Natural Polyphenol-Stabilized Highly Cross-Linked UHMWPE for Joint Implants

Abstract

Radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) with high mechanical strength, wear resistance, and oxidative stability is critical for the long-term performance and life span of joint implants. The use of antioxidants and/or radical scavengers has proven efficient in stabilizing cross-linked UHMWPE against oxidation, whereas challenges remain to explore new methods to offer not only oxidative stability but also superior wear resistance and mechanical properties. This chapter introduces the use of natural polyphenols with three hydroxy groups to stabilize irradiated UHMWPE. Dodecyl gallate (DG) and gallic acid (GA) are blended with UHMWPE and consolidated by compression moulding prior to e-beam irradiation. The polyphenols show a slight phenol loss and offer improved oxidation stability. Such a strong antioxidation potency even shows a significant protection against the oxidative challenges. The antioxidation mechanisms have been investigated. The tensile and impact properties of these polyphenol-stabilized highly cross-linked UHMWPE after accelerated ageing in accordance with ASTM (American Society of Testing Materials) F2003 are superior to those of the irradiated and remelted UHMWPE. Pin-on-disc (POD) wear tests of these materials demonstrate low wear comparable to highly cross-linked and remelted UHMWPE. The oxidation and antioxidation mechanisms with the presence of polyphenols are investigated by analysing the oxidation products and oxidation kinetics. The antioxidants are potent to protect the polymer from oxidation with the presence of unsaturated lipids, which is encouraging for the prevention of the in vivo oxidation of UHMWPE implants related to the synovial lipids.