Dissolution effect and cytotoxicity of diamond-like carbon coatings on orthodontic archwires

Nickel–titanium (NiTi) has been used for implants in orthodontics due to the unique properties such as shape memory effect and superelasticity. However, NiTi alloys are eroded in the oral cavity because they are immersed by saliva with enzymolysis. Their reactions lead corrosion and nickel release into the body. The higher concentrations of Ni release may generate harmful reactions. Ni release causes allergenic, toxic and carcinogenic reactions. It is well known that diamond-like carbon (DLC) films have excellent properties, such as extreme hardness, low friction coefficients, high wear resistance. In addition, DLC film has many other superior properties as a protective coating for biomedical applications such as biocompatibility and chemical inertness. Therefore, DLC film has received enormous attention as a biocompatible coating. In this study, DLC film coated NiTi orthodontic archwires to protect Ni release into the oral cavity. Each wire was immersed in physiological saline at the temperature 37 °C for 6 months. The release concentration of Ni ions was detected using microwave induced plasma mass spectrometry (MIP-MS) with the resolution of ppb level. The toxic effect of Ni release was studied the cell growth using squamous carcinoma cells. These cells were seeded in 24 well culture plates and materials were immersed in each well directly. The concentration of Ni ions in the solutions had been reduced one-sixth by DLC films when compared with non-coated wire. This study indicated that DLC films have the protective effect of the diffusion and the non-cytotoxicity in corrosive environment.     

Formation of a nano-pattering NiTi surface with Ni-depleted superficial layer to promote corrosion resistance and endothelial cell-material interaction

Zirconium ion implantation was performed on NiTi alloy to suppress Ni ion release as well as to improve corrosion resistance and cell-material interaction. A thicker Ni-depleted nano-scale composite layer formed after Zr implantation and the corrosion resistance was evidently increased in aspects of increased E _br ? E _corr (difference between corrosion potential and breakdown potential) and decreased corrosion current density. 2.5/2 NiTi sample possessed the highest E _br ? E _corr, more than 500 mV higher than that of untreated NiTi, suggesting a significant improvement on pitting corrosion resistance. Ni ion release rate of Zr–NiTi was decreased due to the depletion of Ni in the superficial surface layer and the diffusion resistance effect of the ZrO₂/TiO₂ nano-film. Increased surface wettability induced by increased surface roughness was obtained after Zr implantation. Zr–NiTi samples were found to be favorable to endothelial cells (ECs) proliferation, especially after 5 and 7 days culture.     

Fabrication and biocompatibility of polyethyleneimine/heparin self-assembly coating on NiTi alloy

NiTi alloy has been used widely as biomaterials. But because of toxic effects possibly caused by excess Ni ions released during the corrosion process in the physiological environment, it is still a controversial material. Fabricating medicine-loaded coating, which is expected to decrease the release of Ni ions and improve the biocompatibility of the materials, is a potential way to solve the problem. In this paper, NiTi alloy is coated by polyethyleneimine/heparin films via layer-by-layer (LBL) self-assembly method. UV-Vis, FT-IR, atomic force microscopy (AFM) and contact angle measurements are used to characterize the microstructure of coatings and select the best fabrication conditions. Potentiodynamic polarization researches in sodium chloride and dynamic clotting time experiment are utilized to study its corrosion resistance capability and biocompatibility of coatings, respectively. The results indicate that PEI/heparin multilayer coating can improve the biocompatibility of NiTi alloy surface.     

Effect of ceramic conversion treatments on the surface damage and nickel ion release of NiTi alloys under fretting corrosion conditions

Recent researches have demonstrated that surface modification can improve the fretting wear resistance of NiTi alloys in air or enhance their aqueous corrosion resistance without fretting. However, little is known about the behaviour of surface engineered NiTi under fretting corrosion conditions. This is important for such body implants as orthodontic arch wires and orthopedic bone fixation devices because they need to withstand the combined attack of corrosion from body fluid and mechanical fretting. In this study, a NiTi alloy was ceramic conversion (CC) treated at 400 and 650 °C. The effect of the surface treatment on the fretting corrosion behaviour of NiTi alloy was investigated using fretting corrosion tests in the Ringer’s solution. The experimental results have shown that the CC treatment can convert the surface of NiTi into a TiO₂ layer, which can effectively improve the fretting corrosion resistance of NiTi alloy and significantly reduce Ni ion release into the Ringer’s solution. Detailed SEM observations revealed that the untreated samples were severely damaged by adhesion and delamination; the high temperature (HT) (650 °C/1 h) treated samples were damaged mainly by spallation and adhesion; and the low temperature (LT) (400 °C/50 h) treated samples were characterised by mild abrasion. Mild oxidation and corrosion were also observed for all three types of samples tested under fretting corrosion conditions.     

