Bare NiTi Research Articles

Electrodeposition of Sacrificial Layer, Al2O3/ZnTPP film, onto NiTi Orthodontic Wire: Surface Characterizations and Electrochemical Investigations

Background: NiTi (nickel-titanium) alloy wires are widely used in orthodontics due to their unique properties, such as shape memory and superelasticity. However, these wires can be susceptible to corrosion in the oral environment, which can compromise their mechanical performance and longevity. Zinc tetraphenyl porphyrin (ZnTPP) is a corrosion inhibitor that forms a protective layer on the aluminum oxide (Al2O3) surface, acting as a barrier against corrosive agents. Objective: The electrodeposition of a sacrificial layer of Al2O3 with ZnTPP was carried out onto Ni- Ti orthodontic wire to enhance the corrosion resistance. Methods: 10 mM aluminum nitrate was dissolved in 10 mL of 0.1 M phosphate buffer solution (PBS), which was used as an electrolyte. Firstly, electrodeposition of Al2O3 on NiTi wire was carried out by using cyclic voltammetry by potential scanning between 0 and -2.0 V at a scan rate of 50 mV/s for 50 cycles. Secondly, 10 mL of 1 mM ZnTPP in 0.1 M PBS and ethanol (1:1) was prepared and used as an electrolyte. Electrodeposition of ZnTPP onto Al2O3/NiTi wire was achieved by cyclic voltammetry through the potential window of 0 to -2.0 V at a scan rate of 50 mV/s for 50 cycles. Results: The ZnTPP/Al2O3/NiTi wire displayed a potentiodynamic polarization resistance of 412931 Ω, with high stability compared to the bare NiTi wire (396421 Ω). Additionally, the corrosion rate for the ZnTPP/Al2O3/NiTi wire was measured as 0.254 mm/year, which was notably lower than that of the bare NiTi wire (0.540 mm/year). This decrease in corrosion rate can be attributed to the presence of the ZnTPP/Al2O3 film, which renders the NiTi wire electrically insulative and significantly increases its impedance compared to the bare NiTi wire. Conclusion: The bilayer coating of Al2O3 and ZnTPP has proven to significantly improve the corrosion resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic archwires with improved corrosion stability.

Oxidized Ethylene Glycol/ZrO2-coated NiTi Orthodontic Arch Wires: Surface Characterization and Electrochemical and Corrosion Studies

Background: Orthodontic arch wires, typically made of Nickel Titanium (NiTi), are widely utilized in dental procedures for correcting teeth misalignment and jaw issues due to their favorable mechanical attributes and cost-effectiveness. However, these NiTi wires are prone to corrosion in the oral environment, leading to diminished mechanical stability, compromised aesthetics, and potential health concerns for patients. Objective: There is a growing demand to augment the corrosion resistance and stability of orthodontic wires. Hence, this study aimed to address these issues. Herein, zirconium dioxide (ZrO2) and oxidized ethylene glycol (OEG) films were deposited onto NiTi wires to improve the corrosion resistance and stability. Methods: NiTi wires were modified by a two-step process involving electrodeposition of ZrO2 and oxidized ethylene glycol (OEG) film. The surface characterizations of coated material (OEG/ZrO2/NiTi) were carried out by using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), and Electron Microprobe Analysis (EMap) to confirm the elemental composition of the coated NiTi wire. Results: The OEG/ZrO2/NiTi wire exhibited a potentiodynamic polarization resistance of 547037 Ω and higher stability than the bare NiTi wire (396421 Ω). The corrosion rate for OEG/ZrO2/NiTi wire was found to be 0.040 mm/year, which was comparatively lower than a bare NiTi wire (0.069 mm/year). Due to the formation of OEG/ZrO2 film, NiTi wire became electrically insulative and showed a higher impedance than bare NiTi wire. Conclusion: The bilayer coating of ZrO2 and OEG has proven to significantly improve the corrosion resistance and stability of the wires. Thus, these materials can be considered for coating orthodontic arch wires with improved corrosion stability.

