NiTi Surface Research Articles

Research on corrosion behavior and biocompatibility of NiTi alloy processed with combined dealloying and annealing treatment

This paper presents a novel method to prepare hydrophilic nanoporous functional surface with combined dealloying and annealing treatment to improve the corrosion resistance and biocompatibility of NiTi components. Surface modification mechanism is discussed with microscopic characterization of NiTi nanoporous structures. Hydrophilic and biocompatible performance is achieved through specifically tailoring the dimensions and chemical compositions of nanoporous layer. The corrosion resistance of NiTi samples is investigated in 0.9 wt% NaCl solution and evaluated with potentiodynamic polarization and electrochemical impedance spectroscopy tests. The results indicate that material corrosion resistance is significantly enhanced with TiO2 formation during dealloying treatment, while annealing promotes the oxidation and densification of dealloyed layer raising the energy barrier for ion transportation during corrosion. Furthermore, as the dealloying temperature increases, the surface defects of the sample decrease resulting in better corrosion resistance. The research can provide guidance for NiTi surface modification to enhance its biomedical applications.

Exploring the potential of laser-textured metal alloys: Fine-tuning vascular cells responses through in vitro and ex vivo analysis

Medical stents are vital for treating vascular complications and restoring blood flow in millions of patients. Despite its widespread effectiveness, restenosis, driven by the complex interplay of cellular responses, remains a concern. This study investigated the reactions of vascular cells to nano/microscale wrinkle (nano-W and micro-W) patterns created on laser-textured nitinol (NiTi) surfaces by adjusting laser processing parameters, such as spot overlap ratio and line overlap ratio. Evaluation of topographical effects on endothelial and smooth muscle cells (SMCs) revealed diverse morphologies, proliferation rates, and gene expressions. Notably, microscale wrinkle patterns exhibited reduced monocyte adhesion and inflammation-related gene expression, demonstrating their potential applications in mitigating vascular complications after stent insertion. Additionally, an ex vivo metatarsal assay was utilized to bridge the gap between in vitro and in vivo studies, demonstrating enhanced angiogenesis on laser-textured NiTi surfaces. Laser-textured NiTi exhibits a guided formation process, emphasizing their potential to promote swift endothelialization. These findings underscore the efficacy of laser texturing for tailored cellular interactions on metallic surfaces and offer valuable insights into optimizing biocompatibility and controlling cellular responses, which may pave the way for innovative advances in vascular care and contribute to the ongoing improvement of stent insertion.

Exploration microstructural evolution and wear mechanisms of wire arc additive manufacturing NiTi/Nb bionic composite materials

NiTi/Nb layered heterogeneous structure (LHS) materials with different layer spacings were designed and fabricated using composite wire arc additive manufacturing. The NiTi/Nb LHS samples consisted of NiTi phase and β-Nb phase, and no other intermetallic compounds were formed. The NiTi layer in the NiTi/Nb LHS sample changes from a homogeneous eutectic microstructure to a gradient heterogeneous eutectic microstructure as the layer thickness increases. The Nb layer grains are much smaller than the NiTi layer grains, and no obvious texture is formed in the NiTi/Nb LHS samples. NiTi/Nb LHS samples still have a certain recoverable strain at room temperature, with a maximum recoverable strain of 4.36 % after 10 cycles of 10 % strain compression. The wear rate of the NiTi layer of the NiTi/Nb LHS samples was lower than that of the Nb layer. The main wear mechanisms on the Nb surface are abrasive wear, adhesive and oxidative wear while the main wear mechanism on the NiTi surface is adhesive wear. When the layer thickness ratio of NiTi layer to Nb layer is 2:1, the NiTi/Nb LHS samples form a gradient heterogeneous eutectic structure in the NiTi region, which in turn enhances the wear resistance of the LHS samples. In this study, cross-scale NiTi alloy and Nb heterogeneous components were constructed by wire arc additive manufacturing, which showed good wear resistance. The design provides a new solution for integrated additive manufacturing repair of heterogeneous metals in engineering applications.

