Seishi Goto

Hydrothermal preparation of fibrous apatite and apatite sheet

Abstract Hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 :HA) with highly designed microstructures is required for bone filling materials and tissue engineering of cultured bones. This study deals with the shape control of HA particles and preparation of HA sheet from fibrous HA. Fibrous particles of HA with the aspect ratio of about 60 were prepared hydrothermally at 150 °C from the mixed solution of calcium acetate and phosphoric acid. The aspect ratio of the fibrous particles depended on the concentration and the value of Ca/P ratio of the mixed solution. The HA sheet must be a biostable material according to the soaking test with simulated body fluid.

In situ observation of defects in hydroxyapatite up to 1200°C by ultraviolet Raman spectroscopy

Abstract Raman spectra of hydroxyapatite have been successfully obtained at temperatures up to 1200°C for the first time by using a new system of ultraviolet (UV) Raman spectroscopy. With increasing temperature, the intensity of a band ascribed to the stretching vibration of the OH ion continuously decreased. The total intensity of bands in the wavenumber range of 3300–3800 cm−1 did not change significantly up to about 800°C, whereas they decreased at temperatures higher than about 800°C. This result is interpreted as producing oxy-hydroxyapatite due to dehydration of hydroxyapatite over 800°C. The withdrawal of water is accompanied by the creation of defects. This consideration is strongly supported by results of thermodynamic calculations and the line width of the Raman band.

Advantage of anti-Stokes Raman scattering for high-temperature measurements

We present the results of experiments that assess the viability of anti-Stokes scattering to investigate in situ materials at high temperatures. Both anti-Stokes and Stokes Raman measurements have been performed at various high temperatures using hafnia as a test material. As compared with Stokes Raman spectra, anti-Stokes spectra were observed with lower thermal emission backgrounds in accordance with Planck’s equation. The intensity ratio of anti-Stokes to Stokes scattering approaches 1 as the temperature increases at high temperatures satisfying the Boltzmann distribution law. These results clearly demonstrate the advantage and feasibility of anti-Stokes Raman scattering for the elimination of the thermal emission in comparison with Stokes scattering.

Hydrothermal Preparation of Granular Hydroxyapatite with Controlled Surface

Microstructure designed hydroxyapatite granules from about 50 μm to 1 mm in size were prepared by hydrothermal vapor exposure method at temperatures from 105 oC to 250 oC under the saturated vapor pressure of pure water. As starting materials, powder of α-tricalcium phosphate, gelatin and a vegetable oil were used. The size of granules, the shape of particles in the granules, and the microporosity of about 0.1 μm in size of the granules were controlled. The granular hydroxyapatite prepared at 200 oC under the saturated vapor pressure of pure water for 20 h was composed of rod-shaped crystals of about 40 μm in length with mean aspect ratio of 50. Rod-shaped hydroxyapatite crystals were locked together to make micropores of about 0.1 μm in size. It was non-stoichiometric hydroxyapatite with calcium deficient composition. This granular hydroxyapatite should have the advantage of adsorptive activity, because it has large specific crystal surface and micropores. Introduction Hydroxyapatite (Ca10(PO)4(OH)2; HA) is known as the major component of human bones. Sintered HA with random crystal surface has already been used as a bone-repairing material which can directly bond to natural bones in bony defect. It has been known to be biocompatible and osteoconductive [1]. If materials of HA could have the tailored specific crystal surface, the HA materials should have the advantage of adsorptive activity. The authors reported various kinds of HA materials prepared by the unique hydrothermal methods [2-11]. In the present study, HA granules with tailored crystal surface were prepared by the hydrothermal vapor exposure method [7,8,10]. The granules must be suitable as scaffold for cultured bone, for bone graft material and for drug delivery system (DDS). Experimental Commercial powders of α-tricalcium phosphate (α-Ca3(PO4)2: α-TCP, Taihei Chemical Industrial Co., Ltd., Japan) were used as the starting material. After the addition of 10 mass% gelatin (Wako Chemical Co., Japan) aqueous solution, the obtained slurry was dispersed in the vegetable oil at 70 oC, and then stirred at the rate of 0-600 r.p.m. In order to control granules size. The samples were filtered off to recover, washed with ethanol, and dried at 105 oC in air. After heating at 1200 oC for 1 h in air, the samples were set in a 105 cm autoclave with 30 cm of pure water, and then they were exposed to vapor of the pure water at the temperatures from 30 oC to 250 oC under saturated vapor pressure for 20 h (Fig. 1). Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 19-22 doi:10.4028/www.scientific.net/KEM.254-256.19

