Metal ion reinforced hydrogel/Ti6Al4V bionic composite joint bearing interface with extraordinary mechanical and biotribological properties

Artificial joints are facing challenges of high friction and severe wear, which limits their application in the high stress-loading conditions of joint bearing interfaces. Inspired by the soft/hard structure of articular cartilage/subchondral bone in a natural joint and the presence of lubricating proteoglycan/lubricin on cartilage surface, a polyanionic hydrogel coating rich in carboxylates/sulfonates was constructed on a porous Ti6Al4V substrate through ultraviolet radiation combined with metal ion bridging method. In addition, metal ions were adopted to form ionic coordination bonds with the polyanionic hydrogel layer to enhance its mechanical properties. Characterization results showed that the hydrogel layer was firmly adhered to the porous Ti6Al4V surface, and the as-obtained metal ion reinforced hydrogel/Ti6Al4V joint bearing interfaces displayed improved hydrophilicity and mechanical properties. Notably, compared with Al3+ and Fe3+, Ca2+ reinforced PVA-PAA-PSPMK/DT-Ti6Al4V joint bearing interface in deionized water exhibited a lower friction coefficient (∼0.068), which was similar to that of fresh porcine cartilage, and only slight scratches on the worn surface. Moreover, after 4 h of lubrication in phosphate buffer (PBS) or calf serum, its stable and low friction coefficient further revealed its great application potential in physiological environments. The lubrication mechanisms were also discussed in detail. This work presents a simple and effective method to develop hydrogel/Ti6Al4V bionic composite joint bearing interfaces with advanced performance.