Chitin-protein biomaterials: Natural examples of reinforced concrete

<h2>Summary</h2> Chitin, the second most abundant polysaccharide in nature, often associates with structural proteins (SPs) to form chitin-SP composite biomaterials—natural analogs of reinforced concrete. This review highlights their occurrence in squid beaks, crustacean shells, and insect cuticles. Advances in genomics and proteomics now enable the identification and functional characterization of the specific SPs embedded within these composites. The review synthesizes the current understanding of the molecular mechanisms of composite formation and clarifies how SPs govern microstructure and mechanical performance. These insights not only deepen our understanding of natural biomaterials but also inform the design of biomimetic materials that emulate these intricate biological processes.