The influence of hydroxyapatite coatings with different structure and crystallinity on osteogenesis stimulation

NiTi alloys are actively used in medicine as implants because of their mechanical properties. At the same time, however, the NiTi surface is not biologically active, which has a negative effect on osteogenesis. In addition, Ni is capable of causing various toxic reactions in the human body. It is therefore necessary to create a composite coating that is both bioactive and prevents the release of Ni ions. It has been shown that by changing the modes of plasma assisted RF sputtering of a calcium phosphate target, it is possible to obtain coatings with different contents of the amorphous phase. The coatings formed consist of hydroxyapatite and amorphous calcium phosphate. On the surface of a sample not treated with argon plasma, there are no phases containing calcium or phosphorus, although these elements are present on the surface. The different ways in which the CaP coatings were applied also affected their structure. It was found that the CaP coatings of samples M2 and M3 have mediocre corrosion resistance, dissolving quickly. This has a positive effect on the ability to osteogenesis, which was discovered as a result of in vitro tests. These tests have shown that the sample obtained at Idischarge = 30 A and Ubias = 30 V has the highest bioactivity and produces the lowest percentage of dead cells.

Laser deposition of titanium layer to enhance two-way shape memory behavior of Nitinol sheet

One of the long-standing mechanical challenges associated with shape memory alloys (SMAs) is achieving and stabilizing an evolving two-way shape memory effect (TWSME) through thermomechanical training/cycling. In most martensitic NiTi SMAs that exhibit zero TWSME at room temperature, the TWSMEs typically require hundreds of cycling repetitions to track trivial values. This demonstrates a promising solution to overcome this challenge. The surface of NiTi SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers on the NiTi surface using a laser beam. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 cycles when the optimum number of five Ti layers was deposited, which was much higher than that of the NiTi sheet (0.3% TWSME) and the sample with a single-time laser path irradiation (1.8%). This was attributed to the low coefficient of thermal expansion of the Ti vs. NiTi sheet, which prevented reverse bending during heating, and the formation of Ti-rich intergranular Ti2Ni(Ox) precipitates, which hindered dislocation movement. Meanwhile, in this sample, owing to the generation of a large residual tensile stress and a large heat-affected zone that led to a reduction in plastic zones, the one-way shape memory effect (OWSME) was retained at values above 90% with good stability over cycling. However, the introduction of additional Ti layers can cause problems in terms of oxygen accumulation within the NiTi sheet, which should be considered when designing a product.

Surface Modification of NiTi Alloy with Sputtered Tantalum Coatings to Improve its Hardness, Corrosion Resistance and Biocompatibility

In this research, titanium alloys including smart nitinol (NiTi) were studied. The (NiTi) alloy tends to emitting (Ni) toxic ions due to its low resistance to corrosion within the body conditions over time. For (NiTi) coating process, the magnetron plasma sputtering (DC) technique was used with Aragon gas ratio of (90%) and Oxygen of (10%) in order to coat the alloy with Tantalum and its Oxide (Ta2O[Formula: see text] thin films. This is one of the methods used to improve the biocompatibility and better adhesion stability of the membrane on the (NiTi) surface, since Tantalum and its oxides are biocompatible and are not affected by the body fluids. Hardness, corrosion and biocompatibility were tested. The results showed improvement in the nominated properties using this coating technique. The hardness for the non-coated sample was (630 Kgf/mm[Formula: see text], meanwhile, the coated sample recorded (762 Kgf/mm[Formula: see text] using sputtering power of (25 W) with a thickness of (226 nm). Tantalum and its precipitated oxides on a pillar of thickness (90.4–226 nm) also exhibited a biocorrosion enhancement, when it was immersed in a Simulated Body Fluid (SBF). The corrosion rate for the non-coated sample was (1.204 × 10[Formula: see text], meanwhile for the coated sample, its value was (3.453 × 10[Formula: see text] at sputtering power of (15 W), considered as the lower corrosion rate. The scanning electron micrographs also showed an increase in the biocompatibility for the coated nitinol alloys (NiTi) in comparison with the non-coated, ones since it showed a clear formation of Hydroxyapatite (HA) on the sample surface after immersion in the SBF. This behavior was confirmed by the XRD measurements, which presented higher HA peaks on the coated samples surface in comparison with the non-coated samples.

