Chitosan is a high molecular weight polymer derived from the natural product chitin which is found in the shells of shrimp, crabs and other animals. It is a linear polysaccharide composed of randomly distributed ß-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitin is a biodegradable polysaccharide that is similar to cellulose. Like cellulose, chitin and its derivative chitosan are fibrous materials. Chitosan is made from chitin by removing acetyl groups (CH3-CO) with diluted acids or strong bases. By controlling the number of acetyl groups removed along the polymer chain (or by adding new groups to sites that once had an acetyl group), chemists can tune the properties of chitosan to make it more versatile. The amount of free amino groups is measured as the degree of deacetylation.