Nanostructured Ag+-substituted fluorhydroxyapatite-TiO2 coatings for enhanced bactericidal effects and osteoinductivity of Ti for biomedical applications

Yong Huang,1,* Guiqin Song,1,* Xiaotong Chang,1 Zhenhui Wang,2 Xuejiao Zhang,1 Shuguang Han,3 Zhuobin Su,4 Hejie Yang,5 Dongdong Yang,6 Xiaojun Zhang7 1College of Lab Medicine, Hebei North University, Zhangjiakou, China; 2Department of Nuclear Medicine, People’s Liberation Army No 251 Hospital, Zhangjiakou, China; 3Institute of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, China; 4The First Affiliated Hospital, Hebei North University, Zhangjiakou, China; 5State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an, China; 6School of Physics and Optoelectronic Engineering, Ludong University, Yantai, China; 7Department of Physics, Fourth Military Medical University, Xi’an, China *These authors contributed equally to this work Background: Poor mechanical properties, undesirable fast dissolution rate, and lack of antibacterial activity limit the application of hydroxyapatite (HA) as an implant coating material. To overcome these limitations, a hybrid coating of Ag+-substituted fluorhydroxyapatite and titania nanotube (TNT) was prepared.Methods: The incorporation of silver into the HA-TiO2 hybrid coating improves its antimicrobial properties. The addition of F as a second binary element increases the structural stability of the coating. The TNT/F-and-Ag-substituted HA (FAgHA) bilayer coating on the Ti substrate was confirmed by X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS).Results: The results indicate that the FAgHA/TNT nanocomposite coating has a dense and uniform morphology with a nano-rod-like structure. The solubility measurement result shows that the substitution of F- ions into the AgHA structure has a positive effect on the dissolution resistance of HA. The adhesion strength of FAgHA/TNT has significantly increased because of the interlocking of the roughened surface with nano-rod-like particles that entered into the voids of the TiO2 nanotubes. Compared with that of the bare Ti, the corrosion current density of FAgHA/TNT-coated Ti substrate decreased from 3.71 to 0.18 µA, and its corrosion resistance increased by almost two orders of magnitude. Moreover, despite pure HA, the FAgHA killed all viable Staphylococcus aureus after 24 hours of incubation. Although the fabricated FAgHA/TNT coating is hydrophobic, it induced deposition of the typical spherical apatite when immersed in a simulated body fluid (SBF); the osteoblasts spread very well on the surface of the coating. In addition, in vitro cell culture tests demonstrated cell viability and alkaline phosphatase (ALP) similar to pure HA, which indicated good cytocompatibility. Interestingly, compared with bare Ti, FAgHA/TNT-coated Ti surface was innocent for cell vitality and even more beneficial for cell osteogenesis in vitro.Conclusion: Enhancing the osseointegration and preventing infection in implants, the FAgHA/TNT-coated Ti makes implants more successful. Keywords: titania nanotube, silver, fluorhydroxyapatite, bactericidal effects, osteoin­ductivit