In vitro corrosion behavior of TiN layer produced on orthopedic nickel-titanium shape memory alloy by nitrogen plasma immersion ion implantation using different frequencies (original) (raw)
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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.
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+ .
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
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.
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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
Nickel-titanium shape memory alloys (NiTi) have potential applications as orthopedic implants because of their unique super-elastic properties and shape memory effects. However, the problem of out-diffusion of harmful Ni ions from the alloys during prolonged use inside a human body must be overcome before they can be widely used in orthopedic implants. In this work, we enhance the corrosion resistance of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Results of atomic force microscopy (AFM) indicate that both C 2 H 2-PIII&D and C 2 H 2-PIII do not roughen the original flat surface to an extent that can lead to degradation in corrosion resistance.
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.
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.
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.