Friction and wear analysis of Al-5052/NiTi surface composites fabricated via friction stir processing

This work presents a comprehensive analysis of the wear behaviour of Al 5052 alloy reinforced with Nitinol (NiTip) shape memory alloy using friction stir processing (FSP). Multi-pass FSP was performed to improve the dispersion of NiTip in the base material. The reinforced NiTip significantly enhanced the wear resistance of the base material and led to a reduction in the coefficient of friction by 17% and 15% at 15 N and 25 N loads respectively, suggesting improved tribological properties. The corrosion resistance also showed a significant improvement in the four-pass FSPed specimen as compared to the base metal. The qualitative analysis of the study is in agreement with the quantitative results.

Nickel ion release and surface analyses on instrument fragments fractured beyond the apex: a laboratory investigation

BackgroundTo analyse the changes in surface and nickel ion release characteristics of fractured root canal shaping instruments in a simulated body fluid environment.MethodsA total of 54 new instruments were studied. The instrument groups consisted of five different NiTi alloys and a stainless-steel alloy. To standardize instrument fracture, a torsional type of failure was created on each instrument. The fractured specimens of each instrument group were randomly divided into three static immersion subgroups of 1 h, 7-day, and 30-day (n = 3). Simulated body fluid (SBF) was prepared to mimic human blood plasma by Kokubo&Takadama protocol for ex situ static immersions at 37ºC. The surfaces were examined via scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. To determine the quantitative ion release, the retrieved SBFs were analyzed using inductively coupled plasma mass spectrometry. Two-way ANOVA and Tukey post hoc tests sought the statistical significance of the nickel ion values(p < 0.05).ResultsIn 1 h of immersion, the newly formed structures, exhibiting mostly oxygen signals, were widespread and evident on NiTi surfaces. In contrast, fewer structures were detected on the SS surface in that subgroup. In 7 days of immersion, a tendency for a decrease in the density of the new structures was revealed in NiTi groups. The oxygen signals on NiTi group surfaces significantly increased, contrary to their decrease in SS. Signals of sodium, chlorine, and calcium were detected, indicating salt precipitates in groups. In 30 days of immersion, salt precipitates continued to form. The Ni-ion release values in all instrument groups presented significant differences in comparison to the SBF control in all immersion periods(p < 0.001). No significant differences were observed in immersion time periods or instrument groups(p > 0.05).ConclusionsWithin the limitations of the presented study, it was concluded that the fractured SS and NiTi root canal instruments release Ni ions in contact with body fluid. However, the Ni ion release values determined during the observation periods are lower than the critical toxic or allergic thresholds defined for the human body. This was due to the ionic dissolution cycle reaching a stable state from 1-hour to 30-day exposure to the body fluid of fractured instruments.

Improved corrosion protection of a NiTi implant by an electrodeposited HAp-Nb2O5 composite layer

