Zirconia ceramics were coated with poly(L-lactic acid)-vaterite composite for introducing osteoconductivity. Aluminum silicate (imogolite) nanotubes were successfully applied to the composite coatings via a dipping process and subsequent heat treatment for the enhancement of cell attachment, using the hydrophilicity of imogolite. The heat treatment improved the adhesive strength between the imogolite and the composite coatings. Osteoblast-like cell cultures on the samples showed that the imogolite coating enhanced the cell attachment.

View full abstract

Silica/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) composites were prepared for achievement of new medical devices having bioactivity, biodegaradability and excellent mechanical-elongation property for the use in bone regeneration. The composites were prepared using three different types of silicon alcoxides, Tetraethylorthosilicate (TEOS), Diethoxydimethylsilane (DEODMS) and 3-aminopropyltriethoxysilane (APTES), as a silica source. The composites prepared with TEOS possessed both abilities of soluble silica releasing and hydroxyapatite forming in simulated body fluid, while the composites prepared with the other sources didn’t show them. The chemical structure and tensile properties of the composites prepared with TEOS were evaluated. Fourier transform infrared reflection and ¹³C cross polarization magic angle spinning nuclear magnetic resonance spectroscopic analyses demonstrated that the crystallinity of polymer phase in the composites was reduced by adding the silica. The composites containing <25 wt % of silica exhibited a large failure strain (~700%).

View full abstract

Bone marrow-derived mesenchymal stromal cells (BMSCs) are pluripotent progenitor cells that can regenerate different skeletal tissues in response to environmental signals. Scaffolds play a critical role in tissue engineering, and their microstructure is essential for inductive bone formation. In the present study, we have used highly porous, structurally stable three-dimensional apatite-fiber scaffolds (AFSs) and investigated their ability to support cell proliferation and differentiation. BMSCs in/on AFSs were proliferated in a three-dimensional manner when both micro- and macro-pores were present. The characteristic structure of the AFS enhanced calcification, production of extracellular matrix (ECM), and osteogenic differentiation, especially endochondral ossification. Furthermore, BMSCs cultured in/on AFSs did not undergo adipogenesis and selectively underwent osteogenic differentiation. These results suggest that AFSs provide a suitable environment for bone regeneration and have potential applications for tissue engineering.

View full abstract

The electronic structure of antiferromagnetic CaFe₂O₄ is calculated by using a generalized gradient approximation considering on-site Coulomb interaction between d-electrons (GGA+U). We found that the antiferromagnetic phase is the most stable among non-magnetic, ferromagnetic, and antiferromagnetic phases. With GGA+U, the band gap energy of CaFe₂O₄ is calculated to be ca. 1.9 eV. The lower conduction band consists of the Fe 3d states split into t_2g and e_g states by the octahedral FeO₆ environment. The Ca 3d states distribute upper conduction bands. On the other hand, the valence band is mainly composed of the interaction between Fe 3d and O 2p states. The valence band maximum is approximately located at the Z-point and the conduction band minimum at the X-point. This means that antiferromagnetic CaFe₂O₄ is an indirect energy gap material. The absolute value of the magnetic moment at Fe sites is calculated to be 4.16 µ_B, which is very close to experimental values.

View full abstract

Fluorine-substituted hydroxyapatite (F-HAp) and stoichiometric hydroxyapatite (HAp) were prepared for investigation of their dielectric properties. Two kinds of dielectric relaxation were observed in HAp of each kind. One was attributed to the orientation of OH⁻. The relaxation strength was decreased strongly by the F-substitution. The activation energies (0.63 eV for HAp and 0.62 eV for F-HAp) of OH⁻ reorientation were independent of the F-substitution. The other relaxation was larger, where the activation energies were affected strongly by F-substitution. The F-substitution increased the activation energies from 0.73 to 0.88 eV. This increase of activation energies was related strongly to the increase of chemical stability by F-substitution in HAp.

