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PROJECT


Grant-in-Aid for Youg Scientists (B) (Hiroharu Ajiro)

Grant Name: Grant-in-Aid for Young Scientists (B)
Research Area:Polymer Chemistry
Title of Project:Novel drug release control system by surface cationic hydrogel with poly(N-vinylamide) gel
Project Leader:Hiroharu Ajiro
Term of Project:FY 2012-2013

N-Vinylacetamide (NVA) and N-vinylformamide (NVF) are vinyl monomers, and contain non-conjugated vinyl group which is directly connected to a nitrogen atom. A series of polymerization and materials applications using N-vinylamides have been reported. The unique structure provides a partly cationic poly(vinylamine) (PVAm) after polymerization and the subsequent hydrolysis. It is noteworthy that non-ionic poly(N-vinylacetamide) (PNVA) and poly(N-vinylformamide) (PNVF) have a stable swelling ratio (S.R.) against various pH and temperature conditions, whereas the hydrolyzed part changes to a cationic PVAm. Recently, we applied an interpenetrating polymer network (IPN) to poly(N-vinylamide) hydrogel, to overcome their low radical polymerizability and limited copolymerization. In these experiments, we developed a novel gradient hydrogel: a surface polyion complex (sPIC) gel, which was composed of a non-ionic hydrogel interior core and a chemically bounded polyion complex layer on the outer surface. The sPIC gel forms a polyion complex layer of PVAm and poly(acrylic acid) (PAAc) around pH 7, whereas the surface was swollen at pH2 and pH 12 due to electrostatic repulsion. The total volume of the sPIC gel is well maintained at any pH because the main interior volume inside is composed of non-ionic PNVA and PNVF. In previous studies, we demonstrated a controlled drug release model using fluorescein isothiocyanate (FITC)-dextran (Mw = 9500), which was released at pH 2 from a sPIC gel due to the expanded mesh size of the surface, and this release was suppressed at pH 7 by the sPIC gel because a shrunken polyion complex layer was formed on the surface. It was also able to repeatedly turn on and off the control of this releasing behavior. In this study, we apply this sPIC gel system for various drug models using several different anionic polymers for polyion complex parts.

References:
(1) Y. Takemoto, H. Ajiro, T.Asoh, M. Akashi, “Fabrication of Surface-Modified Hydrogels with Polyion Complex for Controlled Release”, Chem. Mater. 2010, 22(9), 2923-2929.
(2) H. Ajiro, Y. Takemoto, T. Asoh, M. Akashi, “Novel Polyion Complex with Interpenetrating Polymer Network of Poly(acrylic acid) and Partially Protected Poly(vinylamine) Using N-Vinylacetamide and N-Vinylformamide”, Polymer 2009, 50, 3503-3507.
(3) H. Ajiro, J. Watanabe, M. Akashi, “Diversification of Nonionic Amphiphilic Poly(N-vinylacetamide) Hydrogels by a Double Network Approach”, Chem. Lett. 2007, 36, 1134-1135.




                                           
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