Squid beak inspired water processable chitosan composites with tunable mechanical properties

Natural biological composites often couple light weight with tunable and spatially controlled mechanical properties including stiffness, toughness, and hardness. Examples include the toughness of seashells, the hardness of the chiton tooth, and the stiffness gradient of the squid beak. While seashells and the chiton tooth have a mineralized inorganic component, the squid beak is entirely organic. The squid beak is known as one of the hardest fully organic materials. The hydrated squid beak has a large stiffness gradient from soft, at the interface with the squid mouth, to hard at the tip. This gradient occurs from the spatially controlled cross-linking of chitin nanofibers with a protein matrix aided by catecholamines. Here, we introduce a water processable deacetylated chitin composite with tunable mechanical properties from spatially controlled cross-linking assisted by catecholamines. Given the natural abundance of chitin and the ease of water processing, this composite can find applications for bridging mechanically mismatched materials.