Her-Hsiung Huang

Ion release from NiTi orthodontic wires in artificial saliva with various acidities

NiTi orthodontic wire products from different manufacturers would have different corrosion resistance. We assayed the corrosion resistance, in terms of ion release, of different NiTi orthodontic wires in artificial saliva with various acidities. Four types of as-received commercial NiTi orthodontic wires were immersed in artificial saliva (37 degrees C) at pH 2.5-6.25 for different periods (1-28d). The amount of Ni and Ti ions released from NiTi wires was determined using an atomic adsorption spectrophotometer. Surface morphology and roughness of wires were related to the corrosion resistance. Results showed that the manufacturer, pH value, and immersion period, respectively, had a significantly statistical influence on the release amount of Ni and Ti ions. The amount of Ni ions released in all test solutions was well below the critical value necessary to induce allergy and below daily dietary intake level. The amount of Ti ions released in pH>/=3.75 solution was mostly not detectable, representing that the TiO(2) film on NiTi wires exhibited a good protection against corrosion. Pre-existed surface defects on NiTi wires might be the preferred locations for corrosion. The NiTi wire with the highest release amount of metal ions had the maximal increase in surface roughness after immersion test, while a rougher surface did not correspond to a higher metal ion release.

Effects of fluoride concentration and elastic tensile strain on the corrosion resistance of commercially pure titanium

The corrosion resistance of commercially pure (CP) titanium in 1% NaCl + 0 approximately 1% NaF solution (pH = 6) under different elastic tensile strains was investigated by using electrochemical impedance spectroscopy (EIS) measurement technique. The polarization resistance (Rp), which is inversely proportional to the corrosion rate, of CP titanium in the test solution was obtained from the EIS data. Different elastic tensile strains, namely 0%, 1%, 2%, and 4%, were applied on the test specimens by using a tensile test machine during the corrosion tests. Corrosion morphology was characterized by using a scanning electron microscope. Surface chemical analyses were performed by using energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The results showed that the NaF concentration and the elastic tensile strain had a statistically significant influence on the Rp (P<0.001). The Rp decreased on increasing the NaF concentration and the elastic tensile strain. When the NaF concentration was lower than 0.10%, the Rp value (> 3.4 x 10(5) omega cm2) was mainly ascribed to the formation of a protective titanium dioxide (TiO2) on the metal surface, regardless of the elastic tensile strain applied. However, when the NaF concentration was higher than 0.1%, the protectiveness of TiO2 was destroyed by fluoride ions, leading to severe corrosion of CP titanium.

Effect of fluoride and albumin concentration on the corrosion behavior of Ti-6Al-4V alloy

The purpose of this study was to investigate the effect of fluoride and albumin concentration on the corrosion behavior of Ti-6Al-4V alloy in acid artificial saliva (pH 5/37 degrees C) using potentiodynamic polarization and linear polarization test. Chemical analyses of the surface passive film were characterized using X-ray photoelectron spectroscopy. The results showed that either the NaF (0-0.5%) or the presence of albumin (0-0.2%) in 0.1% NaF-containing media had a significant influence on the corrosion potential (E(corr)), corrosion rate (I(corr)), passive current density (I(pass)), and polarization resistance (R(p)) (p<0.01). The I(corr) and I(pass) values increased on increasing the NaF concentration, but decreased with the presence of albumin in NaF-containing media. The R(p) value decreased on increasing the NaF concentration, but increased with the presence of albumin in NaF-containing media. When the NaF concentration was higher than 0.1%, the protectiveness of TiO(2) passive film formed on Ti-6Al-4V alloy was destroyed by fluoride ions, leading to the formation of Na(2)TiF(6). The presence of albumin, regardless of the concentration, in 0.1% NaF-containing acid media improved the corrosion resistance of Ti-6Al-4V alloy.

Formation of TiO2 nano-network on titanium surface increases the human cell growth

OBJECTIVES This study was to improve human cell growth on titanium (Ti) used for dental implants through formation of a nano-network surface oxide layer created by an electrochemical anodization treatment. METHODS An electrochemical anodization treatment was used to produce a network oxide layer on Ti surface. Surface characterization of the network layer was carried out using thin film X-ray diffractometer and field emission scanning electron microscopy. Human bone marrow mesenchymal stem cells (hMSCs) were made to express green fluorescent protein (GFP) by retroviral transduction. The GFP signal was measured in situ to assess in vitro and in vivo cell growth on Ti surfaces. In vivo experiments on Ti-supported cell growth were carried out on the back skin of nude mice. Alizarin red staining and immunofluorescent staining were used to observe cell differentiation. RESULTS A multilayer TiO(2) nano-network was produced rapidly on Ti surface using a simple electrochemical anodization treatment. The TiO(2) nano-network layer on the anodized Ti surfaces significantly improved in vitro and in vivo hMSC growth, as assessed by measurement of GFP fluorescence, relative to hMSC growth on untreated Ti surface. The TiO(2) nano-network layer on the anodized Ti surfaces can also induce the differentiation of hMSCs after 28-day in vivo test. SIGNIFICANCE The formation of TiO(2) nano-network on the Ti surfaces can increase the hMSC growth in vitro and in vivo.

