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This paper reports a detailed study of how repeated r.f. magnetron sputtering from a hydroxyapatite (HA) powder target affects the nature and reproducibility of a sequential series of thin-film coatings deposited onto Ti6Al4V substrates. An evaluation of the effective lifespan of the HA sputter targets and the reproducibility of the calcium phosphate (CaP) coatings produced from them has been made from Fourier transform infrared spectroscopy, XPS and, as appropriate, atomic force microscopy and SEM/energy dispersive x-ray analyses. The annulus region of the target surface, from which sputtering under r.f. magnetron conditions normally occurs, showed severe surface degradation after only one deposition run, as indicated by significant PO 4 3− and OH − depletion. This deterioration continued after each subsequent deposition cycle but to a much lesser extent than that observed in the initial sputtering period. The layers produced from all of the sputter runs contained the expected Ca 2+ and PO 4 3− species characteristic of a CaP system but were OH − deficient in the as-deposited state. However, the chemical and morphological properties of the coatings did not change significantly until after the third consecutive sputter cycle. Hence, these data indicate that, even though a significant level of degradation of the HA target occurs at the outset of the sputtering procedure, the general plasma conditions employed here have a dominant influence on the coating properties until a critical degradation condition is met. As such, the compacted HA powder targets of interest can have a life-cycle greater than single usage without detriment to the chemistry and morphology of the coatings produced from them.

A comparative stress analysis of a polymeric composite hip joint replacement was performed. A prototype short carbon-fiber reinforced PEEK (CF/PEEK) prosthesis was manufactured by injection molding. Finite element (FE) analysis was conducted on intact femurs and femurs fitted with the CF/ PEEK and the titanium prostheses under various loading conditions. FE models were validated by experimental strain gauge measurements by using synthetic femurs. There was a good agreement between the two methods except in the hoop strain of the femur in the calcar region because of the assumption of the isotropic material properties. The stem stresses were lower for the CF/PEEK prosthesis than for the titanium prosthesis. The maximum stress was in the spigot of the CF/PEEK prosthesis, but in the middle third of the stem of the titanium prosthesis. Stress generated in the cement was almost equal for both prostheses although more load was transferred, via cement, to the femur with the CF/ PEEK prosthesis because the load transfer took place over a larger area. An out-of-plane component of the joint load causes higher prosthesis and cement stresses.