Porous hydrogels possessing mechanical
toughness were prepared
from sacran, a supergiant liquid crystalline (LC) polysaccharide produced
from
Aphanothece sacrum
. First, layered
hydrogels were prepared by thermal cross-linking of film cast over
a sacran LC solution. Then, anisotropic pores were constructed using
a freeze-drying technique on the water-swollen layered hydrogels.
Scanning electron microscopic observation revealed that pores were
observable only on the side faces of sponge materials parallel to
the layered structure but never on the top or bottom faces. The pore
size, porosity, and swelling behavior were controlled by the thermal-cross-linking
temperature. To clarify the freezing effect, a freeze–thawing
method was used for comparison. The freeze–thawed hydrogels
also formed layers but no pores. The mechanical properties and network
structures of hydrogels were also studied, clarifying that porous
hydrogels, even those with a high quantity of pores, were tough owing
to the pores orienting along the layer direction like tunnels.
We propose a self-similar assembly to generate planar orientation of megamolecular polysaccharides on the nanometer scale and submicron scale. Evaporating the aqueous liquid crystalline (LC) solution on a planar air-LC interface induces polymer layering by self-assembly and rational action of macroscopic capillary forces between the layers. To clarify the mechanisms of nanometer- and submicron-scale layering, the polymer films are investigated by electron microscopy.
Liquid crystalline hydrogels (LCGs)
with layer structures and oriented
pores were created using sacran which is a cyanobacterial heteropolysaccharide
possessing functional sulfate, carboxylate, and amide groups in common
with glycosaminoglycan. The LCG biocompatibility with L929 mouse fibroblasts
was confirmed under the appropriate conditions. Enhanced growth and
proliferation of L929 cells without exhibiting any toxicity were confirmed.
The water contact angle and protein adsorption ability on the LCG
were well-controlled by the cross-linking degree. Additionally, fibroblasts
were finely oriented on the LCG side face where layer edges made a
striped morphology on its surface, whereas the flat top faces of the
LCG did not induce any specific cell orientation.
Control of cell extension direction is crucial for the regeneration of tissues, which are generally composed of oriented molecules. The scaffolds of highly oriented liquid crystalline polymer chains were fabricated by casting cyanobacterial mega-saccharides, sacran, on parallel-aligned micrometer bars of polystyrene (PS). Polarized microscopy revealed that the orientation was in transverse direction to the longitudinal axes of the PS bars. Swelling behavior of the micropatterned hydrogels was dependent on the distance between the PS bars. The mechanical properties of these scaffolds were dependent on the structural orientation; additionally, the Young's moduli in the transverse direction were higher than those in the parallel direction to the major axes of the PS bars. Further, fibroblast L929 cells were cultivated on the oriented scaffolds to be aligned along the orientation axis. L929 cells cultured on these scaffolds exhibited uniaxial elongation.
Cyanobacteria are regarded as very eco-friendly microreactors for the production of various biomolecules such as polysaccharides by fixing not only carbon but also nitrogen in water. Cyanobacterial polysaccharides having various functional groups such as hydroxyls, carboxyls, sulfates, etc. have the ability to interact with metals or inorganics, to create bionanocomposites. Sacran, a supergiant cyanobacterial anionic polysaccharide extracted from the extracellular matrix of Aphanothece sacrum which is mass-cultivated in freshwater, is mainly used to create functional bionanocomposites. Gel-type bionanocomposites of sacran with various metal cations are formed and showed photoresponsive functions. Metal recovery is performed from the sacran bionanocomposite gels. Sacran chains are complexed with multi-wall carbon nanotubes (MWCNT) to give viscose dispersion from which MWCNT bionanocomposites can be collected by electrophoresis. The MWCNT/sacran dispersion retains the capability of adsorbing various metal ions to form hardened hydrogel beads. Finally, natural inorganic sepiolite can be used for sacran bionanocomposites which show an efficient neodymium ion adsorption ability. Thus, cyanobacterial polysaccharides are useful for preparing eco-friendly and functional bionanocomposites with various hard materials.
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