4. Results and discussion
4.1. Preparation of chitosan NPs and chitosan NFs
Preparation steps of chitosan NPs and chitosan NFs starting from crab shells is schematically presented in Fig. 1(a). Crab shell is identified as a composite structure having three separate layers. Top most layer is called as epicuticle which is a nonchitin surface vainer mainly for the protection of the crab shell surface. Second and third layers are together called as procuticle. The topmost layer of the procuticle is identified as exocuticle and the bottom layer is referred to as endocuticle. Both these layers mainly consist of calcite crystals which are bound together by a complex matrix of chitin and protein fibers. The striking feature of this fiber matrix is that they show twisted plywood pattern, which is commonly referred to as Bouligand pattern. Individual fiber has a thickness of approximately 60–70 nm which can be further divided to even smaller nanofibers having diameters approximately 3–5 nm (Chen et al., 2008 and Raabe et al., 2005)