Electrochemical Properties of Cs and La Co-doped CaWO₄ Oxide Ion Conductor

To clarify the contribution of defect structure of CaWO₄-based system on the oxide ion conduction properties, we doped both cesium and lanthanum ions into CaWO₄ as Ca₀.₉CsxLa₀.₁−xWO₄.₀₅−x. Scheelite-type structured solid solution can be obtained for the Cs-rich region (x ≥ 0.05) with oxygen deficiency, while second phase appears for La-rich region (x ≤ 0.025) assuming excess oxide ions. In the present system, a bend in Arrhenius plot of conductivity is observed around 850 °C as the typical CaWO₄-based system even co-doping with La ions. In terms of the compositional dependence, ionic conduction develops from x = 0.05 with the amount of cation vacancy below 800 °C, while the conductivity enhancement starts at the La-rich region above 900 °C. This indicates that not only oxide ion vacancy but also interstitial attribute to the oxide ion conduction at high-temperature, which is also suggested by the activation energy

Impartation of hydroxyapatite formation ability to ultra-high molecular weight polyethylene by deposition of apatite nuclei

Special Section: Selected Extended Papers from the International Conference of the 19th Asian BioCeramic SymposiumThe authors aimed to impart hydroxyapatite formation ability to ultra-high molecular weight polyethylene (UHMWPE) by deposition of apatite nuclei (ApN) by the following two methods. The first method was electrophoretic deposition (EPD). A porous UHMWPE was placed between electrodes in the ApN-dispersed ethanol and constant voltage was applied. By this treatment, the ApN were migrated from anode-side surface to the cathode one through the pores by an electric field in the pores of the UHMWPE and deposited inside the pores. The second method was direct precipitation (DP) of the ApN. A porous UHMWPE was soaked in a simulated body fluid (1.0SBF) with higher pH than the physiological one and subsequently, its temperature was raised. By this treatment, the ApN were precipitated in the pores of the UHMWPE directly in the reaction solution. For both methods, the ApN-deposited UHMWPE showed HAp formation ability not only on the top surface but also inside the pores near the surface of the porous UHMWPE in 1.0SBF although the adhesion strength of thus-formed HAp layer was higher in the case of the EPD in comparison with the DP, oxygen plasma treatment before the DP enabled to achieve a similar level of the HAp layer adhesion to the EPD

Development of Apatite Nuclei Precipitated Carbon Nanotube-Polyether Ether Ketone Composite with Biological and Electrical Properties

We aimed to impart apatite-forming ability to carbon nanotube (CNT)-polyether ether ketone (PEEK) composite (CNT-PEEK). Since CNT possesses electrical conductivity, CNT-PEEK can be expected to useful not only for implant materials but also biosensing devices. First of all, in this study, CNT-PEEK was treated with sulfuric acid to form fine pores on its surface. Then, the hydrophilicity of the substrate was improved by oxygen plasma treatment. After that, the substrate was promptly immersed in simulated body fluid (SBF) which was adjusted at pH 8.40, 25.0 °C (alkaline SBF) and held in an incubator set at 70.0 °C for 1 day to deposit fine particles of amorphous calcium phosphate, which we refer to as ‘apatite nuclei’. When thus-treated CNT-PEEK was immersed in SBF, its surface was spontaneously covered with hydroxyapatite within 1 day by apatite nuclei deposited in the fine pores and high apatite-forming ability was successfully demonstrated. The CNT-PEEK also showed conductivity even after the above treatment and showed smaller impedance than that of the untreated CNT-PEEK substrate

Evaluation of calcium phosphate coating on biodegradable Mg-Al-Zn-Ca alloy formed under ordinary conditions on temperature and pressure

Octacalcium phosphate (OCP) coating was formed on the surface of Mg–Al–Zn–Ca alloy (AZX612) by anodically oxidized and subsequently immersed in a supersaturated aqueous solution containing phosphate and calcium ion under ordinary temperature and pressure. The formed OCP layer consisted of both the inner layer of the fine crystallites and the outer layer of the large crystallites, and the inner layer remained on the alloy even after the ultrasonication process. In simulated body fluid, AZX612 treated with both anodic oxidization and subsequent OCP coating process showed higher corrosion resistance than those treated with only anodic oxidization

Immobilization and collection of enzymes by hydroxyapatite/maghemite composite particles with magnetism

Feature: The 58th Symposium on Basic Science of CeramicsApatite nuclei (ApN) were precipitated by raising the pH of simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. The maghemite (γ-Fe2O3) particles were attached to the ApN, and the particles were subsequently soaked in SBF adjusted at pH = 7.60, 36.5 °C for one day. By this treatment, the ApN induced hydroxyapatite (HA) formation and the γ-Fe2O3 particles were encapsulated with HA particles with approximately 1–2 µm in diameter. The specific surface area of thus-obtained HA/Fe2O3 particles was almost 27 times as large as that of the commercially obtained HA particles. Urease or superoxide dismutase (SOD) was immobilized on the surface of the HA/Fe2O3 particles in ultrapure water, and the particles were collected by using a neodymium magnet. It was indicated that more than 90 % of urease or SOD was collected by using the HA/Fe2O3 particles. By using the urease immobilized on the HA/Fe2O3 particles, furthermore, urea dispersed in buffered solution almost completely decomposed. As the immobilization efficiency of urease increased, the urea decomposition was promoted

