Corrosion behavior and biocompatibility of strontium and fluorine co-doped electrodeposited hydroxyapatite coatings

To improve the corrosion resistance and biocompatibility of biomedical titanium, strontium (Sr) and fluorine (F) were simultaneously incorporated in hydroxyapatite (HAp) to form SrFHAp coating on titanium (Ti) via electrodeposition. The microstructure, phase composition, corrosion resistance, and cytocompatibility of the films were studied. Results revealed that by incorporating F− and Sr2+ ions in HAp, the density of the coating markedly increased, i.e., a lower porosity than common HAp coating. The SrFHAp layer was dense and uniform, with nano-needle-like crystals of apatite, which aligned vertically to the substrate. The SrFHAp crystals were calcium-deficient apatite, and Sr2+ ions and F− ions were homogeneously distributed in the coating. The SrFHAp coating showed lower dissolution rate than HA coating. Potentiodynamic polarization test manifested that the SrFHAp-coated titanium exhibited superior corrosion resistance than HAp single-coated sample. In addition, osteoblasts cellular tests revealed that the SrFHAp coating was more effective to improve the in vitro biocompatibility of Ti compared with HAp coating.