Abstract
Anodic oxidation is an easy and cheap surface treatment to form nanostructures on the surface of titanium items for improving the interaction between metallic implants and the biological environment. The long-term success of the devices is related to their stability. In this work, titanium nanotubes were formed on a dental screw, made of titanium CP2, through an anodization process using an “organic” solution based on ethylene glycol containing ammonium fluoride and water. Then, the electrochemical stability in the Hank’s solution of these “organic” nanotubes has been investigated for 15 days and compared to that of titanium nanotubes on a similar type of sample grown in an inorganic solution, containing phosphoric and hydrofluoridric acids. Morphological and crystallographic analysis were performed by using scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) tests. Electrochemical measurements were carried out to study the stability of the nanotubes when are in contact with the biological environment. The morphological measurements revealed long nanotubes, small diameters, smooth side walls, and a high density of “organic” nanotubes if compared to the “inorganic” ones. XRD analysis demonstrated the presence of rutile form. An appreciable electrochemical stability has been revealed by Electrochemical Impedance Spectroscopy (EIS) analysis, suggesting that the “organic” nanotubes are more suitable for biomedical devices.
Highlights
The natural and amorphous oxide layer (2–5 nm) present on a titanium surface provides its excellent corrosion resistance
X-Ray diffractometry (XRD) analysis demonstrated the presence of rutile form
An appreciable electrochemical stability has been revealed by Electrochemical Impedance Spectroscopy (EIS) analysis, suggesting that the “organic” nanotubes are more suitable for biomedical devices
Summary
The natural and amorphous oxide layer (2–5 nm) present on a titanium surface provides its excellent corrosion resistance. This is one of the reasons why titanium is widely used as implant material [1,2]. In order to improve the interaction between a titanium implant and a biological environment, the mechanical, physical, chemical, electrochemical or biochemical surface modifications of medical devices are needed [3,4,5,6]. The anodic oxide film grown on titanium substrate may exhibit a compact, porous or nanotubular structure by changing the anodizing process parameters, such as the voltage applied, the duration of the anodizing, the electrolyte composition, and so on [7,8,9,10,11,12,13,14]. Hilario et al [17] investigated the influence of the morphology and the crystalline structure of the titanium nanotubes on the apatite-forming ability, suggesting the Metals 2018, 8, 489; doi:10.3390/met8070489 www.mdpi.com/journal/metals
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