Wear performance and debris-size distribution of vitamin E (DL-a tocopherol, VE)-added ultrahigh molecular weight polyethylene (UHMWPE) was evaluated using a knee-simulator test. VE was mixed with GUR 1050 UHMWPE powder at 0.3 wt%, and the tibial components of the knee joint were made by direct compression molding. The VE-added UHMWPE showed consistently lower wear volume throughout the test. ß

Vitamin E (VE) has been added to ultrahigh-molecular-weight polyethylene (UHMWPE) acetabular cups and tibial trays primarily to reduce oxidative damage to the polymer. The aim of this study was to investigate the relative wear rates of UHMWPE-containing VE compared with virgin UHMWPE. The ability of VE to reduce the amount of inflammatory cytokines produced from stimulated peripheral blood mononuclear cells (PBMNCs) was also investigated. Stimulation was achieved by exposure of PBMNCs to either lipoplysaccharide (LPS) or VE-containing UHMWPE (VE-UHMWPE). In the present study, results showed that the wear rates of UHMWPE with or without VE were not significantly different. Particles generated by UHMWPE with and without VE were not significantly different in size distribution. The production of osteolytic mediators, tumor necrosis factor-alpha, interleukin 1β (IL-β), IL-6, and IL-8 were significantly reduced in (PBMNCs) stimulated with either LPS + VE compared with LPS or VE-UHMWPE particles compared to virgin UHMWPE particles. This trend was also observed when VE was added as a liquid to UHMWPE wear particle-stimulated PBMNCs. The exact mechanism of how VE affects the release of inflammatory mediators from particle-stimulated macrophages is not yet understood. It is likely to involve the anti-inflammatory and/or antioxidant effects of VE.

We investigated ultrahigh-molecular-weight-polyethylene (UHMWPE) samples prepared by various conditions with terahertz-time-domain spectroscopy (THz-TDS). Degradation of the virgin UHMWPE samples by ␥ irradiation induced a drastic increase of the absorption ranging continuously over the THz region. The increase of the absorption continuum is interpreted to originate in the oxidation of the amorphous region within the sample. Only slight THz spectral changes induced by the ␥ irradiation were, however, observed for the UHMWPE samples doped with 0.1 and 0.3 wt % vitamin E. This result agrees with the earlier indication that vitamin E has an antidegradation effect on UHMWPE. The present result shows that the THz-TDS can be used for the quality control of UHMWPE by monitoring the absorption continuum in the THz region.The terahertz-time-domain spectroscopy (THz-TDS) has made great progress owing to recent advances in the THz generation and THz detection techniques by using ultrashort laser pulses. 1,2 The THz transmission technique has been applied to plastic-package imaging and inspection of an inner IC chip. 3 It is the key point of this inspection that plastics are transparent to the THz radiation, although they are opaque for infrared and visible light. For this reason, the THz-TDS can be a useful tool for a nondestructive diagnosis of inner parts of plastics.Polyethylene ͑-͓CH 2 −CH 2 ͔ n -͒ is one of the polymer plastics which are widely used in versatile applications. Among various types of polyethylene, ultrahigh-molecularweight polyethylene (UHMWPE) is used as medical polymers in contact with living tissues or biological fluids. 4,5 For example, UHMWPE is, at present, implanted to human bodies as artificial acetabular cup components and as artificial knee joint components. Prior to surgical implants of UHMWPE, the ␥ irradiation is widely used for sterilization. Free radicals formed by the ␥ irradiation cause aging oxidation, resulting in degradation of UHMWPE. 6 Because the life of implanted UHMWPE is dependent on degree of degradation, 4 investigation of ␥ irradiation effects on UHMWPE is critical for success in the implants. Mid-IR absorption has been applied to measuring degree of oxidative degradation by monitoring the carbonyl band ͑ ϳ1720 cm −1 ͒. 6 For this inspection it is necessary to cut out a thin slice from test objects. A nondestructive method for inspecting inner UHMWPE is, therefore, beneficial for the quality control of UHMWPE as source materials.In this study we examined the applicability of the THz-TDS to the degradation diagnosis of UHMWPE. This inspec-tion method is in a nondestructive and contactless manner. To investigate the influences of the ␥ irradiation we carried out the THz-TDS of UHMWPE samples with and without the ␥ irradiation. We also examined the changes of the THz spectra induced by the ␥ irradiation for the UHMWPE samples doped with vitamin E (␣-tocopherol), which additive is known to be highly effective in reducing the oxidative degradation. 7 We prepared UHMWPE plates with...

We study metastable dynamical breaking of supersymmetry in A n quiver gauge theories. We present a general analysis and criteria for the perturbative existence of metastable vacua in quivers of any length. Different mechanisms of gauge mediation can be realized.

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