Figure 10.

Illustration of three main polymorphs of chitin. (a) AFM images of three polymorphs of ChNFs obtained from the same acid/base extraction process. α-Chitin can be extracted from crab shells (Potamon ibericum), β-chitin from squid pens (Sepia sp.), and γ-chitin from moth cocoons (Orgyia dubia). Adapted with permission from ref (151). Copyright 2017 Elsevier. The gray arrows indicate the orientation of chitin macromolecules within the crystalline domains, with the arrows pointing away from the reducing end. Molecular structure and hydrogen H-bonding in (b1) α-chitin and (c1) β-chitin. Note: the intersheet bonding is absent in the case of β-chitin. Adapted with permission from ref (152). Copyright 2009 Elsevier. Structure of (b2) α-chitin and (c2) β-chitin in different projection planes (ac, bc, and ab). Adapted with permission from ref (9). Copyright 2006 Elsevier.