M.A. Arenas

In vitro assessment of Staphylococcus epidermidis and Staphylococcus aureus adhesion on TiO2 nanotubes on Ti–6Al–4V alloy

The aim of this study was to evaluate Staphylococcus sp. adhesion to modified surfaces of titanium alloy (Ti-6Al-4V). Specimens of Ti-6Al-4V alloy 6-4 ELI-grade 23 that meets the requirements of ASTM F136 2002A (AMS 2631B class A1) were anodized in a mixture of sulfuric/hydrofluoric acid at 20 V for 5 and 60 min to form nanoporous (NP) and nanotubular (NT) oxide layers with pore diameter of 20 and 100 nm, respectively. The amount of fluorine incorporated in the oxide films from the electrolyte was 6 and 4 wt %, respectively. Bacterial adherence was studied using laboratory strains and six clinical strains each of Staphylococcus aureus and Staphylococcus epidermidis. Lower adherence of laboratory strains was demonstrated on fluoride nanostructured surfaces in comparison with the fluoride-free surfaces. Significant differences between clinical strains and laboratory strains were also found (p < 0.0001, Kruskal-Wallis test) when NP and NT specimens were compared with chemically polished (CP) surfaces. The results of the tests using multiple clinical strains confirmed a decrease in bacterial adherence on F-containing titanium oxide surfaces, suggesting a potential applicability of this surface, with a confirmed added value of decreasing clinical staphylococci adherence, for medical prosthetic devices.

Doped TiO2 anodic layers of enhanced antibacterial properties

Ti-6Al-4V joint replacement implants foster uncemented fixation in orthopaedic surgery. However, bacterial colonization competes with host cells and ultimately may produce implant-related difficult-to-treat infections, justifying the efforts to obtain infection-resistant materials. In a previous work, the authors demonstrated the antibacterial properties of anodic fluoride-TiO2 nanostructured layers on Ti-6Al-4V alloy. In this work, the anodizing bath has been modified in order to grow fluoride-TiO2 barrier layers (FBL). A bacterial adherence protocol, run with reference and six different clinical strains of Staphylococcus aureus and Staphylococcus epidermidis, showed a statistically significant decrease in the percentage of covered surface (p<0.0001, Kruskal-Wallis test) for FBL specimens when compared with non fluoride-containing specimens, i.e. chemically polished Ti-6Al-4V and F-free TiO2 barrier layers. The results obtained on the F-barrier layers allowed discrimination between the effects of the presence of fluoride in the layer and the layer nanostructure on bacterial adhesion.

Influence of the nanostructure of F-doped TiO2 films on osteoblast growth and function

The aim of this study was to evaluate the proliferation and mineralization ability of mouse osteoblastic MC3T3-E1 cells on F-containing TiO2 films with different morphology and nanostructure that previously confirmed antibacterial properties. F-containing TiO2 films were fabricated by anodizing Ti-6Al-4V alloy ELI -grade 23. By using a mixture of H2SO4/HF acid at 20 V for 5 and 60 min, a TiO2 film grows with nanoporous (NP) and nanotubular (NT) features, characterized with a pore diameter of 20 and 100 nm, respectively. Fluoride-TiO2 barrier films (FBL) were produced in 1M NH4H2PO4/0.15M NH4F solution at constant voltage controlled at 20 V for 120 min. The amount of F incorporated in the nanostructured oxide films was 6 at % and of 4 at %, for the NP and NT, respectively, while for the FBL film was 12 at %. MC3T3-E1 cells exhibited different behavior when seeded and grown onto these surfaces. Thus, F-doped TiO2 films with NP structures increased proliferation as well as osteogenic gene expression and the mineralization capacity of these osteoblastic cells. These results confirm that anodizing process is suitable to fabricate multifunctional surfaces on Ti-6Al-4V alloy with improved not only antibacterial but also osteogenic properties useful for bone fixation of prosthetic devices

Use of anodized titanium alloy as drug carrier: Ibuprofen as model of drug releasing

The use of osteoarticular implants has improved the quality of life of millions of patients. In this work nanotubular structures tailored made on Ti6Al4V substrates was used as drug delivery system of ibuprofen as a proof of concept. Three different nanotubular films with different sizes and forms (NT, NT+ and NTb) were analysed. Samples were soaked in a solution of 660 mg ibuprofen/20 mL n-pentane. The ibuprofen release in aqueous medium was evaluated by liquid chromatography reversed-phase (RP-HPLC). To calculate the observed constant k, the amount of ibuprofen released was plotted versus the time using linear regression according to the zero-order, first-order, second-order and Higuchi model. The release of ibuprofen was constant and independent of the concentration. The kinetic constant obtained was 0.021 (NT), 0.022 (NT+) and 0.013 (NTb) being the correlation factor of 0.98 (zero-order) where the maximum correlation factor was reached. These results indicate that the delivery process from NT and NT+ is similar and slower that NTb. In all the cases was inside the therapeutically range. These results showed the potential of these modifications in order to develop implants that can carry different molecules of medical importance.

