Improvement on corrosion resistance of NiTi orthopedic materials by carbon plasma immersion ion implantation (original) (raw)
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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2005
Nickel-titanium shape memory alloys (NiTi) are useful materials in orthopedics and orthodontics due to their unique super-elasticity and shape memory effects. However, the problem associated with the release of harmful Ni ions to human tissues and fluids has been raising safety concern. Hence, it is necessary to produce a surface barrier to impede the out-diffusion of Ni ions from the materials. We have conducted acetylene, nitrogen and oxygen plasma immersion ion implantation (PIII) into NiTi alloys in an attempt to improve the surface properties. All the implanted and annealed samples surfaces exhibit outstanding corrosion and Ni out-diffusion resistance. Besides, the implanted layers are mechanically stronger than the substrate underneath. XPS analyses disclose that the layer formed by C 2 H 2 PIII is composed of mainly TiC x with increasing Ti to C concentration ratios towards the bulk. The nitrogen PIII layer is observed to be TiN, whereas the oxygen PIII layer is composed of oxides of Ti 4+ , Ti 3+ and Ti 2+ .
2008
In the present work, the NiTi surface was modified by nitrogen plasma immersion ion implantation (PIII) in an effort to improve the corrosion resistance and mitigate nickel release from the materials. The implanted nitrogen depths and thicknesses of the surface TiN barrier layers were varied by changing the pulsing frequencies during PIII. In order to determine the optimal parameters including the pulsing frequencies, electrochemical tests including open circuit potential (OCP) measurements and potentiodynamic polarization tests were conducted on the untreated and N-implanted NiTi in simulated body fluids (SBF). Our results reveal that the nitride layer produced using a frequency of 50 Hz has the best stability under the OCP conditions and the TiN layer produced using 200 Hz has the highest potentiodynamic stability after immersion in SBF for a long time. The observation can be correlated to the temperature during PIII and the thickness of TiN layer. The TiN layer on the NiTi surface favors deposition of CaP composites thereby compensating for the instability of the TiN layer produced at a higher frequency.
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.
Thin Solid Films, 2005
Nickel-titanium shape memory alloys (NiTi) are potentially useful in orthopedic implants due to their super-elasticity and shape memory properties. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, we describe our fabrication of TiN barrier layers in NiTi by nitrogen plasma immersion ion implantation followed with vacuum annealing at 450-C or 600-C. Our results show that the barrier layer is not only mechanically stronger than the NiTi substrate, but also is effective in impeding the out-diffusion of Ni from the substrate. Among the samples, the 450-Cannealed TiN barrier layer possesses the highest mechanical strength and best Ni out-diffusion impeding ability. The enhancement can be attributed to the consolidation of the TiN layer resulting from optimal diffusion at 450-C.
Journal of Biomedical Materials Research Part A, 2007
Stainless steel and titanium alloys are the most common metallic orthopedic materials. Recently, nickel-titanium (NiTi) shape memory alloys have attracted much attention due to their shape memory effect and super-elasticity. However, this alloy consists of equal amounts of nickel and titanium, and nickel is a well known sensitizer to cause allergy or other deleterious effects in living tissues. Nickel ion leaching is correspondingly worse if the surface corrosion resistance deteriorates. We have therefore modified the NiTi surface by nitrogen plasma immersion ion implantation (PIII). The surface chemistry and corrosion resistance of the implanted samples were studied and compared with those of the untreated NiTi alloys, stainless steel, and Ti-6Al-4V alloy serving as controls. Immersion tests were carried out to investigate the extent of nickel leaching under simulated human body conditions and cytocompatibility tests were conducted using enhanced green fluorescent protein mice osteoblasts. The X-ray photoelectron spectroscopy results reveal that a thin titanium nitride (TiN) layer with higher hardness is formed on the surface after nitrogen PIII. The corrosion resistance of the implanted sample is also superior to that of the untreated NiTi and stainless steel and comparable to that of titanium alloy. The release of nickel ions is significantly reduced compared with the untreated NiTi. The sample with surface TiN exhibits the highest amount of cell proliferation whereas stainless steel fares the worst. Compared with coatings, the plasma-implanted structure does not delaminate as easily and nitrogen PIII is a viable way to improve the properties of NiTi orthopedic implants. 2007 Wiley
Surface and Coatings Technology, 2007
Nickel-titanium (NiTi) shape memory alloys are potentially very useful in orthopedic and dental implantation, since the materials possess super-elasticity and shape memory effects that other current medical metallic materials do not have. Possible nickel ion release, however, hampers their medical applications, particularly in orthopedic implants where fretting is always expected at the articulating surface. We have utilized plasma immersion ion implantation (PIII) to alter the surface chemistry of the materials in order to reduce nickel release. The enhanced corrosion resistance and surface mechanical properties have been reported previously. This paper describes the cytocompatibility and in vivo performance of the PIII treated and untreated samples. NiTi discs with 50.8% Ni were treated by nitrogen and oxygen PIII at 40 kV. After PIII, titanium nitride (TiN) and packed titanium oxide (TiO) are formed on the surface. The degree of cell proliferation on the untreated and oxygen treated samples is slightly inferior to that on the nitrogen treated sample. However, in vivo bone formation on the nitrogen plasma treated samples is better compared to the untreated control and oxygen treated one at all time points. Our work thus provides the evidence that nitrogen plasma modified NiTi alloys are potentially suitable for orthopedics without inducing harmful biological effects.
