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1.3. CHITIN AND CHITOSANS
1.3.1. General
Annually (2012) more than 3000 research
articles and a corresponding number of patent
applications are being published in the chitosan field. Chitosans are in
practice the only naturally occurring (and hence, biodegradable) cationic
biopolymer (carrying positive charges) near pH 7, which are produced
commercially.
Because of their cationic properties chitosans interact with almost all kinds of
surfaces, particles, cells and macromolecules that are negatively charged.
This is the basis for a wide variety of applications, including for example drug
and gene delivery, mucoadhesion, flocculation etc. Chitosans are in some
cases antimicrobial, although the basis is not fully understood. In drug/gene
delivery chitosans may be preferred over synthetic polycations due to their
low cytotoxicity.
1.3.2. Chitin
Chitosans are formed directly from chitin, the structural polymer found in the
exoskeleton of crustaceans and insects. Crab and shrimp shells are the major
sources for commercial production (and solves also a waste problem in the
shrimp industries):
Chitin is a homopolymer of 4-linked N-acetyl-
β
-D-glucosamine (Abbreviated
GlcNAc = A):
O
CH
2
OH
OH
HN
O
O
CH
2
OH
OH
NH
O
O
CH
2
OH
OH
NH
O
O
CH
2
OH
OH
NH
O
O
O
O
O
CH
3
CH
3
CH
3
CH
3
Figure 29. Chitin structure (Haworth)