Preparation of tantalum-containing coatings on NiTi shape memory alloys with enhanced in vitro cytocompatibility and antibacterial effectiveness

In this work, the magnetron sputtering method is used to deposit tantalum-containing coatings on NiTi shape memory alloys under various sputtering atmospheres including (i) 100% argon, (ii) 16.6% oxygen and 83.4% argon, and (iii) 16.6% nitrogen and 83.4% argon. This research examines how the sputtering atmosphere can impact surface morphology, roughness, wettability, biocompatibility, in vitro cytocompatibility, and antibacterial performance of tantalum-containing coatings. The calculation of nickel ions release by coupled inductively coupled plasma-optical emission spectrometry displayed that none of the coated samples showed any traces of nickel, unlike the bare NiTi substrate. This has led to an improvement in biocompatibility. Topographical measurements demonstrated the formation of a smooth surface under the argon-oxygen atmosphere, whereas the deposited layer in the argon-nitrogen atmosphere exhibited irregular ups and downs. The coatings deposited under the argon-nitrogen atmosphere result in a hydrophobic surface with many hills and valleys which can considerably enhance protein and cellular absorption. Besides, the samples coated under an argon-oxygen atmosphere with a smooth surface exhibited excellent antibacterial efficiency only as early as 6 h of incubation. This is probably due to the formation of amorphous tantalum pentoxide.

Enhanced in vitro immersion behavior and antibacterial activity of NiTi orthopedic biomaterial by HAp-Nb2O5 composite deposits

NiTi is a class of metallic biomaterials, benefit from superelastic behavior, high biocompatibility, and favorable mechanical properties close to that of bone. However, the Ni ion leaching, poor bioactivity, and antibacterial activity limit its clinical applications. In this study, HAp-Nb2O5 composite layers were PC electrodeposited from aqueous electrolytes containing different concentrations of the Nb2O5 particles, i.e., 0–1 g/L, to evaluate the influence of the applied surface engineering strategy on in vitro immersion behavior, Ni2+ ion leaching level, and antibacterial activity of the bare NiTi. Surface characteristics of the electrodeposited layers were analyzed using SEM, TEM, XPS, and AFM. The immersion behavior of the samples was comprehensively investigated through SBF and long-term PBS soaking. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) infective reference bacteria were employed to address the antibacterial activity of the samples. The results illustrated that the included particles led to more compact and smoother layers. Unlike bare NiTi, composite layers stimulated apatite formation upon immersion in both SBF and PBS media. The concentration of the released Ni2+ ion from the composite layer, containing 0.50 g/L Nb2O5 was ≈ 60% less than that of bare NiTi within 30 days of immersion in the corrosive PBS solution. The Nb2O5-reinforced layers exhibited high anti-adhesive activity against both types of pathogenic bacteria. The hybrid metallic-ceramic system comprising HAp-Nb2O5-coated NiTi offers the prospect of a potential solution for clinical challenges facing the orthopedic application of NiTi.

Improvement of Cu and Zr doped Diamond-like carbon coatings on comprehensive performance of Ni-Ti alloy potentially used in braided vascular stent

Wear and corrosion between braided wires will not only release toxic nickel ions, but also cause fatigue fracture of Ni-Ti alloy-based braided stents. In this study, Cu and Zr doped Diamond-like carbon (DLC) film containing Cr intermediate layer and Cr:C gradient layer were prepared with the total thickness of about 2.17 μm and 2.05 μm, respectively. In order to study the improvement of DLC coating on the comprehensive properties of Ni-Ti based stent, the nano-mechanical, tribological, electrochemical corrosion, nickel ion release and cytotoxicity properties were all evaluated. The results showed that the nano hardness and elastic modulus for Zr-DLC film were 12.32 GPa and 138.49 GPa, respectively increased by 192% and 102% compared with bare NiTi. Cu-DLC and Zr-DLC coatings can not only significantly reduce the friction coefficient, but also greatly reduce the wear rate such as by three orders of magnitude in dry sliding condition compared with bare NiTi. Zr-DLC film reduced the icorr value with a reduction amount of 96.1%, with the values of 8.41 × 10−8 and 3.26 × 10−9 A/cm2 for NiTi and Zr-DLC, respectively. After 28 days of soak experiment in phosphate buffer solution, the total nickel ion release amount was only 5.6 ng/L for Cu-DLC and 6.9 ng/L for Zr-DLC, which was reduced by 96.1% and 95.2%, respectively. The relative cell proliferation rate results showed that NiTi and Zr-DLC were both Grade 0, which indicated good cytotoxicity result. However, the cytotoxicity of Cu-DLC reached grade 2 (the relative cell proliferation rate was 71.73%). Based on the above results, Zr-DLC showed good comprehensive performances and was expected to be used as a protective layer on the surface.

