ABSTRACT
Chitosan is a polymer of N-acetylglucosamine and glucosamine, obtained naturally from the shells of crustaceans (Illum, 1998). It has shown pharmacological activity in wound healing, against microbes, for treatment of ulcers, and also as a cholesterol-reducing agent (Azad et al., 2004; Felt et al., 1998; Sugano et al., 1988). However, being a nontoxic and nonimmunogenic polymer, it has been widely used as a drug delivery matrix. Because it is obtained from natural sources, chitosan is a cost-effective polymer. It is also available in different molecular weights and degree of deacetylation (Illum, 1998). Chitosans have been used to prepare gels, capsule shells, solid lipid nanoparticles, nanoparticles, and microparticles for the delivery of various small therapeutic agents, peptides, vaccines, DNA, and genes (Chaudhury and Das, 2011; Illum, 1998). However, the solubility prole of chitosan has raised concern for oral peptide delivery. This is because chitosan is easily soluble in dilute acidic conditions while it is insoluble in neutral pH, water, and organic solvents (George and Abraham, 2006). As a result, oral drug delivery systems (DDS) made of chitosan were incapable of protecting protein and peptide drugs. This problem was solved by the derivatization of chitosan molecule by reacting with different functional groups or with other polymers or peptides. These newly formed chitosan derivatives showed superior stability in acidic pH conditions and could slowly release drugs in neutral or intestinal pH. Such modications paved a new way for the delivery of macromolecules through the oral route. Among them, insulin delivery has been the most attempted and researched topic among scientists.
