Takeshi Toyama

Electrically polarized micro-arc oxidized TiO2 coatings with enhanced surface hydrophilicity

The use of micro-arc oxidation titania (MAO TiO2) coatings to modify titanium surfaces improves the biocompatibility of implant surfaces. To obtain hydrophilic MAO TiO2 coating surfaces electric polarization, which induces surface electric fields in the materials and produces surface charges, was performed in this study. Electric polarization of the MAO TiO2 coatings was confirmed by measuring the thermally stimulated depolarization current. After electric polarization treatment the MAO TiO2 coatings did not exhibit any obvious changes in surface roughness, morphology, or phase components. X-ray photoelectron spectroscopy results indicated that electric polarization resulted in oxidation of the cathodic-faced surfaces and reduction of the anodic-faced surfaces. This result suggests that the existence of a concentration gradient of oxide ions/oxygen vacancies produced the stored space charge in the coatings. Reduction of the deionized water contact angle on the polarized MAO TiO2 surfaces was maintained for longer periods compared with the non-polarized surface. Our study demonstrated that metastable electric fields across the MAO TiO2 coating produced by electric polarization made it durably wettable by reducing the interfacial surface tension between the material and water.

Bone responses to zirconia implants with a thin carbonate-containing hydroxyapatite coating using a molecular precursor method

Thin carbonate-containing hydroxyapatite (CA) films coating partially stabilized zirconia (Y-TZP) were prepared (CA-Y-TZP) to establish a metal-free implant system. CA was coated using a molecular precursor method. The CA film was deposited on the surface of Y-TZP using a precursor solution, which was a mixture of a calcium-ethylenediaminetetraacetic acid (EDTA) complex and phosphate compounds. The deposited CA film was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy measurements. A focus ion beam system technique revealed that the thickness of the CA film was less than 1.0 µm. Biological evaluations of CA-Y-TZP were performed by immersion experiments in simulated body fluid (SBF) and implantation experiments in the tibiae and femoral condyles of rabbits. In the SBF immersion experiment, apatite deposition progressed more on CA-Y-TZP at the early stage of immersion than on Y-TZP without the CA coating. Animal experiments revealed that bone formation on CA-Y-TZP was similar with than on Y-TZP. Histomorphometrical evaluations showed a significantly higher bone-to-implant contact ratio and bone mass on CA-Y-TZP after implantation into the femoral trabecular bone of rabbits. Therefore, CA-Y-TZP appears to be applicable as a metal-free implant.

Surface free energy predominates in cell adhesion to hydroxyapatite through wettability.

The initial adhesion of cells to biomaterials is critical in the regulation of subsequent cell behaviors. The purpose of this study was to investigate a mechanism through which the surface wettability of biomaterials can be improved and determine the effects of biomaterial surface characteristics on cellular behaviors. We investigated the surface characteristics of various types of hydroxyapatite after sintering in different atmospheres and examined the effects of various surface characteristics on cell adhesion to study cell-biomaterial interactions. Sintering atmosphere affects the polarization capacity of hydroxyapatite by changing hydroxide ion content and grain size. Compared with hydroxyapatite sintered in air, hydroxyapatite sintered in saturated water vapor had a higher polarization capacity that increased surface free energy and improved wettability, which in turn accelerated cell adhesion. We determined the optimal conditions of hydroxyapatite polarization for the improvement of surface wettability and acceleration of cell adhesion.

Effects of a multilayered DNA/protamine coating on titanium implants on bone responses.

DNA coating on dental titanium (Ti) implants is attracting attention due to its osteogenic properties. The aim of the present study was to evaluate in vitro and in vivo bioactivities of a multilayered DNA/protamine (D/P) coating on Ti implant by simulated body fluid (SBF) immersion experiments and implantation experiments into extracted sockets of rat molars. Two types of DNA, 300 base pair (bp) and 7000 bp fragments, were used. Protamine was initially immobilized onto Ti implants using a tresyl chloride-activated method and DNA and protamine were then alternatively deposited after the immobilization of protamine by a layer-by-layer technique. A multilayered D/P-coating was confirmed by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy measurements. The deposition of apatite progressed more on the surfaces of multilayered D/P-coated Ti implants than on those of nontreated Ti implants in SBF immersion experiments. Animal implantation experiments showed that multilayered D/P-coated Ti implants provided a significantly higher bone-to-implant (BIC) contact ratio 3 weeks after implantation. No significant difference was observed in the BIC ratio 9 weeks after implantation. The results of the present study demonstrated that a multilayered D/P-coating promoted new bone formation at the early stages of the bone healing process.

