Effect of Surface Modification by Nitrogen Ion Implantation on the Electrochemical and Cellular Behaviors of Super-elastic NiTi Shape Memory Alloy (original) (raw)
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Materials Science and Engineering: C, 2010
Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO 2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids.
Corrosion products and mechanism on NiTi shape memory alloy in physiological environment
Despite many investigations on the corrosion behavior of NiTi shape memory alloys (SMAs) in various simulated physiological solutions by electrochemical measurements, few have reported detailed information on the corrosion products. In the present study, the structure and composition of the corrosion products on NiTi SMAs immersed in a 0.9% NaCl physiological solution are systematically investigated by scanning electron microscopy (SEM), x-ray energy dispersion spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). It is found that attack by Cl− results in nickel being released into the solution and decrease in the local nickel concentration at the pitting sites. The remaining Ti reacts with dissolved oxygen from the solution to form titanium oxides. After long-term immersion, the corrosion product layer expands over the entire surface and XPS reveals that the layer is composed of TiO2, Ti2O3, and TiO with relatively depleted Ni. The growth rate of the corrosion product layer decreases with immersion time, and the corrosion product layer is believed to impede further corrosion and improve the biocompatibility of NiTi alloy in a physiological environment. It is found that the release rate of nickel is related to the surface structure of the corrosion product layer and immersion time. A corrosion mechanism is proposed to explain the observed results.
Applied Surface Science, 2007
Water plasma immersion ion implantation (PIII) was conducted on orthopedic NiTi shape memory alloy to enhance the surface electrochemical characteristics. The surface composition of the NiTi alloy before and after H 2 O-PIII was determined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was utilized to determine the roughness and morphology of the NiTi samples. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were carried out to investigate the surface electrochemical behavior of the control and H 2 O-PIII NiTi samples in simulated body fluids (SBF) at 37 8C as well as the mechanism. The H 2 O-PIII NiTi sample showed a higher breakdown potential (E b) than the control sample. Based on the AFM results, two different physical models with related equivalent electrical circuits were obtained to fit the EIS data and explain the surface electrochemical behavior of NiTi in SBF. The simulation results demonstrate that the higher resistance of the oxide layer produced by H 2 O-PIII is primarily responsible for the improvement in the surface corrosion resistance.
Journal of The Electrochemical Society, 2009
The complex surface morphology and large exposed surface area induce electrochemical instability on porous NiTi shape memory alloys in human body fluids. Consequently, leaching of toxic nickel ions from the alloys impede wider applications of the materials in the biomedical fields, especially as bone implants. Electrochemical impedance spectroscopy ͑EIS͒ is a useful tool to evaluate the electrochemical stability of surface film in simulated body fluids ͑SBF͒ and to identify the most effective surface modification techniques for porous NiTi alloys. In the present work, EIS is employed to characterize porous NiTi alloys that have been modified by various processes in SBF at 37°C to evaluate the relationship between the surface film structure and electrochemical stability. Two different equivalent circuits involving a dual oxide film model with a porous outer layer and an inner barrier layer are proposed to model the experimental data acquired under open-circuit conditions for the control sample ͑dense NiTi͒ and porous NiTi alloys, respectively. The modeled results reveal that both chemical treatment and oxygen plasma immersion-ion implantation are effective surface modification techniques to form a protective film with higher electrochemical stability on the surface of porous NiTi alloys.
A Review Study on Biocompatible Improvements of NiTi-based Shape Memory Alloys
International Journal of Innovative Engineering Applications, 2021
Review paper NiTi-based shape memory alloys (SMAs) have many applications, especially for implantation, however since they are not a passive material so it is important to investigate them from different biocompatible perspectives. In this study, we introduced the important physical characteristics of NiTi alloys, then we explained different biocompatible terminologies, including carcinogenic, genotoxic, cytotoxicity, mutagenic, allergic, and corrosivity. We collected some important previous works that investigated the biocompatibility of NiTi-based SMAs and the different techniques used for improving the alloy and diminishing the hazard due to Ni-leakages.
