Vitamin E-grafted crosslinked ultrahigh-molecular weight polyethylene (VE-HXPE) inhibits fluid absorption and has long term oxidative stability

Abstract

Oxidation of in vivo-absorbed lipids such as squalene and cholesterol may limit the life of melted or annealed crosslinked polyethylene (HXPE) implants. Combining vitamin E with HXPE (VE-HXPE) increases the oxidation resistance of HXPE. This study investigates the fluid absorption characteristics and long-term oxidative stability of VE-HXPE and HXPE implants. VE-HXPE and HXPE cubes were soaked in squalene at 37±2°C and compressively loaded at 500/50N (R=0.1) for 500h and time dependence of squalene absorption was determined. Additionally, serum lubricant absorbed by 40mm HXPE and VE-HXPE acetabular components during a 45 million cycle (Mc) hip wear test was gravimetrically determined. HXPE and VE-HXPE ASTM type V dog bones were aged at 70°C under 0.482MPa of 100% oxygen for up to 33weeks and the oxidation index was determined using FTIR. The HXPE and VE-HXPE acetabular components absorbed 126.3±49.0mg and 33.1±6.7mg of bovine serum respectively during the 45Mc wear test. FTIR measured OI≤0.05 for VE-HXPE and OI=2.05±1.48 for HXPE after 33weeks and 4weeks of aging respectively. The results are explained in terms of differences in crystallinity and chemistry of the amorphous phase in blended VE-HXPE.