Fabrication of anodized titanium with immobilization of hyaluronic acid to improve biological performance

Titanium (Ti) is used widely as a dental implant material in clinical dentistry and as an orthopedic implant material. Anodized titanium enhances the biocompatibility of Ti, which is improved further by hyaluronic acid (HA) immobilization on the anodized Ti surface. Plasma treatment of metal surfaces creates functional groups to introduce bioactive materials. This study evaluated a new bioactive functionalized Ti surface produced by immobilizing hyaluronic acid (HA) onto –NH₂ functionalized anodizing Ti surfaces to improve the biological, physical and chemical properties of Ti. A porous microstructure was formed on Ti by anodizing, followed by the introduction of NH₂ groups by plasma polymerization and immobilization of HA onto the –NH₂ functionalized anodizing Ti surfaces.     

Modification of titanium oxide layer by calcium and phosphorus

The aim of the study was to investigate the possibility of calcium and phosphorus ion implantation into an oxide film applied onto titanium during anodic passivation. The corrosion resistance of modified titanium in Tyrode's physiological solution has been identified. Anodic oxidation was carried out in two solutions. The first contained 20 g dm⁻³ NaH₂PO₂ in 4.3 M H₃PO₄ (K1), whereas the other, 20 g dm⁻³ Ca(H₂PO₂)₂ in 4.3 M H₃PO₄ (K2). Voltage of 100 and 150 V was applied. It has been found out that it is possible to incorporate Ca and P into the emerging passive layer. The application of the voltage of 150 V makes it very porous. It has been also demonstrated that titanium so modified presents higher resistance to corrosion in the investigated environment than titanium not modified in Tyrode's solution.     

Surface energy measurements of coated titanium dioxide pigment

In this study surface energy measurements have been carried out on titanium dioxide pigments coated with different types of organic compounds. The organic coatings investigated were polymethylsiloxane and octyl triethoxy-silane. The level of coating applied was increased from 0.2 up to 1.5 wt%. Contact angles were measured using an advancing sessile drop method. To allow for the fact that measurements were made on pressed discs of particles rather than on a perfectly flat surface, a correction was applied to convert each measured contact angle to the true Young's contact angle. Surface energies were calculated from the corrected contact angles using the Owens and Wendt equation. From the values of surface energy it was possible to determine at what coating level the surface characteristics changed from hydrophilic to hydrophobic and hence when complete coverage had taken place. For both the siloxane and the silane coatings it was found that complete coating coverage occurred at an addition level of around 0.8 wt%. The surface energies of all the coated pigments were found to correlate well with their dispersion behaviour in liquid paraffin.     

Self-organized porous titanium oxide prepared in Na2SO4/NaF electrolytes

The anodic formation of nanoporous TiO₂ on titanium was investigated in Na₂SO₄ electrolytes containing low concentrations of NaF (0.1-1 wt.%). It was found that under optimized electrolyte conditions and extended polarization, a self-organized nanostructure consisting of porous TiO₂ is obtained. The porous structure is arranged in sections of arrays with single pore diameters of typically 100 nm and an average spacing of 150 nm. The pores are open at the top and covered by oxide at the bottom. Compared with earlier work, we show that using a neutral NaF electrolyte significantly thicker porous layers can be obtained than in acidic solutions.     

Characterisation of titanium oxide film grown in 0.9% NaCl at different sweep rates

The nature of the anodic oxide film that forms on titanium on titanium in 0.9% NaCl has been investigated using a wide range of techniques. A linear relationship was found between the critical current density required for passivation of titanium in 0.9% NaCl and the sweep rate. Anodic oxide films formed on titanium in 0.9% NaCl appear to consist of two layers, an inner compact layer, the growth of which continues to follow a high field growth law, and a porous less protective outer porous layer. XPS and XRD indicated that passive films on titanium consist mainly of TiO₂. However, hydroxides and lower oxides are also present, especially in rapidly grown films. XRD data indicated that in 0.9% NaCl the anodic oxide film is formed through the preferential removal atoms in the plane of (0 0 2) in the course of electrochemical reaction. A model based analysis XPS spectra was proposed to explain the growth rate dependence of the degree of protection offered by anodic oxide films on titanium. XPS clearly demonstrated the present of Ti(III) and Ti(II) cations in the passive film. This is strong evidence that cation migration more likely dominates over anion migration in the growth mechanism of anodic oxide film. XPS data also revealed that the concentrations of Ti(III) and Ti(II) species within the oxide films increased as the oxide/metal interface was approached.     