Bioactivity Treatment to Polylactic Acid Fabric Cloth and Foam by Precipitation of Apatite Nuclei

An aqueous solution with doubled ion concentration of simulated body fluid (2.0SBF) was prepared. In order to impart hydroxyapatite formation ability to polylactic acid (PLA) matrixes, the PLA fabric cloth and foam were immersed in 2.0SBF and the pH value was increased. By this treatment, apatite nuclei were precipitated on the PLA matrixes. By immersing in physiological SBF, hydroxyapatite layer was formed on the surface of the PLA matrixes and hydroxyapatite formation ability was successfully performed

Impartation of apatite-forming ability to chitosan nanofibres by using apatite nuclei

Special Section: Selected Extended Papers from the International Conference of the 19th Asian BioCeramic SymposiumChitosan nanofibre–apatite nuclei composites obtained by mixing apatite nuclei which possess high apatite-forming ability with chitosan nanofibre have been expected to be novel bone restorative materials with suitable properties such as light weight, low coefficient of thermal expansion, high mechanical strength, biocompatibility and bioactivity. In this study, the authors prepared three types of apatite nuclei by changing the reaction time aimed to optimise their crystallinity and fabricated their composites with chitosan nanofibre. In order to evaluate the bioactivity in vitro, the authors tested apatite-forming ability in simulated body fluid. As a result, the materials showed enough apatite-forming ability in a short time by mixing chitosan nanofibre and apatite nuclei with extremely low crystallinity and their high reactivity in simulated body fluid

Dependence property of isoelectric points and pH environment on enzyme immobilization on maghemite/hydroxyapatite composite particles

We aimed to establish enzyme immobilization technology using the maghemite/hydroxyapatite (Fe₂O₃/HA) composite particles as enzyme immobilization carriers and to clarify the enzyme adsorption characteristics of the composite particles. Seven kinds of enzymes with various isoelectric points (pI) were immobilized on the Fe2O3/HA composite particles in buffered solution adjusted at pH = 7.40 or pH = 10.0, 36.5 °C. Effects of the enzyme pI and the solution pH on the immobilization were investigated. In both of the two kinds of buffered solutions, there was an increase or decrease distribution with a maximum local value for |pH-pI|, which indicated the charge state of the enzymes. The interaction between HA on the composite particles and adsorbed enzymes was expected to be the largest when |pH-pI| = 1–2. It was suggested that α-chymotrypsin, whose adsorbed amount was the most among the seven kinds of the enzymes, in addition, formed a monolayer on the surface of the composite particles in the buffered solution at pH = 7.40, 36.5 °C

Development of bioactive zirconium–tin alloy by combination of micropores formation and apatite nuclei deposition

In previous studies, Zr gained apatite-forming ability by various methods; however, it took more than 7 days in simulated body fluid (SBF) to gain apatite-forming ability. In this study, the authors developed the method to achieve apatite-forming ability in Zr alloy within 1 day in SBF by a combination with apatite nuclei that promote apatite formation in SBF. First, Zr–Sn alloy was soaked in concentrated sulphuric acid, and pores in micro-level were formed on the surface of Zr–Sn alloy. To attain apatite forming ability in Zr–Sn alloy, second, apatite nuclei were formed in the micropores. To evaluate apatite-forming ability, thus-obtained Zr–Sn alloy with apatite nuclei was soaked in SBF; hydroxyapatite formation was observed on the whole surface of the Zr–Sn alloy plates. From this result, it was clarified that higher apatite-forming ability was attained on the apatite nuclei-treated Zr–Sn alloy with micropores in comparison with that without micropores. When adhesive strength of formed hydroxyapatite film with respect to Zr–Sn alloy plates was measured, high-adhesive strength of the formed apatite film was attained by forming micropores and subsequently precipitating apatite nuclei in the fabrication process because of an interlocking effect caused by hydroxyapatite formed in the micropores

Improvement of hydroxyapatite formation ability of titanium-based alloys by combination of acid etching and apatite nuclei precipitation

The authors aimed to improve hydroxyapatite formation ability of Ti6Al4V, Ti-15Mo-5Zr-3Al alloy, Ti-12Ta-9Nb-6Zr-3V-O alloy (Gummetal®) and commercially pure Ti (cpTi) mesh by a combination of acid etching and apatite nuclei precipitation. Surfaces of specimens were etched with H₂SO₄ for pores formation on the specimens. Thus-etched specimens were soaked in an alkalinised simulated body fluid (SBF), which was adjusted at higher pH than that of conventional SBF and this solution was subsequently heated. By this treatment, apatite nuclei were precipitated in the pores of the specimens. By a soak in the conventional SBF to check hydroxyapatite formation ability, hydroxyapatite was covered the entire surfaces of the specimens within 1 day and high hydroxyapatite formation ability was successfully shown. The adhesion strength of the hydroxyapatite film formed in the above SBF test showed larger value as increasing the surface roughness of the specimens by adjusting the above acid etching condition depending on the kinds of Ti-based alloys. This is because the adhesion of the hydroxyapatite film occurred by the mechanical interlocking effect. In addition, this method showed shape selectivity of the materials because similar hydroxyapatite formation ability could be introduced to the cpTi mesh