Synthesis of nature inspired, phosphorylcholine moieties and poly(ethylene oxide) brushes containing copolymers which synergise steric repulsion and hydration lubrication for articular cartilage

Inspired by nature, a hydrophilic diblock brush copolymers containing both phosphorylcholine groups and PEO side chains were synthesized by successive RAFT polymerization of the zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) and PEO-containing macromonomer poly(ethylene oxide) methyl ether methacrylate (PEOMEMA) for the first time.  Lubricating effect of several diblock brush copolymers and one gradient copolymer of MPC and PEOMEMA was evaluated by tribological measurements in the systems PDMS–glass and cartilage–glass which were placed in PBS solutions of the polymers. The best lubrication was provided by the diblock copolymer with relatively long pMPC block and the copolymer of gradient structure. Average dynamic coefficient of friction (COF) in the system PDMS–glass at concentration of the copolymers 0.4 mg/ml was only 0.004– 0.007, while COF values of the copolymers in the system cartilage-glass after 450 cycles of sliding 0.06–0.07. Excellent lubrication effect of the diblock and gradient copolymers of MPC and PEOMEMA is attributed to hydration lubrication provided by pMPC synergistically combined with steric repulsion provided by PEOMEMA. Entrapment of diblock brush copolymers between sliding surfaces was sufficient to provide the lubrication effect. This enhances the efficacy of the diblock brush copolymers as potential additives for intraarticular injections.