Chitin is a naturally occurring linear polymer composed of repeating β(1,4)-N-acetylglucosamine units (Figure 18). It’s a natural polysaccharide biopolymer created by organisms and exists in the shells of arthropods such as shrimps, crabs, insect exoskeletons, in cell walls of fungi and bacteria, and in certain hard structures in invertebrates and fish.  Its second only to cellulose, as the most plentiful biopolymer in the world.   This extremely versatile molecule can form solid structures on its own as in insect wings, or can combine with other components like calcium carbonate to make even stronger substances like the shell of a clam.

Why is chitin such a strong molecule?

Chitin is a rigid and crystalline polymer, contributing to its strength and  The molecular weight of chitin can be as high as 10⁶ Da.  Chitin, like cellulose and keratin, is a structural polymer and is made from smaller monomers, or monosaccharides which are structural polymers that form strong fibers. When secreted inside or outside of cells, the fibers form strong bonds between each other which adds strength to the entire structure. These glycosidic bonds hold the monosaccharides together making it hard to break.  In addition, the interactions between the nitrogen side-chains increases its stability. Both of these factors increase the strength of chitin as a molecule.  Glycosidic bonds in many polysaccharides are hard to break and require special enzymes to break.