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The wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/million cycles) is much lower than the more widely used polyethylene-on-metal bearings (30-100 mm3/million cycles). However, there remain some potential concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically in the human body. The aim of this study was to investigate the wear, wear debris and ion release of fully coated surface engineered MOM bearings for hip prostheses. Using a physiological anatomical hip joint simulator, five different bearing systems involving three thick (8-12 microm) coatings, TiN, CrN and CrCN, and one thin (2 microm) coating diamond like carbon (DLC) were evaluated and compared to a clinically used MOM cobalt chrome alloy bearing couple. The overall wear rates of the surface engineered prostheses were at least 18-fold lower than the traditional MOM prostheses after 2 million cycles and 36-fold lower after 5 million cycles. Consequently, the volume of wear debris and the ion levels in the lubricants were substantially lower. These parameters were also much lower than in half coated (femoral heads only) systems that have been reported previously. The extremely low volume of wear debris and concentration of metal ions released by these surface engineered systems, especially with CrN and CrCN coatings, have considerable potential for the clinical application of this technology.

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Although the wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/10(6) cycles) is much lower than the more widely used polyethylene-on-metal bearings, there are concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically, in the human body. The aim of this study was to investigate the possibility of reducing the volume of wear, the concentration of metal debris and the level of metal ion release through using surface-engineered femoral heads. Three thick (8-12 microm) coatings (TiN, CrN and CrCN) and one thin (2 microm) coating (diamond-like carbon, DLC), were evaluated on the femoral heads when articulating against high carbon content cobalt-chromium alloy acetabular inserts (HC CoCrMo) and compared with a clinically used MOM cobalt-chromium alloy bearing couple using a physiological anatomical hip joint simulator (Leeds Mark II). This study showed that CrN, CrCN and DLC coatings produced substantially lower wear volumes for both the coated femoral heads and the HC CoCrMo inserts. The TiN coating itself had little wear, but it caused relatively high wear of the HC CoCrMo inserts compared with the other coatings. The majority of the wear debris for all half-coated couples comprised small, 30 nm or less, CoCrMo metal particles. The Co, Cr and Mo ion concentrations released from the bearing couples of CrN-, CrCN- and DLC-coated heads articulating against HC CoCrMo inserts were at least 7 times lower than those released from the clinical MOM prostheses. These surface-engineered femoral heads articulating on HC CoCrMo acetabular inserts produced significantly lower wear volumes and rates, and hence lower volumetric concentrations of wear particles, compared with the clinical MOM prosthesis. The substantially lower ion concentration released by these surface-engineered components provides important evidence to support the clinical application of this technology.

Polydiacetylene xBCMU and 9PA crystals, solutions and solution-cast films vary in colour due to differences in backbone order and planarity. Associated with the colour changes are increases in the Raman frequencies of the triple and double backbone bond vibrational modes from those values found in the highly ordered single crystals. These increases are strongly correlated and the ratio of the change in the frequency of the triple bond mode to that of the double bond mode is found to be 1.6 (iO.l) over a wide variation in order. This ratio is compared with the values of 0.3 found under uniform strain and 1.1 predicted by a model of acetylenic to butatrienic delocalisation. The relationship between the Raman frequencies of the yellow solutions and melts and those of the crystal phases suggests that in the former the backbone has a continuous and smoothly curving 'worm-like' conformation. Models involving the break-up of the conjugated system by large-angle bond rotations appear to be incorrect for polydiacetylenes. These results have important consequences for theoretical models that predict the dependence of electron delocalisation on backbone order and planarity in polydiacetylenes.

The micromechanics of reinforcement of a model composite system consisting of a continuous high-modulus (HM) carbon fibre embedded in an epoxy resin have been investigated. The composite was subjected to incremental tensile loading up to full fibre fragmentation, while the strain in the fibre was monitored at each level of load using a laser Raman spectroscopic (LRS) technique. The average strain in the fibre increased linearly with applied matrix strain up to a value of 0.8 %, when the first fibre fracture occurred. After fracture, the strain in the fibre was found to build from the tips of the fibre breaks, reaching a maximum value in the middle of each fragment. The shape of the load transfer profiles at the locality of the fibre tips indicated that the stress transfer efficiency had been affected by the fracture process. The length of interfacial debonding at the point of fibre fracture was found to be driven by the strain energy of the fractured fragments.The interfacial shear stress (ISS) distributions at various levels of applied load along individual fragments, have been derived from the load transfer profiles using a balance of forces analysis. The shape of the ISS profiles confirmed that interfacial debonding initiated from the tips of the fibre breaks, whereas good fibre/matrix adhesion was retained around the mid-length of each fragment. By increasing the applied strain to 1.8%, the maximum ISS values also increased in spite of the presence of debonding at the fibre tips. An upper ISS limit of 42 MPa was calculated at this point. Further increases of the applied strain to 5% resulted in significant reductions in the values of the maximum ISS, as well as an increase, of the frictional slip towards the middle of each fragment. Finally, by employing the assumptions of the conventional fragmentation test, the calculated value of the nominal interfacial shear strength at the point of full fragmentation was lower by a factor of 2 than the value measured by the LRS method.