Atmospheric pressure plasma surface modification of titanium for high temperature adhesive bonding

In this investigation surface treatment of titanium is carried out by plasma ion implantation under atmospheric pressure plasma in order to increase the adhesive bond strength. Prior to the plasma treatment, titanium surfaces were mechanically treated by sand blasting. It is observed that the contact angle of de-ionized water decreases with the grit blast treatment time. Optical microscopy and scanning electron microscopic (SEM) analysis of untreated and atmospheric plasma treated titanium are carried out to examine the surface characteristics. A substantial improvement in the surface energy of titanium is observed after the atmospheric pressure plasma treatment. The surface energy increases with increasing exposure time of atmospheric pressure plasma. The optimized time of plasma treatment suggested in this investigation results in maximum adhesive bond strength of the titanium. Unmodified and surface modified titanium sheets by atmospheric pressure plasma were adhesively bonded by high temperature resistant polyimide adhesive. The glass transition temperature of this adhesive is 310 °C and these adhesively bonded joints were cured at high temperature. A substantial improvement in adhesive bond strength was observed after atmospheric pressure plasma treatment.     

二氧化钛的疏水改性及其表征

在水相体系中,以二氧化钛为原料,用十六烷基三甲基溴化铵（CTAB）对其进行湿法表面改性。以疏水度为主要考察指标,通过单因素条件实验及正交实验,研究了体系pH值、改性剂用量、改性温度、改性时间等因素对改性效果的影响。结果表明：当体系pH值8、改性剂用量（占二氧化钛总质量的分数）5％、改性时间2．5h、改性温度65℃时,二氧化钛疏水度由13．87％提高至59．89％。     

Influence of water content on nanotubular anodic titania formed in fluoride/glycerol electrolytes

A study has been carried out of nanotubular anodic films formed on titanium at 20 V in fluoride/glycerol electrolyte, containing up to 50 vol.% water. Anodizing was terminated at a charge of 1 C cm⁻². Addition of water resulted in an increased current and significantly reduced tube length associated with increased oxygen gas evolution. Films formed in the absence of added water were amorphous by electron diffraction, whereas water addition also led to the formation of anatase and rutile. The barrier layer was relatively thin for electrolyte of low water content, due to either a voltage drop in the electrolyte close to the anode or to a change in the film composition affecting the electric field across the layer. Ribbing of the external walls of the nanotubes was more evident in the presence of water. It is suggested that dissolution of a fluoride-rich layer, which separates the nanotubes, accompanies the nanotube growth, with the dissolution allowing transient film formation at the external walls of the nanotubes when the residual layer is sufficiently thin.     

Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell

0-18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 °C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activity is seen. The results suggest that TiO₂ may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO₂ as electrolyte.     

Anodic dissolution of titanium in chloride-containing ethylene glycol solution

Anodic dissolution behavior of titanium in chloride-containing ethylene glycol was examined using a rotating disk electrode. A potential-independent dissolution current flowed depending on the rotation speed, species and concentration of chloride salts. In solutions with lower concentrations of chloride, a potential-independent current was controlled not only by the mass transfer process but also by the charge transfer, and the kinetic-controlling current depends on solution conductivity. In concentrated chloride solutions, the current was controlled only by mass transfer process and decreased with increase in chloride concentration. A smaller current also flowed in a solution with a high concentration of titanium species. These results indicated that the diffusion-controlling species are titanium species, not chloride ions. Electrochemical impedance spectroscopy revealed that a titanium chloride salt layer, which maintains titanium species at a high concentration, accumulates a low charge (0.1 μF cm⁻²) and becomes thicker with increase in applied potential, is formed between the titanium substrate and diffusion layer during the mass transfer-controlling dissolution.     

