Structural organization and biological activity of chitin nanofibrils

Chitin, the second most abundant structural biopolymer, has a complicated, multilevel supermolecular construction. All chitins are developed from superfine fibrils having diameters in the nano to micro scales, and each nanofibril contains ordered nanocrystallites inserted into low-ordered non crystalline domains. Acid hydrolysis can be used to dissolve away regions of the marginal domains so that the water-insoluble, highly crystalline residue can be converted into a stable suspension by vigorous mechanical shearing action. Highly crystalline chitin nanofibrils, otherwise called 'whiskers', exhibit enormous surface improvement that allows them to impart strength to several materials such as poly(caprolactone), soy proteins, natural rubber, poly(vinyl alcohol), chitosan, and silk fibroin. Apart from their ability to improve mechanical integrity, chitin nanofibrils may interact well with enzymes, platelets, growth factors, and other cell compounds existing in living tissues. Thus, the wound recovery ability and the ability to induce the formation of granulation tissues are obtained so that the applicability of chitin nanofibrils in medical areas is supported. In this chapter, the structural building principles and nanofibril structure of chitin from various sources and the methods of preparation of nanofibrillated chitin are discussed. Biological activities, as well as attempts to modify chitin nanofibril, are subsequently described.