Papers by Author: Tsukasa Ikeda

Abstract: Bacterial cell-to-cell communication system quorum sensing (QS) could be effectively controlled with polymer gel sheets which possess affinity to QS signals. Cyclic oligosaccharide cyclodextrin (CD) was successfully immobilized onto 2-hydroxypropyl cellulose gel sheets to trap the QS signals produced in one of the opportunistic pathogen Serratia marcescens. In gram-negative bacteria including S. marcescens, N-acylhomoserine lactones (AHL) with different length of acyl-chains were produced as the QS signal autoinducer. The inclusion complex formation between AHL and CD is responsible for the artificial decrease of the AHL concentration inside and outside of cells. Because the QS system is the AHL-concentration dependent mechanism that activates the specific gene transcription, the AHL trapping method was simple and greatly effective to intercept the QS system. By using the 2-hydroxypropyl-β-CD immobilized gel sheets, the prodigiosin of which production was regulated by the AHL-mediated QS system could be reduced to approximately 20%.

Abstract: To control the microstructure and the responsive rates of hydrogels, a temperature-induced phase separation (TIPS) method applied to an organic-inorganic hybrid hydrogel. A copolymer between thermosensitive poly(N-isopropylacrylamide), polyNIPA, and a vinyl monomer possessing a trimethoxysilyl group was synthesized by radical reaction. Its cross-linking could be carried out by hydrolytic polycondensation of trimethoxysilyl groups. During both reactions, the pre-gel solution was separated into two phases by heating above a lower critical solution temperature of the elongating polyNIPA copolymer. The responsive rates of the microporous gel could be controlled by characteristic diffusion path length as the thickness of micropore wall, instead of the macroscopic sample size. Therefore, the shrinking rates of the hydrogel could be successfully maximized by fixing the phase-separated, microporous polymer network. Besides the interconnectivity of generated pores, the thermally triggered shrinking kinetics was investigated.

Abstract: To control and maximize the shrinking rates of thermo-sensitive organic-inorganic (O-I) hybrid gels, microporous structure of gels could be controlled by ice-templating. Water-swollen gels easily became porous after freezing. Applying the freezing method effectively accelerate the shrinking rates of the poly(N-isopropylacrylamide), polyNIPA-based O-I hybrid gels by two different ways. One is the interpenetrating network with polyNIPA and polysiloxane. The other is the copolymer network of NIPA and a vinyl monomer possessing the trimethoxysilane, of which crosslinking was carried out by sol-gel reaction. Their thermally-triggered shrinking kinetics was investigated by measuring the weight change of gels. Shrinking coefficients (D) were determined by fitting the shrinking data with the Fick’s model. The coefficients after applying the freezing method increased to approximately 10-3 cm2s-1 while those before freezing were on the order of 10-5 - 10-6 cm2s-1.