Cyanobacterial supra-polysaccharide: Self-similar hierarchy, diverse morphology, and application prospects of sacran fibers.

The biological functions of polysaccharides are influenced by their chemistry and chain conformation, which have resulted in various functional applications and new uses for polysaccharides in recent years. Sacran is an intriguing ampholytic polysaccharide with several key properties such as metal adsorption, anti-inflammatory nature, and transdermal drug-carrying capacity. It has an extremely high molecular weight over 107 g/mol, which is much higher than those of the previously reported microbial polysaccharides. In particular, it has a remarkable self-orienting characteristic over a large length scale, which could produce a bundle with twisted morphologies from the nanoscale to the microscale with diameters of ~1 µm and lengths of >800 µm. In this review, morphological variations, as well as novel self-organization and hierarchical self-assembly are comprehensively discussed. Sacran fibers deform into various forms, such as two- and three-dimensional flexible fibers and micro-nano fragments, during their evaporation. The self-assembly and disassembly of the sacran are explained in terms of the preparation process and factors that influence the morphology. This review will pave the way for the development of novel modules such as humidity-sensitive actuators, micro-patterned cell scaffolds, and uniaxially oriented membranes.

Super-Moisturizing Materials from Morphological Deformation of Suprapolysaccharides.

The evaporative interface on polysaccharides has evolved to form hierarchical structures with moisture sensitivity to enable organisms to live in drying environments. Here, the discovery of the morphological instability of polysaccharides, especially the reversible self-assembly/disassembly between micron-fibers and microparticles in response to changes in aquatic environments, is reported. This is similar but different to the dynamic instability observed in cytoskeletal proteins, in terms of an accompanying the polymeric deformation. The formation of the polymeric fibers containing crystalline structures can be flexibly controlled by controlling the polymer concentration and salt concentration in aqueous mixtures. Moreover, the microparticles having crosslinking points in the interior acquire the ability to retain a larger number of water molecules in drying environments and behave as super-moisturizing materials.

Magnetorheological Response for Magnetic Elastomers Containing Carbonyl Iron Particles Coated with Poly(methyl methacrylate).

The magnetorheological response for magnetic elastomers containing carbonyl iron (CI) particles with a diameter of 6.7 µm coated with poly(methyl methacrylate) (PMMA) was investigated to estimate the diameter of secondary particles from the amplitude of magnetorheological response. Fourier-transformed infrared spectroscopy revealed that the CI particles were coated with PMMA, and the thickness of the PMMA layer was determined to be 71 nm by density measurement. The change in the storage modulus for magnetic elastomers decreased by coating and it was scaled by the number density of CI particles as ΔG~N2.8. The diameter of secondary particle of CI particles coated with PMMA was calculated to be 8.4 µm. SEM images revealed that the CI particles coated with PMMA aggregated in the polyurethane matrix.

Convective meniscus splitting of polysaccharide microparticles on various surfaces.

In contrast to convective self-assembly methods for colloidal crystals etc., "convective meniscus splitting method" was developed to fabricate three-dimensionally ordered polymeric structures. By controlling the geometry of evaporative interface of polymer solution, a deposited membrane with uniaxial orientation and layered structures can be prepared. Here it is demonstrated that xanthan gum polysaccharide microparticles with diameter ~ 1 µm can bridge a millimeter-scale gap to form such a membrane because the capillary force among the particles is more dominant than the gravitational force on the evaporative interface. This method is applicable for various substrates with a wide range of wettability (water contact angle, 11°-111°), such as glass, metals, and plastics. The specific deposition can be also confirmed between frosted glasses, functional-molecules-modified glasses, and gold-sputtered substrates. By using such a universal method, the membrane formed on a polydimethylsiloxane surface using this method will provide a new strategy to design a functional polysaccharide wall in microfluidic devices, such as mass-separators.

Vapor-Sensitive Materials from Polysaccharide Fibers with Self-Assembling Twisted Microstructures.

Polysaccharides play a variety of roles in nature, including molecular recognition and water retention. The microscale structures of polysaccharides are seldom utilized in vitro because of the difficulties in regulating self-assembled structures. Herein, it is demonstrated that a cyanobacterial polysaccharide, sacran, can hierarchically self-assemble as twisted fibers from nanoscale to microscale with diameters of ≈1 µm and lengths >800 µm that are remarkably larger than polysaccharides previously reported. Unlike other rigid fibrillar polysaccharides, the sacran fiber is capable of flexibly transforming into two-dimensional (2D) snaking and three-dimensional (3D) twisted structures at an evaporative air-water interface. Furthermore, a vapor-sensitive film with a millisecond-scale response time is developed from the crosslinked polymer due to the spring-like behavior of twisted structures. This study increases understanding of the functions of fibers in nature and establishes a novel approach to the design of environmentally adaptive materials for soft sensors and actuators.

Micelle-Mediated Self-Assembly of Microfibers Bridging Millimeter-Scale Gap To Form Three-Dimensional-Ordered Polysaccharide Membranes.

Micelle-mediated three-dimensional-ordered polysaccharide membranes are constructed by introducing cationic/anionic surfactant into a liquid crystalline polysaccharide solution. Upon drying mixtures of the polysaccharide solution with the surfactant such as cetyltrimethylammonium bromide or sodium dodecyl sulfate (SDS), the polymeric microfibers deposit as a nucleus to form a membrane, bridging millimeter-scale gap with high probability. In particular, in a solution with SDS micellar structures, the microscale fibers with diameter ∼1 µm disassemble into nanoscale fibers with diameter ∼50 nm. This transformation allows the polymeric network to become finer in nanoscale, and the vertical membrane is formed much more easily than that from a pure polysaccharide solution. Furthermore, it is clarified that the vertical membrane has been successfully formed with three-dimensionally ordered microstructures with a linearly oriented and layered structure. This method will shed light on the preparation of hybrid materials with biocompatibility and responsivity to stimuli such as magnetics, electrics, and optics via hybridization with nanomaterials dispersed by surfactants.