Surface characterization of passive film on NiCr-based dental casting alloys

Surface characterization of passive film formed on different NiCr-based dental casting alloys in an acidic artificial saliva was investigated by using electrochemical impedance spectroscopy (EIS) measurement and potential decay test. The polarization resistance (R(p)), which is inversely proportional to corrosion rate, of passive film was obtained from the EIS data. The stable passive current density, passivating rate, and passivity decay rate of passive film were evaluated by potential decay test. Surface chemical analyses of passive film were performed by using X-ray photoelectron spectrometer and Auger electron spectrometer. Results showed that the R(p), stable passive current density, passivating rate, and passivity decay rate, respectively, were significantly different among the various NiCr-based alloys (p<0.001). The presence of higher Cr (maximum 31-37 at%; mainly as Cr(2)O(3)) and Mo (maximum 10-11 at%; mainly as MoO(3)) contents in the passive film led to a higher R(p), lower stable passive current density, faster passivating rate, and lower passivity decay rate. The presence of Be (>20 at%; mainly as BeO) in the passive film was detrimental to both the corrosion resistance and the stability of passive film. The presence of small amount of Ti (<6 at%; mainly as TiO(2)) in the passive film did not show any influence on the characterization of passive film.

Electrochemical behavior of the simulated heat-affected zone of A516 carbon steel in H2S solution

Electrochemical behavior of the simulated grain-coarsened heat-affected zone (HAZ) of A516 carbon steel in an H2S containing acidic chloride solution was investigated by electrochemical impedance spectroscopy (EIS) measurement at open circuit potential at 25 °C. EIS measurement was made for the specimens, prepared with three different heat input conditions (15, 30 and 45 kJ.cm−1) by thermal simulation with a Gleeble machine, in the H2S containing solution. The results show that the corrosion process of the simulated grain-coarsened HAZ can be divided into two stages regardless of the heat input condition. At an early stage, the impedance which is characterized by one large semicircle in the Nyquist plot increases with immersion time. At a later stage, the precipitation of sulfide film modifies the surface properties and leads to a variation in the EIS data by revealing a capacitive effect in the low frequency region. The polarization resistance initially increases with immersion time but then decreases gradually. Equivalent circuits containing two or three time constants are proposed to represent the corrosion processes at different stages.

Direct growth of oriented Mg–Fe layered double hydroxide (LDH) on pure Mg substrates and in vitro corrosion and cell adhesion testing of LDH-coated Mg samples

This work presents a novel method for directly forming highly-oriented Mg–Fe–CO3 LDH coating on pure Mg samples by treating the sample in pH 5.6 aqueous Fe3+/HCO3−/CO32− at 50 °C, and then immersing it in pH 9.5 aqueous HCO3−/CO32− at 50 °C. The former step was performed to yield Mg2+ in aqueous solution at pH 5.6 by corroding the Mg sample. A two-layered thin film was thus formed on the Mg substrate, of which the outer layer (∼1 μm-thick) comprised fine platelet-like Mg–Fe–CO3 LDH. The latter treatment in pH 9.5 aqueous HCO3−/CO32− at 50 °C resulted in the growth of the fine LDH platelets into a strongly-oriented Mg–Fe–CO3 LDH. The chemical formula of the Mg–Fe–CO3 LDH is Mg0.74Fe0.26(OH)2(CO3)0.13·mH2O. The method used herein involves a metal salt-free system, which requires no addition of Mg(NO3)2 and Fe(NO3)3. Several in vitro tests of the Mg–Fe–CO3 LDH coating on a Mg sample were performed. Based on the measured contact angle between the sample surface and human whole blood, the Mg–Fe–CO3 LDH coating can improve the hydrophilicity of a pure Mg surface. According to the results of an in vitro corrosion test in revised simulated body fluid (R-SBF), the Mg–Fe–CO3 LDH coated sample had a much higher corrosion resistance than the pure Mg substrate. The results of in vitro human mesenchymal stem cell adhesion tests showed that the Mg–Fe–CO3 LDH coated sample had a better cell spreading and cell–cell interaction behavior than the pure Mg substrate.