The mechanical and biological characteristics of NiTi alloy provide opportunities in biomedical fields ranging from orthopedics to intravascular stents. However, Ni ion release when the alloy is exposed to corrosive body fluid can lead to long-term health-related concerns. Improved surface engineering via the application of biological layers on the NiTi can contribute to higher corrosion resistance. HAp-based layers were cathodically deposited from an aqueous electrolyte containing calcium nitrate, ammonium dihydrogen phosphate, and concentrations of suspended Nb2O5 particles from 0 to 1 g/L under pulsed current conditions. Surface morphology, topography, and surface chemistry of the electroplated layers were characterized by FESEM, AFM, and FTIR analysis, respectively. The corrosion behavior of the bare and coated samples in Ringer's solution was evaluated by EIS and potentiodynamic polarization; the corroded surfaces were imaged by FESEM. A more compact and smoother surface was formed in the presence of particulate Nb2O5 inclusions. The composite coating showed excellent anti-corrosion properties, increasing the polarization resistance of pure HAp films by >10 times. FESEM imaging of corroded surfaces showed the partial detachment of plate-like HAp crystals from the surface of the coated NiTi in contrast to the pitting of the bare NiTi surface. The surface modification of NiTi by electrodeposited HAp-Nb2O5 composite coatings might play an important role in the future use of NiTi in clinical applications.

Corrosion and passive film characteristics of 3D-printed NiTi shape memory alloys in artificial saliva

Electrochemical tests and surface analysis were applied to study the corrosion behavior and passive film characteristics of three-dimensional-printed NiTi shape memory alloys fabricated by laser-powder bed fusion (L-PBF) in artificial saliva at 37 °C. The passivity of L-PBF NiTi shows to be influenced by the process parameters and resulting morphological and physicochemical surface properties. The results show that the defects at the surface of L-PBF NiTi can promote the passivation rate in the early stages of exposure but a slowly formed passive film shows the best corrosion protection. The thickness of the passive film is positively correlated with its corrosion protective performance. The L-PBF NiTi alloy prepared at a linear energy density of 0.2 J·m−1 and volumetric energy density of 56 J·mm−3 shows the least defects and best corrosion protection. An outer Ti-rich and inner Ni-rich dense passive film could be also obtained showing higher corrosion resistance.Graphic

Migration of endothelial cells on the surface of anodized Ni-Ti stent strut.

Stent is widely regarded as the main treatment for curing cardiovascular diseases such as stenosis. Previous research has revealed that the damage of endothelial cells (EC), i.e., the components of endothelium, during stent implantation, could lead to severe complications, such as restenosis. To prevent restenosis, enhancements have been made to surface biocompatibility to accelerate the stent endothelialization process. Anodization on the Ni-Ti is a simple and efficient surface modification method to improve the biocompatibility of the Ni-Ti stent surfaces by enhancing the surface hydrophilicity, leading to an increase in the EC activities. The EC activity is known to be affected by the blood flow. Flow change by stent structure may result in EC dysfunctions, thereby leading to restenosis. It is thus essential to investigate the EC activities resulting from the anodization on the Ni-Ti surface under flow conditions. To study the influence of the endothelialization process on the Ni-Ti stent surface through anodization. The EC attachment and morphology on the anodized stent strut were observed under both with and without the flow conditions. A parallel plate flow chamber was designed to generate a constant wall shear stress (WSS) to study the flow effect on the EC behavior. The hydrophilicity of the Ni-Ti stent strut surface was enhanced by a TiO2 layer fabricated via anodization. The EC distribution on the surface of the anodized nitinol stent strut was observed after 24 h of static (without flow) and flow exposure (with flow) experiment. Under the static condition, the EC density on the surface of the anodized Ni-Ti stent strut was higher compared with the control. Under the flow condition, the enhancement of the EC density on the surface of the stent strut with anodization was reduced. The EC demonstrates a long and thin spindle-shaped morphology under the flow condition. Unlike the static condition, the EC is demonstrating a long and thin morphology in response to the flow under the flow condition. By improving the surface hydrophilicity, the anodization could enhance the EC migration onto the strut surface, and subsequently, accelerate the Ni-Ti stent endothelialization process. The improvement of the surface hydrophilicity is lower under the flow conditions when compared with the static conditions.