In Vitro Osteogenic Activity of Rat Bone Marrow Derived Mesenchymal Stem Cells Cultured on Transparent Hydroxyapatite Ceramics

Direct observation of cultured cells on various materials has benef it for assessment of fundamental cellular functions including cell attachment, spreading, prol iferation and differentiation on the materials. For this purpose, we made transparent hydroxyapatite (tHA) ceramics, where cultured rat bone marrow-derived mesenchymal stem cells (rMSCs) could be visible by phase contrast microscopy immediately after plating. The seeded rMSCs adhered and proliferated on the tHA ceramics. Furtheremore, the cells cultured on the tHA ceram ics were able to differentiate into osteoblasts under osteogenic conditions and showed comparable osteogenic act ivity to the cells cultured on tissue culture polystyrene dishes. The results suggested tha cultured cells could be monitored in a time dependent manner using the tHA ceramics.

In Vitro Osteogenic Activity of Rat Mesenchymal Cells Cultured on Transparent β-Tricalcium Phosphate Ceramics

We have cultured mesenchymal cells (MSC) on various types of ceramic disks and used these tissue-engineered ceramics for hard tissue regeneration. In this approach, observation of cultured cell morphology is important even if culture substrata are calcium phosphate ceramics, which usually show bioactive nature. However, due to the opaque nature of the ceramics, cells observation is very difficult. Here, we demonstrate light microscopic observation of rat MSC cultured on transparent β-tricalcium phosphate ceramics (β-TCP). The culture was performed in osteogenic medium. Thus, the cell differentiated into bone-forming osteoblasts, which fabricated a mineralized matrix on the ceramic disks. Microscopic observation revealed that the cascade of osteogenic differentiation after attachment/proliferation of MSC on the ceramic disks was similar to that on a culture grade polystyrene dish. These results confirmed the excellent property of β-TCP for MSC culture leading to hard tissue regeneration.

Solubility of silica-alumina gels in different pH solutions : discussion on the hydration of slags and fly ashes in cement

Abstract The solubility of silica-alumina gels with different compositions were measured in different pH solutions. The solubilities of a silica-alumina gel is remarkably affected by its composition and the pH of the solution. There is a gel with a composition of Si/Al atomic ratio of about 7/3. When the Al/(Si+Al) ratio of silica-alumina gel is less than 0.7, the composition of the liquid phase is more rich in Al 2 O 3 than that of the gel, that is, the surface of gel becomes rich in SiO 2 . Conversely, when the Al/(Si+Al) ratio of gel is more than 0.7, the composition of the liquid phase is more rich in SiO 2 than that of the gel, and the surface of gel becomes rich in Al 2 O 3 . In the hydration of silica-alumina glasses such as slag and fly ash, the reason why the hydration proceeds or not, is whether the surface of reacting glass becomes rich in Al 2 O 3 or not.

Hydrothermal Preparation of Porous Hydroxyapatite with Tailored Crystal Surface

Porous sheets of hydroxyapatite (Ca10(PO)4(OH)2; HA) with about 50 µm to 1 mm in thickness and porous HA granules of about 50 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA sheets with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 30 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Porous Hydroxyapatite with Tailored Crystal Surface Prepared by Hydrothermal Method

Porous plates of hydroxyapatite (Ca10(PO4)6(OH)2; HA) with about 0.5 to 5 mm in thickness and porous HA granules of about 40 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA plates with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 20 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 to 0.5 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Evaluation of the Hydraulic Reactivity of Calcium Aluminate Glass Containing Silicate Ion with Discrete Variational Xα Method

ABSTRACT This study investigated changes in the chemical properties of calcium aluminate glass with the impurity of silicate ions through computable calculation with discrete variation Xα (DV-Xα). The previous study showed that the hydraulic reactivity of calcium aluminate glass decreased with the increase on the added amount of silicate ion to the component of calcium aluminate glass. From the calculation results of DV-Xα, it was known that the bulk bond strength of calcium aluminate glass increased with the substitution of Si for Al in the cluster crystal structure. The bond strength would be closely related with the hydraulic reactivity. Therefore, the increase of bonding strength lowered the hydraulic activity of calcium aluminate glass. These results clarified the decrease of hydraulic reactivity of calcium aluminate glass containing silicate ions.