切相关。时至今日，研发具备持久稳定性的可靠软骨润滑材料或涂层仍面临巨大挑战。受天然软骨独特的生化结构与力学性能启发，本研究报道了一种新型软骨水凝胶：该水凝胶由顶层复合润滑层与底层机械承载层构成，通过在含多级结晶相的强韧水凝胶基体的亚表层共价制备厚聚电解质刷相得以实现。得益于基体的多重网络耗散机制，该水凝胶可实现11.8 MPa的高压缩模量、约2%蠕变应变的可逆蠕变恢复，以及在生理介质中优异的抗溶胀性能（体积变化率v/v0 < 5%）。以低粘度磷酸盐缓冲液（Phosphate Buffered Saline, PBS）作为润滑剂时，该水凝胶在2.06 MPa的高接触压力下，历经10万次往复滑动循环仍展现出持久的润滑性能（平均摩擦系数（Coefficient of Friction, COF）≈0.027），磨损量可忽略不计，且测试区域内的塌陷凹坑可实现形变恢复。该水凝胶的卓越润滑性能可媲美甚至优于天然动物软骨，可作为超高分子量聚乙烯（Ultra High Molecular Weight Polyethylene, UHMWPE）可植入关节材料的柔性涂层使用，其润滑稳定性优于当前商用体系。