View full abstract

Preparation of injectable hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) paste utilizing sodium alginate (Na-Alg) and influence of additives on the paste properties were investigated. The HAp/Col at the HAp and collagen mass ratio of 80:20 synthesized by a simultaneous titration method was pelletized to 100–212 µm. The HAp/Col powder and that treated with 100 mM CaCl₂ (Ca-HAp/Col) were used as starting powders. A paste was prepared by mixing of the starting powder and Na-Alg solution at one of several powder/liquid ratios. The paste was directly injected into 100 mM CaCl₂ solution to confirm setting capability, and examined a viscosity, hardening behavior, compressive strength and decay property. In addition, the paste supplemented with an organic acid or a calcium compound as an additive was also prepared to examine influences of the additive on paste properties. The organic acid was chosen from citric, succinic, malic, lactic and glycolic acids, and the calcium compound was chosen from Ca(OH)₂, Ca(CO)₃, CaSO₄·0.5H₂O and calcium citrate.
The prepared paste was set by direct injection to 100 mM CaCl₂ solution. The suitable mixing conditions of the paste were a P/L ratio of 0.6 at the 90:10 mass ratio of Ca-HAp/Col and solution of low viscous Na-Alg. All additives increased the paste viscosity; however, the mechanisms were different between organic acids and calcium compounds. Organic acids rapidly decreased pH to form Alg gel by deposition of Alg. Contrarily, calcium compounds supplied Ca²⁺ ions to form egg-box structure for gelation of Alg, and the reaction depended on solubility of compound. Additives also increased decaying time but could not realize anti-decay in the present conditions. The results suggested that the HAp/Col injectable paste can be utilized in rapid prototyping materials and might be good candidate for injectable artificial bone with further improvement in anti-decay property.

View full abstract

Porous and non-porous titania microspheres with the anatase or rutile phase were successively prepared by the sol–gel process followed by heat treatment at various temperatures. The pore size of the prepared microspheres was effectively controlled by incorporating silica nanoparticles of different diameters. The apatite-forming ability of the microspheres was investigated in a simulated body fluid, with ion concentrations nearly equal to those of human blood plasma. Results indicated that the titania microspheres with either anatase or rutile structure induced the formation of calcium phosphate compounds (CaPs) on the microsphere surface. The deposition of CaPs was more pronounced on the TiO₂ microspheres calcined at 600°C (anatase structure) and 800°C (rutile structure), compared to that calcined at 500°C (anatase structure). Additionally, anatase microspheres with smooth surface and low specific surface area favored the formation of CaPs, compared to porous microspheres. This indicates that nanoscale pores do not essentially favor apatite formation.

View full abstract

Oral malodor is produced by microbial putrefaction of food debris, resulting in the formation of volatile sulfur compounds (VSCs), such as hydrogen sulfide (H₂S) and methyl mercaptan, produced in the mouth. VSCs also have a bad influence on the periodontium and cause discoloration of dental alloy. Thus, an adsorbent that highly adsorbs VSCs would be useful for a healthy mouth and may prevent tooth decay. We investigated the possibility of adsorbing H₂S using heat-treated Magnesium aluminum hydrotalcite. We found that H₂S is adsorbed onto heat-treated hydrotalcite materials in an aqueous solution using gas chromatography with a flame photometric detector (FPD/GC), and the sulfide was found between the layers of the hydrotalcite structure by conducting a powder X-ray diffraction (XRD) analysis and using infrared spectroscopy (FT-IR). The amounts of adsorbed sulfide were higher for hydrotalcite heat-treated at 500 and 600°C for 30 min. The hydrotalcite material is expected to be an adsorbent material and useful for maintaining good oral hygiene.