医用多孔NiTi合金表面微弧氧化改性研究

为解决多孔Ni Ti合金耐蚀性降低和Ni离子释放量增大而引起的使用安全性问题.本文采用微弧氧化技术对医用多孔Ni Ti合金进行表面改性处理,研究结果表明,微弧氧化处理并未改变多孔Ni Ti合金原有的孔隙结构和孔隙率,只在其外表面和孔隙内表面均形成了典型的微弧氧化多孔涂层.该涂层主要由氧化铝相组成,并含有少量的Ti和Ni元素,且外表面涂层的Ti和Ni含量要略低于孔隙内表面涂层.微弧氧化涂层提高了多孔Ni Ti合金的表面接触角,将原有的亲水表面转变成了疏水表面.经微弧处理后,多孔Ni Ti合金的耐蚀性较基体提高了1个数量级以上,Ni离子释放量也较基体降低了1个数量级以上.     

Determination of corrosion rate of orthodontic wires based on nickel‐titanium alloy in artificial saliva

The goal of this study was to determine corrosion behavior of three orthodontic wires based on nickel‐titanium alloy (NiTi) in artificial saliva at temperature of 37 °C as function of immersion time. Following orthodontic wires were used: uncoated (NiTi), rhodium coated (Rh NiTi) and nitrified (N NiTi) orthodontic wires. Corrosion of investigated orthodontic wires were monitored by measuring of Ni²⁺ and Ti⁴⁺ ions released in artificial saliva by inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) after 3, 7, 14, 21 and 28 days of immersion. Obtained results indicate that corrosion reaction of the NiTi wires in artificial saliva follows the parabolic rate law. According to the obtained values of parabolic corrosion rate constants, corrosion susceptibility of orthodontic wires decreases in the following order: Rh NiTi wire (K_p = 2.48 μg²/cm⁴ h) > NiTi wire (K_p = 1.6 × 10^–3 μg²/cm⁴ h) > N NiTi wire (K_p = 6.0 × 10^–4 μg²/cm⁴ h). These results indicate that in comparison with uncoated NiTi wire, rhodium coating significantly increases corrosion susceptibility, while nitrification effectively suppresses the release of Ni²⁺ and Ti⁴⁺ ions.     

Electrochemical Corrosion Behavior of the DLC Coated and Uncoated NiTi Alloys

A dense and well-adhered diamond-like carbon （DLC） coating was prepared on the nickel-titanium （NiTi） alloys by plasma immersion ion implantation and deposition （PIIID）. Potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by the DLC coating. The Ni ions release of the NiTi alloys was effectively blocked by the DLC coating.     

Stability of plasma electrolytic oxidation coating on titanium in artificial saliva

Bioactive PEO coating on titanium with high Ca/P ratio was fabricated and characterized with respect to its morphology, composition and microstructure. Long-term electrochemical stability of the coating and Ti⁴⁺ ion release was evaluated in artificial saliva. Influence of the lactic acid and fluoride ions on corrosion protection mechanism of the coated titanium was assessed using AC and DC electrochemical tests. The PEO-treated titanium maintained high passivity in the broad range of potentials up to 2.5 V (Ag/AgCl) for up to 8 weeks of immersion in unmodified saliva and exhibited Ti⁴⁺ ion release <0.002 µg cm^?2 days^?1. The high corrosion resistance of the coating is determined by diffusion of reacting species through the coating and resistance of the inner dense part of the coating adjacent to the substrate. Acidification of saliva in the absence of fluoride ions does not affect the surface passivity, but the presence of 0.1 % of fluoride ions at pH ≤4.0 causes loss of adhesion of the coating due to inwards migration of fluoride ions and their adsorption at the substrate/coating interface in the presence of polarisation.     

NiTi合金表面液相阴极等离子体沉积氧化铝陶瓷涂层的研究

在NiTi合金表面通过液相阴极等离子体技术制备了氧化铝(Al2O3)陶瓷涂层。采用X射线衍射和扫描电镜对涂层的相组成以及表面形貌进行了表征和分析,证实在材料表面形成了由α-Al2O3和γ-Al2O3组成的涂层,发现涂层具有粗糙多孔结构。在模拟体液中对NiTi合金的Ni离子释放情况进行了检测,发现液相阴极等离子体改性后显著降低了Ni离子的释放。为NiTi合金植入体的表面改性提供了一条新途径。     

Nickel ion release from orthodontic NiTi wires under simulation of realistic <Emphasis Type="Italic">in-situ</Emphasis> conditions

