Sophisticated Nanostructure in Stone Part of Sea Urchin Tooth: Enlightenment for Artificial Composites

Sea urchin teeth, which are used to scrape rocks for food, assume significant mechanical functions. Unraveling their design strategies could provide inspiration for the pursuit of high-performance artificial composites. In this work, we used scanning electron microscopy, transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy to probe the elaborate nanostructure in the stone part of Glyptocidaris crenularis tooth. Our results show that the mesocrystalline matrix, though diffracting as a single crystal, is composed of highly oriented nanocrystals and shares almost coincident crystal orientation with its central single-crystal fiber. Interestingly, the fiber and matrix are fitted together by numerous single-crystal nanostrips rather than being completely separated by an organic sheath. This sophisticated architecture may endow the tooth with sufficient structural stability to prevent catastrophic fractures.