In vitro degradation behavior and biocompatibility of Mg–Nd–Zn–Zr alloy by hydrofluoric acid treatment

In this paper, Mg–Nd–Zn–Zr alloy (denoted as JDBM) coated with hydrofluoric acid (HF) chemical conversion film (MgF₂) was researched as a potential biodegradable cardiovascular stent material. The microstructures, in vitro degradation and biocompatibility were investigated. The field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) showed that a compact MgF₂ film was formed on the surface of JDBM. The corrosion rate decreased in artificial plasma from 0.337 to 0.253 mm·y^? 1 and the electrochemical measurement demonstrated that the corrosion resistance of JDBM alloy could be obviously improved due to the protective MgF₂ film on the surface of the substrate. Meanwhile, the hemolysis ratio of JDBM decreased from 52.0% to 10.1% and the cytotoxicity met the requirement of cellular application after HF treatment. In addition, JDBM and MgF₂ film showed good anti-platelet adhesion, which is a very favorable property for implant material in contact with blood directly.     

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

The aim of this work is to investigate the surface characteristics and corrosion behavior of NiTi (50.6 at.% Ni) shape memory alloy coated by a ceramic-like and highly biocompatible material, iridium oxide (IrO₂). IrO₂ coatings were prepared by thermal decomposition of H₂IrCl₆ · 6H₂O precursor solution at the temperature of 300 °C, 400 °C and 500 °C, respectively. The surface morphology and microstructure of the coatings were investigated by scanning electron microscope (SEM) and glancing angle X-ray diffraction (GAXRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the surface elemental composition. Corrosion resistance property of the coated samples was studied in a simulated body fluid at 37 ± 1 °C by electrochemical method. It was found that the morphology and microstructure of the coatings were closely related to the oxidizing temperatures. A relatively smooth, intact and amorphous coating was obtained when the H₂IrCl₆·6H₂O precursor solution (0.03 mol/L) was thermally decomposed at 300 °C for 0.5 h. Compared with the bare NiTi alloy, IrO₂ coated samples exhibited better corrosion resistance behavior to some extent.     

The location of atomic hydrogen in NiTi alloy: A first principles study

A first principles density functional theory study to investigate the H defect in NiTi alloy is presented. We have determined the interstitial H atom position in bulk B2 phase NiTi alloy. H positions on both the Ti and Ni terminated NiTi surfaces are calculated. Surface adsorptions of H atom on Ni/Ti terminated surfaces are calculated for a low surface coverage of 1.96 × 10¹⁴ cm^?2. We have also calculated the penetration barrier energy for an H atom from the surface site to the bulk lattice site.     

Corrosion behavior of biomedical Ti–24Nb–4Zr–8Sn alloy in different simulated body solutions

Corrosion behavior of a multifunctional biomedical titanium alloy Ti–24Nb–4Zr–8Sn (wt.%) in 0.9% NaCl, Hank's solution and artificial saliva at 37 °C was investigated using open circuit potential, impedance spectroscopy and potentiodynamic polarization techniques, and some results were compared with pure titanium and Ti–6Al–4V alloy. The results showed that the alloy exhibited good corrosion resistance due to the formation of a protective passive film consisting mainly of TiO₂ and Nb₂O₅, and a little of ZrO₂ and SnO₂. Ca ions were detected in the passive film as the alloy immersed in Hank′s and artificial saliva solutions and they have negative effect on corrosion resistance. The EIS results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface, and they all transformed into stable bilayer structure as the immersion time increased up to 24 h. The polarization curves demonstrated that the alloy had a wider passive region than pure titanium and Ti–6Al–4V alloy and its corrosion current density (less than 0.1 μA/cm²) is comparable to that of pure titanium.     

