Papers by Author: Akiyoshi Osaka

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Authors: A.G. Dias, M.A. Lopes, Kanji Tsuru, Satoshi Hayakawa, José D. Santos, Akiyoshi Osaka
Abstract: This work reports the structure of two glass ceramics prepared in the calcium phosphate system, MK5B and MT13B, using 31P MAS-NMR technique. The results obtained showed that the network of MK5B consisted mainly of Q1 and Q2 groups. Besides these two groups, MT13B material also present Q3 units. The Qn groups detected in both glass ceramics seem to be correlated to the crystalline phases present in their microstructure.
Authors: Sabrina Barheine, Satoshi Hayakawa, Akiyoshi Osaka, Christian Jaeger
Abstract: The incorporation of ions in the lattice of hydroxyapatite alters significantly its structure. Particularly, if anions such as trigonal borate units are accommodated in the lattice severe distortions must occur around the substitution site because of different geometric shape, electric charge and anion size. Solid-state NMR has been used to investigate this problem in detail for a hydroxyapatite sample synthesized by high temperature solid state reaction. The results clearly verify the existence of network distortions. Indeed, only about 1/3 of the total phosphate content forms crystalline hydroxyapatite (also found in XRD) whereas the residual amount is contained in two different phosphate sites with 31P chemical shifts of 5.5 ppm and 2.3 ppm, but broad resonances lines suggesting disorder. Furthermore, a novel proton signal at -0.6 ppm was found which is directly associated with the borate incorporation. No specific correlation of the two structurally different borate units with the two phosphate groups is found.
Authors: Satoshi Hayakawa, Keita Uetsuki, Akinori Kochi, Yuki Shirosaki, Akiyoshi Osaka
Abstract: A recently developed “GRAPE® technology” provides titanium or titanium alloy implants with spontaneous apatite-forming ability in vitro, which requires properly designed gaps and optimum heat treatment in air. In this study, pure titanium pieces were thermally oxidized in air and pre-irradiated by UV-light under different environmental conditions such as in air or in ultra-pure water before aligning pairs of specimens in the GRAPE® set-up, i.e., two pieces of titanium substrates were aligned parallel to each other with optimum gap width (spatial design). Then, they were soaked in Kokubo’s simulated body fluid (SBF, pH7.4, 36.5°C) for 1-2 days to clarify how the UV-light pre-irradiation affects the in vitro apatite nucleation on the substrates under the specific spatial design. UV-light pre-irradiation in water led to the deposition of a large number of apatite particles within 1 day, and showed apatite X-ray diffraction, although UV-light pre-irradiation in air and non-pretreated specimens gave the deposition of a few apatite particles and did not show any apatite X-ray diffraction. These results indicated that the rate of primary heterogeneous nucleation of apatite increased by UV-light pre-irradiation in ultra-pure water. TF-XRD patterns of the surface of the substrates thermally oxidized in air at 500°C showed the peak at 2θ = 27º assignable to the 110 diffraction of rutile phase of titanium dioxide (ICDD-JCPDS data #21-1276). Previous studies reported that the primary heterogeneous nucleation must be induced by Ti-OH groups on titanium oxide layer. Probably, the UV-light pre-irradiation in ultra-pure water can increase the number of Ti-OH groups on the surface, resulting in accelerated primary heterogeneous nucleation of apatite.
Authors: Satoshi Hayakawa, K. Shibata, Kanji Tsuru, Akiyoshi Osaka
Authors: Jin Ming Wu, Min Wang, Akiyoshi Osaka
Abstract: A bioactive composite coating consisting of one layer of titania and one layer of apatite was formed on Ti substrate. The first layer of crystalline titania was deposited on Ti at low temperatures either through oxidation of Ti by hydrogen peroxide solution or through hydrolysis of TiF4 or TiCl4 solution. It was shown that the crystalline titania, either in the form of anatase or rutile, induced formation of the second layer of apatite in a simulated body fluid. However, the trace elements in the titania layer affected greatly apatite formation. The Cl incorporated in the titania layer did not hinder apatite formation while F did. The two-layer composite coating should enhance bonding of Ti implants to bone tissue.
Authors: Lei Ren, Akiyoshi Osaka, B. Yu, Wei Shi, Dong Tao Ge, Song Chen, Qi Qing Zhang
Abstract: Ca2+-containing porous gelatin-siloxane hybrids were prepared using sol-gel process, post-gelation soaking, and freeze-drying. The porosity and pore size of the hybrids could be well controlled by the freezing temperature and the pH value of the soaking solution. The pore characteristics were related to the structure change during the soaking treatment. A bone-like apatite layer was able to form in the Ca2+-containing porous gelatin-siloxane hybrids upon soaking in a stimulated body fluid. The porous gelatin-siloxane hybrids could release gentamicin sulfate which is an antibiotic drug in bone chemotherapy. Thus, those hybrid materials are proposed to find application as novel bioactive and biodegradable scaffolds in bone tissue engineering.
Authors: Xiao Xiang Wang, Akiyoshi Osaka
Authors: Yuki Shirosaki, Kanji Tsuru, Satoshi Hayakawa, Akiyoshi Osaka
Abstract: Porous chitosan-silicate hybrids were prepared by freeze-drying the precursor sol solutions synthesized from chitosan and 3-glycidoxypropyltrimethoxysilane (GPTMS). Degradability of and the release of cytochrome C in to phosphate buffer saline solution (PBS) were examined as a function of the GPTMS content. The hybrids were less degradable with larger GPTMS contents, and the cytochrome C release profile was so controllable as to give either burst release or slow one due to the GPTMS content. Thus, the present porous chitosan-silicate hybrids were considered applicable to drug delivery systems.
Authors: K. Shibata, Kanji Tsuru, Satoshi Hayakawa, Akiyoshi Osaka
Authors: Akiyoshi Osaka, Dimitri Aslanidis, Satoshi Hayakawa, Kanji Tsuru
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