Defect engineering endows NiTi stents with photothermal-enhanced catalytic activity for high-efficiency tumor therapy

NiTi stents are widely used in clinic for palliative care to relieve obstruction caused by Gastrointestinal (GI) cancers, which have high morbidity and mortality rates. However, tumor invasion and tumor overgrowth around the stent after surgery may lead to re-obstruction of the lumen. Thus, it is urgent to endow NiTi stents with excellent tumor suppressive ability and good biocompatibility. In this study, Ce-BTC was firstly prepared on the surface of NiTi pretreated by alkaline heat, followed by pyrolysis in Ar atmosphere at 450 °C. Then, a composite coating consisting of defective cerium oxide and black Ni-Ti hydroxide/oxide was constructed on NiTi surface, which exhibited tumor microenvironment-response and hyperthermia-enhanced catalytic ability. Under near-infrared light irradiation, the photothermal performance of black Ni-Ti hydroxide/oxide and hyperthermia-enhanced catalytic activity of defective cerium oxide can achieve a synergistic effect of photothermal therapy and tumor catalytic therapy. Thereafter, defective cerium oxide can sustainably inhibit the proliferation of residual tumor cells by the generation of reactive oxygen species. Moreover, the composite coating has no obvious cytotoxicity to normal cells. This work provides a new insight for the preparation of stimulus-responsive antitumor stents for palliative treatment of gastrointestinal cancer.

Passive film formation and corrosion resistance of laser-powder bed fusion fabricated NiTi shape memory alloys

Electrochemical tests and surface analysis measurements were performed to study the corrosion behavior in a 0.9 wt.% NaCl solution at 37 °C of three NiTi shape memory alloys fabricated by laser-powder bed fusion (L-PBF). The passive film characteristics and corrosion resistance of L-PBF NiTi showed different features as a function of their preparation process settings. The passivation rate for L-PBF NiTi surfaces including defects, such as keyhole pores and cracks which showed high electrochemical activity accelerating the passivation reaction process, was higher in the early stages of immersion, but the corrosion resistance provided by such a rapidly formed passive film containing higher defect density is lower than that for an initially defect-free surface. The thickness of the passive film including a higher defect density does not necessarily relate to the corrosion resistance. The L-PBF NiTi prepared at a linear energy density of 0.2 J/m and volumetric energy density of 56 J/mm3 shows the least defects. Also, an outer Ti-rich and inner Ni-rich dense and corrosion protective passive film could be obtained for these L-PBF NiTi samples, which also results in a relatively low Ni ion release rate. A passive film model based on thickness, composition and defect density properties as a function of processing conditions is proposed to explain the difference in corrosion resistance of the various L-PBF NiTi.

An investigation on the optimum laser machining parameters and its effect on NiTi shape memory alloy

Nickel – Titanium (Nitinol) alloy is one of the most popular and economical SMA whose machining is difficult because of its properties. Heat has a prominent effect on this material's properties. Machining of NiTinol requires a large amount of cutting force, resulting in a high rate of tool wearing. Therefore, researchers have made an effort to ameliorate the machinability of this material to achieve a finer surface quality with the minimum heat-affected zone in the non-conventional machining process. As a Laser machine is used for various versatile machining processes at a micro level, so in this study, the objective is to find the optimum process parameters of Laser and its effect on the surface of NiTi which leads to ease machining barriers such as burr formation and crack formation, heat affected zone, white layer, recast layer and many more surface defects during laser machining. Lower frequency, high power, and lower speed in the machining process improve the mechanical properties, distortion, and residual stress. The obtained results demonstrated the optimum cutting speed in the laser machining process of NiTi alloy.

Fabrication of Antibacterial TiO2 Nanostructured Surfaces Using the Hydrothermal Method.