Carbon layers formed on steel and Ti alloys after ion implantation of C+ at very high doses

Ion implantation is a useful technique to tailor surface properties of steel and Ti alloys. In particular, very high dose C⁺ implantation (in the range of 10¹⁸ ions cm⁻²) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation of carbon doses up to 8×10¹⁸ ions cm⁻² has been performed on 440C martensitic stainless steel and Ti6Al4V substrates under similar conditions and tribological and surface analysis results have been compared. Surface hardening occurred for all ion implantation conditions up to doses of 10¹⁸ ions cm⁻²1, 2, 3. Higher doses resulted in a different behaviour for both materials. The stainless steel showed a softening while a twofold hardness increase was maintained in the Ti alloy. Nevertheless, at the higher implanted dose a decrease in hardness was also observed in the Ti alloy. Small area XPS analyses were performed to evaluate the chemical states after ion implantation and establish a relationship with the observed surface hardening. Depth profile XPS analyses showed that for a dose of 4×10¹⁸ ions cm⁻² a carbon layer (with concentration over 85% at. C) was formed in the near surface region for both materials.     

The electrochemical behavior of a Ti50Ni47Fe3 shape memory alloy

The corrosion performance of Ti₅₀Ni₄₇Fe₃ alloy in 0.9% NaCl physiological, artificial saliva and Hank's solutions with different pH values at 37 °C was investigated by means of open circuit potential (OCP) measurement and linear polarization (LP) measurement techniques, respectively. The OCP stabilized at − 0.2925, − 0.3111 and − 0.3454 mV/SCE in sequence for 0.9% NaCl, artificial saliva and Hank's solutions, respectively. LP results demonstrated that the Ti₅₀Ni₄₇Fe₃ alloy has a low passive current and a wide passive range. The surface roughness and in-depth distribution of the passive films after immersion in corrosion media was characterized by using Atomic Force Measurement (AFM) and X-ray electron spectroscopy (XPS). AFM results shows that the electrochemical measurements have little influence on the surface roughness of the Ti₅₀Ni₄₇Fe₃ alloy, and the XPS analysis results revealed that the outer passive film consisting mainly of a layer of TiO₂ which is deemed to be important for all biomaterials.     

Surface characterization and wear behavior of ion implanted NiTi shape memory alloy

The aim of this study was investigation of changes in the modified near-surface layer on the NiTi shape memory alloy, caused by ion implantation as well as their influence on the mechanical and shape memory properties of this material. Surface of NiTi has been modified by nitrogen ion beam at several fluences 1 × 10¹⁷ cm^?2, 1 × 10¹⁸ cm^?2 and 2 × 10¹⁸ cm^?2 at the energy 50 keV. The effect of implantation parameters on surface characteristics and wear properties was investigated using dry-sliding-wear test, depth sensing indentation test and scanning profilometry method. The experimental results have shown how the ion implantation treatment can change the original surface: reducing Ni content in the surface, increasing the surface hardness (furthermore, the hardness improvement extended to the regions much deeper than the implanted layer), and improving the sliding wear resistance. The experimental results of surface treatment conditions and mechanical properties of the modified NiTi alloys are compared, analyzed and discussed in this paper.     

In vitro stability study of organophosphonic self assembled monolayers (SAMs) on cobalt chromium (Co–Cr) alloy

Surface modification of cobalt chromium (Co–Cr) alloy is being investigated as a possible solution to the biomedical challenges arising from its usage. Self assembled monolayers (SAMs) of organophosphonic octadecylphosphonic acid (ODPA) were formed on the oxide surface of Co–Cr alloy by chemisorption using the solution deposition technique. High quality and well-ordered SAMs were formed which were characterized using Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle measurements and ellipsometry. The resulting monolayers were then exposed to in vitro conditions using phosphate buffered saline (PBS) solution. The samples were analyzed for a period of 1, 3, 7 and 14 days. The resulting samples were characterized using XPS, AFM and Contact angle measurements. XPS atomic concentrations and detailed high energy elemental scans gave an insight into the trends of elemental concentrations over the duration of the study. SAMs were found to be strongly bound to the oxide surface after PBS exposure. AFM gave the topographic details of SAMs presence by island formation before and after SAM formation and also over the duration of the PBS exposure. Contact Angle Measurements confirmed the hydrophobicity of the surface after SAM formation and indicated a slight disorder of the SAM alkyl chain upon exposure to PBS. Thus, ODPA SAMs were successfully coated on Cobalt Chromium (Co–Cr) alloy surface and were found to be stable and strongly bound after PBS exposure.     

