Comparative study of structure and properties of thermal spray coatings using conventional and nanostructured hydroxyapatite powder, for applications in medical implants

Abstract

The objective of this paper is to study and compare the structure and properties of thermal spray coatings prepared with conventional and nanostructured hydroxyapatite powder, in order to assess their suitability for future use in medical implants. Four coatings were prepared via Atmospheric Plasma Spray process (APS). Two kinds of feedstock material were employed for the spray process, namely, commercial XPT-D-703 hydroxyapatite powder for half the samples and novel nanostructured PYRO 4 hydroxyapatite powder, which had previously been mechanically treated, for the remaining samples. The substrate of all the samples was stainless steel 304. Finally, the plasma spray parameters were altered for two out of the four coatings, each produced with a different type of powder, in order for a sufficient amount of porosity to be achieved for future incorporation of biomolecules. The coatings were also examined in terms of bioactivity in vitro. It was concluded that the coating produced with the nanostructured powder, under lower plasma energy and at greater spraying distance presented the best results regarding its roughness, bioactive response, crystallinity, adherence and porosity content.