Chihiro Mochizuki

The effect of composition of calcium phosphate composite scaffolds on the formation of tooth tissue from human dental pulp stem cells.

Different approaches towards making 3-dimensional (3-D) bioengineered tooth for future replacement therapy have been developed including scaffold-based tooth regeneration. However, selection of optimal scaffold for future clinical application remains a challenge. In the present study, we tested biocompatibility of four different types of 3-D scaffolds for tooth-tissue regeneration, including a pure poly(lactide-co-glycolide) (PLGA) (70/30, mol/mol) scaffold and three types of calcium phosphate contained composites scaffolds that were 50 wt% of PLGA combined with 50 wt% of hydroxyapatite (HA), tricalcium phosphate (TCP) or calcium carbonate hydroxyapatite (CDHA) respectively. These scaffolds were fabricated by the particle leaching in combination with phase separation technology. Surface modification of these scaffolds was further performed by an ammonia plasma treatment and anchorage of collagen technology. Effect of composition of the composite scaffolds on proliferation of human dental pulp stem cells (DPSCs) was accessed using in vitro MTT assay and in vivo BrdU labeling. Differentiation capability of the DPSCs in the scaffolds was analyzed by measurement of the levels of calcified tissue formation and ALP activity. Our results showed that while the calcium phosphate contained compound is able to support regeneration of tooth tissue effectively, the PLGA/TCP scaffold is more appropriate for the proliferation and differentiation of DPSCs. Furthermore, seeding of dissociated 4-dpn rat tooth bud cells on the PLGA/TCP scaffold generated dentin- and pulp-like tissues. Our results demonstrate that the PLGA/TCP scaffold is superior to the other three scaffolds for tooth-tissue regeneration, especially for dentin formation.

Crystallinity control of apatite through Ca-EDTA complexes and porous composites with PLGA

Apatite compounds with different levels of crystallinity were prepared using Ca-EDTA complexes. Ca-deficient hydroxyapatite (CDHA) with low crystallinity was synthesized by ultrasonic stirring of a mixture of Ca-EDTA complex, phosphoric acid, and ammonium hydroxide in hydrogen peroxide aqueous solution. Mixtures of carbonate hydroxyapatite (HA) and CDHA with higher crystallinity were also prepared from a solution involving the same complex. The porous composites with lower or higher crystallinity apatite with a copolymer of poly(L-lactide-co-glycilide)(70/30) (PLGA(70/30)) were fabricated by a solution-casting/particles leaching method. The apatites and porous composites were characterized, and it was found that the degradation of composites of apatite with a low level of crystallinity was fastest in phosphate-bufferd saline (PBS) solution compared with other apatite composites with higher levels of crystallinity; however, the rate was smaller than that of PLGA alone. Plasma treatment influenced the degradation of composites in PBS and apatite precipitation in simulated body fluid (SBF). Hydroxyapatite deposition on the PLGA composite with the low crystallinity occurred six times faster than that on PLGA alone after immersion in SBF. The incorporation of apatite into the PLGA matrix did not cause any adverse effects on cell attachment in an assay employing human gingival fibroblasts. This study suggested that the current apatite and PLGA porous composite will be a promising scaffold material for tissue engineering.

Application of carbonated apatite coating on a Ti substrate by aqueous spray method

The fabrication and characterization of a carbonate-containing apatite film deposited on a Ti plate via an aqueous spray method is described. The mist of the spray solution emitted from a perpendicularly oriented airbrush was made to strike a warmed Ti substrate. The thicknesses of the sprayed film and those heat-treated at 400 °C-700 °C under Ar gas flow were in the range 1.21-1.40 μm. The results of elemental analyses and Fourier transform infrared spectroscopy of the powders that were mechanically collected from the surface of the sprayed film suggest that the film was Ca(10)(PO4)6(CO3) · 2CO2 · 3H2O. The presence of the carbonate ion and the lattice CO2 molecule was confirmed via the aforementioned analyses; the finding was also consistent with the X-ray diffraction patterns of the films and the chemical identity of the sprayed and heat-treated films that were measured using X-ray photoelectron spectroscopy. The sprayed film comprises a characteristic network structure, which contains round particles within the networks, as was observed by field-emission scanning electron microscopy. A scratch test indicated that the shear stress of the sprayed film (21 MPa) significantly improved to 40 and >133 MPa after heat-treatment at 600 °C and 700 °C, respectively, under Ar gas flow for 10 min.

