Papers by Author: Akira Monkawa

Abstract: Real time adsorption behaviors of six proteins with different isoelectric points on hydroxyapatite (HAp) nanocrystal surfaces have been investigated by using HAp sensors for quartz crystal microbalance with dissipation technique (QCM-D). The dissipation (D)–frequency (f) plots clearly showed that the different types of protein adsorption behaviors; the D-f plots of acidic proteins lie on one straight line with a constant slope under all initial protein concentrations, while those of neutral and basic proteins lie on two straight lines with different slopes. The acidic proteins formed a monolayer, while the neutral and basic proteins could cause conformational changes with the adsorbed amount of proteins. The QCM-D technique with novel HAp nanocrystal sensor is useful for the liquid phase changes of proteins on the surface.

Abstract: Hydroxyapatite (HAp)-alginate gels were developed as drug delivery carriers of the anti-cancer drug, water-insoluble paclitaxel (Taxol). The spray-drying technique was employed for loading the paclitaxel into spherical HAp microparticles with 1 to 20 μm in diameter. The microparticles loaded with 2.4 or 7.3wt% of paclitaxel were then mixed with sodium alginate, which was followed by Ca2+-mediated gelation. The compressive strength of the HAp-alginate gels and the release of paclitaxel from the gels in a medium were investigated in vitro. The alginate matrix was effective for the achievement of controlled release of anti-cancer drugs.

Abstract: Homogeneous nano-thin layer of hydroxyapatite (HAp) nanocrystals on the gold surface was fabricated by an electrophoretic deposition method (EPD); the HAp nanocrystals were dispersed into ethanol and the applied voltage was varied. The HAp nanocrystals were prepared by a wet method at 4 °C and 80 °C, which were characterized by X-ray diffraction and Fourier-transform infrared spectroscopy. The micro-thin layer of HAp nanocrystals was initially formed, and the ultrasonic treatments can remove the surplus nanocrystals from the surface. The nanostructure of the surface was investigated by atomic force microscopy and contact angle measurement. The thickness of coating layers was approximately 20nm and the root mean square (RMS) roughness was under 6.6 nm, which was clearly depended on the crystal sizes, applied voltages and applied times.

Abstract: Silk fibroin (SF) films containing 5wt% of CaCl2 were prepared by a cast-film method from the degummed SF and then immersed into the simulated body fluid (SBF) to deposit hydroxyapatite (HAp) crystals. The multilayer film of HAp and SF (5-layers), and pure SF film (4-layers) were prepared by a thermo-compression method at 130 °C and 3MPa for 4min. The ratio of β-sheet structure against other structures in both samples showed almost same value of 55.8% and 55.1%. The swelling ratio and in vitro biodegradation were examined by incubating in phosphate-buffered saline (PBS) with and without protease XIV for 1 to 14 days. The changes of sample weight and its tensile strength were investigated. The multilayer film showed slower biodegradation and higher mechanical strength compared with pure SF film.

Abstract: Hydroxyapatite/chondroitin sulfate (HAp/ChS) microparticles with the perfectly spherical shape and the averaged particle sizes of 4.1, 7.8, 19.9 and 29.4 µm were fabricated by a spray dry method under the different atomizing pressures and the concentrations of suspensions. The contents of ChS in the microparticles were varied at 1.49, 3.18, 7.82, 14.2 wt%, and the ChS elution rate in distilled water from the microparticles was increased with the increase of ChS contents. The adsorption isotherms of cytochrome C on the microparticles in 1/10 diluted phosphate buffer saline (PBS) were followed to the Langmuir’s equation regardless of the change of ChS contents, while those of catalase were not followed. The HAp/ChS microparticles can adsorb greater amount of cytochrome C than pure HAp microparticles, but less amount of catalase than pure HAp. The electrostatic interaction between the proteins and ChS was of great importance in the adsorption properties.

Abstract: Hydroxyapatite/collagen (HAp/Col) composite scaffold with unidirectionally elongated pores (scaffold-U) was fabricated by the unidirectional solidification with ice growth and subsequent freeze-dry process. The pore architecture in the composite was evaluated by using scanning electron microscopy (SEM) and micro computed tomography (micro-CT) with a high resolution. The SEM observation showed that the scaffold-U had unidirectional pores elongated along the vertical direction (i.e. ice growth direction), however the horizontal cross-section showed quite different pore morphology: spindle-shaped pores with random direction. The 3-D micro-CT image of the scaffold-U simultaneously showed the microstructure of the unidirectionally elongated pore and the cross-sectional pore, indicating that the interconnected micropores were successfully fabricated along the ice growth direction. The micro-CT is a powerful tool for the visualization of 3-D pore structure.

Abstract: Hydroxyapatite (HAp) also shows the high absorption ability for proteins with low degradations. In this study, to modify the absorption ability and to obtain high surface area, metal ions (Zn, Mg, Fe) were introduced in preparing the HAp nanocrystals, and porous microparticles were subsequent fabricated by a spray drying method. HAp microparticles with Zn, Mg, Fe ions had a single phase of low crystalline HAp. The specific surface area of the HAp, Mg-HAp, Fe-HAp and Zn-HAp were 87, 150, 152, 167 m2/g, respectively. In the adsorption experiment of a lysozyme as a basic proteine, Zn-HAp showed the highest adsorption ability. On the other hand, the HAp microparticles witn metal ions showed higher adsorption ability for BSA as a acitic protein than pure HAp microparticles.

Abstract: Mesoporous HAp aggregates were composed of needle-like crystals that were aligned to the c-axes direction perpendicular to the flat surface of plate-like aggregates. The pore size distributions of the HAp aggregates increased with increasing heat treatment temperature e.g. 3-20 and 26-52 nm, respectively, before and after heat-treated at 600 °C. The adsorption proteins on the mesoporous HAp aggregates were investigated by liquid chromatography using the HAp aggregates as an adsorbent. Elution molarity ratios of acidic proteins on the mesoporous HAp aggregates before and after heat-treatment at 600 °C increased with increasing molecular weight in the order of ferritin > fibrinogen > catalase > albumin, whereas the elution molarity ratios of basic proteins were considerably lower than those of acidic proteins. These results suggested that penetration of the large size acidic proteins into the pore of the as-prepared mesoporous HAp aggregate was slightly inhibited but were the proteins could easily penetrate into the pore of the heat-treated mesoporous HAp aggregates and then were selectively adsorbed on the mesoporous wall consisting of the a-surface of the HAp aggregate. Conversely, the basic proteins could be adsorbed on the wide outer surface of the plate-like HAp aggregates. Therefore, the elution molarity ratios of basic proteins decreased with decreasing the specific surface area by the heat treatment, independent of the mesoporous structure.