Chitosan is a linear polysaccharide composed of randomly distributed
ß-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine
(acetylated unit). Chitosan is produced commercially by deacetylation of chitin,
which is the structural element in the exoskeleton of crustaceans (crabs, shrimps etc.).
The degree of deacetylation (%DA) can be determined by NMR spectroscopy,
and the %DA in commercial chitosans is in the range 60-100 %. The amino
group in chitosan has a pKa value of ~6.5, thus, chitosan is positively
charged and soluble in acidic to neutral solution with a charge density
dependent on pH and the %DA-value. In other words, chitosan is bioadhesive
and readily binds to negatively charged surfaces such as mucosal membranes.
Chitosan enhance the transport of polar drugs across epithelial surfaces,
and is biocompatible and biodegradable. Purified qualities of chitosans are
available for biomedical applications.
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