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.

Improvement of TiN coating on comprehensive performance of NiTi alloy braided vascular stent

In order to improve the wear and corrosion resistance of Ni–Ti alloy-based braided stent, High-temperature nitriding technology was used to prepare the TiN coating with different process parameters. Based on the systematic evaluation of nano-mechanical properties, tribological properties, electrochemical corrosion properties, nickel ion release properties and cytotoxicity, the feasibility of the application of the TiN coating in braided peripheral vascular stents was explored. The results showed that TiN coating included the TiN layer of about 1μm and nitrided layer of 50μm under the process parameters of 800 °C and 1h. The nano hardness and elastic modulus for TiN film were 20.50GPa and 281.66GPa, respectively. TiN coating can not only significantly reduce the friction coefficient in dry sliding and lubrication state, but also greatly reduce the wear rate such as by three orders of magnitude in dry sliding condition. TiN film reduced the icorr value with a reduction amount of 75.1%, with the value of 8.41 × 10−8 and 2.09×10−8A/cm2 for NiTi and TiN, respectively. After 28 days of soak experiment in phosphate buffer solution, the total nickel ion release amount of sample TiN#4 and bare NiTi were 0.094 and 1.452ng/m, which was reduced by 93.5%. The relative cell proliferation rate results showed that TiN samples all exceeded 90%, which mean that the cytotoxicity grade was 0. Based on the above results, TiN showed good nano-mechanical, tribological, electrochemical corrosion, nickel ion release and cytotoxity properties, and was expected to be used as a protective layer on the surface of Ni–Ti alloy stent.

Porous thermosensitive coating with water-locking ability for enhanced osteogenic and antibacterial abilities.

Preferable antibacterial property and osteogenesis are the permanent pursuit for metallic implants. However, it is difficult to satisfy both the properties. In fact, implants may be contaminated with bacteria during storage and surgery, leading to inflammation. Therefore, the antibacterial property of biomaterial surfaces is required not only in the human environment but also at room temperature. In this study, porous structures loaded with a thermosensitive poly (N-isopropylacrylamide) (PNIPAM) hydrogel on a nitinol (NiTi) substrate were constructed. When the temperature is 25 ​°C, almost all bacteria cannot adhere to the sample surface due to the abundant hydration layer of the PNIPAM hydrogel. Meanwhile, when the temperature is 37 ​°C, the structure of the PNIPAM hydrogel collapses and the hydration layer disappears due to the temperature change. However, the porous structures lock water in the pores, which results in a high-hydration-rate sample surface. This surface has few bacterial adhesion sites; nevertheless, the adhesion of larger cells to the surface is not impeded by the porous structure. In addition, the PNIPAM hydrogel is soft and biocompatible, so the sample can have better cell adhesion and proliferation than a bare NiTi alloy. Based on these results, it can be concluded that the porous NiTi sample loaded with the thermosensitive PNIPAM hydrogel has the antibacterial property before implantation and the dual function of inhibiting bacterial adhesion and promoting cell adhesion and proliferation after implantation, which shows promising applications in the biomedical field such as orthopedic implantation.

Corrosion resistance of a superelastic NiTi alloy coated with graphene–based coatings

The mechanical responses under superelastic loading cycles and the corrosion protection capacity of two graphene–based coatings applied to a NiTi alloy were evaluated. Graphene oxide (GO) and a composite of reduced graphene oxide (rGO) incorporated in a block copolymer of styrene–ethylene–butylene–styrene (SEBS) were deposited on the substrate via dip–coating. The morphology of the coatings was characterized by scanning electron microscopy (SEM) before and after uniaxial loading cycles up to 6%. Atomic force microscopy (AFM) was also used to evaluate the roughness of the coatings, which was expressed in terms of average roughness (Ra). The corrosion behavior was studied by potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis (MSA). SEM images suggested that both GO and rGO + SEBS create uniform coatings on the substrate. The measured Ra was 25 ± 3 nm for the bare NiTi, 24 ± 3 nm for the GO coated NiTi, and 8 ± 2 nm for the rGO + SEBS coated NiTi. Both coatings presented the capacity of following several superelastic cycles, maintaining their morphological integrity. PP and EIS showed that only the rGO + SEBS coating results in a significant improvement in terms of corrosion resistance. Furthermore, rGO + SEBS decreased the oxygen vacancies in the passive film when compared with the bare NiTi and GO coating.