The increasing use of nickel containing devices in orthodontics and the growing prevalence of nickel allergy in the population significantly increases the interest in biocompatibility studies of these devices. The decisive factor determining the biocompatibility of orthodontic wires is their corrosion behaviour. Therefore seven nickel titanium levelling arches, one titanium molybdenum, a cobalt chromium and three stainless steel wires were analysed with respect to their corrosion behaviour under realistic conditions. Potentiostatic tests to determine rupture potentials in artificial saliva and static immersion tests in artificial saliva (AS) or lactic acid (LA), as well as immersion tests with mechanical, thermal and combined mechanical and thermal stresses were performed. Subsequently, the surfaces of the wires were investigated employing scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) and the nickel release into the corrosion media of the specimens was measured with inductively coupled plasma mass spectrometry (ICP-MS). The results yield information not only about the relative corrosion tendency of the wires under in vitro conditions but also give a quantitative estimation about the nickel ion release of the orthodontic wires during in vivo treatment. Generally, the maximum release of nickel ions was two orders of magnitude below the daily dietary intake level. Mechanical and thermal loading increases nickel release in the immersion tests by a factor of 10 to 30. Two NiTi wires (Dentaurum Tensic, Forestadent Titanol Low Force) examined showed lower rupture potentials and a higher tendency towards corrosion in the immersion tests than the others due to their surface composition. However these differences are levelled off by long-term mechanical and thermal loading.     

Structure and properties of TiC/Ti coatings fabricated on NiTi by plasma immersion ion implantation and deposition

A titanium carbide (TiC) nanostructured coating and Ti intermediate layer are fabricated on NiTi by plasma immersion ion implantation and deposition (PIII&D) to improve the surface properties. The chemical composition and structure are determined by X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Nano-indentation is used to evaluate the mechanical properties of the thin film and the biological characteristics are assessed by electrochemical measurement and soaking tests in simulated body fluids. Based on the potentiodynamic polarization and Ni release data after the polarization test, the Ti/TiC nanostructure coating has better corrosion resistance compared to the NiTi substrate and there is significantly less Ni ion release from the NiTi substrate into the simulated body fluids than the uncoated NiTi alloy.     

医用镍钛合金表面涂覆技术研究概述

镍钛(NiTi)合金因其优异的形状记忆和超弹性性能,良好的耐腐蚀性和生物相容性,在生物医学领域得到了广泛应用。为了避免直接使用可能出现的生物不相容和细胞毒性,采用表面涂覆技术在合金表面涂覆纳米到微米量级厚度的功能薄膜,使其具有比基体更优良的生物相容性、抗腐蚀性和耐磨性等特殊功能。表面涂覆技术与其它表面改性技术相比,具有约束条件少、技术类型广、材料选择空间大等优势,目前应用最为广泛。对电化学沉积、等离子喷涂、磁控溅射、溶胶凝胶法、浸涂技术制备的涂层微观结构、力学性能和耐腐蚀等性能进行综述,并分析各技术的优缺点。随着涂覆技术的发展及制备涂层性能的进一步提高,NiTi合金在牙齿矫正丝、人工关节骨茎、血管成形环等多种医疗领域中的应用将更加广泛和深入。     

NiTi合金生物医用材料表面改性的研究进展

NiTi合金由于其形状记忆效应、超弹性和低模量等优良性能在生物医学领域得到广泛应用。然而,在生理环境中镍离子释放会诱发毒性和炎性反应,因此需要对其进行表面改性。从表面氧化、表面涂层和表面接枝大分子等方面综述了近年来国内外NiTi合金表面改性的研究进展,评述了各种表面改性技术的优势和缺陷,指明了NiTi合金表面改性的未来发展趋势。     

不同等离子源形成的DLC涂层对NiTi合金腐蚀行为的影响

采用等离子浸没离子注入和沉积(PIIID)法分别以C2H2和石墨为等离子源在NiTi合金表面形成DLC涂层来提高该合金的耐腐蚀性.利用Raman光谱和扫描电镜分析膜层结构.利用电化学测试和原子吸收光谱测试涂层前后基体的耐腐蚀性和Ni离子析出.结果表明:采用等离子浸没离子注入和沉积法以乙炔和石墨为等离子源在NiTi合金表面形成均匀致密、结合力良好的DLC涂层.两种涂层都明显地提高了NiTi合金的耐腐蚀性能和有效地抑制了Ni离子的溶出.     

Oxidized nickel–titanium foams for bone reconstructions: chemical and mechanical characterization

This work examines NiTi foams that have been treated using a new oxidation treatment for obtaining Ni-free surfaces that could allow the ingrowth of living tissue, thereby increasing the mechanical anchorage of implants. A significant increase in the real surface area of these materials can decrease corrosion resistance and favour the release of Ni. This chemical degradation can induce allergic reactions or toxicity in the surrounding tissues. This study determines the porosity, surface characteristics, phase transformation, mechanical properties, corrosion behaviour and Ni release into the simulated body fluid medium of foams treated by a new surface oxidation treatment that produces Ni-free surfaces. These foams have pores in an appropriate range of sizes and interconnectivity, and thus their morphology is similar to that of bone. Their mechanical properties are biomechanically compatible with bone. The titanium oxide on the surface significantly improves corrosion resistance and decreases nickel ion release, while barely affecting transformation temperatures.     

