Biopolymers such as polysaccharides, cytoskeletal proteins, and DNAs show helical structures in molecular scale and self-orientation in a larger scale. Those characters are the key to functionality and morphogenesis of various hierarchically structured materials. Sacran is one of the fascinating cyanobacterial polysaccharides which could naturally form the incredibly giant fiber in micrometer to millimeter scale. It is extracted from cyanobacteria, Aphanothece sacrum, which has attached our interest due to the extremely high molecular weight (&gt; 1.6 × 107 g/mol) and the self-orienting giant micro-fibers (∼1 µm of outer diameter and &gt; 20 μm length) during the drying process that cannot be encountered in any others polysaccharide. The giant fiber is apparently constructed though self-orientation of the rigid polysaccharides and self-assembly to build a rod-like microdomain. In this study, to clarify the formation mechanism and microgeometry of fibers, the effect of polymer concentrations, evaporation speeds, and ionic concentrations are validated. The samples were prepared by drying sacran solution on a glass substrate at room temperature under control of the initial polymer concentration, evaporation speeds and concentrations of ionic solution (HCl, NaCl, and CaCl2). By controlling evaporation speeds, it was found that the twisting structure could be formed by folding of the snaking structure (Fig.1). The fiber form showed significantly different, depending on the drying speed. To clarify the ionic effect on the assembly and disassembly of the microfibers, in HCl or NaCl solutions, the microfibers were disassembled state as small fragments. In contrast, the microfiber maintained the structure in CaCl2 solution because Ca2+ is capable to bind with the carboxylate groups as a crosslinker. This clarification of the microstructure will help not only understanding of geometric self-assembly of polysaccharides but also developments of biomimetic applications such as artificial muscle, biomimetic template and, micro-spring materials.

Snaking/twisting fibers formation of cyanobacterial supra-polysaccharides in drying process

2019 Spring National Meeting

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