A facile and cost-effective practical approach to develop clinical applications of NiTi: Fenton oxidation process

ABSTRACT To date, numerous attempts have been made to modify the surface condition of NiTi shape memory alloy to fully benefit from its desirable characteristics, and develop its potential clinical applications. In this survey, the Fenton oxidation process as a newly presented technique for surface modification of NiTi, was employed to address two major priorities in biomedical applications of NiTi, i.e. corrosion improvement and suppression of Ni ion release. To meet these priorities, two important variables involved in the Fenton oxidation process, namely immersion time and electrolyte temperature, were controlled. Results suggested that the application of such an oxidation process may considerably improve the corrosion behaviour of NiTi. The Fenton oxidation process carried out at 65°C for 24 h yields the lowest corrosion current density, 74% lower than bare NiTi. Additionally, Ni ion releases from the surface of NiTi after Fenton's oxidation decreases by ∼97%.

In-situ formation of TiN-TiO2 composite layer on NiTi shape memory alloy via fluidized bed reactor

In this work, the NiTi alloy was oxynitrided in a fluidized bed reactor to attain an in-situ TiN-TiO2 protective composite layer. Samples were treated at 540 ± 10 °C for various holding times ranging between 0 h and 8 h. Microstructural evolution on the surface was analyzed by scanning electron microscopy, X-ray diffraction, hardness test, electrochemical behavior, Ni ion release, and bioactivity. Quantitative phase analysis from X-ray diffraction pattern of the treated sample for 8 h showed that TiN (71.3%) and TiO2 (23.0%) were dominant phases on surface. Hardness results revealed as the oxynitriding time increased from 0 h to 8 h, hardness values increased from 263.4 HV0.1 to 1227.4 HV0.1. Scanning electron microscopy observation and energy dispersive X-ray spectroscopy mapping micrographs showed that the grown of TiN with dendritic branches was hindered by Ni-rich regions. Electrochemical measurements using polarization and electrochemical impedance spectroscopy analysis revealed corrosion resistance of the oxynitrided samples was increased by ~170% from 173.3 kΩ cm2 for the bare NiTi alloy to 473.1 kΩ cm2 for the treated NiTi sample for 8 h. It was found that concentration of the released Ni ions decreased from 0.070 (bare NiTi) mg/l to 0.028 mg/l (treated for 8 h) after oxynitriding treatment. Enhanced biocompatibility of the surface treated sample for 8 h was explained by formation of thick and homogenous TiN-TiO2 composite layer. Finally, bioactive behavior of the oxynitrided samples were studied using simulated body fluid.

Laser-induced wettability gradient surface on NiTi alloy for improved hemocompatibility and flow resistance.

Blood contacting materials with anti-thrombotic surfaces are highly demanded in clinics. Despite considerable research on surface modifications, limited progress has been made on effective prevention of thrombosis for artificial implants such as mechanical valve prosthesis. Herein, wettability gradient surface, which can ideally exhibit good hemocompatibility and low flow resistance, was developed for potential reduction of thrombosis. The wettability gradient surface on a model substrate of nickel-titanium (NiTi) alloy was prepared via a simple and economic method that combined laser microfabrication and surface stearic acid self-assembly approach. Scanning electron microscopy (SEM) observation confirmed that the wettability gradient surface was composed of a smooth NiTi region and three porous regions with different pore sizes and distances. Contact angle measurement revealed that, together with a low surface energy layer, the structural topography gradient could create a wettability gradient surface on NiTi alloy which could drive droplet motion. When compared with bare NiTi, such wettability gradient surface exhibited better anti-adhesion property, which was beneficial to the hemocompatibility and thus showing a lower hemolysis rate. Additionally, the wettability gradient surface also showed much lower flow resistance than bare NiTi. These results demonstrate that the developed wettability gradient surface may be used to reduce thrombosis.

