Suspension plasma-sprayed fluoridated hydroxyapatite coatings: Effects of spraying power on microstructure, chemical stability and antibacterial activity

Nanostructured fluoridated hydroxyapatite (FHA) coatings were deposited on Ti substrates using the suspension plasma spraying (SPS) process. The effects of the plasma spraying power on the microstructure and properties of coatings were intensively studied. The X-ray diffraction pattern showed that the as-sprayed coatings mainly consisted of the hydroxyapatite (HA) phase, and the crystal size was estimated to be dozens of nanometers. With the increase of the spraying power, the amount of decomposed phases, crystallinity, and crystal size increased. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of fluorine in the as-sprayed coatings. The corrosion in simulated body fluid (SBF) was studied using potentiodynamic polarization tests, and the results indicated that the coating greatly enhanced the corrosion resistance of the Ti substrate. The chemical stability was assessed by measuring the weight loss of the coatings before and after immersion in a citric acid-modified phosphate buffered saline (PBS) solution at various intervals. The results showed that increasing the spraying powers decreased the dissolution rate of coatings. The in vitro bioactivity was characterized by soaking coatings in the SBF solution for different times, and the obtained results suggested that the spraying power levels affected the initial nucleation rate of the bone-like apatite on the coating surface. The antibacterial activity was investigated using optical density (OD) growth curves and colonyforming unit assays. The coating prepared at a low spraying power had relatively high antibacterial activity with respect to Staphylococcus aureus.