The properties of the anodic oxide films formed on titanium and its implant alloys Ti-5Al-4V and Ti-6Al-4Fe are investigated in this paper. Anodic oxide films were prepared by electrochemical treatment in 3M sulphuric acid solution at 60 V for 1 min, followed by a thermal treatment consisting of heating at 500 8C for 24 h and then cooling in water. Electrochemical impedance spectroscopy (EIS) measurements were carried out at open circuit potential. Nyquist and Bode spectra exhibit a two-time constant system, attesting an oxide with two layers: a barrier inner oxide and a porous outer one. All spectra change in time, indicating a thickening of the films. Open circuit potentials were monitored (long-term, 25,000 exposure hours) in Ringer 2 solution of different pH values (6.98, 4.35, 2.5) for titanium, Ti5Al-4V and Ti-6Al-4Fe alloy but without treatment with the purpose to compare the biomaterial behaviour. It was pointed out some variations of the open circuit potentials around electropositive values, suggesting slow dissolution, re-passivation or adsorption processes.

Titanium alloys are among the most used metallic biomaterials, particularly for orthopedic applications. Ever since the pioneer titanium alloy (Ti6Al4V) has been used as biomaterial, lack of biocompatibility has been extensively reported and propelled research on improved materials with appropriate mechanical behavior and adequate biocompatibility. Studies have indicated that vanadium produces oxides harmful to the human body; in order to replace vanadium containing Ti alloys, Ti-6Al-7Nb was developed. Today this alloy is the preferred choice for cementless total joint replacements. It is very important to produce a nanostructured bioactive metal implant with appropriate mechanical properties and we applied a chemical and thermal treatment that converts the surface of titanium alloy into bioactive surface. Therefore, bioactive Ti6Al7Nb might represent an alternative for advanced orthopedic implants under load-bearing conditions.Eleven mini-pigs weighting around 50 kg, with free access to food pellets and water, were the experimental animals for this study. Ten of these pigs (one is the control) were anesthetized and after shaving, disinfection and draping, a straight 3 cm incision was made and the implants (plate and pin) were implanted into the epiphyses of the tibiae. Surgical procedures were performed bilaterally. At 6 months after implantation, the mini-pigs were sacrificed.After sacrifice, the segments of the proximal tibia epiphyses containing the implanted plates and pins were cut of, fixed in phosphate-buffered formalin and dehydrated in serial concentrations of ethanol after which they were embedded in polyester resin and then cutted and grounded to a thickness of 75-100 µm. With these samples a lot of observations were made: Scanning Electron Microscopy observations, histological examination at implant surface and histological examination of the bone-implant surface and SEM-EDX examinations were also made.All the results revealed that the plates and pins are in direct contact with newly formed bone without any intervening soft tissue layer. We regard osteoinductive ability of nanostructured Ti6Al7Nb as one of the advantages of this implant in consideration for clinical applications.

Titanium possesses an excellent corrosion resistance in biological environments because the titanium dioxide formed on its surface is extremely stable. When aluminium and vanadium are added to titanium in small quantities, the alloy achieves considerably higher tensile properties than of pure titanium and this alloy is used in high stress-bearing situations. But these metals may also influence the chemostatic mechanisms that are involved in the attraction of biocells. V presence can be associated with potential cytotoxic effects and adverse tissue reactions. The alloys with aluminium and iron or with aluminium and niobium occur to be more suitable for implant applications: it possesses similar corrosion resistance and mechanical properties to those of titanium-aluminium-vanadium alloy; moreover, these alloys have no toxicity.In this paper, pure Ti, Ti-6Al-7Nb and Ti-6Al-4Fe with a nanostructured surface were studied. Data about mechanical behavior are presented. The mechanical behavior was determined using optical metallography, tensile strength and Vickers microhardness.For the electrochemical measurements a conventional three-electrode cell with a Pt grid as counter electrode and saturated calomel (SCE) as reference electrode was used. AC impedance data were obtained at open circuit potential using a PAR 263A potentiostat connected with a PAR 5210 lock-in amplifier. The ESEM and EDAX observation were carried out with an environmental scanning electronic microscope Fei XL30 ESEM with LaB6-cathode attached with an energy-dispersive electron probe X-ray analyzer (EDAX Sapphire). After 3 days of immersion in simulated body fluid the nucleation of the bone growth was observed on the implant surface.It resulted that the tested oxide films presented passivation tendency and a very good stability and no form of local corrosion was detected. The mechanical data confirm the presence of an outer porous passive layer and an inner compact and protective passive layer. EIS confirms the mechanical results. The thicknesses of these layers were measured. SEM photographs of the surface and EDX profiles for the samples illustrate the appearance of a microporous layer made up of an alkaline titanate hydrogel. The apatite-forming ability of the metal is attributed to the amorphous sodium titanate that is formed on the metal during the surface treatment.The results emphasized that the surface treatment increases the passive layer adhesion to the metal surface and improves the biocompatibility of the biomedical devices inducing the bone growth on the implant surface.