Enzymatic grafting of amylose on chitin nanofibers for hierarchical construction of controlled microstructures

We have previously reported that re-dispersible amidinium chitin nanofibers are obtained from an amidinated chitin by CO2 gas bubbling with ultrasonic treatment in water. On the other hand, amylose is precisely synthesized by phosphorylase-catalyzed enzymatic polymerization. In this study, grafting of amylose on the amidinium chitin nanofibers was investigated by the phosphorylase-catalyzed enzymatic polymerization to produce amylose-grafted chitin nanofiber materials. Depending on the reaction conditions, the reaction mixtures turned into hydrogels. The hydrogels were constructed via the formation of double helixes from a part of amylose graft chains closely present among the nanofibers. Microstructures, which were hierarchically constructed by lyophilization of the hydrogels, were changed from network to porous morphologies in accordance with the molecular weights of amylose graft chains. Most of the amylose graft chains with higher molecular weights, which did not participate in double helixes, formed amorphous membranes in the nanofiber networks by lyophilization, to construct porous structures.