Shinsuke Ifuku
Prof, Graduate School of Engineering, Tottori University
Born in Kanagawa prefecture in 1974. He graduated from the Department of Chemistry, Faculty of Science, Tokyo University of Science. He completed the master's program at the Graduate School of Agriculture, Kyoto University, and is certified as a doctoral research instructor. He is a doctor of agriculture. He joined Tottori University in 2008 after working as a postdoctoral researcher at the University of British Columbia, Canada. He also serves as the representative director of the university-launched venture "Marine Nanofiber Co., Ltd." He strives for social implementation of the technology utilizing "chitin nanofibers", which are a local resource.
The polysaccharide, chitin, is the main component of crab shells, which is an abundant biomass. But it has poor solubility, so it is rarely used. Recently, a mechanical treatment technique for converting chitin into "nano-chitin" has been developed. Nanochitin is a fine fibrous substance with a width of about 10 nm and uniformly dispersible in water, so it is easy to process. Since it is also possible to search for functions, various functions have been clarified. Nanochitin has an effect on the skin, an effect associated with oral administration, and an effect on plants sprayed with it. It is expected that the utilization of the new materials derived from these unused resources will be promoted by clarifying unknown potential functions.
Snow crab is famous in the Tottori prefecture and nationwide. Especially in Sakaiminato city, the catch of red snow crab is the best in Japan. The meat of snow crab removed from its shell is used as a frozen processed food. Since the crab shells in the processing plant are not mixed with other residues, clean waste shells can be obtained. In this paper, new materials prepared from crab shells in Tottori prefecture and their functions will be introduced. That is, chitin from crab shell was converted into nanochitin, and its effects on the skin were clarified.
Chitin is a polysaccharide with an acetylglucosamine-bound chemical structure. Its structure is similar to cellulose. In addition to crab and shrimp shells, chitin is also found in the outer skin of insects and in the cell walls of mushrooms and fungi. The amount biosynthesized is estimated to be 1 x 1011 tons/year, and it is one of the most abundant biomasses on earth. The industrial raw material for the production of chitin is mainly crab and shrimp shells, which contain 20-30% chitin. The other components are mainly calcium carbonate and protein, which can be removed with hydrochloric acid and sodium hydroxide, respectively (Fig. 1). The causative crustacean allergen is a protein called tropomyosin, which is derived from the muscle tissue of the crab, and the protein contained in crab shells is not regarded as an allergen. Nanochitin is obtained by grinding purified chitin in water. The crushed material is a uniform fibrous material with a width of approximately 10 nm (Fig. 2). The reason it can be converted into nano-chitin by crushing is that all natural chitin exists as fibrous nano-chitin (Fig. 3). Therefore, when chitin is crushed in water, the size of the final product is at the nanochitin scale. Therefore, nano-chitin can be produced not only from crab shells but also from other sources. So far, nanochitin has been obtained from shrimp shells, mushrooms, cicada husks, silk moth pupae, crickets, and bees. One of the characteristics of nanochitin is its high dispersibility in water. Therefore, nanochitin is processed into threads, sponges, films, hydrogels, and so on. In addition, it is possible to make a prototype product by blending it with existing cosmetics and foods. Furthermore, it can be evaluated by in vitro or iin vivo tests to search for physiological functions. Chitin has been called the “last biomass” left behind because of the large amount that is not being used. The reason chitin is not used is its poor solubility. On the other hand, since nanochitin is uniformly dispersed in water, it is easy to process.
Chitin and its deacetyl derivative, chitosan, affect the inflammatory, proliferative, and remodeling phases of wounds and promote their healing. Therefore, it has been used as a wound dressing material. This is because it stimulates various cells such as neutrophils, macrophages, fibroblasts, vascular endothelial cells, and cutaneous epithelial cells. Therefore, the healing effect of partially deacetylated nanochitin on wounds was examined. An aqueous dispersion of nanochitin was applied to wounds on the backs of rats every two days for 8 days, and the healing effect was verified. Histological evaluation revealed partial regeneration of epithelial tissue on day 4 and complete regeneration of epithelial tissue on day 8 after application. In addition, when the collagen fibers of the skin tissue were selectively stained by Masson’s trichrome staining, remarkable production of collagen fibers was observed in the dermis layer. On the other hand, when commercially available chitin or chitosan powder was administered, epithelialization was only slightly observed.
