Kiyoko Sakamoto

Synthesis and evaluation of various layered octacalcium phosphates by wet-chemical processing

Octacalcium phosphate was synthesized by hydrolysis of α-tricalcium phosphate through a wet-chemical processing. Using the same wet-chemical processing in presence of various succinate ions, the preparation of some complexed octacalcium phosphates was attempted. The products were examined by X-ray diffraction method. These complexed octacalcium phosphates intercalated with succinic acid, L-asparatic acid, and methyl succinic acid showed an expanded basal spacing in the octacalcium phosphate unit cell dimensions. The microstructure was observed by scanning and transmission electron microscopy.

Shape-controlled synthesis of hydroxyapatite from α-tricalcium bis(orthophosphate) in organic-aqueous binary systems

Hydrolyses of α-tricalcium bis(orthophosphate) Ca3(PO4)2 (α-TCP) were carried out in a heterogeneous solvent system (hydrophobic organic solvent-water). The hydroxyapatites (HAp) formed were deficient in calcium (Ca/P = 1.56–1.61, a-axis = 0.9440 nm, c-axis = 0.6880 nm) and contained acid phosphate (and sometimes carbonate depending on the organic solvent used). The HAp was in the form of needles with a length (1–4 μm) that depended on the polarity of the hydrophobic organic solvent. The aspect ratio was highest in 1-octanol with a polarity of ET = 48.3. On the other hand, in a hydrophobic organic solvent system without OH groups such as n-octane (ET = 31.1), HAp formed fine particles that are similar to HAp prepared in a system without an organic solvent. Thus, hydrophobicity and OH groups of organic solvents affect the crystal growth of HAp.

Fluoride ion-promoted reaction of β-tricalcium phosphate to fluoridated hydroxyapatite

Abstract Solvothermal reaction of β-tricalcium phosphate (β-TCP) [Ca 3 (PO 4 ) 2 ] with ammonium fluoride in water-1-octanol biphase proceeds to afford fluoridated hydroxyapatite (FHAp) [Ca 10 (PO 4 ) 6 (OH) 2(1− x ) F 2 x ] quantitatively. It was found that FHAps with various fluoride contents were more easily prepared under mild reaction conditions and that higher crystallinity of FHAp was obtained, compared with the reaction of α-TCP with fluoride ions. The solvolysis reaction of β-TCP did not proceed without fluoride ions, whereas the reaction of α-TCP proceeded with or without fluroide ions. This indicates that the former reaction is promoted by fluoride ions.

Formation of nano-sized layer composite by intercalation to aluminium tri-hydrogen bis (orthophosphate) monohydrate

Abstract Aluminium tri-hydrogen bis (orthophosphate) monohydrate [AlH3(PO4)2·H2O] is known as a material with a layered structure. We have synthesized the pure single phase of AlH3(PO4)2·H2O by solvothermal reaction, with high efficiency. It was formed by the reaction of Al(OH)3 with H3O4 at 75 wt% : The optimum molar ratio of H3PO4 to Al(OH)3 is 7.5. The mixture of H3PO4 and Al(OH)3 in 1-propanol was refluxed at 94 °C for 24 hours under stirring. Furthermore, we intercalated phenylphosphonic acid into AlH3(PO4)2 · H2O at room temperature and obtained a material with nano-sized layers (d = 1.52 nm). Measurements of XRD and DTA-TG, and observations of SEM and TEM were made on products.

Formation of Hydroxyapatite from Mechanochemically Treated β-Tricalcium Bis (Orthophosphate)

β-tricalcium bis (orthophosphate) [Ca3(PO4)2] (β-TCP) was mechanochemically treated with mortar grinder. The ground β-TCP was hydrolyzed in an aqueous ammonium solution (pH=11.0) at 90 to give Ca-deficient HAp involving small amount of CO3 2- ions. With an increase in grinding time of β-TCP, it was hydrolyzed easily. Well-crystalline Ca-deficient HAp was obtained after grinding of β-TCP for 7 hours and the successive hydrolysis.

