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Dive into the research topics where Akira Monkawa is active.

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Featured researches published by Akira Monkawa.


Journal of Biomaterials Science-polymer Edition | 2007

Three-dimensional porous hydroxyapatite/collagen composite with rubber-like elasticity

Shunji Yunoki; Toshiyuki Ikoma; Akira Monkawa; Eriko Marukawa; Shinichi Sotome; Kenichi Shinomiya; Junzo Tanaka

A three-dimensional porous hydroxyapatite/collagen (HAp/Col) composite with a random pore structure was fabricated using freeze-drying processes; the self-organized HAp/Col nanocomposite with a weight ratio of 80.5:19.5, freeze-dried, was kneaded in 100 mM sodium phosphate buffer, frozen at −20°C and freeze-dried. The cross-linkage of Col molecules was introduced dehydrothermally at 140°C in vacuo. The porous composite had a porosity of 94.7% with pore sizes between 200 and 500 μm. The compressive stress for the wet porous composite in phosphate buffer saline (PBS) was gradually decreased during 20 days incubation with a small amount of weight loss. The cyclic and time-course compression tests showed good repeatability of stress and well-recovery of its height, and caused no collapse of the porous composite. The implantation of the porous composite in rat bone holes showed the biodegradable property and new bone formation occurred in the pores without inflammatory response. The porous composite fabricated has good flexibility and rubber-like elasticity, and is a promising bone regenerative material.


Key Engineering Materials | 2007

Protein Adsorption on Hydroxyapatite Nano-Crystals with Quartz Crystal Microbalance Technique

Tomohiko Yoshioka; Toshiyuki Ikoma; Akira Monkawa; Toru Tonegawa; Dinko Chakarov; Bengt Kasemo; Nobutaka Hanagata; Junzo Tanaka

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.


Key Engineering Materials | 2006

Electrophoretic Deposition of Hydroxyapatite Nanocrystal

Akira Monkawa; Toshiyuki Ikoma; Shunji Yunoki; Kazushi Ohta; M. Tanaka

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.


Key Engineering Materials | 2006

Biodegradation of Multilayer Silk Fibroin and Hydroxyapatite Composite Material

Rikako Kino; Toshiyuki Ikoma; Shunji Yunoki; Akira Monkawa; Atsushi Matsuda; Go Kagata; Tetsuo Asakura; Masanobu Munekata; M. Tanaka

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.


Key Engineering Materials | 2007

Preparation of Hydroxyapatite-Alginate Gels as a Carrier for Controlled Release of Paclitaxel

Tomonori Yoshioka; Toshiyuki Ikoma; Akira Monkawa; Shunji Yunoki; Tetsuya Abe; Masataka Sakane; Junzo Tanaka

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.


Key Engineering Materials | 2006

Hydroxyapatite/Chondroitin Sulfate Microparticles with Different Particle Size and its Adsorption Ability of Proteins

Hajime Watanabe; Toshiyuki Ikoma; Guoping Chen; Akira Monkawa; M. Tanaka

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.


Key Engineering Materials | 2006

Protein Adsorption Ability of Porous Hydroxyapatite Microparticle with Metal Ions

Toru Tonegawa; Toshiyuki Ikoma; Akira Monkawa; Guoping Chen; M. Tanaka

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.


Key Engineering Materials | 2006

Evaluation of Pore Architecture in Hydroxyapatite/Collagen Scaffold Using Micro Computed Tomography

Shunji Yunoki; Toshiyuki Ikoma; Akira Monkawa; Kazushi Ohta; Masanori Kikuchi; M. Tanaka

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.


Key Engineering Materials | 2006

Mesoporous Structure and Protein Adsorption Property of c-Axis Oriented Apatite Aggregates

Kazushi Ohta; Masanori Kikuchi; Toshiyuki Ikoma; Shunji Yunoki; Akira Monkawa; M. Tanaka

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.


Materials Letters | 2006

Control of pore structure and mechanical property in hydroxyapatite/collagen composite using unidirectional ice growth

Shunji Yunoki; Toshiyuki Ikoma; Akira Monkawa; Kazushi Ohta; Masanori Kikuchi; Shinichi Sotome; Kenichi Shinomiya; Junzo Tanaka

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Junzo Tanaka

Tokyo Institute of Technology

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Shunji Yunoki

Industrial Technology Research Institute

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Kazushi Ohta

National Institute for Materials Science

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M. Tanaka

Tokyo Institute of Technology

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Kenichi Shinomiya

Tokyo Medical and Dental University

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Masanori Kikuchi

Tokyo University of Science

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Shinichi Sotome

Tokyo Medical and Dental University

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Nobutaka Hanagata

National Institute for Materials Science

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Eriko Marukawa

Tokyo Medical and Dental University

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