Chitosan polymer is a linear polysaccharide composed of randomly distributed beta -(1→4)- linked D-glucosamine (deacetylated units) and n-acetyl-d-glucosamine (acetylated units). It is made by treating the chitin shells of shrimp and other crustaceans with an alkaline substance, such as sodium hydroxide.

The amino group in chitosan has a pKb value of ~6.5, which is significantly protonated in neutral solution and increases with increasing acidity (decreasing pH) and % da values. This makes chitosan water-soluble and a bioadhesive that readily binds to negatively charged surfaces such as mucous membranes. The free amine group on the chitosan chain can form a cross-linked polymer network with dicarboxylic acid, so as to improve the mechanical properties of chitosan. Chitosan enhances the transport of polar drugs on the epithelial surface, with biocompatibility and biodegradability.

Chitosan polymer has many commercial uses. It can be used in agriculture as a seed treatment and biocide to help plants fight fungal infections.