Characterization of passive oxide film on a Ti–5%Ta–1.8%Nb alloy on exposure to severe oxidizing conditions

This paper presents the results of a study on the characteristics of the passive oxide film that forms on the surface of an α + β Ti–5%Ta–1.8%Nb alloy, which possesses good corrosion resistance in severe oxidizing environment of boiling 11.5 M nitric acid. Through systematic structure–property studies, the microstructure with low corrosion rate (< 1 mpy) in liquid, vapor and condensate phases of nitric acid was identified. The characteristics of the passive film, which imparts corrosion resistance to the alloy, are influenced by its microstructure, temperature and concentration of the acid. The microstructure, thickness and composition of the oxide film were characterized using different techniques. TiO₂, Nb₂O₅ and Ta₂O₅ formed on exposure to vapor and condensate phases, while TiO₂ was observed on exposure to the liquid phase. Detailed microstructural studies showed that the passive film consists of nano-crystalline phases of titanium and tantalum oxides, predominantly anatase in an amorphous matrix. Based on these studies, the mechanism of corrosion of the alloy is derived.     

Diffusion bonding of titanium alloy to micro-duplex stainless steel using a nickel alloy interlayer: Interface microstructure and strength properties

In the present study, diffusion bonding of titanium alloy and micro-duplex stainless steel with a nickel alloy interlayer was carried out in the temperature range of 800–950 °C for 45 min under the compressive stress of 4 MPa in a vacuum. The bond interfaces were characterised by scanning electron microscopy, electron probe microanalyzer and X-ray diffraction analysis. The layer wise Ni₃Ti, NiTi and NiTi₂ intermetallics were observed at the nickel alloy/titanium alloy interface and irregular shaped particles of Fe₂₂Mo₂₀Ni₄₅Ti₁₃ was observed in the Ni₃Ti intermetallic layer. At 950 °C processing temperature, black island of β-Ti phase has been observed in the NiTi₂ intermetallics. However, the stainless steel/nickel alloy interface indicates the free of intermetallics phase. Fracture surface observed that, failure takes place through the NiTi₂ phase at the NiA–TiA interface when bonding was processed up to 900 °C, however, failure takes place through NiTi₂ and β-Ti phase mixture for the diffusion joints processed at 950 °C. Joint strength was evaluated and maximum tensile strength of ∼560 MPa and shear strength of ∼415 MPa along with ∼8.3% ductility were obtained for the diffusion couple processed at 900 °C for 45 min.     

Characterization of Sol-gel-derived TiO2 and TiO2-SiO2 Films for Biomedical Applications

In order to improve the corrosion resistance and biocompatibility of NiTi surgical alloy, TiO2 and TiO2-SiO2 thin films were prepared by sol-gel method. The surface characteristics of the film, which include surface composition, microstructure and surface morphology, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectra (XPS), respectively. A scratching test was used to assess the interface adhesive strength between the film and substrate. The corrosion resistance of NiTi alloy coated with oxide films were studied by anodic polarization curves measurement in biological solution. Additionally, a preliminary study of the in vitro bioactivity of the films was conducted. The results indicated that TiO2 and TiO2-SiO2 (Ti/Si=4:1) films have higher electrochemical corrosion resistance and can be used as protective layers on NiTi alloy. In addition, TiO2-SiO2 composite films have better bioactivity than TiO2 film.     

Comparison of biodegradable behaviors of AZ31 and Mg–Nd–Zn–Zr alloys in Hank's physiological solution

The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28 mm/year) was much slower than that of AZ31 (1.02 mm/year) in Hank's solution for 240 h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.     

Microstructure,mechanical property and corrosion behaviors of interpenetrating C/Mg-Zn-Mn composite fabricated by suction casting

A novel interpenetrating C/Mg-Zn-Mn composite was fabricated by infiltrating Mg-Zn-Mn alloy into porous carbon using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composite have been evaluated by means of SEM, XRD, mechanical testing and immersion test. It was shown that the composite had a compact structure and the interfacial bonding between Mg-Zn-Mn alloy and carbon scaffold was very well. The composite had an ultimate compressive strength of (195 ± 15) MPa, which is near with the natural bone (2–180 MPa) and about 150-fold higher than that of the original porous carbon scaffold, and it still retained half of the strength of the bulk Mg-Zn-Mn alloy. The corrosion test indicated that the mass loss percentage of the composite was 52.9% after 30 days′ immersion in simulated body fluid (SBF) at 37 ± 0.5 °C, and the corrosion rates were 0.043 mg/cm²h and 0.028 mg/cm²h after 3 and 7 days′ immersion, respectively. The corrosion products on the composite surface were mainly Mg(OH)₂ and hydroxyapatite (HA).     

