Bioactive and antibacterial Ti6Al4V for bone contact applications

Silver is a well-known antibacterial agent with broad spectrum activity and low resistance development [1]. An increasing interest is registered for silver nanoparticles because of their large surface area and multiple mode of action (damage of the cell membrane, induction of ROS and release of silver ions) [2]. Despite of a wide research on surface enrichment of titanium surfaces with silver, the identification of an affective technology is a still an open issue. The aim of the present research is the surface modification of Ti6Al4V alloy in order to induce bioactive and antibacterial behaviour. The proposed surface modification process is based on a patented chemical treatment [3,4] that confers to the surface oxide layer a complex topography (micro and nano-scale roughness), and enrichment of hydroxyls groups, suitable for bone contact applications because of its bioactive behaviour (induced precipitation of hydroxyapatite). The research is focused on the introduction of a silver precursor into the process at three different steps (T1-T3) of the patented chemical treatment (CT) with additives (AD) in order to induce the precipitation of silver nanoparticles within the surface oxide layer and to avoid their agglomeration (CT+AD+Ag_T1, CT+AD+Ag_T2 and CT+AD+Ag_T3). FESEM, TEM and XPS analyses, ion release tests and antibacterial tests were performed in order to characterize the surfaces. FESEM, EDS and XPS analyses show the presence of well dispersed metallic silver nanoparticles with dimensions depending on the experimental procedure applied. TEM analyses performed on the cross section of the samples highlight different distribution of the nanoparticles in the thickness of the oxide layer. With the release test it was also possible observe a sustained and reproducible release up to 14 days for each kind of sample (Figure1). Antibacterial properties were evaluated by Kirby Bauer test and by bacterial adhesion test with Staphylococcus aureus ATCC 29213. Kirby Bauer test show an inhibition zone about 3mm around the samples due to the silver release from the surfaces. The adhesion test highlights a reduction of both adherent and not adherent bacteria compared with the control. Considering that infections are still a serious complication in orthopaedic and dental fields, and that bacterial resistance to antibiotics is becoming a critical problem in their treatment, the here proposed surfaces are promising for implants that require osteointegration and antibacterial activity, such as prosthetic cups, steams and dental screws.