Chitosan

Chitosan is a cationic polysaccharide produced by the partial deacetylation of chitin, the structural polymer found in crustacean shells and fungal cell walls. Along its backbone it carries free amino groups that become protonated at mildly acidic pH, giving the molecule a net positive charge. This cationic character, combined with its biocompatibility, biodegradability, mucoadhesive behavior, and film- and gel-forming capacity, makes chitosan a widely used biomaterial rather than a conventional small-molecule drug. Its degree of deacetylation and molecular weight are the principal parameters that tune its solubility, mechanical strength, and biological activity.

In biomedical research chitosan functions mainly as a functional platform or matrix that is blended, crosslinked, or chemically modified to build wound dressings, hemostatic powders, antimicrobial coatings, and tissue-engineering scaffolds. Its protonated amino groups let it associate electrostatically with negatively charged microbial surfaces, which underlies its intrinsic antibacterial and anti-biofilm activity against organisms such as Staphylococcus aureus, and with anionic polymers such as oxidized sodium alginate to form double-network hydrogels with improved mechanical and sustained-release properties. The same reactive amines allow functionalization with metal ions and complexes, including copper(2+), and conjugation with bioactive moieties such as retinoic acid, enabling multifunctional systems that pair antimicrobial protection with hemostasis, remineralization, or antitumor activity. Chitosan is also combined with proteins like collagen and gelatin and used as a fat replacer or edible film in food applications, reflecting the breadth of roles that follow from its shared polysaccharide chemistry.