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471 results on '"Ohya, Yuichi"'

163. Biodegradable Injectable Polymer Systems Exhibiting Temperature-Responsive Irreversible Sol-to-Gel Transition by Covalent Bond Formation

Author

Yoshida, Yasuyuki, Kawahara, Keisuke, Inamoto, Kenta, Mitsumune, Shintaro, Ichikawa, Shinya, Kuzuya, Akinori, and Ohya, Yuichi

Abstract

Biodegradable injectable polymer (IP) systems exhibiting temperature-responsive sol-to-gel transitions between room temperature and body temperature have the potential for use in biomedical applications. However, gelation of such IP systems is a reversible process through physical cross-linking, and the hydrogels thus formed are likely to revert to the sol state under highly wet conditions after injection. In this study, a biodegradable IP system exhibiting temperature-responsive irreversible sol-to-gel transition by covalent bond formation was developed by simple mixing of polymers. A triblock copolymer of poly(caprolactone-co-glycolic acid) and poly(ethylene glycol) (tri-PCG) and tri-PCG with attached succinimide ester groups at both termini (tri-PCG-SA-OSu) were prepared and mixed together with a water-soluble polyamine (typically poly-l-lysine). The obtained IP formulation was in the sol state after mixing, but exhibited a rapid sol-to-gel transition within 30 s upon increasing the temperature to 37 °C. Once formed, the hydrogel did not revert to the sol state, even after cooling to 4 °C, because of the formation of covalent bonds upon transition. The obtained hydrogel soaked in phosphate buffered saline (PBS) exhibited a significantly longer duration time of the gel state. This IP system exhibiting a rapid and irreversible sol-to-gel transition is convenient for medical professionals and possesses great potential for use in biomedical devices for clinical applications such as drug delivery systems and antiadhesive materials.

Published
2017
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164. Biodegradable injectable polymer systems exhibiting a longer and controllable duration time of the gel stateElectronic supplementary information (ESI) available. See DOI: 10.1039/c7bm00357a

Author

YoshidaResearch Fellow of the Japan Society for the Promotion of Science., Yasuyuki, Takai, Hiroki, Kawahara, Keisuke, Mitsumune, Shintaro, Takata, Kazuyuki, Kuzuya, Akinori, and Ohya, Yuichi

Abstract

Here, we report biodegradable temperature-triggered covalent gelation systems exhibiting a longer and controllable duration time of the gel state by a “mixing strategy” utilizing a thiol–ene reaction. We synthesized a tri-block copolymer of poly(caprolactone-co-glycolic acid) and PEG (tri-PCG) as a temperature-responsive injectable polymer (IP) and attached acryloyl groups on both termini (tri-PCG-Acryl). A tri-PCG micelle solution containing hydrophobic hexa-functional polythiol (Solution-A) and a tri-PCG-Acryl micelle solution (Solution-B) were mixed together. After mixing, the solution was still in the sol state at r.t., but exhibited an irreversible sol-to-gel transition in response to temperature. The duration time of the gel state while soaking in PBS could be altered from 1 day to 93 days by changing the mixing ratio of Solution-A/B. The physical strengths of the hydrogels were also controllable by changing the mixing ratio. The IP system showed good biocompatibility and a long duration time of the gel state after subcutaneous implantation.

Published
2017
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169. The effects of molecular structure on sol-to-gel transition of biodegradable poly(depsipeptide-co-lactide)-g-PEG copolymers.

Author

Takahashi, Akihiro, Umezaki, Masaya, Yoshida, Yasuyuki, Kuzuya, Akinori, and Ohya, Yuichi

Subjects
MOLECULAR structure, SOL-gel processes, DEPSIPEPTIDES, COPOLYMERS, HYDROPHILIC compounds, HYDROPHOBIC interactions
Abstract

We report on the effects of number and length of PEG chains in poly(depsipeptide-co-DL-lactide)-g-poly(ethylene glycol) (P(DG-DL-LA)-G-PEG) copolymers on their sol-to-gel transition behavior. The graft-type copolymer is suitable for the systematic study of the effects of molecular structure and hydrophilic/hydrophobic balance on its sol-to-gel transition. We prepared various P(DG-DI-LA)-G-PEG copolymers through coupling reactions between the pendant carboxylic acid groups of P(GD-DL-LA) and the end hydroxyl group of MeO-PEG having various molecular weights. Temperature-responsive sol-to-gel transition of the obtained copolymer solution in phosphate-buffered solution (pH 7.4, ionic strength = 0.14) was investigated by the test tube inverting method and rheological measurements. P(GD-NI.-LA)-G-PEG copolymer prepared from higher molecular weight PEG showed higher sol-to-gel transition temperatures compared with the copolymers prepared from lower molecu-lar weight PEG, although these copolymers have similar weight content of PEG (23-24 wt.%). Similar trends were observed for groups of copolymers whose PEG contents were 27 or 30 wt.%. These results are informative for providing strategies on rational design of thermo-gelling polymers. [ABSTRACT FROM AUTHOR]

Published
2014
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174. Design of Lysosomotropic Macromolecular Prodrug of Doxorubicin Using N-Acetyl-α-1,4-Polygalactosamine as a Targeting Carrier to Hepatoma Tissue

Author

Ouchi, Tatsuro, primary, Tada, Masahiro, additional, Matsumoto, Mitsuo, additional, Ohya, Yuichi, additional, Hasegawa, Kaname, additional, Arai, Yuichi, additional, Kadowaki, Kiyoshi, additional, Akao, Santaro, additional, Matsumoto, Tatsuji, additional, Suzuki, Shigeo, additional, and Suzuki, Masuko, additional

Published
1998
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