Structural change of biomimetic hydroxyapatite coatings due to heat treatment

Biomimetic deposition of hydroxyapatite (HA) coatings on implants could be done for two reasons, one is to study their possible bioactivity, and one is to generate bioactive coatings on implants before implantation surgery to improve the osseointegration. Heat treatment of coated implants can be performed for several reasons, for example, to ensure coating sterility and to increase the adhesion. This paper describes the morphology and crystalline structure changes occurring due to the heat treatment of biomimetic HA coatings on rutile TiO2. Rutile TiO2 surfaces were produced on titanium (Ti) plates by heating at 800 degrees C. Afterwards, these samples were immersed in a phosphate buffer saline solution for 7 days at 37 degrees C in order to deposit HA coatings on their surfaces. These HA coatings were then either untreated or heat treated at 600 or 800 degrees C for 1 hr. The coatings microstructural changes were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cross-sectional TEM samples were produced using a sample preparation method based on focused ion beam microscopy (FIB). Rutile was found to be bioactive due to HA formation on the surface. The 600 degrees C heat treatment of the HA coating changed its morphology, increased its grain size and also increased the porosity. At 800 degrees C the coating was completely transformed to beta-TCP according to XRD. Sample preparation using FIB and TEM analysis proved to be a useful method for high-resolution analysis of biomimetic coatings in cross-section.