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, hydrophilic diblock brush copolymers containing both phosphorylcholine groups and poly(ethylene oxide) (PEO) side chains were synthesized by successive reversible addition-fragmentation chain transfer (RAFT) polymerization of the zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) and the PEO-containing macromonomer poly(ethylene oxide) methyl ether methacrylate (PEOMEMA) for the first time. The lubricating effect of several diblock brush copolymers and one gradient copolymer of MPC and PEOMEMA was evaluated by tribological measurements in polydimethylsiloxane (PDMS)–glass and cartilage–glass systems which were placed in phosphate-buffered saline (PBS) solutions of the polymers. The best lubrication was provided by the diblock copolymer with a relatively long poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC) block and the copolymer of gradient structure. The average dynamic coefficient of friction (COF) in the PDMS–glass system at a copolymer concentration of0.4 mg/mL was only 0.004–0.007, while COF values of the copolymers in the cartilage–glass system after 450 sliding cycles reached 0.06–0.07. The 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 from PEOMEMA. Entrapment of diblock brush copolymers between sliding surfaces was sufficient to provide effective lubrication, thus enhancing the efficacy of the diblock brush copolymers as potential additives for intraarticular injections.