View full abstract

Siloxane-containing vaterite (SiV) particles with red-blood-cell-like morphologies were prepared by a CO₂ gas carbonation process for application as osteogenic devices in bone tissue engineering. The particles release soluble silica species and calcium ions, which are expected to genetically stimulate osteoblasts to enhance bone reconstruction. The released particles possessed the mean diameter of 2 µmΦ with the thickness of approximately 0.7 µm. The Brenauer–Emmett–Teller surface area was estimated to be 76 m²·g⁻¹. In addition, the shape of the nitrogen adsorption–desorption hysteresis of the particles indicated the presence of slit- or wedge-shaped mesoporous structures. The particles were primarily composed of vaterite with aminopropyl-functionalised siloxanes in the silicon mass percentage of approximately 2 wt %. Soluble silica species and a trace amount of calcium ion were released into the physiological pH buffer solution (pH 7.4) during the initial 1 h of soaking. To estimate its potential for loading functional molecules, polylactide (PLA) was used as the model molecule and the SiV particles were prepared in their presence. Fourier transform infrared spectrometry of the sample revealed that PLA formed a carboxylate salt with the calcium ions and was loaded into the mesoporous structures. Upon contact with the buffer solution, the calcium-salt PLA and siloxane were released simultaneously within the initial 1 h of soaking.

View full abstract

Protein adsorption on hydroxyapatite particles with different morphologies was investigated. The nano-sized hydroxyapatite (nano-HAp) was prepared using calcium nitrate tetrahydrate [Ca(NO₃)₄·4H₂O] and diammonium hydrogen phosphate [(NH₄)₂HPO₄] by using a hydrothermal method with varying synthesis temperature and pH conditions. The adsorption properties of proteins onto nano-HAp were studied using three types of proteins: bovine serum albumin (BSA, an acidic protein), myoglobin (MGB, a neutral protein), and lysozyme (LSZ, a basic protein). The adsorption amount of BSA and LSZ per unit specific surface area of nano-HAp increased as the crystallinity improved. In contrast, the improvement in the crystallinity of HAp decreased adsorption affinity to MGB. This adsorption behavior on nano-HAp would be considered by the specific binding of the C- or P-site on HAp towards acidic or basic proteins, respectively.

View full abstract

Poly(methyl methacrylate) (PMMA) microspheres several tens micrometers in diameter, containing highly dispersed sub-micron sized magnetite (Fe₃O₄) particles, were successfully prepared via an emulsion polymerization process. Both oleic acid and sodium olate acted as suitable agents for high dispersion of the Fe₃O₄ particles in the starting monomer solution (MMA). Spherical PMMA particles encapsulating 65–72 mass % (30–38 vol %) of the Fe₃O₄ were obtained. The magnetic properties of the Fe₃O₄ loaded PMMA microspheres depended on the amount of Fe₃O₄ present in the resultant microspheres. The saturation magnetization and coercive force of the microspheres were 49–63 emu·g⁻¹ and 162–170 Oe, respectively. The rate of an increase in temperature by heat generated from an agar phantom dispersed with a microsphere sample was 1 K·min⁻¹ under an alternating magnetic field (100 kH, 300 Oe). This material is expected to be utilized as a thermal seed for hyperthermic treatment of deep-seated cancers in our bodies using a gap-type alternating current field apparatus in combination with a prospective drug delivery system.

View full abstract

Control of calcification behaviors in osteoconductive ceramics is important for development of novel materials. Calcification behaviors of osteoconductive materials in bony defects can be assessed using a simulated body fluid (SBF). Previous studies of hydroxyapatite (HAp) ceramics have not found a clear relationship between calcification behaviors and morphology, in particular the crystal face, of HAp. In this study we have investigated calcification behaviors of rod-shaped HAp crystals with controlled crystal face in a SBF. The aspect ratios of the rod-shaped HAp was taken to be the area ratio of (the a face)/(the c face) in HAp crystals. HAp with aspect ratios ranging between approximately 10 and 17 was synthesized under hydrothermal conditions. Scale-like precipitates, which should be nonstoichiometric HAp referred to as bone-like apatite, were formed on the HAp crystals soaked in the SBF. The formation rate of bone-like apatite was estimated by measuring decreases in calcium and phosphate ion concentrations of the SBF. The formation rate increased with increasing aspect ratios of the HAp crystals. The results show that bone-like apatite was preferentially formed on the a face of the HAp crystals and that the calcification behaviors of HAp crystals in a SBF can be controlled using the aspect ratio of the HAp crystal, that is, by controlling the crystal face of HAp.

