Anisotropic gels have been studied very widely in the fields of soft-biomaterials due to their possible application as biomedical, optical, and electronic materials. The anisotropy was effected by various stimuli such as self-assembly, directional diffusion, directional freezing, elongation, solvent-cast and so on. The solvent-cast method is one of the most facile methods of film preparation, inducing in-plane molecular orientation of the resulting film by solvent removal stress. If the cast film is cross-linked and re-swells in solvent, the gels should be formed. Such an in-situ hydrogelation method is useful because the dried precursor film has a resistance to decay and soon re-swells in water just before use. Thinner films should have a higher efficiency of polymer chain orientation, but are generally less self-supporting or too thin as film with a thickness of less than one micrometer cannot be used as a precursor of hydrogels in reality. Although the films that are thick enough to self-support should be better for the precursor, molecular orientation is quite difficult to produce. Sacran is a supergiant cyanobacterial polysaccharide with an extremely high absolute molecular weight over 107 g/mol (molecular length: over 30 um) and a very high rigidity parameter, r, of 3.8 to exhibit a liquid crystalline (LC) phase at an extremely low concentration of 0.3 wt%. When sacran LC aqueous solution is cast and annealed at a temperature range of 70-140 oC, anisotropic hydrogels are formed by immersion in water, where the thickness change of the film by swelling is 70 fold higher than the width change. Increase in the film thickness or decrease in sacran chain length reduced the swelling anisotropies, indicating that LC chains with micrometer-scale size comparable with a thickness of self-standing film showed domino-effects to align along the substrate surface during drying. Thus uniaxially-swelling hydrogels were efficiently created.

Super-Anisotropic swelling of hydrogels layered by domino-effects of cyanobacterial LC megamolecules

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.