Corrosion Resistance of Graphene oxide/Silver Coatings on Ni\u2013Ti alloy and Expression of IL-6 and IL-8 in Human Oral Fibroblasts

Graphene based materials (GBMs) have potentials for dental and medical applications. GBMs may cause changes in the levels of cytokine released in the body. This study aimed to study the corrosion resistance of graphene oxide (GO) and GO/silver (GO/Ag) nanocomposite coated nickel-titanium (NiTi) alloy by electrophoretic deposition and to access the viability of human pulp fibroblasts, and the interleukin (IL)-6 and IL-8 expression level. The bare and coated NiTi samples were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, surface profilometry, and X-ray diffraction (XRD). The corrosion resistance of the bare NiTi and coated NiTi samples were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The cell viability of human pulp fibroblasts was accessed by the treated culture medium of the bare NiTi and coated NiTi alloys containing 1% fetal bovine serum. IL-6 and IL-8 expression levels were studied by human enzyme-linked immunosorbent assay (ELISA). Data were analyzed using One-way ANOVA (α = 0.05). Both the GO-coated NiTi and GO/Ag-coated NiTi alloys showed better corrosion resistance, a lower rate of corrosion, and higher protection efficiency than the bare NiTi alloy. The coated NiTi alloys were biocompatible to human pulp fibroblasts and showed upregulation of IL-6 and IL-8 levels.

Preparation and cytocompatibility of Ni-Ti-O nanospindles on NiTi alloy

Abstract The present work reports on the hydrothermal conversion of Ni-Ti-O nanopores anodically grown on NiTi alloy into nanospindles and their cytocompatibility. The results show the amorphous nanopores can transform to anatase nanospindles with length concentrated at 70–110 nm and diameter at 16–24 nm upon hydrothermal treatment at 200 °C in pure water for 2 h. The nanospindles also can promote proliferation of bone marrow mesenchymal stem cells when compared with that of nanopores and bare NiTi alloy thus are promising as biomedical coatings of NiTi alloy.

Electrophoretic deposition of graphene oxide on NiTi alloy for corrosion prevention

Graphene oxide (GO) coating was prepared on the surface of a NiTi shape-memory alloy via a simple and practical electrophoretic deposition method from an aqueous suspension containing GO at low temperatures. The coating was characterized by field emission scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. The adhesion force and stabilization of the GO coating were analyzed by using a coating adhesion scratch testing system. The surface of the GO-coated NiTi exhibited hydrophilicity with a water contact angle of 17.6°. Moreover, the corrosion resistance of NiTi alloy was evaluated by a potentiodynamic polarization test in Hank's solution. The potentiodynamic polarization curves revealed that GO-coated NiTi demonstrated a more positive corrosion potential (Ecorr, −107 mV) than bare NiTi (Ecorr, −186 mV), and the corrosion current density (Icorr) decreased by approximately two orders of magnitude. The improved corrosion resistance and hydrophilicity of NiTi coated with GO compared with those of bare NiTi were mainly attributed to the GO coating.

Preparation, Characterization, and Corrosion Behavior of Calcium Phosphate Coating Electrodeposited on the Modified Nanoporous Surface of NiTi Alloy for Biomedical Applications

In this paper, the surface modification of the NiTi alloy was accomplished by anodizing in the ethylene glycol (EG)-based electrolyte and subsequent heat treatment at 823 K (550 °C) for 30 minutes. The field emission scanning electron microscopy images revealed that anodizing at 30 V led to the formation of a 3-D interconnected nanoporous TiO2 layer on the surface of NiTi. The existence of this oxide layer did not have a negative effect on the superelastic behavior of NiTi. In the next stage, this modified surface of samples was coated with calcium phosphate (Ca-P) ceramic using the pulsed electrodeposition method. Based on the results, anodizing of the NiTi substrate before electrodeposition promoted the quality of the applied coating. Moreover, electrodeposition at the higher current densities of 15 and 20 mA cm−2 increased the possibility of the hydroxyapatite phase formation in the coating rather than the other less stable calcium phosphate phases. Additionally, both the TiO2 layer and the Ca-P coating significantly improved the corrosion resistance of the NiTi alloy and suppressed the release of Ni ions from its surface. At last, in comparison to the bare NiTi, the mechanical locks between the nanoporous structure of the modified sample and the Ca-P coating increased the bonding strength.

