  Chitin is one of the most abundant biomaterials in nature, with 10^10 tons
produced annually as hierarchically organized nanofibril fillers to reinforce
the exoskeletons of arthropods. This green and cheap biomaterial has attracted
great attention due to its potential application to reinforce biomedical
materials. Despite that, its practical use is limited since the extraction of
chitin nanofibrils requires surface modification involving harsh chemical
treatments, leading to difficulties in reproducing their natural prototypal
hierarchical structure, i.e. chiral nematic phase. Here, we develop a chemical
etching-free approach using calcium ions, called natural way, to disintegrate
the chitin nanofibrils while keeping the essential moiety for the
self-assembly, ultimately resulting in the reproduction of chitins natural
chiral structure in a polymeric matrix. This chiral chitin nanostructure
exceptionally toughens the composite. Our resultant chiral nematic phase of
chitin materials can contribute to the understanding and use of the reinforcing
strategy in nature.
