Preparation And Performance Of Crosslinked UHMWPE With Oxidation Stability For Total Joint Implants

Since the1960s, medical grade ultra high molecular weight polyethylene (UHMWPE) hasbeen the most relevant material used in total joint replacement. However, oxidation and wear invivo leads to the formation of UHMWPE wear debris and consequently may trigger biologicalreactions that cause osteolysis and implant loosening. Currently, the improvement of the wear andoxidation resistance is one major research directions in the field of artificial joint materials. Theinfluence of UHMWPE structure on its wear properties and UHMWPE oxidation mechanism areimportant basic science issues, which are critical for the development of high performance, andlongevity artificial joints. In this thesis, dodecyl gallate (DG) and gallic acid (GA) were used asstabilizer for highly crosslinked UHMWPE. These antioxidants were blended with UHMWPE andconsolidated by compression moulding prior to e-beam irradiation to prepare the crosslinkedUHMWPE with improved oxidation stability, high strength, low wear for total joint implants.In this study, DG and GA have been demonstrated potent in protecting irradiated UHMWPEagainst accelerated aging at elevated temperatures. The presence of these polyphenols does notinhibit the crosslinking in comparison to the high dose-irradiated vitamin E/UHMWPE. Pin-on-disc (POD) wear tests of these materials demonstrated low wear, which is about60-90%reductionin wear in comparison to the conventional UHMWPE materials in clinical use. In vitro culture withchondrocytes showed improved biocompatibility of these irradiated AO/UHMWPE.In the present work, the oxidation of irradiated AO/UHMWPE at room temperature wasinvestigated by using Fourier transform infrared spectroscopy (FTIR). Trans-vinylene formation,end vinyl consumption and phenols loss upon e-beam irradiation were observed. More specifically,the oxidation products including ketones, hydroperoxides, carboxylic acids, and esters, etc, wereanalyzed in detail in order to understand the effect of polyphenols on the oxidation mechanism ofhighly crosslinked UHMWPE. The formation kinetics of hydroperoxides and ketones wereinvestigated to compare the stabilization potency of these polyphenols with that of vitamin E.In this thesis, the effect of squalene on the oxidative stability of polyphenol-blended highlycrosslinked UHMWPE has been investigated. We confirmed the synovial fluid squalene coulddiffusion into irradiated UHMWPE and the absorption of squalene accelerated oxidation anddegradation in vitro in these materials. Natural polyphenols are efficient to stabilize irradiatedsqualene-doped UHMWPE and the AO concentration of6.9mmol/L was enough to inhibit thesqualene induced UHMWPE oxidation.