Key Engineering Materials Vols. 361-363

Abstract: The adsorption properties of metal ions containing hydroxyapatite (Ca10(PO4)6(OH)2, HAp) were elucidated for the development of protein drug carrier. As-prepared metal ion containing HAp nanocrystal showed plate-like morphology with 10-20nm in length and 5-10nm in width. The metal ion containing HAp microparticles had higher specific surface area than the HAp microparticle. The adsorption amount per unit area of HAp showed higher than those of metal ion containing HAp. The adsorption behavior followed the Langmuir curves for each protein, indicating the monolayer adsorption. The loaded amount of proteins could be one of the most important properties for the application of drug delivery carrier.

Abstract: Boron-containing hydroxyapatite (BHAp) particles were synthesized by the wet chemical processing method and subsequent thermal treatment at the temperature ranging from 700-1200°C, and examined the effect of boron introduction on the microstructure of BHAp. The local structure around boron and phosphorus in the BHAp was analyzed by solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The heat-treatment above 700°C induced the thermal decomposition of HAp to β-TCP and then the chemical reaction between HAp and B(OH)3 was induced above 900°C, resulting in the formation of boron-substituted HAp particles accompanied by the formation of β-TCP and its transformation to α-TCP above 1200°C.

Abstract: Nanosized hydroxyapatite (nano-HA) in narrow size distribution was prepared in the microemulsion system. The experimental factors of pH values and temperature were specially investigated in order to receive nano-HA particles with the required morphologies. Several kinds of nano-HA with different shapes, sizes and crystallization were obtained by regulating the above factors in the experiment. After the as-received nano-HA particles were heat-treated at an elevated temperature, they became a kind of globular particles with an average size of 60nm and showed excellent disperse ability in absolute alcohol.

Abstract: On this paper, methods to obtain Mg-free reagents for synthesizing pure phase Sistabilized α-TCP were established. The Mg contents of synthesized reagents were considerably lower than those in commercially available reactants. Pure Si-doped (2.5 at.-% of P by Si substitution) α-TCP was obtained by solid state reaction from synthetic reagents at temperature as low as 1200°C. When commercial reagents were employed for the solid state synthesis, a mixture of α- and β-TCP was obtained even when the solid state reaction was conducted at 1300 °C.

Abstract: Nanocrystalline hydroxyapatite was prepared by a precipitation method with add of ultrasonic irradiation. In this work the effect of H3PO4 addition rate during synthesis and the influence of the magnesium incorporation into apatite were studded. The results revealed that the morphology and cristalinity of synthesized nanopowders are significantly affected by ultrasonic irradiation. Monophase hydroxyapatite was obtained when magnesium was added into HA lattice during the synthesis with ultrasonic irradiation.

Abstract: A systematic study of the stability of potassium/carbonate co-substituted hydroxyapatite has been carried out, with samples synthesized by aqueous precipitation according to the chargebalanced mechanism: Ca10-xKx(PO4)6-x(CO3)x(OH)2 Samples up to x=1.0 were prepared and their stability determined by heating at a range of temperatures in both air and CO2 environments. Results showed that whilst samples up to x=1.0 can be prepared phase-pure, the stability of these materials is strongly dependent on sintering temperature with the full range of compositions only being stable at 600°C in CO2. The c unit cell parameter increases linearly with x, and, for a fixed composition, decreases linearly with temperature indicating loss of carbonate from the A-site. FTIR showed that samples contained carbonate at both A- and B-sites, and that carbonate content increased with x.

Abstract: The low temperature macro and micro porous hydroxyapatite scaffold was synthesized. The synthetic nanostructured HA powder was prepared by the reaction of Ca(OH)2 and H3PO4. The ultrasound apparatus was used for the separation of the particles during the precipitation process. Hydrogen peroxide (H2O2) was used as a foaming agent. The samples were dried for 3 hours at 120°C. HA (hydroxyapatite) granules exhibited interconnected macro and micro porosity with the micro pore size in the order of 0.01 'm. The specific surface area of the precipitate reached the average value 64.8 ± 11.9 [m2.g-1]. The compressive strength of the low temperature porous HA scaffold granule was very similar to deproteinized bovine bone and other calcium phosphate ceramic materials used in bone regeneration and prepared by high temperature processes. The porosity of the scaffolds 50-75% was determined by mercury porosimetry. In-vitro cytotoxicity test proved the granules to be non toxic.

Abstract: Crystalline hydroxyapatite thin coatings have been prepared using a novel opposing RF magnetron sputtering approach at room temperature. X-ray diffraction (XRD) analysis shows that all the principal peaks are attributable to HA, and the as-deposited HA coatings are made up of crystallites in the size range of 50-100nm. Fourier transform infrared spectroscopy (FTIR) studies reveal the existence of phosphate, carbonate and hydroxyl groups, suggesting that HA coatings are highly crystalline. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.

Abstract: Bone is a complicated heterogeneous, viscoelastic, anisotropic material. Its properties depend on the nature of mechanical forces in addition to the location as well as the age, sex and race of the subject. Human humerus bones retrieved from cadavers were selected and separated in to cortical and cancellous parts. They were heat treated at different temperatures 400°C, 600°C and 800°C respectively to study the crystalline nature and composition of cortical and cancellous region of the humerus bone separately. Hydroxyapatite (HAP) was present as the major phase in the bone powders at 600 and 800°C with well resolved peaks along with other mineral phases of calcium phosphate. No amorphous phases were present indicating that the crystal structure of calcium phosphate compounds is present in crystalline form. FTIR studies further confirm the presence of phosphate vibrational modes of the entire bone mineral along with the presence of carbonates and hydroxyl groups.

Abstract: In vitro reactions of bundles of fibers with diameters 20-500 μm and crushed glasses of fractions 500-800 μm were compared with the reactions of plates of the same bioactive glasses. The samples were immersed in simulated body fluid (SBF) for 2-7 days. After immersion the changes on the surfaces of the samples were observed by SEM/EDXA. Layer formation on the glass surface was found to vary with glass composition, sample shape and local condition of single particle/fiber. However, only some fibers or particles formed similar in vitro reaction layers as the plates. The product form did not change the in vitro bioactivity of particles or fibers exposed to the bulk immersion solution. When the glasses were used as fiber bundles or particle beds, the packing degree and the flow of body fluids within the system interfered with the reactivity. Also a clear correlation between in vivo layer formation in bone and in vitro of the glass plates could be found.