Synthesis and characterizations of zwitterionic copolymer hydrogels with excellent lubrication behavior

Various studies on hydrogel applications as cartilage substitutes and artificial joints have been previously conducted. In this study, a copolymer hydrogel comprising zwitterionic sulfobetaine methacrylate (SBMA) and 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers is synthesized in an aqueous system via free-radical polymerization. A P(MPC-co-SBMA) copolymer hydrogel network is formed via the additional polymerization of the alkane carbon-carbon double bond from the combination of MPC and SBMA polymer chains using ethylene glycol dimethacrylate (EGDMA) as the crosslinker. Introduction of MPC in the PSBMA hydrogel under water lubrication improved the compressive stress by almost double and considerably lowered the coefficient of friction (COF) to approximately 0.011. This phenomenon was attributed to the fact that MPC could intertwine with SBMA to increase the crosslink density of the hydrogel and preferentially adhere to the water to reduce the adhesion of the contact between hydrogels, leading to an intertwined copolymer network structure with excellent load-bearing capacity and superior hydration lubrication capability. This study might provide potentially useful information relating to cartilage replacement applications requiring high mechanical strength and excellent friction behavior.