ABSTRACT
Polymer and Its Applications ........................................................................... 64
3.5 Perspectives for the Use of Chitosan and Its Derivatives for Oral Administration........ 65
References ........................................................................................................................... 66
Chitin is a natural polysaccharide, which is widely and abundantly distributed among living
organisms on the Earth. In particular, it is found in the exoskeleton of crustaceans, insects,
and some fungi. Chitosan is a product of the alkaline hydrolysis of chitin, and a copolymer of
N-acetyl-D-glucosamine and D-glucosamine. Generally, chitosan is 70%–100% deacetylated.
It is soluble in acidic aqueous solutions, but insoluble in neutral and alkaline aqueous
solutions [1,2]. These properties are due to the cationization of its amino groups, that is,
the D-glucosamine residues exhibit a pKa value of 6-7 [3]. Chitosan randomly deacetylated by
50%–60%, dissociated from rigid intra-or intermolecular hydrogen bonding, is soluble even
in neutral and weakly alkaline aqueous solutions, and is known as water-soluble chitosan
[4,5]. However, water-soluble chitosan is seldom used. Therefore, chitosan with 70%–100%
deacetylation and a molecular weight (MW) of 10,000-1,000,000 is described in this chapter.