Synthesis and Characterization of Calcium Phosphate-AMP Layered Materials

Calcium phosphate-AMP layered material was synthesized by the hydrolysis of α−TCP in the presence of AMP at pH=6.2. The resulting composite was a mixture of DCPD and calcium phosphate-AMP layered material. The composition and structures of the calcium phosphate-AMP layered material were estimated based on elemental analysis, thermal analysis, and spectroscopic analyses. About 30 wt% of the composite comprises AMP, which is oriented in alternately layered structure of AMP and calcium phosphate layers. Furthermore, the composite showed better cell adhesion than DCPD.

Thermoluminescence of Calcium-Deficient Fluoridated Hydroxyapatite

We recently found that β-tricalcium bis(orthophosphate) (β-TCP) as well as α-TCP was readily hydrolyzed to calcium-deficient fluoridated hydroxyapatite (de-FHAp) [Ca10-z(HPO4)z(PO4)6-z(F·OH)2-z·mH2O] in the presence of NH4F. We examined the thermoluminescence (TL) characteristics of de-FHAp with various fluoride contents prepared from α-TCP and β-TCP. The de-FHAp was compressed and heated at 700◦C and 900◦C for the TL measurement. The de-FHAp treated at 700◦C showed the TL glow peaks at 90◦C and 190◦C. The former peak was higher than the latter. On the other hand, TL glow peaks for the sample of 900◦C appeared at 50◦C, 130◦C, and 165◦C. The difference of these TL glow curves may be due to the structural change of de-FHAp to a mixture of FHAp and β-TCP when the sample was heated at 900◦C. The TL glow peak intensity increased with the fluoride contents in FHAp. The TL intensity of FHAp from α-TCP was higher than that from β-TCP. The intensity of TL glow peak for 90◦C and 190◦C increased linearly with the flux of X-ray irradiation up to about 1.8 C/kg.

Syntheses and Mechanical Properties of Calcium Phosphate--Methacrylate Phosphate Composites

There has been considerable interest in the bioactive bone cements based on calcium phosphates. We report herein the syntheses of surfacemodified composites and their compressive strength. The surface modification of calcium phosphate were achieved by the treatment of calcium phosphate with methacylate ethyl-2-phosphate (MEP) in acetone. Successively, the modified calcium phosphate was mixed with MEP, which were polymerized by heating in the presence of benzoyl peroxide. The compressive strength of the surface-modified composites are as follows; α-TCP∗-MEP composite/21 MPa, β-TCP∗-MEP composite/ 53 MPa, Hap∗-MEP composite/22 MPa. The compressive strength of the corresponding non-modified composites are as follows; α-TCPMEP composite/4 MPa, β-TCP-MEP composite/49 MPa, HAp-MEP composite/11 MPa. By the surface modification of calcium phosphate the compressive strength was substantially improved.

Preparation of Aluminium Phosphate with a Layered Structure by Using Organic Solvent and Its Properties.

We have synthesized the pure single phase of aluminium tri-hydrogen bis (orthophosphate) monohydrate [AlH3(PO4)2·H2O] by using hydrophilic organic solvent, with high efficiency. It is a material with layered structure. The optimum condition to prepare it was as follows; the mixtures of 75wt% H3PO4 and Al(OH)3 (0.1mol) (molar ratio of H3PO4 to Al(OH)3=4.0) was refluxed at 94°C for 6 hours under stirring in 1-propanol (200cm3). Shape of products obtained was needle, and its length increased from 5μm to 80μm with increasing the reaction times. The maximal acid strength and amount of acid of solid surface were pKa=+1.5 and 1.81-2.13 (x10-2mmolg-1), respectively. AlH3(PO4)2·H2O changed to AlPO4 (berlinite, cristobalite-form) and Al(H2PO4)3 (B-form, C-form) by dehydration of monohydrate at 160°C.