Antibacterial And Bioactive Ti6Al4V Surfaces.

Introduction: The prosthetic infections interest 1% of total joint replacement and this percentage increases in the case of revision surgery [1-3]. They represent one of the major complications of orthopedic implants and can lead to prolonged antibiotic therapies (which can last for years) and even to the need of implant removal. The results are patient health concerns and discomfort, together with increased hospitalization times and costs. Moreover, increasing development of bacterial resistance to conventional antibiotics makes the problem more serious. In this context, the development of implant surfaces able to reduce infection risk and to enhance osteointegration rate constitutes a challenge. After implantation, a sort of “race for the surface” between tissue cells and bacteria has been described in the scientific literature [4, 5]. An ideal surface for implants should improve cellular adhesion and reduce bacterial one. Despite of a wide research in the field of antibacterial surfaces, the optimal solution is still far from the clinical application. Objectives: The aim of the present research work is the development of innovative antibacterial and bioactive Ti6Al4V surfaces, able to promote fast and physiological bone integration and to avoid bacterial contamination. Methods: Ti6Al4V disks (10 mm diameter and 2 mm thick, ASTM B348, Gr5, Titanium Consulting and Trading) were surface modified by means of a patented process [6, 7] that foresees a first etching in diluted hydrofluoric acid and a subsequent controlled oxidation in hydrogen peroxide, added with an antibacterial agent (silver in the present work). Modified surfaces were characterized by means of Field Emission Scanning Electron Microscopy (FESEM - SUPRATM 40, Zeiss), X-ray Photoelectron Spectroscopy (XPS, PHI 5000 VERSA PROBE, PHYSICAL ELECTRONICS) and Fourier Transformed Infrared Spectroscopy (FT-IR, IR Hyperion 2000, Tensor 27 - Bruker S.p.A) in order to characterize the surface topography and chemical composition. In vitro bioactivity was investigated by soaking samples in Simulated Body Fluid (SBF) and silver release was quantified in double distilled water. The antibacterial activity of the modified surfaces was tested against S aureus by means of inhibition halo and count of colony forming units tests. Results: Modified Ti6Al4V samples present a titanium oxide layer with a peculiar nanotexture that can be described as a nanometric sponge with Ra of 10nm [6-8]. Silver nanoparticles (20-200 nm) are embedded in this surface layer by the addition of a silver precursor in the hydrogen peroxide bath [7]. XPS analyses indicate that silver is in the metallic form. Ag nanoparticles are responsible of the release of silver ions in water. The amount of released silver is higher than what required to have an antibacterial action and lower that the cytotoxic limit reported in the literature [8]. The results of antibacterial tests confirm this 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: 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 (they induce hydroxyapatite precipitation in SBF), they 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.