Chitin Nanocrystals from Various Biological Sources and Their Chiral Nematic Suspensions in Water

Similar to cellulose nanocrystals (CNCs), rod-shaped chitin nanocrystals (ChNCs) form liquid-crystalline cholesteric (chiral nematic) suspensions in water. In this paper, we report how the biological source from which the ChNCs were obtained influences the properties of their liquid-crystalline suspensions, specifically their phase separation diagram and helical pitch. We isolated ChNCs under the same acid hydrolysis conditions from chitin of various biological sources, i.e., snow crab, shrimp, Antarctic krill, squid, black soldier fly pupae, and oyster mushroom, and investigated their geometrical dimensions and surface charges as well as their liquid-crystalline suspension. Our key result is that the biological source has indeed a major impact on the length and the aspect ratio of the ChNCs, which in turn significantly influences the stability range and the helical pitch of their chiral-nematic aqueous suspensions. Remarkably, a much smaller helical pitch was observed for ChNCs derived from oyster mushroom. Overall, it has become clear that the biological origin of ChNCs indeed matters for their properties and their potential applications.