Chitosans

Chitosans are a family of polysaccharides obtained by partial deacetylation of chitin, a structural polymer found in the exoskeletons of crustaceans and in some fungi. They consist of randomly distributed units of β-(1→4)-linked D-glucosamine and N-acetyl-D-glucosamine. In acidic conditions, the amine groups are protonated, giving chitosans a positive charge. This cationic character underpins many of their properties and applications.

Chitosan is produced commercially by treating chitin with strong alkali, removing acetyl groups to varying extents. The degree of deacetylation (DDA) and the molecular weight influence water solubility, charge density, viscosity, films, gels, and biodegradability. In neutral to basic water, most chitosans are insoluble; they dissolve in dilute acids where amino groups are protonated.

Applications span water treatment, agriculture, food, and biomedicine. In water treatment, chitosan acts as a flocculant and adsorbent for dyes and metals. In biomedicine and wound care, it is used for drug delivery, wound dressings, and tissue engineering due to biocompatibility and mucoadhesivity. In food and cosmetics, it serves as a thickener, film-former, and preservative. Derivatives such as carboxymethyl chitosan and N-alkyl chitosans extend solubility and functionality. Chito-oligosaccharides, shorter chains, have different biological activities and solubility.

Safety and regulation vary by country; chitosan is generally regarded as biocompatible, but allergen concerns exist for shellfish sources. Quality and characteristics depend on the source and processing conditions, which can lead to batch-to-batch variability.