molecular weight between 3.8 and 2,000 kDa. It is an admirable biopolymer for
research and testing of micro- and nanoparticles due to its excellent biocompatibility and biodegradability. In vivo, it is degraded by lysozyme. In addition, the amino
groups give a high charge density to the molecule and are freely available for
chemical reactions and salt formation with acids. With wide solubility of chitosan
in numerous acids, it also intermingles with polyions to formulate complexes and
gels.
2.1.1 Structure of Chitin and Chitosan
In shellfish, including crustaceans, chitin is present in a complex structure with
calcium carbonate, forming the rigid skeleton of carpace, shell and tail. Shrimp
outer skeleton and crab shells are the most suitable biological sources for the
production of chitin [1, 2]. Chitosan is the principal derivative of chitin and is
obtained by a deacetylation process. Chitin and its derivatives have widespread
applications for biological, physiological and biomedical purposes. Crustacean
shell waste mainly consists of protein (30–40% of dry matter), calcium salts
(30–50% of dry matter), chitin (20–30% of dry matter), oil (2–3% of dry matter)
and astaxanthin (200–250 ppm of dry matter), but the proportions may vary with the
species and culture methods [3]. Chitosan can be isolated from crustacean shell,
insect cuticles and the membrane of fungi. The properties of chitosan vary with its
source. The terms chitin and chitosan do not refer to specific compounds but to two
ranges of copolymers, containing the two monomer residues, anhydro-N-acetyl-Dglucosamine and anhydro-D-glucosamine, respectively. Chitin is a polymer of β(1–4)-2-acetamido-2-deoxy-D-glucopyranose. It is one of the most abundant
organic materials on earth and second to cellulose and murein, which are the
main structural polymers of bacterial cell walls. Chitin is analogous to cellulose
and exhibits a highly ordered chain formation. Chitin has the conformation of an
extended ribbon and the chains can pack side by side in a crystalline structure. In
nature, chitin exists in alpha (sheets are antiparallel and packed), beta (sheets are
parallel and packed) and gamma (two parallel sheets are separated by a single
antiparallel sheet) conformations (Fig. 2). Shrimp and crab contain α-chitin, which
is more difficult to extract as compared with β-chitin in squid and cuttlefish.
Chitosan from β-chitin is more hydrophilic and has a more open form. Crustacean
chitosan in situ has a molecular weight of over 2 MDa. Fungal chitosan has a
molecular weight in the range of 30–60 kDa. The fungal material has the advantage
of not containing shrimp protein, which may cause an allergic reaction in 2% of the
population. The principal derivative of chitin is chitosan, produced by alkaline
deacetylation of chitin. Chitosan is a polymer of β-(1–4)-2-amino-2-deoxy-Dglucopyranose [4].
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
273
research and testing of micro- and nanoparticles due to its excellent biocompatibility and biodegradability. In vivo, it is degraded by lysozyme. In addition, the amino
groups give a high charge density to the molecule and are freely available for
chemical reactions and salt formation with acids. With wide solubility of chitosan
in numerous acids, it also intermingles with polyions to formulate complexes and
gels.
2.1.1 Structure of Chitin and Chitosan
In shellfish, including crustaceans, chitin is present in a complex structure with
calcium carbonate, forming the rigid skeleton of carpace, shell and tail. Shrimp
outer skeleton and crab shells are the most suitable biological sources for the
production of chitin [1, 2]. Chitosan is the principal derivative of chitin and is
obtained by a deacetylation process. Chitin and its derivatives have widespread
applications for biological, physiological and biomedical purposes. Crustacean
shell waste mainly consists of protein (30–40% of dry matter), calcium salts
(30–50% of dry matter), chitin (20–30% of dry matter), oil (2–3% of dry matter)
and astaxanthin (200–250 ppm of dry matter), but the proportions may vary with the
species and culture methods [3]. Chitosan can be isolated from crustacean shell,
insect cuticles and the membrane of fungi. The properties of chitosan vary with its
source. The terms chitin and chitosan do not refer to specific compounds but to two
ranges of copolymers, containing the two monomer residues, anhydro-N-acetyl-Dglucosamine and anhydro-D-glucosamine, respectively. Chitin is a polymer of β(1–4)-2-acetamido-2-deoxy-D-glucopyranose. It is one of the most abundant
organic materials on earth and second to cellulose and murein, which are the
main structural polymers of bacterial cell walls. Chitin is analogous to cellulose
and exhibits a highly ordered chain formation. Chitin has the conformation of an
extended ribbon and the chains can pack side by side in a crystalline structure. In
nature, chitin exists in alpha (sheets are antiparallel and packed), beta (sheets are
parallel and packed) and gamma (two parallel sheets are separated by a single
antiparallel sheet) conformations (Fig. 2). Shrimp and crab contain α-chitin, which
is more difficult to extract as compared with β-chitin in squid and cuttlefish.
Chitosan from β-chitin is more hydrophilic and has a more open form. Crustacean
chitosan in situ has a molecular weight of over 2 MDa. Fungal chitosan has a
molecular weight in the range of 30–60 kDa. The fungal material has the advantage
of not containing shrimp protein, which may cause an allergic reaction in 2% of the
population. The principal derivative of chitin is chitosan, produced by alkaline
deacetylation of chitin. Chitosan is a polymer of β-(1–4)-2-amino-2-deoxy-Dglucopyranose [4].
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
273