Bioactive nanocrystalline sol-gel hydroxyapatite coatings

Sol-gel technology offers an alternative technique for producing bioactive surfaces for improved bone attachment. Previous work indicated that monopha sic hydroxyapatite coatings were difficult to produce. In the present work hydroxyapatite was synthesized using the sol-gel technique with alkoxide pr ecursors and the solution was allowed to age up to seven days prior to coat ing. It was found that, similar to the wet-chemical method of hydroxyapatit e powder synthesis, an aging time is required to produce a pure hydroxyapat ite phase. A methodology that has been successfully used to produce nanocry stalline hydroxyapatite thin film coatings via the sol-gel route on various substrates including alumina, Vycor glass, partially stabilized zirconia, Ti-6Al-4V alloy and single crystal MgO is described. Coatings produced on M gO substrates were characterized by X-ray diffraction and atomic force micr oscopy, while the analogous gels were examined with thermogravimetric and d ifferential thermal analyses. The coatings were crack free and the surface was covered with small grains, of approximately 200 nm in size for samples fired to 1000 degrees C. Coating thickness varied between 70 and 1000 nm de pending on the number of applied layers. (C) 1999 Kluwer Academic Publisher s.