[Industrial and Medical Material Applications of a Mega-polysaccharide Derived from Cyanobacteria]

Polysaccharides (PS) are one form of biomass occurring in great abundance on earth and are promising organic material alternatives to petroleum-based ones. We have focused on PS produced by cyanobacteria. Aphanothece sacrum, which is a freshwater unicellular cyanobacterium, produces large amounts PS as a main component of the extracellular matrix. We successfully extracted the PS sacran from A. sacrum biomaterials and demonstrated that sacran contains carboxyls and sulfate groups. Furthermore, the constituent sugars of the sacran extracted were determined to be fucose, rhamnose, xylose, arabinose, mannose, glucose, galactose, glucuronic acid, galacturonic acid, and galactosamine. The sequence of sacran is still under investigation. In addition, we confirmed that the sacran was a supergiant with a high absolute molecular weight of 2.35×10⁷ g/mol. Sacran shows a self-orienting behavior in dilute solution at a concentration range over 0.25 wt% to form a liquid crystalline structure. Using this property, it is possible to prepare a sacran cast film with an orientation structure, especially swelling in the thickness direction, to form anisotropic hydrogels. The anisotropy and degree of swelling of the hydrogels could be controlled by varying the heating temperature of the sacran cast file. Furthermore, sacran could be combined successfully with rayon as new fiber materials, and the sacran-rayon complex materials showed increased water absorption compared with the original rayon. This article introduces various applications of sacran in the industrial and medical fields.