Yoshitomo Toda

Preparation and characterization of β-tricalcium phosphate co-doped with monovalent and divalent antibacterial metal ions

Ag(+) and Zn(2+) or Cu(2+) ions were co-doped with beta-tricalcium phosphate (AgZn-TCP and AgCu-TCP), and their substitution models, antimicrobial activities, mechanisms and cytotoxicities were investigated. The lattice constants (a-axis and c-axis) of AgZn-TCP and AgCu-TCP decreased linearly with the amount of Zn(2+) or Cu(2+) ions up to 9.09 mol.%, which indicated that Ag(+) ions were doped at the Ca(4) site and a vacancy in the beta-TCP structure, and Zn(2+) or Cu(2+) ions were doped at the Ca(5) site. Antibacterial activities of AgZn-TCP and AgCu-TCP on Escherichia coli and Staphylococcus aureus were higher than those of Ag(+) ions-doped beta-TCP (Ag-TCP) and pure beta-TCP. These antimicrobial activities suggested that an interaction occurred between bacteria and Ag(+), Zn(2+) and Cu(2+) ions eluted from AgZn-TCP and AgCu-TCP and between bacteria and the free radicals generated by antibacterial agents or in bacterial cells. AgZn-TCP and AgCu-TCP can be used over long periods of time with high antimicrobial activity, because the rate at which Ag(+) ions are released from AgZn-TCP and AgCu-TCP is slower than that at which Ag(+) ions are released from Ag-TCP. However, it is necessary to determine the suitable amounts of Ag(+), Zn(2+) and Cu(2+) ions in AgZn-TCP and AgCu-TCP by considering both their antimicrobial activities and cytotoxicities, because beta-TCP doped with a large amount of these metal ions exhibits cytotoxicity. Furthermore, AgZn-TCP and AgCu-TCP are considered to be promising materials for use in various fields.

Effect of bone-like layer growth from culture medium on adherence of osteoblast-like cells

The electrical polarization of ceramic HAp had an effect on the acceleration of bone restoration. Cell behavior in the bone-like growth layer was investigated. The deposits on the ceramic HAp was grown and formed layers by soaking in alpha-minimum essential medium supplemented with 10% fetal bovine serum (alpha-MEM supplemented with 10% FBS). The shapes of the adhering cells on the grown layer gradually changed from spindle to flat with growth of the layer. On the totally grown layer that was grown on the ceramic HAp by soaking in alpha-MEM supplemented with 10% FBS for 7 days, all the adhering cells were flat and the surface was filled with the grown cells. From these results, it was revealed that the grown layer on the ceramic HAp is one of the activation factors of cell growth. Consequently, cell growth was reinforced by acceleration of the layer growth on the negatively charged surface of the polarized ceramic HAp.

Surface Electric Fields Increase Osteoblast Adhesion through Improved Wettability on Hydroxyapatite Electret

Osteoblasts are susceptible to the surface characteristics of bioceramics and stimulation from outside the cells. The purpose of this study was to evaluate the effects of electrical polarization on surface characteristics and osteoblastic adhesion. The surface characteristics revealed that electrical polarization had no effect on the surface roughness, crystallinity, and constituent elements. According to contact-angle measurements, electrically polarized hydroxyapatite (HA), which provides two kinds of surfaces, negatively charged HA (N-HA) and positively charged HA (P-HA), was even more hydrophilic than that of normal HA (O-HA). Morphological observations and quantitative analyses revealed that the typical adhered cells had a round shape on O-HA but had a spindle or fanlike spreading configuration on N-HA and P-HA 1 h after seeding. After 3 h of cultivation, the rate of the number of spread cells and the size of the focal adhesions on O-HA increased and approached that of N-HA and P-HA. However, the cell areas positively stained for actin, which indicates the degree of cell spreading, were distinctly larger on N-HA and P-HA than that on O-HA. The number of focal adhesions per cell was also less than that on N-HA and P-HA.

