Inducing the Bone Growth on Different Titanium Alloys

When aluminium and vanadium are added to titanium alloys implants 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. 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 were studied. The implant materials were prepared by chemical treatment consisting in immersion in 10M aqueous NaOH solution at 60º C for 24 hours. Optical metallography, tensile strength and Vickers microhardness tests were made and completed with ESEM and EDAX observations.

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. It can be observed that the Na concentration is bigger just under the surface and starts to decrease as is analysed deeper in the passive layer. 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 emphasised 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.