Nanochitin brings moisture to the skin and enhances the barrier function. The effect of nanochitin on human skin was verified using a human three-dimensional skin model consisting of normal human epidermal cells. For the skin model after 48 hours, application of nanochitin was able to suppress the decrease of granules in the stratum granulosum. In addition, the structure of the tissue from the spinous layer to the basal layer could be maintained. When nanochitin is applied, a dense film is formed on the epidermis. It is presumed that the film contributes to the protection of the skin against external stimuli and bacteria, and to the maintenance of water content and balance. In addition, the effect of applying nanochitin to the back of nude mice was verified. The epithelial tissue swelled 4 hours after application. This seems to be due to the retention of water in the skin. In addition, the area of collagen fibers in the dermis layer increased 8 hours after application. This involves the production of fibroblast growth factor (FGF) associated with the application of nanochitin.
The dorsal surface of shaved mice was coated with partially deacetylated nanochitin every two days for a total of 6 times. The length of the hair after 12 days was measured. As a result, hair elongation by nanochitin was observed and compared with the untreated case, and the average length reached four times the length in antreated cases. In addition, the histological findings of the skin collected and stained with hematoxylin and eosin showed the transition of hair roots from the resting phase to the growing phase. For the cell test, dermal papilla cells were cultured for 3 days in a medium containing nanochitin, and the proliferative ability of the cells was evaluated. In addition, the amount produced of fibroblast growth factor (FGF-7) involved in the activation of hair matrix cells forming the hair shaft, and vascular endothelial growth factor (VEGF) that promotes angiogenesis around the hair root, were measured. As a result, it was clarified that nanochitin increases the number of viable dermal papilla cells. In addition, the production of VEGF and FGF-7 increased depending on the concentration of nanochitin. Many of the mechanisms of the hair growth effect are due to the direct action of the active ingredient that reaches the dermal papilla cells at the base of the hair follicles. The surface layer of the skin is said to be negatively charged, and nanochitin, which is positively charged by amino groups, reaches the deep part of the hair follicle by electrostatic interaction, activates cells, and produces factors related to hair growth.
The author has been engaged in the development of nanocellulose in the past. Since nanocellulose has excellent physical characteristics, it has drawn attention as a new material because of the expectation that it can strengthen plastics and reduce their weight. Subsequently, the author arrived at Tottori University, started research and development of nanochitin, which is a local resource, and got the desired substance soon thereafter. This is because there was a technology for producing nanocellulose and crab shells are a nanochitin source. Since nanochitin has the same morphology and physical properties as nanocellulose, elasticity and breaking strength can be significantly improved without impairing the transparency of the plastic, and thermal expansion can be significantly suppressed. However, nanochitin is overwhelmingly disadvantageous in terms of resource quantity and cost, so it is not realistic to use it as a reinforcing material on a large scale. Therefore, in order to develop its use, it is essential to clarify the characteristics unique to chitin nanofibers, abandon the mass-purpose area, and concentrate on the small-quantity, high-value-added area. Chitin and its deacetyl derivative chitosan have physiological functions and are used in medical devices such as wound dressings and emergency hemostatic agents. In addition, because of its dieting effect and antibacterial properties, it is used as an additive for health foods, food additives, and fibers. Therefore, we searched for the physiological functions of nanochitin. As a result, the author revealed a surprisingly wide variety of functions. That is, the effects associated with its application to the skin (promoting wound healing, alleviating dermatitis, hair growth) and effects associated with oral administration (alleviating inflammation of the intestinal epithelium, suppressing lipid absorption, blood cholesterol level, improvement of intestinal flora), etc. In addition, the effects of administration to plants (promotion of growth, induction of disease resistance) were also clarified. We believe that nanochitin use has the potential to spread nationwide in the future. To that end, we must continue to discover unknown functions of nanochitin and increase its value.