View full abstract

Depressions were generated on a titanium oxide coating of 100 nm thickness by irradiation with a femtosecond laser with a pulse width of 100 fs when the laser output was below 10 mW. When the number of pulses was five or less, irregularities were found to be generated on the coating surface in the area corresponding to the periphery of the pulses, where the laser intensity is low, while titanium oxide was removed from the area corresponding to the center of the pulses. The formation of microstructures is expected on the surface of titanium oxide coatings by setting the output of a femtosecond laser in the periphery of the pulses to below a certain value.

View full abstract

Hydroxyapatite (HAp) coating on commercially available polyimide (PI) films in simulated body fluid (SBF) was examined. Aqueous sodium hydroxide treatment of PI films under proper conditions proceeded surface-selective hydrolysis of PI molecules, which resulted in displaying carboxylic acid groups on the film surfaces. These surface-hydrolyzed PI films had ability to induce deposition of minerals having similar characteristics to that of HAp thereon when incubated in 1.5SBF, a solution having 1.5 times higher inorganic ion concentrations than those of SBF. No deposition was observed for the case of unmodified PI films under the same condition. Additional pretreatments with aqueous calcium chloride for the surface-hydrolyzed PI films realized complete surface coverage on the films by thin mineral layers in 1.5SBF. The present process for PI films is simple and low-cost, and can be widely applicable to other substrates of polymers that can generate carboxylic acid groups by alkaline hydrolysis.

View full abstract

Surface morphology of materials brings various new properties to the surface, and thus, the control of the surface morphology is very important. In this paper, surface morphology control of sol–gel derived films using several processes has been reviewed. Hot water treatment (bottom up process), combination of UV-irradiation and chemical etching (top down process), and micropattern formation using a hydrophobic-hydrophilic patterned surface were reported.

View full abstract

Microstructure often has a significant impact on the physical properties of electroceramics, and such a view is being widespread. In this article, two of our recent microstructure investigations in electroceramics are reviewed. In the first example, atomic-scale structure of grain boundaries in zinc oxide, which plays important role in generation of the electrical function, was analyzed. It was suggested that a role of praseodymium doping is to facilitate the formation of acceptorlike defects such as zinc vacancy. In the second case, dynamics of nanodomains in piezoelectric single crystals was investigated. In-situ transmission electron microscopy observations revealed that reorientation of nanodomains is the dominant behavior of polarization reversal. I believe that such microscopic viewpoints help us better understand the origin of intriguing physical properties in electroceramics.

View full abstract

Mesoporous materials prepared through the self-assembly of surfactants have attracted wide attention because of their many potential applications. The mesostructural, compositional, and morphological controls of mesoporous materials have been extensively studied thus far. In particular, the macroscopic alignments of one-dimensional (1D) mesochannels and their controls are quite important for the creation of advanced functional materials. In most cases, the direction of mesochannels in mesoporous films lies parallel to the substrate. Vertical orientation of the mesochannels can realize high diffusion and accessibility of guest species from the outside. Here, I review the recent progress on this emerging research field. Various methods have been proposed for the preparation of vertically oriented mesoporous thin films using high magnetic field, shear flow, modification of the substrate, and other methods. I also briefly introduce their applications and a perspective for the future.

View full abstract

In this study, photofunctional ceramics such as phosphors and photocatalysts were synthesized by various solution methods. Titanium oxide (TiO₂) photocatalysts were synthesized via hydrothermal reactions of water-soluble titanium complexes. Single-phase anatase, rutile, brookite, and bronze were prepared using different pH levels and ligands. Thin films fabricated from bronze-phase TiO₂ showed photoinduced hydrophilicity, and the hydrophilic state was maintained for 5 days in darkness. Y₂O₃:Eu and YBO₃:Tb phosphors with spherical, hexagonal-plate, and cubical shapes were prepared by precipitation from homogeneous solutions; nanoparticles of these oxides were also prepared. The morphology of the prepared Ag₃PO₄ photocatalyst particles was controlled to be rhombic dodecahedral, dodecapodal, or tetrapodal by precipitation from homogeneous solutions. Oxide up-conversion phosphors were investigated, and CeO₂ doped with Yb, Er, Ho, or Tm by parallel synthesis using the polymerizable complex method was found to be a superior polychromatic up-conversion phosphor.

