Introduction An ideal surface for orthopedic implants should improve cellular adhesion and reduce bacterial one. A proper stimulation of the cell activity is the last request to the new biomaterials, intended for bone substitution and osseointegration. In this regard, the scientific literature suggests that the surface modification on a nanoscale is a major source of innovation. Furthermore, numerous solutions have been proposed to face the problem of the bacterial contamination and to prevent the development of prosthetic infections. The considered solutions are based on inorganic antibacterial agents, such as silver (Ag) copper or zinc, which have been introduced to overcome the growing problem of bacterial resistance to antibiotics. The aim of the present research work is the development of innovative antibacterial and bioactive titanium alloy (Ti6Al4V) surfaces, able to promote fast and physiological bone integration and avoid bacterial contamination. Materials and methods Ti6Al4V disks were surface modified by means of a patented process that foresees a first etching in diluted hydrofluoric acid and a subsequent controlled oxidation in hydrogen peroxide, added with Ag.The surface topography and chemical composition of modified surfaces were characterized by means of Field Emission Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy (XPS) and Fourier Transformed Infrared Spectroscopy (FT-IR). In vitro bioactivity was investigated by soaking samples in Simulated Body Fluid (SBF) and Ag release was quantified in double distilled water. The modified surface antibacterial activity was tested against Staphylococcus aureus ATCC 29213 by means of inhibition halo on agar medium and quantitative bacterial adhesion assays by using a sonication protocol to dislodge adherent microorganisms. Results Modified Ti6Al4V samples present a titanium oxide layer with a peculiar nanotexture that can be described as a nanometric sponge. Ag nanoparticles are embedded in this surface layer by the addition of an Ag precursor in the hydrogen peroxide bath. XPS analyses indicate that Ag is in the metallic form. Ag nanoparticles are responsible of Ag ion release in water: the released Ag amount is higher than what required to have an antibacterial action and lower that the cytotoxic limit reported in the literature. The results of antibacterial tests confirm these data and reveal an effective antibacterial behaviour of modified surfaces against S. aureus. Moreover a reduced bacterial adhesion has been observed on nanotextured surfaces compared to the polished ones. The modified surfaces are rich in hydroxyls groups (FT-IR and XPS evidence) and they are able to induce hydroxyapatite precipitation after immersion in SBF. Conclusions In this study, a nanotextured titanium oxide layer rich in hydroxyl groups and embedded with Ag nanoparticles has been obtained. Modified surfaces are bioactive by inducing hydroxyapatite precipitation in SBF, release Ag ions and present an antibacterial action against S. aureus. Considering the reported results, the obtained innovative Ti6Al4V surfaces are promising for orthopaedic applications to induce fast and physiological bone integration and to reduce the incidence of prosthetic infections.
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