Surface characterisation of the evolving nature of radio frequency (RF) magnetron sputter deposited calcium phosphate thin films after exposure to physiological solution

The initial behaviour and ultimately the long-term performance of calcium phosphate (Ca–P) coatings for hard tissue implant applications are influenced by their dissolution properties. For this study, Ca–P coatings were deposited onto Ti-6Al-4V substrates using RF magnetron sputtering. The physico-chemical nature of these deposited layers was then determined both before and after annealing at 400 °C using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Furthermore, their dissolution behaviour in phosphate buffered saline (PBS) solution was also examined using similar techniques. The data shows clearly that the as-deposited coatings are amorphous when compared with the more crystalline coatings produced after annealing at 400 °C. These as-deposited coatings completely dissolve after exposure to the PBS for only 24 h; however, the dissolution rate of the annealed coatings is more restrained. Whereas the XPS and FTIR data show no change in the chemical nature of the annealed coatings after 30 days, the AFM results reveal subtle changes in the surface topography of the coatings after only 1 h of immersion. These data clearly show the utility of surface analytical techniques, such as AFM in combination with more established techniques for examining the surface properties of Ca–P coatings. Furthermore, the study also shows that calcium phosphate coatings deposited at low power using RF magnetron sputtering can undergo a decreased dissolution rate under physiological conditions they when subjected to post deposition annealing.