Tribological mechanism of micro-arc oxidation coatings prepared by different electrolyte systems in artificial seawater

The micro-arc oxidation (MAO) coatings were prepared in four different electrolyte systems, including mixed acid, phosphate, phosphate-aluminate and phosphate-silicate electrolytes. The friction and wear properties of MAO coatings in ambient air, seawater and four groups of saline solutions related to seawater were investigated. The results showed that the addition of silicate to phosphate could increase the density of the coating. The phosphate-aluminate ceramic layer exhibited the lowest wear rate in various environments. Additionally, the friction coefficient and wear rate of MAO coating in seawater were lower than those in ambient air, which was due to the boundary lubrication effect of seawater. Meanwhile, the presence of divalent metal salts in seawater made its lubricity better than other salt solutions.     

Effect of hydrogen on stresses in anodic oxide film on titanium

Stresses in anodic oxide film on titanium thin film/glass electrode in pH 8.4 borate solution were investigated by a bending beam method. The increases in compressive stress observed with cathodic potential sweeps after formation of anodic oxide film were attributed to the volume expansion due to the compositional change of anodic oxide film from TiO₂ to TiO_2−x(OH)_x. The instantaneous responses of changes in stress, Δσ, in the anodic oxide film to potential steps demonstrated the reversible characteristic of the TiO_2−x(OH)_x formation reaction. In contrast, the transient feature of Δσ for the titanium without anodic oxide film represented the irreversible formation of TiH_x at the metal/oxide interphase. The large difference in stress between with and without the oxide film, has suggested that most of stresses generated during the hydrogen absorption/desorption reside in the anodic oxide film. A linear relationship between changes in stress, Δ(Δσ)_des, and electric charge, ΔQ_des, during hydrogen desorption was found from the current and stress transients, manifesting that the stress changes were crucially determined by the amount of hydrogen desorbed from the oxide film. The increasing tendency of −Δ(Δσ)_des with increasing number of potential steps and film formation potential were discussed in connection with the increase in desorption amount of hydrogen in the oxide film with increasing absorption/desorption cycles and oxide film thickness.     

A study on the formation of titania nanopillars during porous anodic alumina through-mask anodization of Ti substrates

The formation of anodic titania during porous anodic alumina (PAA) through-mask anodization has been analysed for varying anodization conditions on mechanically polished bulk Ti surfaces. Titania nanopillars were formed through the porous masks in both oxalic and phosphoric acid electrolytes. For applied potentials above 40 V the titania formed along narrow channels through the alumina pore bottoms resulting in root-like attachments of the titania pillars to the Ti substrate. We further demonstrated that high-field anodization can be used for PAA through-mask anodization. The formation of titania changed with increased current density which resulted in more efficient oxide growth through the alumina pores. When the Al/Ti samples were immersed in the electrolyte without exclusively exposing the Al surface to the electrolyte the titania formed solely on top of the alumina pore bottoms which resulted in that the titania structures were detached from the Ti substrates during selective removal of the PAA templates.     

Bioactive and electrochemical characterization of TiO2 nanotubes on titanium via anodic oxidation

