Enhanced analysis of biomaterials by synchrotron diffraction

There is an increasing body of evidence that prosthetic implants based upon titanium alloys attain improved performance when coated with calcium hydroxyapatite (HAP). Such coatings appear to promote osteointegration and bone in-growth. Plasma spraying is the most frequently employed route to coating fabrication. Detailed chemical and structural characterisation of these coatings is essential for (i) coating technology development, (ii) ensuring consistent material quality and (iii) assessing coating performance. The work presented here employed combined conventional powder diffraction and glancing angle synchrotron diffraction to examine the in vitro performance of apatite coatings formed by plasma spraying. Coatings were exposed to simulated body fluid and foetal calf serum, and changes to the coating chemistry and structure determined. A new analysis method, synchrotron depth profiling tomography, has been applied to obtain structural features through the coating depth. The dissolution and re-precipitation behaviour of the coatings was found to be significantly different for each media. For the first time, it has been possible to identify and quantify the formation of a nanocrystalline, carbonated HAP phase. It has been possible to simultaneously model all coating phases apparent within the X-ray diffraction data and thus quantify changes to film composition. DPT has also revealed subtle changes in coating features with depth and these may have a significant impact on coating dissolution. The findings are discussed in the context of kinematic models for the coating behaviour and implications for the performance of such coatings in vivo.