Insight into divergent chemical modifications of chitosan biopolymer: Review.

Chitosan is used in many applications due to its biodegradability, biocompatibility, nontoxicity, nonadhesiveness, and film-forming capabilities. Chitosan has antibacterial and antifungal activities, which are two of its other desirable attributes. However, chitosan can only dissolve in acidic liquids (1-3 % acetic acid), limiting its practical application. The hydroxyl and amino functional groups in the chitosan backbone are essential for chemical modification, which is a viable alternative for overcoming this obstacle. So, N- or O-, and N, O-substituted chitosan may yield derivatives with increased water solubility, biocompatibility, biodegradability, and bio-evaluation. In the same manner, the physicochemical properties of chitosan, including its mechanical and thermal properties, can be improved by cross-linking reactions. This review provides an overview of chitosan, including its origins and their solubility. Also, the review extend and discuss in details most of all chemical reactions that happened on the amino group, hydroxyl group, or both amino group and hydroxyl group to create modified chitosan-based organic materials. Finally, the problems that still need to be solved and probable future areas for study are discussed.