Titanium alloy surfaces with antibacterial and bioactive properties to counteract prosthetic bacterial infections.

Background: Prosthetic infections interest 1% of total joint replacement and represent one of the major complications of orthopedic implants. They can lead to prolonged antibiotic therapies and even to the need of implant removal. The results are patient health concerns and discomfort, together with increased hospitalization times and costs. In this context, the development of implant surfaces able to reduce infection risk and enhance osteointegration rate constitutes a challenge. 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 to avoid bacterial contamination. Materials/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 silver. 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 silver 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. Silver nanoparticles are embedded in this surface layer by the addition of a silver precursor in the hydrogen peroxide bath. XPS analyses indicate that silver is in the metallic form. Silver nanoparticles are responsible of silver ion release in water. The released silver amount is higher than what required to have an antibacterial action and lower that the cytotoxic limit reported in the literature (Figure 1A). 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 (Figure 1B/C). 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. Conclusion: An innovative and patented surface treatment has been applied to Ti6Al4V alloy. A nanotextured titanium oxide layer rich in hydroxyl groups and embedded with silver nanoparticles has been obtained. Modified surfaces are bioactive by inducing hydroxyapatite precipitation in SBF, release silver ions and present an antibacterial action against S. aureus. Considering the reported results, the obtained Ti6Al4V surfaces are promising for orthopaedic applications in order to induce fast and physiological bone integration and to reduce the incidence of prosthetic infections.