Chitin

Chitin is a long-chain polymer of N-acetylglucosamine (GlcNAc) units linked by β-1,4-glycosidic bonds. It is the second most abundant natural polymer after cellulose and forms a major structural component in the exoskeletons of arthropods (such as insects, arachnids, and crustaceans) and in the cell walls of fungi and some algae. In these organisms, chitin provides strength and rigidity and often occurs as crystalline microfibrils embedded in proteins and minerals to create composite materials.

Chitin is insoluble in water and most solvents due to extensive hydrogen bonding, which gives it high mechanical strength and chemical resistance. Its properties depend on the degree of acetylation and crystallinity. It can be deacetylated to produce chitosan, which is more soluble in acidic aqueous solutions. Enzymes such as chitinases and chitin deacetylases enable its degradation in nature and in industrial processes.

Biosynthesis occurs through chitin synthase enzymes that polymerize GlcNAc units at the growing chain, depositing chitin into the organism’s cell wall or exoskeleton. In fungi, chitin is a major cell wall component; in arthropods, it outlines the protective cuticle and internal structures.

Applications of chitin and its derivatives, especially chitosan and chitooligosaccharides, include biomedicine (wound healing, drug delivery, tissue engineering), agriculture (seed coatings, plant protection), and water treatment (adsorbents for dyes and heavy metals), as well as food processing and packaging. They are valued for biodegradability, biocompatibility, and non-toxicity, though solubility and processing can depend on the degree of deacetylation. Ongoing research seeks sustainable extraction and processing from crustacean shells and fungal sources.