Morphology and immersion behavior of plasma-sprayed hydroxyapatite/bioactive glass coatings

A series of hydroxyapatite/bioactive glass (HA/BG) coatings have been plasm a-sprayed on Ti6Al-4V substrate using HA/BG powders that were prepared by b oth sinter-granulation and direct mixing methods. The morphology and immers ion behavior of these coatings in a simulated body fluid (SBF) were investi gated. The results showed that in-house fabricated BG and sinter-granulated HA powders were irregularly shaped and dense. When 5 wt % or more BG was a dded in HA, the powder became rough and porous. X-ray diffraction (XRD) pat terns showed that the presence of BG enhanced the decomposition of HA struc ture during fabrication of the powders. Reasonably high bond strengths were obtained from all coatings. The granulated type HA/BG coatings showed no s ignificant differences in bond strength from the mixed type HA/BG coatings. The plasma spray process itself and the presence of BG enhanced the decomp osition of apatite. Surface morphology of all sinter-granulated type coatin gs was similar to that of monolithic HA coating, that was comprised of patc hes of smooth and shiny glassy film and irregularly-shaped particles on its surface. The dissolution depth of plasma-sprayed coatings immersed in SBF was largely dependent on the type and composition of the coating. Granulate d type HA/BG coatings were much less dissolvable than monolithic HA or mixe d type HA/BG coatings. It seems that the presently used granulation method for the preparation of HA/BG powders plays a predominant role in determinin g the dissolution behavior of the plasma-sprayed coatings. (C) 2000 Kluwer Academic Publishers.