Anodic nanostructuring of titanium in organic and inorganic electrolytes. Influence on cell adhesion

CAJIAO CHECCHIN VALENTINA CHIARA; GRAVINA ANABELA NOEL; FERNÁNDEZ LORENZO MÓNICA

Conferencia; 2020 Express Conference on the Physics of Materials and its applications in Energy and Environment (e-CPM2020); 2020

Titanium and its alloys are widely used in orthopedic implants for their mechanical properties and for being bio-inert, so an active search is made to improve their properties, particularly those related to osseointegration.(1) In this work it is proposed to modify the surface topography of the material through anodizing in organic and inorganic medium, generating nanostructures, specifically nanotubes, to select the optimal conditions for osseointegration. To identify the most favorable nanostructures, the adhesion of pre-osteoblastic cells was evaluated.Mirror polished grade 2 Titanium (DTi) discs were used, which were anodized at 5, 7, 10 and 15 V, in two cycles of two hours each, to obtain TiNT. A cell with two electrodes was used, having a graphite rod as the cathode and the DTi as the anode. Two types were used as electrolytes: an inorganic one, composed of an aqueous solution of HF/H3PO4 generating TiNT and, an organic one, consisting of HF/H3PO4/Ethyleneglycol generating TiNT-EG. At the same time, the anodized records were made, and the current density (J) vs Time (t) data were plotted. Measurements of cell adhesion as a function of voltage for both electrolytes were performed in the MC3T3-E1 pre-osteoblastic line and the area covered by cells on the samples of each condition was evaluated using Acridine Orange staining. The % of Area Covered (%AC) of the samples was referred to the control (DTi, 100% AC) for each group, TiNT and TiNT-EG. Biological tests were performed in triplicate using ANOVA as statistical analysis and Tuckey comparison test. The analysis of %AC vs anodizing potential for each group, TiNT and TiNT-EG, revealed a dissimilar behavior in cell adhesion for TiNT at the different potentials and a more homogeneous and favorable behavior regarding cell adhesion in TiNT-EG. In the first group (TiNT) it was found that the most favorable and statistically equal condition to the control corresponded to the TiNT-7 V samples (114.56 %AC), the other potential conditions (5, 10 and 15 V) showed values lower than %AC concerning the control (p-value˂0,0001). It should be noted that in the case of 10 V anodizing, a more marked decrease in adhesion was observed. For the second group (TiNTEG), cell adhesion was obtained in all cases equal or greater than the control, this more homogeneous and favorable behavior would be linked to the nature of the electrolyte which would induce the generation of a more uniform nanostructure. In particular, the TiNTEG-15V condition showed the highest %AC value (140.09%) with a significant difference from the control (p-value ˂0,0001).To explain the different cellular behavior in the case of the TiNT samples in the inorganic electrolyte, the evolution of the current transients recorded during anodizing was analyzed. It should be noted that in the 7 V condition, two peaks can be observed in the NT formation zone, so according to what is reported in the literature (1), the formation and self-organization events that may occur successively would result in a more cell friendly surface. On the other hand, at 10 V a different behavior can be noted that would correspond to the generation of a compact oxide in the first minutes but, considering that then the current density constantly increases, pores of larger diameter and shorter would be generated (2) and the typical self-organization of nanotubes that could be observed in the case of samples anodized at 7 V would not be achieved. These processes could be related to the inhibition of cell adhesion due to the formation of nano/microstructures that are not friendly to cells. (1)We can conclude then that the electrolyte used and the potential applied are fundamental factors in the formation of friendly nanostructures for cell adhesion. Also, organic media are more appropriate than aqueous media due to under these conditions up to 40% more adhesion is obtained than in the case of polished control.