SYNCHRONOUS ELECTROCHROMISM OF LITHIUM ION BATTERY WITH CHEMICALLY FABRICATED TRANSPARENT THIN FILMS

Electrochromism synchronous to the charge/discharge of a novel Li ion battery having Li3Fe2(PO4)3 and Li4Ti5O12 thin-film electrodes fabricated by a chemical process, the molecular precursor method, was discovered. A cathode of transparent Li3Fe2(PO4)3 thin film with a thickness of 80 nm was fabricated by heat treating a precursor ethanol solution including a Li(I) complex of nitrilotriacetic acid, an Fe(III) complex of ethylenediaminetetraacetic acid, and (dibutylammonium)2H2P2O7 ⋅ 0.5H2O at 550°C for 10 min in air. An anode of transparent Li4Ti5O12 thin film with a thickness of 90 nm was fabricated by heat treating a precursor ethanol solution including a Li(I) complex of nitrilotriacetic acid, a Ti(IV) complex of the identical organic ligand, and hydrogen peroxide at 550°C for 30 min in air. The precursor films for both electrodes were fabricated with a spin-coating method. The thermal reactions of the novel precursors were examined in detail by means of thermogravimetry and differential thermal analysis in order to examine the components and heat-treatment temperature. The crystal structure and surface morphology of the thin-film electrodes fabricated on glass substrates pre-coated with a fluorine-doped tin oxide film were examined with X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The rechargeable function of the assembled sandwich-type battery using an electrolytic solution containing LiPF6 was measured by the repeated charge and discharge test at a constant current of 10 μA; a maximum voltage of 3.6 V was recorded. The color changes of the transparent thin-film battery between colorless before charging and a blue-gray color after charging occurred synchronously and repeatedly with the charge/discharge cycles. The intercalation of Li+ ions into the Li4Ti5O12 thin-film anode may be related to the drastic color change and the unprecedented visualization of the electrochemical reaction of a novel Li ion battery.

Characterization and Bone Response of Carbonate-Containing Apatite-Coated Titanium Implants Using an Aqueous Spray Coating

We performed thin carbonate-containing apatite (CA) coating on titanium (Ti) by an aqueous spray coating (ASC) method that consisted of a Ca-CO3-PO4 complex. Two different CA coatings were produced by two different spray amounts and were heat-treated after spraying. We evaluated three-dimensional structures, adhesiveness to Ti, and durability of the CA film. In addition, we performed immersion experiments in simulated body fluid (SBF), and bone responses were evaluated after implantation into a femoral bone defect in rats. The bonding ability of ASC-coated implant into the bone was examined by push-in tests. Unique network structures with small particles were identified on CA coatings. Although heat treatment produced no significant difference in surface morphology, scratch tests revealed that heat treatment improved the adhesion of CA coatings to Ti. Crystal formation progressed on CA-coated specimens, and the sample placement direction influenced crystal formation and growth in SBF immersion. Animal implantation experiments revealed significantly greater bone-to-implant contact ratio and bone mass in both cortical and bone marrow, respectively, four weeks after implantation. Push-in tests suggested that the bonding of the CA coating to Ti is clinically acceptable. Therefore, we conclude that CA coating to Ti by the ASC method would be possible for clinical applications, including dentistry.

Cathodoluminescence spectra of Ga–In–O polycrystalline films fabricated by molecular precursor method

Cathodoluminescence (CL) spectra were measured from polycrystalline Ga–In–O (GIO) films prepared by the molecular precursor method (MPM). Bandgap-energy (Eg) and conductivity were successfully controlled by changing in the mixing ratio of the Ga and In precursor solutions. Although none of the films exhibited a near-band-edge emission, their CL emissions exhibited energy shifts by reflecting changes in Eg and ligand field in the GIO alloys. The results indicate a practical use of MPM-grown GIO films for deep ultraviolet optoelectronic devices.

HIGH TEMPERATURE OXIDATION BEHAVIOR OF C/C COMPOSITE COATED WITH BORATE GLASS

Oxidation tests at temperature from 600 to 1100° in air were carried out for uncoated and B2O3 glass coated C/C composites. The rate determining process of oxidation of uncoated C/C composite was changed from the surface chemical reaction to gas diffusion through boundary layer as the oxidation temperature increases. And, degraded morphologies for each rate determining process were different. Oxidation resistance of B2O3 coated C/C composite was improved comparing to uncoated material. The effect of B2O3 film, however, was insufficient in severe environment because of high volatility and imcomplete coating on vertical cross sectional surfaces.