Nitrogen plasma-implanted nickel titanium alloys for orthopedic use
Surface and Coatings Technology, 2007
Nickel-titanium shape memory alloys (NiTi) have attracted much attention as orthopedic materials due to their shape memory effect and superelasticity. However, this alloy consists of equal amounts of nickel and titanium and Ni is well known to cause allergy or other deleterious effects in living tissues. To improve the surface corrosion resistance and mitigate Ni leaching, we have modified the surface chemistry of this alloy with the aid of nitrogen plasma immersion ion implantation (PIII). The implanted surfaces were characterized by X-ray photoelectron spectroscopy (XPS). Electrochemical corrosion and nano-indentation tests were conducted to assess the corrosion resistance and surface hardness. Immersion tests were carried to investigate the extent of Ni leaching under simulated human body conditions and cell cultures employing enhanced green fluorescent protein mice osteoblasts were used to evaluate the cyto-compatibility of the materials. The XPS results reveal that a thin layer of TiN with higher hardness is formed on the surface after nitrogen-PIII. The corrosion resistance of the implanted sample is also superior to that of the untreated NiTi and SS. The release of Ni ions is significantly reduced compared to the untreated NiTi and both the treated and untreated NiTi alloys favor osteoblast attachment and proliferation. The sample with surface titanium nitride exhibits the largest degree of cell proliferation whereas stainless steel fares the worst.
Corrosion Engineering, Science and Technology, 2019
NiTi shape memory alloy, both before and after low-temperature oxynitriding under glow discharge conditions combined with the production of a nano-sized outer carbon coating, was investigated. The study compares two types of carbon coatings: produced via the RFCVD (radio frequency chemical vapour deposition) and IBAD (ion beam-assisted deposition) methods. The latter was also enriched by randomly distributed silver nanoparticles. The study showed slight changes in roughness parameters and increased corrosion resistance after surface treatment processes. The largest impedance module and corrosion potential and the smallest density of corrosion current were achieved for samples with a carbon coating produced via the RFCVD process. The presented surface modifications using hybrid processes can extend the use of NiTi alloy in medicine due to the increased biocompatibility.
Journal of Biomedical Materials Research Part A, 2007
NiTi shape memory alloy is one of the promising orthopedic materials due to the unique shape memory effect and superelasticity. However, the large amount of Ni in the alloy may cause allergic reactions and toxic effects thereby limiting its applications. In this work, the surface of NiTi alloy was modified by nitrogen plasma immersion ion implantation (N-PIII) at various voltages. The materials were characterized by X-ray photoelectron spectroscopy (XPS). The topography and roughness before and after N-PIII were measured by atomic force microscope. The effects of the modified surfaces on nickel release and cytotoxicity were assessed by immersion tests and cell cultures. The XPS results reveal that near-surface Ni concentration is significantly reduced by PIII and the surface TiN layer suppresses nickel release and favors osteoblast proliferation, especially for samples implanted at higher voltages. The surfaces produced at higher voltages of 30 and 40 kV show better adhesion ability to osteoblasts compared to the unimplanted and 20 kV PIII samples. The effects of heating during PIII on the phase transformation behavior and cyclic deformation response of the materials were investigated by differential scanning calorimetry and three-point bending tests. Our results show that N-PIII conducted using the proper conditions improves the biocompatibility and mechanical properties of the NiTi alloy significantly.
Surface and Coatings Technology, 2013
Titanium carbide coatings have a broad range of biomedical applications because of their high hardness, low friction, excellent corrosion resistance, and good biocompatibility. NiTi alloys are also widely used in surgical implants in orthodontics and orthopedics. In order to improve the surface properties, nanostructured titanium carbide coatings are deposited on NiTi by plasma immersion ion implantation and deposition after a titanium interlayer has been fabricated on the NiTi substrate. The structure and corrosion behavior which impact the biological properties are investigated systematically by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, atomic force microscopy, and electrochemical impedance spectroscopy in simulated body fluids at 37°C. The TiC thin films with a C/Ti ratio of 1.087 have the (220) orientation. The EIS results demonstrate that the Ti/TiC multilayer provides significantly better corrosion resistance and stability compared to the uncoated NiTi substrate.