Abstract
A Ti–23Nb–0.7Ta–2Zr–1.2O alloy (at %), called “gum metal”, was deposited by direct-current magnetron sputtering (DCMS) on an under layer of copper. By varying the working pressure during the deposition, columnar TNTZ (Ti–Nb–Ta–Zr) nanoarchitectures were obtained. At low working pressures, the upper layer was dense with a coarse surface (Ra = 12 nm) with a maximum height of 163 nm; however, the other samples prepared at high working pressures showed columnar architectures with voids and an average roughness of 4 nm. The prepared coatings were characterized using atomic force microscopy (AFM) for surface topography, energy dispersive X-ray spectroscopy (EDX) for atomic mapping, scanning electron microscopy (SEM) for cross-section imaging, contact angle measurements for hydrophilic/hydrophobic balance of the prepared surfaces, and X-ray diffraction (XRD) for the crystallographic structures of the prepared coatings. The morphology and the density of the prepared coatings were seen to influence the hydrophilic properties of the surface. The antibacterial activity of the prepared coatings was tested in the dark and under low-intensity indoor light. Bacterial inactivation was seen to happen in the dark from samples presenting columnar nanoarchitectures. This was attributed to the diffusion of copper ions from the under layer. To verify the copper release from the prepared samples, an inductively coupled plasma mass spectrometer (ICP-MS) was used. Additionally, the atomic depth profiling of the elements was carried out by X-ray photoelectron spectroscopy (XPS) for the as-prepared samples and for the samples used for bacterial inactivation. The low amount of copper in the bulk of the TNTZ upper layer justifies its diffusion to the surface. Recycling of the antibacterial activity was also investigated and revealed a stable activity over cycles.
Highlights
Thin films of titanium alloys are highly used in biomedical fields due to their lightness, low elasticity modulus, good mechanical strength, biocompatibility, and anticorrosion behavior [1,2]
In previous studies [10,11,12], we reported the beneficial effect of Cu ions on enhancing the catalytic/photocatalytic bacteria inactivation when added to a gum metal thin film (GMTF)
We showed the effect of copper content on the structure, morphology, and mechanical properties of GMTF [18]
Summary
Thin films of titanium alloys are highly used in biomedical fields due to their lightness, low elasticity modulus, good mechanical strength, biocompatibility, and anticorrosion behavior [1,2]. After developing Ti–Nb–Zr–Ta (TNTZ) bulk alloys, in particular the multifunctional Ti–23Nb–0.7Ta–2Zr–1.2O alloy (at %), called “gum metal”, it has been shown that these alloys can be used in the form of super-elastic thin films These films present an important potential for medical applications and/or microactuation, such as for stents for neurovascular blood vessels or membrane-based micropumps [6,7,8,9]. In our previous studies [13,14,15], we reported the mechanical properties of a superelastic Ti-based GMTF showing increased bacterial inactivation under light concomitant to a biocompatible property in darkness [16,17]. The novelty of this work resides in the preparation of a coating allowing fast bacterial inactivation with reduced ion release
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