Novel tribological properties of anodic oxide coating of aluminum impregnated with iodine compound

Abstract Several iodine compounds are well known as solid-state lubricants in the halogen family, however, satisfactory results of their use in the manufacturing industry have not been reported. Subsequently the anodic oxide coating of aluminum impregnated with iodine compound in the concrete inclusion complex with iodine was prepared successfully by an electrochemical method and tribological properties of obtained anodic oxide coating were investigated [Proceedings of INTERFINISH 2000 15th World Congress and Exhibition Congresshaus Garmish-Parten—Kirchen, (2000)]. Iodine compound was found in micro-pores as iodine (I) of 0.1 mass% and formed iodophor of an amorphous structure. The tribological properties of obtained anodic oxide coating were estimated by friction and wear testing. The yielded coefficient of dynamic friction of a sample with iodine compound was less than 0.1. Obtained anodic oxide coating impregnated with PTFE, namely TUFRAM. The coefficients of dynamic friction of obtained anodic coating ADC12 aluminum die casting or A6061 aluminum alloy have proved to be lower in comparison with thin-film Sn on anodic oxide coating by electroplating. From these results, the impregnation of iodine compounds in the micro-pores of anodic oxide coating has proved to lower the coefficient of dynamic friction. We think this phenomenon originates from the orthorhombic system and lamellar structures of the iodine compound used this time, which are well known as solid lubricants.

Fabrication of Two Dimensional Silicon Carbide Fiber-Reinforced Silicon Carbide Composite by Electrophoretic Deposition and Hot-Pressing

In this study, Tyranno SA fiber cloth was coated with carbon black and SiC powder containing sintering aids by means of electrophoretic deposition method, and SiC/SiC composites with three different fiber volume fractions were fabricated using the Tyranno SA cloth by hot-pressing at 1700oC. The sufficient formation of the SiC matrix between each fiber could be observed. The composite fractured in non-brittle manner, and bending strength decreased with increasing fiber volume fraction. The crack propagation and fracture behavior depended on the fiber volume fraction. These differences in bending strength and fracture behavior would be caused by the difference in the interfacial bonding between fiber cloth and the matrix.

Chemicovector Effect of Nano-Size-Hydroxyapatite Doped YSZ Ceramics on Apatite Formability in SBF

To produce ceramics with high mechanical strength and bioactivity, we developed the little amount of nano-sized hydroxyapatite (HA)-doped zirconia composite ceramics (nanoHA-Z). The bioactivity of the nanoHA-Z was studied by in vitro estimation with simulated body fluid (SBF). Scanning electron microscopy observation showed deposited bone-like apatite layer entire covering the surface of nanoHA-Z ceramics in SBF. The enhanced apatite formability was attributed to higher Ca and PO4 concentrations in the vicinities of the nanoHA-Z surfaces due to the dissolution of the β-tricalcium phosphate decomposed from the added HA. Utilization of Chemicovector effect was proved to be one of the powerful approaches for improvement method of biomaterials.

Synthesis of New Biocompatible Apatite-Type Rare-Earth Silicates

Series of apatite-type rare-earth silicates were synthesi zed by a solid state reaction at 1400 °C as a new biomaterial. The synthesized apatite-type rare-earth silicate s were analyzed by X-ray diffraction (XRD) and infrared spectroscopy (IR), and lattice parameters we e calculated. Single phase of the apatite-type rare-earth silicates was obtained, and the lattic e parameters became smaller with the increase of the rare-earth content or increasing of an atomic numbe r of the substituted ions. The ceramic apatite-type rare-earth silicates were obtained by a sintering at 1400 °C, and its biocompatibility was estimated by in vitro and in vivo tests. The ceramic apatite-type rare-earth silicates had a good cell proliferation, and no inflammation was obser ved in the vicinity of the implanted ceramic. It was suggested that the ceramic apatite -type rare-earth silicates could use as a biocompatible material.

Preparation of Black Pearl Luster Powder and Its Optical Property

新規な光輝材として黒色真珠光沢粉体を調製し，その光学特性を明らかにした。原料には，粒子径の異なる天然白雲母に二酸化チタンを被覆した真珠光沢粉体と，その白雲母を被覆している二酸化チタンを還元するために金属チタン粉末を用いた。また，二酸化チタンの還元度合を変えるために，白雲母を二酸化チタンで被覆した真珠光沢粉体に対する金属チタン粉末の混合割合を3～40 mass％の範囲で実験した。これらの混合粉体を小型混合粉砕機でさらに混合し，真空中850℃で12時間焼成した。焼成後，小型混合粉砕機で粉砕し，粉砕した粉末を水簸分級法で残存した金属チタン粉末を分離し，還元粉末をろ過乾燥し，還元真珠光沢粉体を得た。最も黒くなる真珠光沢粉体は，平均粒子径7 μmの銀色真珠光沢粉体に金属チタン15 mass％混合して還元した還元真珠光沢粉体と，これらをさらに大気中で低温酸化した酸化還元真珠光沢粉体とを混合することによって隠蔽力の高い黒色真珠光沢粉体が得られることを明らかにした。