New Ni-free superelastic alloy for orthodontic applications

A potential new Ni-free Ti alloy for biomedical applications was assessed in order to investigate the superelastic behavior, corrosion resistance and the biocompatibility. The alloy studied was Ti19.1Nb8.8Zr. The chemical composition was determined by X-ray microanalysis, the thermoelastic martensitic transformation was characterized by high sensitivity calorimeter. The critical stresses were determined by electromechanical testing machine and the corrosion behavior was analyzed by potentiostatic equipment in artificial saliva immersion at 37 °C. The results were compared with six different NiTi orthodontic archwire brands. The biocompatibility was studied by means of cultures of MG63 cells. Ni-free Ti alloy exhibits thermoelastic martensitic transformation with M_s = 45 °C. The phase present at 37 °C was austenite which under stress can induce martensite. The stress–strain curves show a superelastic effect with physiological critical stress (low and continuous) and a minimal lost of the recovery around 150 mechanical cycles. The corrosion resistance improves the values obtained by different NiTi alloys avoiding the problem of the Ni adverse reactions caused by Ni ion release. Cell culture results showed that adhered cell number in new substrate was comparable to that obtained in a commercially pure Ti grade II or beta-titanium alloy evaluated in the same conditions. Consequently, the new alloy presents an excellent in-vitro response.     

Silk fibroin immobilization on poly(ethylene terephthalate) films: Comparison of two surface modification methods and their effect on mesenchymal stem cells culture

Silk fibroin (SF) has played a curial role for the surface modification of conventional materials to improve the biocompatibility, and SF modified poly(ethylene terephthalate) (PET) materials have potential applications on tissue engineering such as artificial ligament, artificial vessel, artificial heart valve sewing cuffs dacron and surgical mesh engineering. In this work, SF was immobilized onto PET film via two different methods: 1) plasma pretreatment followed by SF dip coating (PET-SF) and 2) plasma-induce acrylic acid graft polymerization and subsequent covalent immobilization of SF on PET film (PET-PAA-SF). It could be found that plasma treatment provided higher surface roughness which was suitable for further SF dip coating, while grafted poly(acrylic acid) (PAA) promised the covalent bonding between SF and PAA. ATR-FTIR adsorption band at 3284 cm^? 1, 1623 cm^? 1 and 1520 cm^? 1 suggested the successful introduction of SF onto PET surface, while the amount of immobilized SF of PET-SF was higher than PET-PAA-SF according to XPS investigation (0.29 vs 0.23 for N/C ratio). Surface modified PET film was used as substrate for mesenchymal stem cells (MSCs) culture, the cells on PET-SF surface exhibited optimum density compared to PET-PAA-SF according to CCK-8 assays, which indicated that plasma pretreatment followed by SF dip coating was a simple and effective way to prepare biocompatible PET surface.     

Inhomogeneous structure of near-surface layers in the ion-implanted NiTi alloy

This paper reports the application of nitrogen ion implantation for modification of a shape memory alloy. It is known that the problem of creating a protective surface coating for the shape memory alloy is the most acute for potential applications of this material. Thus, the problem of increasing surface protective properties and, at the same time, simultaneous preservation of functional properties of shape memory materials is a subject of research and development [Pelletier H, Muller D, Mille P, Grob J. Surf Coat Technol 2002;158:309.]. The surface characterization of nitrogen implanted (fluence 10¹⁸ cm^?2 and energy 50 keV) equiatomic commercial NiTi alloy samples was performed with the assistance of high resolution transmission electron microscopy (HTEM) techniques and modifications of phase composition before and after irradiation are studied at room and martensitic transformation temperatures by X-ray diffraction methods. Differential scanning calorimetry (DSC, TA Instruments) was used to characterize the transformation sequence and transformation temperatures for the initial and surface-modified materials. Experimental results of an inhomogeneous structure of near-surface layers in the ion-implanted NiTi alloy are discussed in this paper.     