Preparation of titanium phosphate white pigments with titanium sulfate and their powder properties

Titanium oxide that has photocatalytic activity is used as white pigment for cosmetics. A certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. In this work, as novel white pigment, titanium phosphates were synthesized with titanium sulfate and phosphoric acid for cosmetics. Their chemical composition, powder properties, photocatalytic activity, color phase, moisture retention, and smoothness were studied. These titanium phosphates had less photocatalytic activity to protect the sebum on the skin. Samples without heating and those heated at 100 °C showed high reflectance in the range of visible light. Sample prepared in Ti/P = 3/2 had higher moisture retention than samples prepared in other Ti/P ratios.

Wettability and surface free energy of polarised ceramic biomaterials.

The surface modification of ceramic biomaterials used for medical devices is expected to improve osteoconductivity through control of the interfaces between the materials and living tissues. Polarisation treatment induced surface charges on hydroxyapatite, β-tricalcium phosphate, carbonate-substituted hydroxyapatite and yttria-stabilized zirconia regardless of the differences in the carrier ions participating in the polarisation. Characterization of the surfaces revealed that the wettability of the polarised ceramic biomaterials was improved through the increase in the surface free energies compared with conventional ceramic surfaces.

Influence of pH, concentration of sodium lactate as an additive and ultrasonic treatment on synthesis of zinc phosphate white pigments.

Zinc oxide that has the photocatalytic activity is used as a white pigment for cosmetics. A certain degree of sebum on the skin is decomposed by the ultraviolet radiation in sunlight. In this work, zinc phosphates were prepared from zinc nitrate and phosphoric acid at pH 5 and 7 with and without the addition of sodium lactate and ultrasonic treatment as a novel white pigment for use in cosmetics. The chemical composition, powder properties, photocatalytic activity, colour phase, moisture retention and smoothness of the zinc phosphates were studied. The obtained materials had a Zn/P ratio of about 1.5, which corresponds to zinc orthophosphate Zn3(PO4)2. Samples prepared with ultrasonic treatment indicated the high ratios of large particles in scanning electron microscopy images and particle‐size distributions. The photocatalytic activity of these zinc phosphate particles was too less to protect the sebum on the skin. The materials obtained and their thermal products at 100°C showed a high reflectance within the range of visible light. The slipping resistance and roughness of the powder were enough low for use in cosmetics.

REMOVAL OF CESIUM FROM SEA SLUDGE THROUGH DECOMPOSITION OF ORGANIC MATTER WITH AQUEOUS HYDROGEN PEROXIDE

The radioactive cesium scattered from the Fukushima Nuclear Power Plant has caused a pollution problem in Japan. To tackle such accidents, many technologies have been developed to remove radioactive cesium from water. However, the technology to decontaminate the sludge is much less advanced than that for water. Thus, we focus on the decomposition of organic matter by H2O2 for decontaminating the sludge. The maximum decontamination of the sea sludge by H2O2 was found to be 2.6 times higher than that by water alone, and the greatest decontamination was obtained using 34.5% H2O2. We believe the extent of decontamination increased for this solution because the solution pH was near the pHpzc, which would suppress the ability of the sludge to absorb Cs ions. We also examined the effect of time on the decontamination of the sea sludge; however, only a small increase in decontamination (1.7 times the initial value) was observed.

PURIFICATION SYSTEM OF OCEAN SLUDGE BY ACTIVATING MICROORGANISMS

Ocean sludge exerts a very big environmental load to local sea area. Here, attention was paid to micro-bubble technology for application to the purification of sludge. The important point in this technique is to activate the bacteria existing in the area by micro-bubbles. We had developed a method for decomposing the sludge by using of microorganisms in an aerobic state by micro-bubble. In this study, our objects are to develop a new powerful purification system for sedimentary sludge using a micro-bubble device and by activating microorganism. As the results of our experiments, we succeeded in reducing the time needed to purify the sludge.

Synthesis of Sulfate-ion-substituted Hydroxyapatite from Amorphous Calcium Phosphate

The composition of Hydroxyapatite (HAp) is expressed by the formula Ca10(PO4)6(OH)2. Many reports have been published on the synthesis of HAp in which Ca ions are substituted by various cations (e.g., Sr, Ba). On the other hand, studies on the synthesis of sulfate-ion-substituted hydroxyapatite (SAp) have rarely been conducted. The present study investigated the conditions for the synthesis of SAp from amorphous calcium phosphate (ACP, Ca3(PO4)2• nH2O) as the starting material, which can readily incorporate various ions into its structure. Sodium sulfate (Na2SO4) was added to ACP, and then, the mixture was hydrothermally processed at 220°C for 3 h. SAp obtained under these conditions had a Ca-deficient-type HAp structure. The SO4/PO4 molar ratio in SAp increased with increasing amounts of added Na2SO4, reaching a maximum value of 0.5, meaning that 1/3 of the PO4 3– ions contained in HAp were substituted by SO4 2– ions.