Unraveling the internal microstructure of biogenic and bioinspired calcite single crystals

Modern materials design is largely based on composite structures aimed at a synergistic integration of multiple components with a diverse range of properties. Biologically grown minerals provide an intriguing example of sophisticated organic–inorganic nanocomposite structures resulting in excellent mechanical characteristics. Among the mineral phases utilized by living organisms to generate hard tissues, calcium carbonate—especially the calcite polymorph—is ubiquitous and has been studied intensively. Biogenic calcite crystals often show hierarchical organization spanning multiple length scales, and the occluded organic phases are now known to be intimately associated with the mineral host. Here, we discuss the internal micro- and nanostructure of two selected types of calcite biominerals—the sea urchin spine and prismatic single crystals extracted from mollusk shells. This article highlights recent advances in translating the key principles of biological mineralization into design strategies for synthetic materials and presents analogies between biogenic and synthetic calcite single crystals.