Implant-associated infections (IAI) are a common cause for implant failure, increased medical costs, and critical for patient healthcare. Infections are a result of bacterial colonization, which leads to biofilm formation on the implant surface. Nanostructured surfaces have been shown to have the potential to inhibit bacterial adhesion mainly due to antibacterial efficacy of their unique surface nanotopography. The change in topography affects the physicochemical properties of their surface such as surface chemistry, morphology, wettability, surface charge, and even electric field which influences the biological response. In this study, a conventional and cost-effective hydrothermal method was used to fabricate nanoscale protrusions of various dimensions on the surface of Ti, Ti6Al4V, and NiTi materials, commonly used in biomedical applications. The morphology, surface chemistry, and wettability were analyzed using scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and water contact angle analysis. The antibacterial efficacy of the synthesized nanostructures was analyzed by the use of Escherichia coli bacterial strain. XPS analysis revealed that the concentration of oxygen and titanium increased on Ti and Ti6Al4V, which indicates that TiO2 is formed on the surface. The concentration of oxygen and titanium however decreased on the NiTi surface after hydrothermal treatment, and also a small amount of Ni was detected. SEM analysis showed that by hydrothermal treatment alterations in the surface topography of the TiO2 layer could be achieved. The oxide layer on the NiTi prepared by the hydrothermal method contains a low amount of Ni (2.8 atom %), which is especially important for implantable materials. The results revealed that nanostructured surfaces significantly reduced bacterial adhesion on the Ti, Ti6Al4V, and NiTi surface compared to the untreated surfaces used as a control. Furthermore, two sterilization techniques were also studied to evaluate the stability of the nanostructure and its influence on the antibacterial activity. Sterilization with UV light seems to more efficiently inhibit bacterial growth on the hydrothermally modified Ti6Al4V surface, which was further reduced for hydrothermally treated Ti and NiTi. The developed nanostructured surfaces of Ti and its alloys can pave a way for the fabrication of antibacterial surfaces that reduce the likelihood of IAI.

Enhancing the corrosion behavior of Ti–6Al–4V and Nitinol alloys by simple chemical oxidation in H2O2

This study investigated the effect of hydrogen peroxide treatment on the corrosion behavior of two Ti biomaterial alloys (Ti–6Al–4V and Nitinol (NiTi)). The obtained oxides were characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Even though both oxidized alloys are constituted mostly by TiO2 oxide on their surfaces, different topographies were obtained: a non-porous film with mud-cracked structure type was formed on Ti–6Al–4V while some micropores were observed on the NiTi surface. Oxidized NiTi samples also exhibited Ni species present as oxides and hydroxides in the form of Ni2+ and Ni3+. The ICP-AES analysis demonstrated that the presence of the oxides reduced the amount of alloying ions released to the simulated physiological environment after the electrochemical tests. The results show that this simple technique without the need for thermal post-treatment is enough to reduce the corrosion current density (icorr) and shift the corrosion potential (Ecorr) to more noble values enhancing the anticorrosive properties of both Ti-based alloys in Ringer solution. Moreover, the hydrophilicity of the surfaces was increased after the treatment.

Density functional theory study of dissociative adsorption of H2 molecules on NiTi (001) surfaces

Ti-based alloys have the potential to be used as hydrogen storage units, including NiTi. In contrast, NiTi alloy is sensitive to H atoms. It has been found that hydrogen can cause embrittlement in NiTi alloys. Thus, it is become indispensable to elucidate the reaction of H2 molecules on the NiTi surface. Using density functional theory, we investigated the dissociation mechanism of H2 molecules on the B2 NiTi (001) surface. We found that H atoms tend to come closer to Ni atoms on the Ti- and Ni-terminated (NiTi) (001) substrate. The calculation results showed that the adsorption energy of H atoms at the hollow site was higher than that at the top site. We identified two dissociation mechanisms of H2 molecules on Ti and Ni terminated on NiTi (001) substrates via the hollow sites of the adsorption route. The adsorption energy values obtained were extremely low, that is, 0.23 and 0.38 eV for the Ni and Ti terminated of NiTi (001) substrates, respectively. The dissociation reaction of H2 molecules, which is an exothermic reaction, can quickly occur on the NiTi (001) surface because of the low activation energy.

