Chemical stability, antibacterial and osteogenic activities study of strontium-silver co-substituted fluorohydroxyapatite nanopillars: A potential multifunctional biological coating

Abstract The hydroxyapatite (HA) coating doped with multiple ions has attracted much attention due to its potential to impart various functions (antibacterial and osteogenic activity, etc.) to plastic surgery and dental implants. In this work, novel nano fluorohydroxyapatite (FHA) coatings substituted simultaneously with Sr2+ and Ag+ (SrAgFHA) were designed and successfully synthesized by one-step electrodeposition. Ag was used to impart antibacterial ability to SrAgFHA, and Sr can balance the potential cytotoxicity of Ag, thereby improving the cell compatibility of the composite coating. The SrAgFHA coating was consisted of closely aggregated/fused hexagonal columnar nanorods of ∼100–150 nm. The nano-coating has higher corrosion resistance than FHA coating and uncoated Ti. Due to the doping of F, SrAgFHA nanorods have a complete single crystal structure and exhibit low degradability, which can ensure the long-term and slow release of Sr2+ and Ag+ ions. This nanorod coating with a low roughness and zeta potential was superhydrophobic and displayed good in vitro bioactivities, such as excellent apatite forming ability, which proves the osteoconductive nature. The results of electrochemical impedance spectroscopy confirmed that by electrodepositing the SrAgFHA coating on the Ti surface, the corrosion resistance was significantly improved. SrAgFHA coating has the best antibacterial effect and osteogenesis ability, for example, the broad-spectrum antibacterial effect on E. coli and S. aureus is 96.5 and 96.8%, respectively, and it can induce osteoblast adhesion, proliferation and differentiation. The rabbit bone defect experiment showed that a large amount of new bone was formed around the SrAgFHA coated implant, and its early bone integration ability was the strongest. In summary, SrAgFHA strikes a balance between superior corrosion resistance, cytocompatibility and excellent antibacterial properties. The multi-element co-doped HA coating has huge clinical application potential in anti-infective repair.