Masahisa Wada

Cellulose–silk fibroin hydrogels prepared in a lithium bromide aqueous solution

Here, we present a new process for the preparation of cellulose–silk fibroin hydrogels using a concentrated lithium bromide (LiBr) aqueous solution. After mixing, the solutions of cellulose and silk fibroin that had each been dissolved separately in aqueous LiBr, the cellulose forms a gel as the solution cools to approximately 70°C, and silk fibroin is regenerated via treatment in methanol. Three grades of cellulose–silk fibroin hydrogels are prepared by controlling the amounts of cellulose and silk fibroin. The gels have highly porous, three-dimensional networks composed of long, interconnected fibrils. Through X-ray diffraction and ATR-FTIR analysis we show that the dissolution-regeneration of cellulose and silk fibroin induces a structural change in the crystal structure of cellulose II and silk II. While the porosity and swelling ratio of cellulose–silk fibroin gels is significantly reduced with the increased silk fibroin content, all the gels show high water uptake. The enzymatic degradation rates of cellulose–silk fibroin gels obviously reflect differences in the silk fibroin content, and cell adhesion and growth on cellulose–silk fibroin gels is enhanced with increased silk fibroin content. These cellulose–silk fibroin gels could provide novel properties that would be useful for biomaterial matrix applications.

X-ray crystal structure of anhydrous chitosan at atomic resolution.

We determined the crystal structure of anhydrous chitosan at atomic resolution, using X‐ray fiber diffraction data extending to 1.17 Å resolution. The unit cell [a = 8.129(7) Å, b = 8.347(6) Å, c = 10.311(7) Å, space group P212121] of anhydrous chitosan contains two chains having one glucosamine residue in the asymmetric unit with the primary hydroxyl group in the gt conformation, that could be directly located in the Fourier omit map. The molecular arrangement of chitosan is very similar to the corner chains of cellulose II implying similar intermolecular hydrogen bonding between O6 and the amine nitrogen atom, and an intramolecular bifurcated hydrogen bond from O3 to O5 and O6. In addition to the classical hydrogen bonds, all the aliphatic hydrogens were involved in one or two weak hydrogen bonds, mostly helping to stabilize cohesion between antiparallel chains.

Thermal expansion behavior of A- and B-type amylose crystals in the low-temperature region

The thermal expansion behaviors of A-type and B-type amylose crystals, which were prepared by recrystallization of short amylose chains synthesized by phosphorylase, were investigated using synchrotron X-ray powder diffraction between 100 and 300K. For both types of crystals, the room-temperature phase (RT phase), which is the usually observed phase, transitioned to a low-temperature phase (LT phase), on cooling. The phase transitions took place reversibly with rapid changes in the unit-cell parameters around 200-270K. The differences between the RT and LT phase were investigated using solid-state (13)C NMR spectroscopy, which revealed there were changes in molecular chain conformations. These results suggest that the phase transition of water molecules on the crystalline surfaces affects the thermal behavior and structure of polysaccharide crystals.

Cellulose hydrogel film for spheroid formation of human adipose-derived stemcells

AbstractsHerein, we present a new process for the formation of cell spheroids in three-dimensional culture systems using cellulose hydrogel film. Transparent cellulose hydrogel film were prepared via dissolution-regeneration with a LiOH/urea aqueous solution and methanol. The cell viability of the cellulose hydrogel film was equivalent to that of cell tissue culture plate, revealing no cytotoxicity. Spheroids of human adipose-derived stem cells (hASCs) were successfully formed on cellulose hydrogel film. Spheroid size strongly depended on the cell seeding density and culture time, becoming larger with increases in both factors. Cell differentiation simultaneously progressed favorably with the spheroid formation of hASCs. These results suggested that cellulose hydrogel film could provide a new option with regard to tissue engineering applications.

Characterization of crystalline linear (1 → 3)-α- d -glucan synthesized in vitro

We investigated the crystal structure and molecular arrangement of the linear (1→3)-α-d-glucan synthesized by glucosyltransferase GtfJ cloned from Streptococcus salivarius using sucrose as a substrate. The synthetic products had two morphologies: wavy fibril-like crystals as major and thin lamellae as minor products. Their structures were analyzed using electron microdiffraction, synchrotron X-ray powder diffraction, and solid-state 13C NMR spectroscopy. The fibrils and lamellae had the same allomorphic form but different molecular arrangements. The wet crystals were in a hydrated form, which converted into an anhydrous form with a significant decrease in crystallinity on drying. The hydrated and anhydrous forms had an extended-chain conformation with 2/1 helix, and the hydrated form was estimated to contain one water molecule per glucose residue. The long glucan chains were folded in the fibril crystals, while the short, extended chains were arranged perpendicular to the base plane of the lamellae.