Abstract
A highly ordered TiO2 nanotube array has been prepared on a commercial pure titanium substrate in a hydrofluoric (HF) electrolyte using a DC power source through two-step anodic oxidation. The morphology, composition, wettability and surface energy of the nanotube array have been characterized by using a field-emission scanning electron microscope (FE-SEM), a transmission electron microscope (JEM-2010) with energy-dispersive X-ray spectrometer EDX (INCA OXFORD), X-ray diffraction method, an atomic force microscope (AFM), an optical contact angle measuring device and the Owens method with two liquids. The electrochemical behaviours of anodic oxidation films with different structures have been investigated in Sodium Lactate Ringer's Injection at 37±1°C by potentiodynamic polarization curve and electrochemical impedance spectroscopy. The formation mechanism of the nanotube array and the advantages of two-step oxidation have been discussed according to the experimental observation and the characterized results. Meanwhile, the structural changes of nanotubes are analysed according to the results of impedance spectroscopy. Cytotoxicity testing and cell adhesion and proliferation have been studied in order to evaluate the bioactivity of the nanotube array film. The diameters of nanotubes are in the range of 120–140 nm. The nanotube surface shows better wettability and higher surface energy compared to the bare substrate. The nanotube surface exhibits a wide passivation range and good corrosion resistance. The growth of the nanotube array is the result of the combined action of the anodization and field-assisted dissolution. The nanotube array by two-step oxidation becomes more regular and orderly. Moreover, the nanotube array surface is non-toxic and favourable to cell adhesion and proliferation. Such nanotube array films are expected to have significant biomedical applications.
Highlights
It is often reported that titanium and its alloys are extensively used as implants in orthopaedics and dentistry for their superior mechanical properties, low modulus, excellent corrosion resistance and good biocompatibility
The surface, lateral and bottom morphologies as well as the element composition of the oxide films anodized under different oxidation parameters were observed by a field-emission scanning electron microscope (FE-SEM) (FEI SIRION 200) and a transmission electron microscope (TEM) (JEM-2010) with an energy-dispersive X-ray spectrometer EDX (INCA OXFORD)
It is obvious that the nanotube structure with two-step oxidation is significantly improved in orderliness and uniformity compared to one-step oxidation
Summary
It is often reported that titanium and its alloys are extensively used as implants in orthopaedics and dentistry for their superior mechanical properties, low modulus, excellent corrosion resistance and good biocompatibility. These excellent properties have already brought widespread clinical success. It is necessary to improve the biological properties of the titanium surface in order to promote the bond between materials and bone. The anodic oxide layer is porous and highly ordered. Interactions between implants and cells mainly depend on surface properties such as topography, composition, surface roughness, wettability and surface energy [28,29]. The initial interaction between nanotubes and cells is observed and discussed
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