NiTi 合金表面激光原位反应合成TiN增强金属基复合材料涂层

采用连续高功率固体Nd-YA G激光辐照, 使预置于NiTi 合金表面的Ti 粉在N₂ 环境中形成TiN 增强Ti 基复合材料涂层。选择适当的激光辐照工艺参数, 获得致密的TiN 增强金属基复合材料激光改性层。SEM 观察及EDAX 成分分析结果表明, TiN/ Ti 金属基复合材料表面改性层与基体NiTi 合金存在良好的冶金结合, 界面处成分均匀过渡, 表面Ni 含量极低。显微硬度测试及磨损实验表明, TiN/ Ti 金属基复合材料改性层显著提高了NiTi 合金的表面硬度和耐磨性, 激光表面改性层可有效地改善NiTi 合金作为生物医学材料使用的表面成分和性能。      

Characteristics and mechanical properties of a (Ti, O, N)/Ti composite coating fabricated on NiTi shape memory alloy via PIIID

In this investigation, (Ti, O, N)/Ti composite coating was fabricated on a NiTi shape memory alloy (SMA) to improve its biocompatibility, bioactivity and wear resistance for its long-term medical applications, using the plasma immersion ion implantation and deposition (PIIID) technique. Scanning electron microscopic (SEM) examination of coating cross-sections showed that the (Ti, O, N)/Ti composite coating was uniform and compact. Energy dispersive X-ray (EDX) analysis not only indicated that the interface between the coating and NiTi SMA substrate was gradual rather than sharp, but it also showed the thickness of the composite coating to be ∼ 1.0 μm. The EDX mapping of cross-sections of (Ti, O, N)/Ti composite coating revealed that Ni was not present on the surface of the coated samples. Nanoindentation tests were performed to evaluate mechanical properties of the composite coating. Pin-on-disc wear test results showed greatly improved wear resistance of (Ti, O, N)/Ti coated NiTi SMA.     

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.     

Tantalum-based multilayer coating on cobalt alloys in total hip and knee replacement

Cobalt–chromium–molybdenum (CoCrMo) alloys are widely used in total hip and knee joint replacement, due to high mechanical properties and resistance to wear and corrosion. They are able to form efficient artificial joints by means of coupling metal-on-polymer or metal-on-metal contacts. However, a high concentration of stress and direct friction between surfaces leads to the formation of polyethylene wear debris and the release of toxic metal ions into the human body, limiting, as a consequence, the lifetime of implants.The aim of this research is a surface modification of CoCrMo alloys in order to improve their biocompatibility and to decrease the release of metal ions and polyethylene debris. Thermal treatment in molten salts was the process employed for the deposition of tantalum-enriched coating. Tantalum and its compounds are considered biocompatible materials with low ion release and high corrosion resistance.Three different CoCrMo alloys were processed as substrates. An adherent coating of about 1 μm of thickness, with a multilayer structure consisting of two tantalum carbides and metallic tantalum was deposited. The substrates and modified layers were characterized by means of structural, chemical and morphological analysis. Moreover nanoindentation, scratch and tribological tests were carried out in order to evaluate the mechanical behavior of the substrates and coating. The hardness of the coated samples increases more than double than the untreated alloys meanwhile the presence of the coating reduced the wear volume and rate of about one order of magnitude.     

Influence of preparation methods on the properties of self-assembled films of octadecylphosphonate on Nitinol: XPS and EIS studies

The NiTi alloy (Nitinol), with its favorable micro-structured properties and self-passivity (resembling that of pure Ti) is used as an implant material for arterial stents and orthodontic wires. During the long term contact of the alloy with aggressive environment of human body, corrosion by releasing Ni^2 + ions can occur. Thus, the usefulness of such material can be dramatically enhanced if its interface structure and surface chemistry are controlled. The octadecylphosphonate interface (ODP) synthesis, which involves a self-assembled covalently (monodentate type) bonded film of octadecylphosphonic acid (ODPA) on the oxide covered NiTi surface, produces stable and corrosion resistant interfaces. This paper introduces integrated approach to the characterization of the NiTi/ODP interfacial architecture as well as the structure of the electrified ODP/solution interface using high-resolution XPS and in situ EIS measurements. The main focus of this work was to determine the influence of the ODPA deposition method (spray and immersion) on the depth-dependent structural characteristics and orientation of ODPA molecules in the surface film by means of angle resolved XPS. Mechanically strong and chemically stable NiTi/phosphonate interfaces have the potential for their successful implementation in stent technologies.