Formation of Nitrogen Doped Titanium Dioxide Surface Layer on NiTi Shape Memory Alloy

Abstract

NiTi shape memory alloys are increasingly being used as bone and cardiac implants. The oxide layer of nanometric thickness spontaneously formed on their surface does not sufficiently protect from nickel transition into surrounding tissues, and its presence, even in a small amount, can be harmful to the human organism. In order to limit this disadvantageous phenomenon, there are several surface engineering techniques used, including oxidation methods. Due to the usually complex shapes of implants, one of the most prospective methods is low-temperature plasma oxidation. This article presents the role of cathode sputtering in the formation of a titanium dioxide surface layer, specifically rutile. The surface of the NiTi shape memory alloy was modified using low-temperature glow discharge plasma oxidation processes, which were carried out in two variants: oxidation using an argon + oxygen (80% vol.) reactive atmosphere and the less chemically active argon + air (80% vol.), but with a preliminary cathode sputtering process in the Ar + N2 (1:1) plasma. This paper presents the structure (STEM), chemical composition (EDS, SIMS), surface topography (optical profilometer, Atomic Force Microscopy—AFM) and antibacterial properties of nanocrystalline TiO2 diffusive surface layers. It is shown that prior cathodic sputtering in argon-nitrogen plasma almost doubled the thickness of the produced nitrogen-doped titanium dioxide layers despite using air instead of oxygen. The (TiOxNy)2 diffusive surface layer showed a high level of resistance to E. coli colonization in comparison with NiTi, which indicates the possibility of using this surface layer in the modification of NiTi implants’ properties.

Multifunctional coatings of nickel-titanium implant toward promote osseointegration after operation of bone tumor and clinical application: a review

“…The findings indicate that, when compared to oxygen-based plasma, cathodic sputtering in an argon-nitrogen plasma considerably enhances the thickness of the nitrogen-doped titanium dioxide layer, thereby enhancing the surface properties of NiTi implants. Furthermore, (TiOxNy) 2 diffusion surface layer demonstrates exceptional resistance to E. coli colonization ( Tarnowski et al, 2021 ).…”

Determination of the Effect of TiN Coating on Self-Fitting Properties of Dental Implants Made of NiTi Alloy

“…In these studies, TiN, , TiO 2 , , Ti, , and hydroxyapatite coatings have been applied for this purpose using different methods. TiN differs from the others in terms of better mechanical properties and biocompatibility; a passive TiO 2 film is formed during its formation. , In a review study, del Castillo et al, investigating TiN coating specific to dental implants, reported that TiN coatings reduce early bacterial colonization and biofilm formation and improve fibroblast cell attachment and adhesion . In addition, Ag–SiO 2 chemically produced by electrophoretic deposition (EPD) method is used in nanocomposite coatings. − Corrosion tests in Ringer’s solution are used to determine the effectiveness of the coatings. , …”

Plasma Modification of Carbon Coating Produced by RF CVD on Oxidized NiTi Shape Memory Alloy under Glow-Discharge Conditions

“…NiTi shape memory alloys used to make long-term implants, such as stents, must be able to limit nickel ion release into the surrounding biological environment (metallosis). Such properties are ensured to varying degrees by the surface layers produced on the NiTi alloy, such as: titanium oxides, in particular rutile-TiO 2 , titanium nitride-TiN, silicon oxide-SiO 2 , amorphous hydrogenated carbon doped with nitrogen-a-C:N:H, amorphous hydrogenated silicon carbide-a-SiC:N:H produced via different surface engineering methods, which are often applied on, e.g., stents [10][11][12][13][14][15]. A prospective material solution for the shape memory NiTi alloy in terms of its application for cardiological implants is the deposition of composite layers consisting of an interlayer of titanium oxide-TiO 2 -rutile, produced by oxidation under glow-discharge conditions, and a thin a-C:N:H external coating produced via RFCVD.…”