Bio-inspired low wear and durable lubrication interfacial system based on thixotropic hydrogel for artificial joints

Inspired by the excellent wear resistance and lubrication of articular joints, a novel bionic interfacial system was proposed by combining thixotropic hydrogel with surface porous Ultrahigh Molecular Weight Polyethylene (UHMWPE). Thixotropic hydrogel, synthesised by gelatin, alginate sodium, tannic acid and weak crosslinking by Ca²⁺ (Gel-TA-Alg@Ca²⁺), was used as a lubricant due to its shear-thinning when loaded, then the recovery viscosity to be benefitted for reserving in surface pores on UHMWPE when unloaded. Surface porous UHMWPE was fabricated by using hydroxyapatite particles as porogen to control its porosity, pore size, surface roughness and surface energy (PE-HA). Gel-TA-Alg@Ca²⁺ significantly reduced average coefficients of friction and wear factors compared to those under normal saline and calf serum solution lubricating after reciprocating tribological testing. Notably, Gel-TA-Alg@Ca²⁺ still maintained thixotropy and was stored in surface pores of UHMWPE even after tribological testing for 7200 min. Thus, durable lubrication could be realised due to the synergistic effect of surface porous structure and thixotropy. Stribeck curves showed the characterisations of mixed, elastohydrodynamic and hydrodynamic, but without boundary lubrications for PE-30HA under three lubricants. The present results might provide the potential application to construct the durable lubrication bionic articular joint interfacial system for artificial joints.