Thermal processing of hydroxyapatite for coating production

✍ Scribed by Gross, K. A. (author);Berndt, C. C. (author)

• Publisher: John Wiley & Sons Inc
• Year: 1998
• Tongue: English
• Weight: 205 KB
• Volume: 39
• Category: Article
• ISSN: 0021-9304
• DOI: 10.1002/(sici)1097-4636(19980315)39:4<580::aid-jbm12>3.0.co;2-b

✦ Synopsis

Thermally processed hydroxyapatite coatings used on dental implants and hip prostheses for enhanced fixation may typically consist of a number of chemical and structural phases. These phases affect coating performance and tissue attachment. Hydroxyapatite was plasma sprayed to examine the phase evolution during processing. Coatings were examined with X-ray diffraction and elemental analysis. Results indicate that phase transformations are produced by (a) preferential removal of hydroxyl and phosphate leading to a change in melt composition, and (b) the high cooling rate due to the thermal spray process. Hydroxyl group removal promotes the amorphous phase and oxyapatite. Further heating produces a less viscous melt fa-cilitating decomposition of hydroxyapatite to tricalcium and tetracalcium phosphate. Phosphate removal during flight produces a more calcium-rich melt preferring tetracalcium phosphate and calcium oxide formation. A proposed model shows the phase location within the lamellae of these coatings. Coating processes must thus prevent removal of hydroxide and phosphate during processing to maximize the hydroxyapatite content.