View full abstract

Urban waste incineration slags have been applied as active fillers of geopolymer. They are classified into two groups. One is Fe-rich and the other is Fe-poor in chemical compositions. When plotted in a ternary diagram in terms of CaO–Al₂O₃–SiO₂, they aligned along with so-called the first hydraulic line and two groups were also noted. One is Ca-rich designated as BFS-group plotted near 45% CaO line close to blast furnace slag compositions. The other is Ca-poor designated as MID-group plotted near 30% CaO line apart from the blast furnace slag compositions. Na-silicate solution, Na₂O·2SiO₂·aq enriched with caustic soda was used as geopolymer liquor. When flooded, some foaming and swelling phenomena were encountered more or less presumably due to the degassing of hydrogen from contaminated Al-metal in the slags. When cured at 80°C and 100%RH, flexural strength tests for pastes revealed two groups of strength, very low and very high, ranging 3–16 MPa for 24 h curing, for instance. The strength was not depending on the iron contents but depending on the degrees of foaming and swelling, i.e., bulk densities of the hardened bodies. Sufficient work time for mixing and casting was able to take for all the slags even to the BFS-group. Matrix binder compositions of hardened pastes analyzed by SEM-EDX were discussed in terms of Al₂O₃/(Na₂O + K₂O), (CaO + MgO)/SiO₂ and SiO₂/Na₂O as well as CaO–Al₂O₃–SiO₂.

View full abstract

The BaTiO₃–Bi(Mg_1/2Ti_1/2)O₃–BiFeO₃ [(1 − x − y)BT-xBMT-yBF] ceramics were prepared by a conventional solid–state synthesis, and their crystal structure and piezoelectric properties were investigated in details. Synchrotron X-ray diffraction (XRD) pattern revealed that a single perovskite phase was obtained for samples at x = 0.050–0.150, y = 0.465–0.735. Splitting of the (111) peak was observed when (x, y) = (0.050, 0.685) and (0.050, 0.735) indicating that crystal structure of samples changed from pseudocubic to rhombohedral phase with increasing BF content. As the BF content increased, the Curie temperature increased. The highest apparent piezoelectric constant d₃₃* values estimated from strain (S) over the applied electric-field (E) value (d₃₃* = S/E) was observed at 300 pm/V for the 0.325BT-0.100BMT-0.575BF ceramics at 25°C and 1 Hz.

View full abstract

Investigations of the lattice dynamics of defects, such as oxygen vacancies, are important to understand the properties of PbTiO₃ and related materials. Herein polarized Raman spectra of epitaxial PbTiO₃ thin films with reduced and re-oxidized treatment were investigated. The oxygen-reduced spectrum displayed an additional mode related to oxygen vacancies, whereas the re-oxidized spectrum was the same as the initial one. The oxygen vacancy content increases as the intensity of additional mode increases, while the intensity of the B₁ mode related to oxygen ions decreases. First-principles calculations of the phonon mode related to oxygen vacancies support the assignment of the additional mode.

View full abstract

Clays for Karatsu ware were prepared from ground three sandstones by a stamp-milling and elutriation processes. The chemical and mineralogical properties were studied and compared with those of Amakusa pottery stones for Arita porcelain. Karatsu clays were composed of α-quartz, feldspar and kaolin minerals without sericite, and the mineral composition of normative α-quartz, feldspar and kaolin were 38–48, 26–37, 17–31 mass %, respectively. Coarse particles in Karatsu clays were angular and rough in shape, and had a very broad particle size distribution. Average particle sizes of coarse particles were 24–29 µm, and maximum particle size were 160–260 µm, respectively. Average particle size of coarse particles was four to five larger than that of Amakusa pottery clay.

View full abstract