Synthesis of articular cartilage‐inspired branched polyelectrolyte polymer for enhanced lubrication

The superlubrication property of articular cartilage is attributed to the hydration lubrication mechanism. This involves the complexation of biomacromolecules with phosphatidylcholine lipids to form a lubricating boundary layer on the surface. Based on this mechanism, a branched polyelectrolyte polymer – PEI-PMPC was synthesised in this study to enhance lubrication via tert-butyl hydroperoxide-initiated grafting polymerisation of 2-methacryloyloxyethyl phosphorylcholine (MPC) onto polyethyleneimine (PEI) with various molecular weights. Following the characterisation of the polymer using nuclear magnetic resonance, a series of tribological tests were performed under different normal loads and different scan rates. The results showed that the PEI-PMPC polyelectrolyte polymer in aqueous solution could effectively reduce the friction coefficient and wear generation between the polyethylene ball and the silica wafer. Additionally, an improvement in the lubrication performance was detected for the PEI-PMPC polyelectrolyte polymer when high molecular weight PEI was used during the reaction, which was attributed to the formation of the hydration shells surrounding the zwitterionic charges of PMPC and the viscosity of the polymer. In conclusion, the PEI-PMPC polyelectrolyte polymer developed herein was characterised by enhanced lubrication, and may be potentially used for biomedical applications such as intra-articular injection to restore joint lubrication.