ABSTRACT
Nanobers are generally dened as bers with diameter of <100 nm and an aspect ratio of >100 nm. Because nanobers have extremely high surface-to-volume ratio, their properties are different from those of microsized bers. Thus, decreasing the width and increasing the aspect ratio of nanobers compared to microbers add unique dimensions to optical, mechanical, medical, electrical, and other characteristics for the development of new promising advanced materials from the application viewpoint. Owing to the environmentally benign, biodegradable, biocompatible, renewable, and sustainable biomass, the nanobers from biopolymers are gaining importance. A variety of naturally occurring nanobers, such as collagen triple-helix bers, broin brils, and keratin brils are known. As these nanobers consist of complex hierarchical organization, they are suggestive of the possibility that nanobers are extracted from biomass-based organized structural units. Among the variety of biomass-based products, cellulose is the most abundant biopolymer found mainly in wood cell walls. The cellulose nanobers are highly crystalline structures. The bundles of nano-bers are embedded in matrix substances such as hemicellulose and lignin matrix that form the wood cell wall. Because cellulose nanobers have extremely tough physical properties, they have potential as high-performance material. Various chemical processes followed by mechanical treatments have been employed mainly for cellulose nanobers preparation. Abe et al. (2007) isolated cellulose nanober bundles of 15-nm-sized nanobers from wood by a simple method. Apart from wood, the cellulose nanobers were isolated from rice straw, potato tuber pulp, and parenchymal cells of bamboo and fruits (Abe and Yano 2009, 2010; Ifuku et al. 2011a). Chitin is known to be cellulose analogs with a (1,4)-β-N-acetyl glycosaminoglycan-repeating structure. After cellulose, chitin is the second most abundant biopolymer, occurring mainly in the exoskeletons of shellsh and insects and the cell walls of mushrooms. Although chitin is a semicrystalline biopolymer with nanosized brillar morphology and excellent material properties, most chitin is thrown away as
8.1 Introduction .......................................................................................................................... 169 8.2 Preparation of Chitin Nanobers from Crab Shell ............................................................... 170 8.3 Preparation of Chitin Nanobers from Prawn Shell ............................................................ 172 8.4 Preparation of Chitin Nanobers from Mushrooms ............................................................. 172 8.5 Preparation of Chitin Nanobers from Dry Chitin Powder ................................................. 173 8.6 Oral Administration Effect of Chitin Nanobers on Inammatory Bowel Disease ............ 176 8.7 Conclusions ........................................................................................................................... 178 References ...................................................................................................................................... 179
industrial waste. Therefore, it is important to make effective use of chitin as an environmentally friendly green material. Because of its linear structure with two hydroxyl groups and an acetamide group, chitin is highly crystalline with strong hydrogen bonding having high binding energy and is arranged as nanosized chitin nanobers in an antiparallel fashion. Because crab and prawn shells have a hierarchical structure made up of chitin nanobers, proteins, and minerals (Raabe et al. 2006), we consider that the preparation method of cellulose nanober is applicable to several species consisting of chitin nanobers. We have developed a simple method for the preparation of chitin nanobers. In this chapter, we describe the available procedures for preparing chitin nanobers and the biomedical applications of the nanobers.
