In vitro dissolution behaviour of two morphologically different thermally sprayed hydroxyapatite coatings

Two types of hydroxyapatite coating on titanium substrates were produced by vacuum plasma spraying and detonation gun spraying. The response of the coatings to immersion in Ringerʹs solution at pH 7.2 and held at 37°C for periods of one, two, four and eight weeks was compared . X-ray diffraction was used to measure changes in crystallinity and residual stresses. Porosity and coating thickness were measured using optical microscopy combined with image analysis. Surface morphology was characterised using scanning electron microscopy and Talysurf measurements. The DGUN coatings were found initially to have a lower crystallinity and porosity but higher surface roughness and residual stress level than the VPS coatings. This resulted in a higher rate of dissolution compared to the more stable VPS coatings.