Cellulose and chitin are some of the most abundant renewable polymers on earth. A key characteristic common to both is that they exist naturally in the form of highly crystalline nanofibers. They provide both rigid and flexible structural support in plant cell walls and in the exoskeletons of arthropods such as crustaceans and insects. Because of inferior mechanical properties such as low weight, very large surface-to-volume ratios and high aspect ratios, cellulose and chitin nanofibers have recently attracted significant interest for wide potential application in polymer reinforcement, flexible display, medical devices, separation membranes and many other areas.The stable crystal structures in cellulose and chitin, however, prevent their molecules from dissolving in most common solvents. When hydrogels and aerogels are prepared from cellulose and chitin, for example, use of specific solvents such LiCl/DMSO and aqueous alkaline systems such as NaOH/urea (for cellulose), and calcium chloride dihydrate-saturated methanol and LiCl/NMP (for chitin) are essential. Not surprisingly, cellulose and chitin nanofibers do not dissolve in water. However, because the entanglement of their nanofibers creates a large hydrophilic surface area and high aspect ratios form a stable network in water, they are homogeneously dispersed. The result is very high viscosity, even with 1 wt% nanofiber. Their nanofibers appear to behave in water as if dissolved, maintaining good crystallinity.In previous studies, we found that an aqueous suspension of cellulose nanofibers was easily transformed into stable and tough hydrogels through alkaline treatment 1,2) . The nanofiber hydrogels had two different kinds of cellulose crystal forms (cellulose I and cellulose II) in response to increasing concentrations of NaOH(aq) solutions, and both gels consisted of a highly porous and crystalline nano-network. In particular, the nanofiber gel with cellulose II demonstrated high tensile strength due to the continuous and strong nano-network formed by the interdigitation of nanofibers during the mercerization process in the crystal conversion from cellulose I to cellulose II. Based on these results, the present study applied the gel preparation to chitin nanofibers. Like cellulose, the crystal structure of -chitin is converted to -chitin by NaOH(aq) treatment. We studied the gelation behavior of -chitin nanofibers and investigate the physical and morphological properties of the hydrogels.The crystal structure of chitin nanofibers (Figure 1), which were extracted from purified squid pen powder, was transformed from -chitin to -chitin by NaOH(aq) treatment above 30 wt%. The crystal conversion involving the interdigitation among adjacent nanofibers caused the formation of stable hydrogels with a -chitin nanofiber network (Figure 2). The use of ethanol voided the dissolution during neutralization and enabled preparation of a highly crystalline hydrogel with high mechanical strength. It achieved a Young's modulus of 16.6 MPa, a tensile strength of 7 MPa and a ...

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The aim of this study was to examine the effects of oral administration of chitin nanofibers (CNFs) and surface-deacetylated (SDA) CNFs on plasma metabolites using metabolome analysis. Furthermore, we determined the changes in gut microbiota and fecal organic acid concentrations following oral administrations of CNFs and SDACNFs. Healthy female mice (six-week-old) were fed a normal diet and administered tap water with 0.1% (v/v) CNFs or SDACNFs for 28 days. Oral administration of CNFs increased plasma levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP), and serotonin (5-hydroxytryptamine, 5-HT). Oral administration of SDACNFs affected the metabolisms of acyl-carnitines and fatty acids. The fecal organic level analysis indicated that oral administration of CNFs stimulated and activated the functions of microbiota. These results indicate that oral administration of CNFs increases plasma levels of ATP and 5-HT via activation of gut microbiota.

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