Abstract
Alkyl imidazolium-based polymer hydrogels were prepared by copolymerizing N-allylimidazolium chloride monomers (AlImCls) bearing four types of alkyl groups with N-isopropylacrylamide and N, N′-methylenebisacrylamide. The conditions for preparing the anion-responsive hydrogels were screened by gelation test before and after the addition of tetrafluoroborate anions. The sol-gel phase transition was observed in N-dodecyl and N-octadecyl AlImCls-based copolymer solutions. Considering the anion selectivity in the gelation test, this phase transition was assumed to be derived from the formation of water-immiscible ion pairs of N-allylimidazolium cations and large anions on the polymers. Microscopic observations revealed that spherical domains with micro-sized diameters were formed in the hydrogels. A hydrophobized fluorescent dye was localized to the microdomains. Observations using time-lapse confocal microscopy and electron microscopy indicated that large microdomains were captured by the gel meshes consisting of thin sub-micron fibers. Based on the data collected during the analysis of the copolymer solutions, the spherical microdomains and the thin gel meshes were presumably formed through the anion-induced aggregation of small copolymer assemblies. Furthermore, the high fluidity of the microdomains was confirmed by measuring fluorescence recovery after photobleaching. In summary, anion-responsive hydrogels with hydrophobic microdomains were developed using ionic salt-based copolymers. These hydrogels are promising as a unique carriers for the use in biotechnology.
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Acknowledgements
This work was supported by a Grant-in-Aid for Young Scientists (B) from the Ministry of Education, Culture, Sports, Science and Technology and the Center for NanoBio Integration. We thank Prof. Kazunari Akiyoshi at Kyoto University for assisting with the TEM observation of the hydrogels and for helpful advice on this study. We thank Prof. Ryosuke Matsuno at Kyushu University for kindly helping us with the analysis of the copolymer solutions.
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Yamaguchi, S., Kawabata, R., Yamamoto, E. et al. Imidazolium-based polymer hydrogels with microdomains as carriers of hydrophobic molecules. Polym J 46, 880–886 (2014). https://doi.org/10.1038/pj.2014.77
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DOI: https://doi.org/10.1038/pj.2014.77
