Influence of surface PMPC brushes on tribological and biocompatibility properties of UHMWPE

Abstract

Extremely efficient lubrication has been observed between natural joint surfaces and the friction coefficients can reach as low as 0.001. However, attaining the ultra-low friction coefficients between articulating cartilage surfaces in any artificial joints remains a challenge for bio-tribologists. In order to obtain the ultra-low friction coefficients as in natural joints, a biomimetic zwitterionic monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) was grafted on the ultra high molecular weight polyethylene (UHMWPE) by UV radiation and self-polymerized to form brush-like structure. The results of total reflection (FT-IR/ATR) spectra and X-ray photoelectron spectroscopy (XPS) spectra indicated successful grafting of PMPC on to the UHMWPE surface (Polymerization of 2-methacryloyloxyethyl phosphorylcholine). The water contact angle of UHMWPE decreased from 80° to 15° after grafting PMPC for 45min. Tribological properties were tested under high contact stress for a longer duration of time. The friction coefficient of the sample grafted with PMPC was found to be much lower than that of untreated UHMWPE at initial stage which increased gradually with the increase of the cycle till it attained the same level as that observed for untreated UHMWPE. The wear rate of modified samples was decreased by 37% and 46% in distilled water and saline, respectively. The highly hydrated PMPC layer provided efficient lubrication at the interface between the sliding couple leading to wear reduction of UHMWPE. Furthermore, blood compatibility of modified artificial joint materials was improved significantly, which has been attributed to the properties and structures of PMPC grafted on the UHMWPE surface.