Characteristic variation of pulsed‐anodized NiTi surface by the adjustment of voltage‐unapplied state

Pulsed anodization of superelastic NiTi alloy in nitric acid electrolyte is a novel surface modification process that enables the formation of an almost Ni‐free TiO2 layer on their surface. The core technology is the modulation of voltage‐unapplied state that is necessary for the chemical reaction with an electrolyte. Here, the effect of the adjustment of the voltage‐unapplied state on the layer characteristics was investigated. Prolongation of the voltage‐unapplied state led to the formation of a thicker TiO2 layer. This result was attributed to the elimination of Ni by nitric acid. As a result, nanometer‐sized pores appearing as vestiges of Ni elimination increased and enlarged concomitantly. Furthermore, by prolonging the voltage‐unapplied state, the amount of Ni ions released into a phosphate‐buffered saline (PBS) solution diminished significantly. Such prolongation enabled significant suppression of the dissolution of the layer itself; thus, Ni ion release from the surface region was considered to be reduced.

Additive Manufacturing: An Opportunity for the Fabrication of Near-Net-Shape NiTi Implants

Nickel–titanium (NiTi) is a shape-memory alloy, a type of material whose name is derived from its ability to recover its original shape upon heating to a certain temperature. NiTi falls under the umbrella of metallic materials, offering high superelasticity, acceptable corrosion resistance, a relatively low elastic modulus, and desirable biocompatibility. There are several challenges regarding the processing and machinability of NiTi, originating from its high ductility and reactivity. Additive manufacturing (AM), commonly known as 3D printing, is a promising candidate for solving problems in the fabrication of near-net-shape NiTi biomaterials with controlled porosity. Powder-bed fusion and directed energy deposition are AM approaches employed to produce synthetic NiTi implants. A short summary of the principles and the pros and cons of these approaches is provided. The influence of the operating parameters, which can change the microstructural features, including the porosity content and orientation of the crystals, on the mechanical properties is addressed. Surface-modification techniques are recommended for suppressing the Ni ion leaching from the surface of AM-fabricated NiTi, which is a technical challenge faced by the long-term in vivo application of NiTi.

Study of Al–SiO2 Aesthetic Composite Coating on Orthodontic Metal Archwire

Nickel–titanium orthodontic wires (NTWs) play an essential role in orthodontic treatment. However, their corrosion and aesthetic properties limit their applications. To improve the aesthetic effects of nickel–titanium orthodontic archwires, we prepared aluminium–silicon dioxide (Al–SiO2) as a biocompatible layer coated onto the NTWs. The Al–SiO2 coating was first fabricated using physical vapor deposition magnetron sputtering, and its physicochemical and biocompatibility properties were investigated. Al–SiO2 layers were well coated on the NTWs. The corrosion currents in the nickel–titanium (NiTi) control, Al–SiO2-coated NiTi experimental, stainless steel (SS) control and Al–SiO2-coated SS experimental groups were 23.72 μA cm−2, 1.21 μA cm−2, 0.22 μA cm−2 and 0.06 μA cm−2, respectively. Al–SiO2-coated NTWs with reduced corrosion current density indicated that the preparation of Al–SiO2 coating on the surface of NiTi and SS could reduce the tendency of electrochemical corrosion. The friction coefficients of orthodontic wires in the NiTi control, NiTi experimental, SS control, and SS experimental groups were 0.68, 0.46, 0.58 and 0.45, respectively. A low friction coefficient was observed in the Al–SiO2-coated NTWs, and the reduced friction coefficient improved the efficiency of orthodontics. Furthermore, the excellent biocompatibility of the NTWs and SS coated with Al–SiO2 indicates that Al–SiO2 as a novel aesthetic layer could improve the physicochemical properties of NTW and SS without causing cytotoxicity, which has considerable potential for modification of NTW and SS surfaces.