The wear, wear debris and functional biological activity of non-crosslinked and moderately crosslinked ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups have been compared when articulating against smooth and intentionally scratched femoral heads. Volumetric wear rates were determined in a hip joint simulator and the debris was isolated from the lubricant and characterized by the percentage number and volumetric concentration as a function of particle size. The volumetric concentration was integrated with the biological activity function determined from in vitro cell culture studies to predict an index of specific biological activity (SBA). The product of specific biological activity and volumetric wear rate was used to determine the index of functional biological activity (FBA). On smooth femoral heads the crosslinked UHMWPE had a 30 per cent lower wear rate, but it had a greater percentage volume of smaller, more biologically active particles, which resulted in a similar index of FBA compared with the non-crosslinked material. On the scratched femoral heads the volumetric wear rate was three times higher for the moderately crosslinked UHMWPE and two times higher for the non-crosslinked UHMWPE compared with the smooth femoral heads. This resulted in a higher wear rate for the moderately crosslinked material on the scratched femoral heads. All the differences in wear rate were statistically significant. There were only small differences in particle volume concentration distributions, and this resulted in similar indices of FBA which were approximately twice the values of those found on the smooth femoral heads. Both materials showed lower wear and FBA than for previously studied aged and oxidized UHMWPE gamma irradiated in air. However, this study did not reveal any advantage in terms of predicted FBA for moderately crosslinked UHMWPE compared with non-crosslinked UHMWPE.

The spinal cord is an integral component of the spinal column and is prone to physical injury during trauma or more long-term pathological insults. The development of computational models to simulate the cord-column interaction during trauma is important in developing a proper understanding of the injury mechanism. Such models would be invaluable in seeking both preventive strategies that reduce the propensity for injury and identifying specific treatment regimes. However, these developments are hampered by the limited information available on the structural and mechanical properties of this soft tissue owing to the difficulty in handling this material in a cadaveric situation. The purpose of the present paper is to report the rapid deterioration in the quality of the tissues once excised, which provides a further challenge to the successful elucidation of the structural properties of the tissue. In particular, the tangent modulus of the tissue is seen to increase sharply over a period of 72 h.