Chitosan is a biopolymer with a wide range of biomedical applications, including wound healing, tissue engineering and tissue repair, and local delivery of cells, drugs, proteins, genes, and other therapeutics. Currently, nasal delivery technology with chitosan shows great potential, with several applications in phase III clinical trials. Furthermore, non-viral gene delivery systems using chitosan as a carrier is the subject of intense research activity.
Chitosan is a linear polysaccharide composed of randomly distributed b-(1®4)-linked D-glucosamine (deacetylated unit; D) and N-acetyl-D-glucosamine (acetylated unit; A). 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 viscosity of a chitosan solution primarily depend on the average molecular weight of the polymer, which can be determined by size exclusion chromatography combined with light scattering detection.
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.
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