Publications & Reports

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Virgin UHMWPE is Not Immune to Oxidative Degradation

Thermal degradation alone, in the absence of free radicals, may be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air irradiated UHMWPE (extruded GUR 1050 and compression molded 1900) were aged up to four weeks at elevated oxygen pressure and the mechanical behavior at the surface and subsurface was examined.

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Microabrasion to Assess Surface Degradation of UHMWPE

Thermal degradation alone, in the absence of free radicals, may be sufficient to artificially age UHMWPE in a manner analogous to natural aging. In the present study, virgin and air irradiated UHMWPE (extruded GUR 1050 and compression molded 1900) were aged up to four weeks at elevated oxygen pressure and the mechanical behavior at the surface and subsurface was examined.Researchers from the Queen's University of Belfast have studied the microabrasive properties at the surface of sterilized and aged UHMWPE components. Microabrasion was found to be a sensitive technique for assessing the surface degradation of UHMWPE.

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Numerical oxidation model for gamma radiation-sterilized UHMWPE

Researchers have developed a quantitative theoretical model for heterogeneous oxidation in UHMWPE. The predictive capability of the model has been illustrated by simulations of shelf aging in air and accelerated aging at elevated oxygen pressures.

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Macro- and Microscopic Evaluation of Fatigue in Medical Grade Ultrahigh Molecular Weight Polyethylene

In this doctoral dissertation, D. Baker evaluates the initiation and propagation of flaws in conventional and highly crosslinked UHMWPE. Of particular interest is a novel form of ultra small angle x-ray scattering, which highlights the fatigue initiation process in conventional and crosslinked UHMWPE.

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Oxidation of Ethylene Oxide Sterilized Cups

Retrieved EtO sterilised acetabular cups usually show less degradation than gamma-ray sterilised cups. Some retrieved EtO sterilised cups have, however, revealed unexpected bulk oxidation. In this study, which will be published in a future issue of Biomaterials, researchers from Turin, Italy, examined a mechanism of oxidation in EtO sterilised acetabular cups after long-term shelf aging and implantation.

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Validation of Oxidation Index Standard after Severe Oxidation

Researchers have investigated whether severe oxidation associated with long-term shelf aging affects the repeatability and reproducibility of oxidation index measurement techniques. This study, which will be published in a future issue of Applied Biomaterials, provided validation of standard oxidation index measurement methods after severe oxidation.

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New Hybrid Constitutive Model for UHMWPE

A new constitutive model has been proposed for the mechanical behavior of UHMWPE under monotonic and cyclic loading histories. This "hybrid model" is the latest addition to a family of physically-inspired constitutive theories for polymers, which incorporate viscoplasticity, as well as viscoelasticity, based upon fundamental, statistically-based deformation mechanisms in polymers.

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Miniature Specimen Shear Punch Test for UHMWPE

A miniature specimen (0.5 mm thickness x 6.4 mm diameter) shear punch test has been developed to evaluate the shear behavior of UHMWPE used in total joint replacement components. In this paper, to appear in Biomaterials, researchers have investigated the shear punch behavior of virgin and crosslinked stock materials, as well as of UHMWPE from tibial implants that were gamma-irradiated in air and shelf aged for up to 8.5 years.

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Wear Surfaces of Highly Crosslinked Acetabular Components

Highly crosslinked acetabular components have been clinically introduced in an effort to reduce volumetric wear rates and concomitantly the rate of late-onset osteolysis. In this report, researchers examined the wear surfaces of three highly crosslinked acetabular components using optical microscopy, scanning electron microscopy, and white light interferometry.

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Development of the Small Punch Test for UHMWPE

This book chapter, made available here with permission of Trans Tech Publications Ltd, traces the historical development of the small punch test and reviews recent research on miniature specimen mechanical test methods for characterizing UHMWPE used in orthopedic components.

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