A prospective material for orthopedic applications: Ti substrates coated with a composite coating of a titania-nanotubes layer and a silver-manganese doped hydroxyapatite layer

Orthopedic implants need to be coated with biomedical coatings that can facilitate osseointegration and mitigate bacterial biofilm formation. Using anodisation and electrodeposition techniques, we modified Ti implants with a double-layer coating made of TiO2 nanotubes (TNT) and hydroxyapatite that was codoped with silver and manganese (AgMnHA). The silver incorporation into hydroxyapatite improves its antimicrobial properties, and the manganese doping offsets the potential cytotoxicity of the incorporated silver. The AgMnHA and the TNT films were characterized with X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results highlight that the manganese and silver ions were evenly incorporated into the AgMnHA/TiO2 coating. Its adhesion strength significantly increased because of the interlocking of the rough TiO2 layer with the bioceramic particles that entered into the voids of the TiO2 nanotubes. The coating decreases the corrosion current density of titanium from 3.71 mu A to 0.19 A, and increases its corrosion resistance by almost two orders of magnitude. The coating can continuously release silver ions into the bacterial suspension, resulting in excellent antimicrobial efficacy with a 100% reduction in viable cells. Both hydroxyapatite and the AgMnHA/TiO2 coating are super hydrophilic; meanwhile, if immersed in a simulated body fluid, they could induce the deposition of typical spherical apatite. In-vitro cell culture tests demonstrated that hydroxyapatite and the AgMnHA/TiO2 coating considerably improved the cell viability and the alkaline phosphatase (ALP) activity. Therefore, the AgMnHA coating has no significant cytotoxicity on osteoblasts, and could generate sufficient osteoblast differentiation for osseointegration. We therefore find that a bilayer AgMnHA/TiO2 coating on Ti implants improves antibiofilm properties that does not offset the hydroxyapatite biocompatibility that is needed for successful osseointegration and bone healing.