Abstract
Nanostructured hydroxyapatite (HA) and HA/nano-zirconia powders were sprayed by both plasma and HVOF spraying. Microstructure characterization on the nanostructured coatings were conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and Raman spectroscopy. Results showed that the nanostructures of the HA feedstock retained to some extent after the thermal spraying depending on the melt state of the powders. The microstructural features of individual HA splats were also characterized through TEM observing both as-sprayed and ion-milled splats. A nanostructure (with ~ 30nm grains) within the surrounding parts of the HA splats was revealed, while significant grain growth (a size up to 5 µm) depending on flattening state was found at the center of the splats. It also revealed that the nano-sized zirconia particles (< 90 nm) retained their fine size after HVOF deposition, and were evenly distributed within the coating. The crystallite size of tetragonal zirconia in the coating was found to be less than 13 nm. The biocompatibility of the coatings was characterized using in vitro incubation testing in simulated body fluid and osteoblast cell culturing. It showed that the presence of the nanostructures in the coatings improved the stability of the coatings (delayed the dissolution). The addition, the presence of the nanostructures contributes to improved mechanical properties.
