Adhered bacteria on titanium surfaces are able to decrease its corrosion potential and impedance values at the lowest frequencies. This result points to the detrimental influence of the biofilm on the passive film formed on the surfaces, independently on the surface finishes.

Titanium is one of the most used metallic biomaterials for biological and implant applications. The spontaneous formation of a protective passive film around 2–5 nm thick, make titanium unique as a biomaterial for implants. Its composition has been described by a three-layer model: TiO2/Ti2O3/TiO and its stability is ultimately responsible for the success of osseointegrated titanium implants. The cases of breakdown of the protective passive film are associated with highly acidic environments induced by bacterial biofilms and/or inflammatory processes that lead to localized corrosion of titanium and, in extreme cases, implant failure. Bearing in mind that the surface design of a titanium implant is a key element involved in the healing mechanisms at the bone-implant interface, the surface modifications have sought to enhance the biomechanical anchorage of the implant and promote osseointegration at the cell-biomolecular level. However, little attention has been paid to the effects of these surface modifications in the microbiologically induced corrosion (MIC). The aim of this work is to evaluate the potential for MIC of titanium in the short term under viable bacterial cells of Streptococcus mutansas a representative microorganism of oral biofilm considered to be a highly cariogenic pathogen.

Discs of 64 mm²surface area of commercially pure titanium, grade 4, were supplied by Biotechnology Institute (BTI, Vitoria, Spain). Four surface treatments were studied: two acid etchings (low roughness, opN and high roughness, opV). In addition, acid etched plus anodic oxidation (opNT). For comparative purposes, two surface finishes have been included: high roughness – corresponding with sandblasting-large grit plus acid (SLA); and, as-machined titanium (mach). The oral strain used for assessing the biofilm formation on the corrosion behavior of Ti surfaces was Streptococus mutansATCC 25175, obtained from the Spanish Type Culture Collection (CECT). The study of MIC from Streptococcus mutanson surfaces of Ti was carried out in an electrochemical cell specifically designed and patented by some of the present authors [1]. A three set up configuration of the electrochemical cell was used in the experiments. The measurement of the corrosion potential and electrochemical impedance was performed at different periods of incubation of bacteria: 2, 7, 15, 21 and 28 days.

Out Slight but continuous decrease in the corrosion potential and impedance values at the lowest frequencies indicate the deleterious influence of the biofilm on the passive film formed on the surfaces, independently on the surface finishes.

This research suggests that the most appropriate surface modification for the dental implant portion at the bone level would be the acid etched of high roughness (opV) surface.

The surface of any implant device plays an important role in their biocompatibility. After implantation, the physico-chemical surface properties of any biomaterial determine its good/bad response against protein adsorption, cell attachment and proliferation and bacterial adhesion [1]. In this sense, the knowledge of hydrophobicity and surface tension of any new-developed biomaterial is an added value for the final product. Polymeric implants, among which are poly-D-Lactic acid (PLDA), are well characterized biodegradable biomaterials that have been proposed as an alternative to metallic implants for fracture fixation. However, their use in the clinical practice has been limited due to insufficient osseointegration and adverse tissue reactions. Recently it has been demonstrated the feasibility of introducing Mg particles within the PLDA matrix as a new strategy to improve the bioactivity and mechanical properties of PLDA whereas simultaneously modulating the degradation rate of Mg [2]. In this work, the surface of new amorphous and crystalline composites of PLDA with two different Mg concentrations are characterized in terms of hydrophobicity and surface tension.

Amorphous and crystalline PLDA from Natureworks were reinforced with Mg particles through a processing route that contained four different stages: drying, hot extrusion, grinding and compression moulding. Two different Mg concentration were used: 1 wt.% and 10 wt.% Hydrophobicity was obtained by goniometry using water as probe liquid (θ_W). The surface tension was determined through the Young Equation using water, formamide and diiodomethane as probe liquids. Van Oss approach was used to split the surface tension into the Lifshitz-van der Waals component (γ^LW) and acid-base component (γ^AB). The acid-base was also divided into the electron-donor (γ⁻) and electron-acceptor parameters (γ⁺).

The water contact angle was similar in amorphous and crystalline samples. Mg always reduced the θ_W value, no matter the Mg concentration used. Reductions were similar for both Mg concentrations. The surface tension in amorphous samples was comprised between 26 and 36 mJ/m² and in crystalline samples was between 30 and 36 mJ/m². Although values were very similar, the deviations observed for crystalline samples were always smaller than for amorphous. An important effect of Mg in the composites was the increase in the parameter γ-.

Mg addition makes the polymer less hydrophobic. The increase of γ⁻ may be related to an increase in the negative surface charge of Mg samples. The hydrophobic reduction plus the more negative surface could impair the bacterial approach and further adhesion to the surface of the new composites, which implies an advance in the fight against infections.