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

•The SrFHAp coating was formed on Ti substrate by ED for the first time.•Dense and uniform SrFHAp layer formed with nano-needle-like crystal morphology.•The Sr and F ions were homogeneously distributed in the SrFHAp coating.•The SrFHAp coating showed higher corrosion resistance than the pure HAp coating.•The SrFHAp coating showed better in vitro biocompatibility than pure HAp coating. 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.