Key Engineering Materials, 2016
NiTi alloy is being increasingly used in medicine due to its unique properties, i.e. shape memory and superelasticity. As a self-passivating material it is characterized by relatively high biocompatibility, however its use for long-term medical implants is questionable due to the nickel content of ≥ 50%. Therefore, the investigations on the surface modification of NiTi alloy are carried out to improve its corrosion resistance and thus reduce the metalosis effect, i.e. the migration of the alloy constituents, especially nickel, into the surrounding tissue.In this paper, the surface topography and corrosion resistance of NiTi alloy (50,8%Ni) both before and after low-temperature nitriding and oxynitriding processes under glow discharge conditions, are presented.The study of surface topography showed a slight increase in roughness parameters after nitriding process and a significant increase in these parameters after the oxynitriding process. A similar trend was observed in the study o...
Surface and Coatings Technology, 2007
Nickel titanium (NiTi) shape memory alloy is a unique material displaying the shape memory effect and superelastic property making it attractive to the orthopedic field. However, with its high nickel content of ∼ 50%, there is concern on health and safety when this material is implanted inside the human body for a prolonged period of time as toxic nickel ions may leach into the body due to corrosion under physiological environment. Previous work demonstrated that the corrosion resistance of this material could be enhanced by implanting a packed oxide layer on the substrate surface using oxygen plasma immersion ion implantation (PIII). The present study aims at improving its bioactivity by further implanting sodium ions into the modified surface using PIII. The chemical composition of the modified surface is characterized by X-ray photoelectron spectroscopy (XPS). Simulated body fluid (SBF) immersion tests for 21 days indicate that implantation of sodium successfully enhances the accumulation of calcium/ phosphorus-rich deposits on the modified surface. Anodic polarization scans suggest that sodium PIII does not affect the corrosion resistance of the oxygen plasma implanted surface. Three-point bending test reveals changes in the bulk mechanical property after PIII. However, superelasticity can be retained in the implanted NiTi materials. Differential scanning calorimetry (DSC) suggests a change in the transition temperature of the substrate which likely causes the change in mechanical property. In conclusion, oxygen and sodium PIII can enhance the bioactivity and corrosion resistance of NiTi, but care must be exercised because this treatment may change the bulk mechanical property.
Biocorrosion investigation of two shape memory nickel based alloys: Ni-Mn-Ga and thin film NiTi
Journal of Biomedical Materials Research Part A, 2007
Thin film nitinol and single crystal Ni-Mn-Ga represent two new shape memory materials with potential to be used as percutaneously placed implant devices. However, the biocompatibility of these materials has not been adequately assessed. Immersion tests were conducted on both thin film nitinol and single crystal Ni-Mn-Ga in Hank's balanced salt solution at 378C and pH 7.4. After 12 h, large pits were found on the Ni-Mn-Ga samples while thin film nitinol displayed no signs of corrosion. Further electrochemical tests on thin film nitinol samples revealed breakdown potentials superior to a mechanically polished nitinol disc. These results suggest that passivation or electropolishing of thin film nitinol maybe unnecessary to promote corrosion resistance.
Journal of Materials Science, 2017
Localized oxidation and corrosion behavior of a nickel-titanium (NiTi) shape memory alloy (SMA) was investigated via static immersion experiments in a simulated body fluid solution. Detailed electron microscopy examinations on the sample surfaces revealed preferential formation of local oxide particles around dislocation networks, which constitute high-energy zones. Moreover, various intermediate phases were detected in addition to the parent NiTi phase around dislocation networks. These are also areas with enhanced diffusion, which promotes Ni release. These findings emphasize the significant role of fine microstructural features, such as dislocation networks, on the oxidation and Ni release, and thus, the biocompatibility of the NiTi SMAs.