Corrosion resistance of different nickel-titanium archwires in acidic fluoride-containing artificial saliva.

OBJECTIVE To test the hypothesis that different nickel-titanium (NiTi) archwires may have dissimilar corrosion resistance in a fluoride-containing oral environment. MATERIALS AND METHODS Linear polarization test, a fast electrochemical technique, was used to evaluate the corrosion resistance, in terms of polarization resistance (R(p)), of four different commercial NiTi archwires in artificial saliva (pH 6.5) with various NaF concentrations (0%, 0.01%, 0.1%, 0.25%, and 0.5%). Two-way analysis of variance was used to analyze R(p) with the factors of archwire manufacturer and NaF concentration. Surface characterizations of archwires were analyzed using scanning electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. RESULTS Both archwire manufacturer and NaF concentration had a significant influence on R(p) of NiTi archwires. Different surface topography was present on the test NiTi archwires that contained the similar surface chemical structure (TiO(2) and trace NiO). The surface topography did not correspond to the difference in corrosion resistance of the NiTi archwires. Increasing the NaF concentration in artificial saliva resulted in a decrease in R(p), or corrosion resistance, of all test NiTi archwires. The NiTi archwires severely corroded and showed similar corrosion resistance in 0.5% NaF-containing environment. CONCLUSIONS Different NiTi archwires had dissimilar corrosion resistance in acidic fluoride-containing artificial saliva, which did not correspond to the variation in the surface topography of the archwires. The presence of fluoride in artificial saliva was detrimental to the corrosion resistance of the test NiTi archwires, especially at a 0.5% NaF concentration.

Microstructure and mechanical properties of surface layer obtained by plasma nitriding and/or TiN coating on high speed steel

Abstract Plasma-nitrided and/or TiN-coated high speed steel was investigated to determine the effect on the microstructure and mechanical properties of changing the N2/(N2 + H2) flow ratio in the nitriding process. Experimental results showed that the nitriding process created a diffusion layer instead of an iron nitride layer. Increasing the N2/(N2 + H2) flow ratio in the plasma nitriding process increased the depth of the diffusion layer and, thus, the subsequent hardness of the nitrided specimen and the nitrided and TiN-coated specimen. This was attributed to a better load-carrying capacity of the diffusion layer. However, increasing the N2/(N2+H2) flow ratio only promoted the wear resistance of the nitrided specimen. The adhesion between the TiN film and the substrate, evaluated using indentation testing, was poorer at a higher N2/(N2 + H2) flow ratio, suggesting that the wear resistance was dominantfy affected by adhesion instead of the load-carrying capacity.

Effect of oxygen plasma immersion ion implantation treatment on corrosion resistance and cell adhesion of titanium surface

OBJECTIVE The study was to investigate the corrosion resistance and cell adhesion of titanium (Ti) surface for dental implant application by oxygen plasma immersion ion implantation (O-PIII) treatments. MATERIALS AND METHODS Commercially pure Ti discs (grade 2) were used as the substrate. O-PIII surface treatments, with different oxygen doses (1 × 10(16) and 4 × 10(16) ions/cm(2)), were performed in a high-vacuum chamber with a radio frequency plasma source. Atomic force microscope, X-ray photoelectron spectrometer and nanoindenter were used to analyze surface topography, chemical composition (three samples per group) and mechanical property (twenty-five samples per group) of Ti specimens, respectively. Corrosion resistance of Ti specimens (five samples per group) was evaluated by potentiodynamic polarization curve measurement in simulated blood plasma solution. The adhesion and spreading of human bone marrow mesenchymal stem cells (hMSCs) on Ti surfaces were studied. RESULTS The results showed that O-PIII treatment had no significant influence on the surface topography of Ti specimens. The thickness of oxide layer (mainly as TiO(2)) on the O-PIII-treated Ti specimens increased with an increase in oxygen dose implanted. The O-PIII-treated Ti specimens possessed higher surface hardness and Youngs modulus than the untreated Ti specimen. Potentiodynamic polarization tests revealed that the O-PIII-treated Ti surfaces had lower corrosion rate (I(corr)) and passive current (I(pass)) than the untreated Ti surface. The adhesion and spreading of hMSCs on Ti surfaces were improved by O-PIII treatment. CONCLUSIONS O-PIII treatment could enhance the corrosion resistance and cell adhesion of Ti surface for dental implant application due to the increase in surface thickness of Ti-oxides (mainly as TiO(2)) on Ti.