The selection of bioactive and electrochemically stable materials for implants having effective corrosion resistance during long-term use in the body is essential. In this study, the bioactive and electrochemical properties of titanium implant materials with a nanotube surface treatment and various types of post-treatments were examined. Two types of amorphous TiO₂ nanotubes were grown homogeneously on the surface: one with a larger diameter (approximately 85 nm) and one with a smaller diameter (approximately 50 nm). Amorphous TiO₂ nanotubes were partially crystallized to anatase and rutile by heat treatment at 500 °C for 2 h. The corrosion potential (E_corr) of the heat-treated sample (HT) had a novel value of 0.102 V due to the stable TiO₂ crystal phase compared to the −0.106 V observed in the anodic oxidation sample (AN). The corrosion current density (I_corr) ranged from 0.20 to 0.64 μA/cm² according to the post-treatment conditions. However, at 0.6 V, where a passive layer had formed, the corrosion resistance of the HT was approximately ten times that of the AN and untreated (UT) samples. After evaluating the hydroxyapatite (HA)-forming ability by immersion in a simulated body fluid (SBF) solution, the CP process induced the adsorption of Ca and P onto HT. A comparison of the time-dependent amount of Ca and P adsorption showed that Ca adsorption plays a role in determining the rate at which hydroxyapatite (HA) is formed. For the induction of HA formation, a level of Ca adsorption above a critical level is required.     

Effect of the solvent on growth of titania nanotubes prepared by anodization of Ti in HCl

The effect of the solvent on the anodic growth of titania nanotubes in HCl dissolved in water, ethylene glycol and 2-propanol was studied. These nanotubes grow with locally rapid breakdown of the passive TiO₂ film forming a forest of nanotubes-bearing microtowers with the background of passive TiO₂ Film. These bundles of assembled-groups of titania nanotubes look like Pillars corals. The low relative permittivity of the 2-propanol led to lowering of dissociation of HCl and hence lowering the activity of H⁺ and Cl⁻ ions which in turn led to suppress of dissolution of titania and increasing the growth rate of the titania nanotubes. The X-ray diffraction pattern showed that the titania nanotubes after annealing change to the crystalline anatase phase. The anodic films showed characteristic coloration with intensity and color that changes (qualitatively) with time of anodization.     

等离子体表面改性技术

简介了等离子体表面改性技术的发展历史,并按等离子改性橡胶、塑料、纤维和织物、酯和胺类表面进行了分类,介绍其最近几年国内外有关等离子体表面改性技术的发展状况.最后展望了等离子体表面改性技术的发展趋势.     

Nano-ATH的表面改性及其在ABS中的应用

选用钛酸酯偶联剂对纳米氢氧化铝(nano-ATH)进行表面改性,以改善其在丙烯腈-丁二烯-苯乙烯共聚物(ABS)中的分散性。利用透射电镜(TEM)表征了nano-ATH的改性效果,研究了改性条件对nano-ATH/ABS复合材料性能的影响。结果表明:在偶联剂用量2.5%,改性时间25min,改性温度80℃的条件下,nano-ATH/ABS复合材料的综合性能较好,改性后nano-ATH的分散性得到改善。     

The effect of electrolyte anions incorporated into anodic oxide films on the experimental transport numbers of ions

The growth of barrier anodic film is considered theoretically with regard to the migration of three ionic carriers: oxygen and metal ions and electrolyte anions. It is shown that the consideration of anion transport leads to the conclusion that the film grows at three interfaces: the metal/oxide and oxide/electrolyte interfaces and the interface between an oxide layer containing electrolyte anions (contaminated layer) and the oxide layer free of them (“pure” layer). The error in the measured transport numbers of metal and oxygen, which is caused by ignoring a contribution of electrolyte anions to the total charge transport, is maximum in the absence of anion motion.     

Formation of porous anodic titanium oxide films in hot phosphate/glycerol electrolyte

The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 μm thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm⁻³ K₂HPO₄ + 0.2 mol dm⁻³ K₃PO₄/glycerol electrolyte containing only 0.04% water at 433 K. The growth efficiency is reduced by increasing the formation voltage to 20 V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20 V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m⁻². The pore diameter is not significantly dependent upon the formation voltage, being ∼10 nm.     

低温等离子体在高分子材料表面改性中的应用

概述了低温等离子体对高分子材料表面改性的主要方法及其低温等离子体技术在提高高分子材料表面亲疏水性、粘结性、导电性和生物相容性等性能方面的应用,特别是对低温等离子体在生物医用高分子材料领域的应用进行了分析和展望。