Effect of trace HA on microstructure,mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy

Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites(x = 0, 0.1 and 0.3 wt%) were characterized by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy dispersion spectroscopy(EDS) and X-ray diffraction(XRD). Results of tensile tests at room temperature show that yield strength(YS) of Mg-2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength(UTS) and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential(Ecorr)of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from-1724 to-1660 m VSCE and the corrosion current density decreases from 479.8 to 280.8 μA cm~(-2) with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.5Sr/HA composites decreases from11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO_4 protective film due to the adsorption of Ca~(2+)on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.     

Influence of aluminum ions implanted on corrosion behavior of zirconium in 1 M H2SO4

In order to study the effect of aluminum ion implantation on the aqueous corrosion behavior of zirconium, specimens were implanted with aluminum ions with fluence ranging from 1 × 10¹⁶ to 1 × 10¹⁷ ions/cm², using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV. The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES), respectively. Transmission electron microscopy (TEM) was used to examine the microstructure of the aluminum-implanted samples. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the aluminum ion implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of implanted zirconium in a 1 M H₂SO₄ solution. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium implanted with aluminum ions. Finally, the mechanism of the corrosion behavior of aluminum-implanted zirconium was discussed.     

Effect of Y on the bio-corrosion behavior of extruded Mg–Zn–Mn alloy in Hank's solution

The bio-corrosion properties of Mg–Zn–Mn alloys with and without Y in Hank's solution at 37 °C were investigated by using electrochemical test and electrochemical impedance spectra (EIS). The results of open circuit potential (OCP) and polarization tests indicated that Y could reduce the cathodic current density. A passivative stage appeared in the Tafel curve of the Y containing magnesium alloy, indicating that a passivative film was formed on the surface of the Y containing magnesium alloy. EIS results showed that the Y containing alloy had higher charge transfer resistance and film resistance, but lower double layer capacity than the alloy without the Y element. The surface reaction product identification by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the surface corrosion products were hydroxide and phosphate (Mg₃Ca₃(PO₄)₄) for Mg–Zn–Mn alloy and phosphate (MgNaPO₄) for the Y containing Mg–Zn–Mn alloys. The XPS results also showed that a Y₂O₃ protective film was formed on the surface of the Y containing magnesium alloy which contributed mainly to the low cathodic current density and the high resistance.     

Effects of monovalent anions and cations on drainage and lifetime of foam films at different interface approach speeds

Ions of inorganic salts are known to affect bubble coalescence via ion size, charge density and polarizability. In this paper, a systematic study of the effect of monovalent anions (F⁻, Cl⁻, Br⁻ and I⁻) and cations (Li⁺, Na⁺ and K⁺) on the lifetime of liquid films between two bubble surfaces is carried out by applying the thin film interferometry method. To mimic realistic conditions of bubble coalescence in a bubble column, drainage and stability of saline water films driven by different interface approach speeds (10–300 μm/s) using a nano-pump was investigated. The results show significant effects of interface approach speed on transient film thickness and radius, film stability and rupture, and lifetime of saline water films. The experiments also indicate that there is a critical approach speed of 35 μm/s for pure deionised water above which the water films instantly coalesce, i.e., no water film can be obtained. High interface approach speed creates corrugation on saline water film surfaces, which rapidly increases the rates of film radial expansion and drainage, and shortens the film lifetime. There is a critical salt concentration above which the saline water film lifetime abruptly increases. This critical concentration is independent of the interface approach speeds of 10–300 μm/s. Our experimental results show a decreasing trend of film lifetime with increasing the size of either the cation or anion (NaF > LiCl > NaCl > NaBr > NaI). The order of the critical concentrations is the opposite of the order of lifetimes. The experimental results highlight the ion-specific effect of salt ions on the water structure and hence the behavior of saline liquid films. These results are relevant to a number of chemical engineering processes taking place in saline water, including mineral separation by flotation using air bubbles in saline water.