The role of mechanically activated area on tribocorrosion of CoCrMo

Co-Cr-Mo alloys are among the most used alloys for orthopedic implants because of their excellent corrosion resistance, mechanical properties, and biocompatibility. Although there is extensive literature on corrosion properties of Co-Cr-Mo alloys, fewer articles are focused on the synergistic effect of corrosion and wear in a simulated physiological solution. It is generally assumed that the current density measured during wear conditions for passive materials comes from the active area. However, there are no clear data supporting this statement. The current article correlates electrochemical measurements with the active area generated during sliding wear tests. Open circuit potential and current measurements, potentiodynamic scans, and electrochemical impedance spectroscopy were carried out on samples under static and sliding wear conditions. These measurements showed the importance of the active area, where the current coming from the surface not being abraded is negligible. Finally, by combining the sliding wear and electrochemical tests, the synergistic effect of wear and corrosion was characterized for this alloy, documenting the metal carbides detachment from the cobalt alloy matrix, which leads to a significant increase of total wear volume.

TiO2 nanotubes with tunable morphologies

Titanium anodic oxide layers with a bottle shaped nanotubular structure have been grown in an electrolyte containing NH4F, applying voltage steps. The grown layers were analyzed using scanning and transmission electron microscopy (SEM and TEM), and Rutherford backscattering spectroscopy (RBS). The results show that a concentration of 0.15 M of NH4F in the anodizing bath, and a step of 10 to 20 V produces an oxide with a double morphology comprised of nanotubes at the oxide/metal interface and nanopores at the oxide/electrolyte interface of the anodic layer. Higher concentration of F− in the bath, 0.3 and 0.45 M NH4F, enhanced the chemical dissolution of the anodic layer resulting in nanotubular structures along the oxide layer. Therefore, the bottle shaped nanotubular structures that show a well defined morphology are obtained in a bath containing a concentration of 0.3 M NH4F and applying a voltage step of 10–20 V.

Anodization Mechanism on SiC Nanoparticle Reinforced Al Matrix Composites Produced by Power Metallurgy

Specimens of aluminum-based composites reinforced by silicon carbide nanoparticles (Al/SiCnp) produced by powder metallurgy (PM) were anodized under voltage control in tartaric-sulfuric acid (TSA). In this work, the influence of the amount of SiCnp on the film growth during anodizing was investigated. The current density versus time response and the morphology of the porous alumina film formed at the composite surface are compared to those concerning a commercial aluminum alloy (AA1050) anodized under the same conditions. The processing method of the aluminum alloys influences the efficiency of the anodizing process, leading to a lower thicknesses for the unreinforced Al-PM alloy regarding the AA1050. The current density versus time response is strongly dependent on the amount of SiCnp. The current peaks and the steady-state current density recorded at each voltage step increases with the SiCnp volume fraction due to the oxidation of the SiCnp. The formation mechanism of the anodic film on Al/SiCnp composites is different from that occurring in AA1050, partly due the heterogeneous distribution of the reinforcement particles in the metallic matrix, but also to the entrapment of SiCnp in the anodic film.

Influence of exposure time on the release of bacteria from a biofilm on Ti6Al4V discs using sonication: An in vitro model

Implant sonication is considered a useful method for the diagnosis of implant-related infections. We designed an in vitro study using Ti6Al4V discs and 5 different bacteria to determine the optimal sonication time for recovery of most bacteria tested to enable use of sonication in clinical practice for microbiological diagnosis of implant-related infections. We carried out a specific protocol for the adherence and subsequent biofilm formation on the materials used. The discs were then sonicated and the retrieved bacteria were quantified. From minute 1 to 5, the amount of recovered organisms grew progressively for all bacteria. Between minute 6 and minute 10, the number was irregular for all strains except E. coli, though no pattern was evidenced. E. coli was the only microorganism with a progressive increase in liberation throughout the process. Significant differences were observed in each of the 10minutes analyzed as concerns the release of the 5 strains (P<0.021) as well as in the mean dislodgement (of the 10minutes) of all tested strains (P<0.00001). Considering that infections in which biofilms are involved could be polymicrobial, we concluded that 5minutes is the optimal time of sonication in order to recover the maximum amount of most bacteria attached to Ti6Al4V discs.