Length-dependent corrosion behavior, Ni2+ release, cytocompatibility, and antibacterial ability of Ni-Ti-O nanopores anodically grown on biomedical NiTi alloy

In the present work, nickel-titanium-oxygen nanopores with different length (0.55–114 μm) were anodically grown on nearly equiatomic nickel-titanium (NiTi) alloy. Length-dependent corrosion behavior, nickel ion (Ni2+) release, cytocompatibility, and antibacterial ability were investigated by electrochemical, analytical chemistry, and biological methods. The results show constructing nanoporous structure on the NiTi alloy improve its corrosion resistance. However, the anodized samples release more Ni2+ than that of the bare NiTi alloy, suggesting chemical dissolution of the nanopores rather than electrochemical corrosion governs the Ni2+ release. In addition, the Ni2+ release amount increases with nanopore length. The anodized samples show good cytocompatibility when the nanopore length is <11 μm. Encouragingly, the length scale covers the one (1–11 μm) that the nanopores showing favorable antibacterial ability. Consequently, the nanopores with length in the range of 1–11 μm are promising as coatings of biomedical NiTi alloy for anti-infection, drug delivery, and other desirable applications.

Characterization of Surface-Treated NiTi Alloy by Various Electrochemical Techniques in Phosphate-Buffered Saline

Sol–gel titania thin film coating was prepared on NiTi surfaces, modified with acidified ferric chloride solution. Nanogrids formed on chemical treatment were uniformly covered with titania coating. Cyclic voltammetry studies in phosphate-buffered saline solution revealed that sol–gel titania-coated surface displayed electrochemical properties which were similar to those observed for pure titanium. During polarization, the passive layer formed on modified NiTi was stable for potentials greater than 0.9 V. The overall resistance measured by electrochemical impedance spectroscopy for sol–gel titania surface was in the order of 105 Ω, which was approximately two orders higher than bare NiTi surface. The current noise analyzed using electrochemical noise measurements was minimum after sol–gel coating, which emphasizes the better protection power of the surface from the attack of corrosive species. Dynamic impedance studies carried out on bare and titania-coated NiTi also supports the results obtained from cyclic polarization.

Enhanced photomechanical response of a Ni–Ti shape memory alloy coated with polymer-based photothermal composites

A simple way to enhance the activation of shape memory effects with light in a Ni–Ti alloy is demonstrated. Using polydimethylsiloxane-carbon nanopowder (PDMS+CNP) composites as coatings, the one-way shape memory effect (OWSME) of the alloy can be triggered using low power IR light from a laser diode. The PDMS+CNP coatings serve as photothermal materials capable to absorb light, and subsequently generate and dissipate heat in a highly efficient manner, thereby reducing the optical powers required for triggering the OWSME in the Ni–Ti alloy. Experimental results with a cantilever flexural test using both, bare Ni–Ti and coated samples, show that the PDMS+CNP coatings perform as thermal boosters, and therefore the temperatures required for phase transformation in the alloy can be readily obtained with low laser powers. It is also shown that the two-way shape memory effect (TWSME) can be set in the Ni–Ti alloy through cycling the TWSME by simply modulating the laser diode signal. This provides a simple means for training the material, yielding a light driven actuator capable to provide forces in the mN range. Hence, the use of photothermal coatings on Ni–Ti shape memory alloys may offer new possibilities for developing light-controlled smart actuators.

Electrochemical synthesis, corrosion behavior and cytocompatibility of Ni-Ti-O nanopores on NiTi alloy

In the present work, we report the anodic growth of Ni-Ti-O nanopores (NPs) on NiTi alloy in ethylene glycol (EG) electrolyte containing H2O and NaBr. It is shown that the NPs with diameter concentrated at 50–60nm can be grown at 10V in EG electrolyte containing 5vol% H2O and 0.48M NaBr. The NP-coated NiTi alloy show lower corrosion current density compared with that of the bare NiTi alloy. In addition, the NPs possess good cytocompatibility and can even promote osteoblast spreading. Good corrosion resistance and cytocompatibility render the Ni-Ti-O NPs promising as coating of the NiTi alloy for biomedical applications.