UHMWPE resin powder (GUR 1050, Ticona, USA) was mixed with Background
Materials & Methods
Vitamin-E (VE)-blended UHMWPE has been developed as a bearing-surface material due to the antioxidant ability of VE and has demonstrated a low wear rate in knee simulator [1]. Additionally, in vitro biological response testing has revealed that wear particles from VE blended UHMWPE induce the secretion of inflammatory cytokines at significantly lower levels compared to conventional UHMWPE [2]. However, as the joint kinematics are different between the knee and the hip, it is not guaranteed that these improvements will be repeated in the hip. In this study, the wear resistance of VE-blended UHMWPE was evaluated in knee and hip simulator tests and the effects of VE concentration and electron-beam irradiation were investigated. VE blended samples (GUR_VE xx%) were manufactured via direct compression molding following the blending of UHMWPE resin powder with VE at several concentrations (0, 0.1, 0.3, 1.0%). Cross-linking for the VE samples was achieved by 10 MeV electron beam at several irradiance doses (30, 90, 300 kGy) and annealed below the melting point of UHMWPE. Knee and hip simulator testing were carried out according to ISO 14243 and ISO 14242, respectively, and the volumetric wear was calculated. The gel fraction was determined by measuring the weight of the samples before and after soaking in decahydronaphthalene at 150°C. The oxidative resistance of the material was determined by measuring the Oxidation Index (OI) following ASTM F2102 before and after compulsory aging (ASTM2003). Radical measurements were made using high-sensitivity X-band ESR.Introduction
Materials and Methods
Electron-beam-irradiated Both pure UHMWPE and Vitamin E added (0.3% w/w) resin was used to produce bulk specimens via vacuum direct compression molding at 220°C under 25 MPa for 30 min. Cylindrical pins (3.5 mm diameter, 40 mm length) for ESR measurement were then machined and placed in vacuum packaging. The pins were irradiated at 300 kGy, with half of each test group annealed at 80°C for 24 hours. Free radical measurements were made using a high-sensitive X-band ESR operating at 9.44 GHz. Detection of Vitamin E radicals was performed by comparing the characteristic symmetrical spectrum of oxidized Vitamin E to the spectra observed for the pins using both g-value and linewidth as references. Crosslink density was measured via gel fraction analysis and was performed in accordance with ASTM D2765. Thin sections (20 × 40 mm2, 200 μm) were machined from the bulk specimens, which were then placed in vacuum packaging, irradiated and annealed at the same conditions as those for the ESR measurements. Two of these thin sections were then placed in a stainless-steel cage (200 µm pore diameter) and were immersed in decahydronaphtalene at 200°C for 24 hours. These specimens were then extracted using soxhlet extractor at 100°C for 24 hours and dried in vacuum at 150°C for 12 hours.INTRODUCTION
MATERIALS & METHODS
The revascularisation and remodelling of allografts used to replace the anterior cruciate ligament in the canine knee were studied by microangiographic, histological and biomechanical methods. The 26 allografts were obtained from the patellar tendons of other dogs and were stored by deep freezing. In a control study a strip of patellar tendon from the same leg was used as an autologous free graft. Microangiography showed that the allografts had been revascularised from the sixth postoperative week, and had later developed an intrinsic vascular pattern similar to that of a normal anterior cruciate ligament. Histologically, the allograft regained a fibrous framework similar to that of a normal ligament, and showed no evidence of immunological rejection. Biomechanical tests on the allograft replacements showed that their mean maximum tensile strength at 30 weeks was about 30% of that of the control ligaments. There were no significant differences between the mechanical properties of the allografts and the autografts.
