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Schmahl, Wolfgang W.; Griesshaber, Erika; Kelm, Klemens; Goetz, Andreas J.; Jordan, Guntram; Ball, Alexander; Xu, Dayin; Merkel, Casjen; Brand, Uwe (2012): Hierarchical structure of marine shell biomaterials: biomechanical functionalization of calcite by brachiopods. In: Zeitschrift fur Kristallographie, Vol. 227, No. 11: pp. 793-804
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Biologic structural materials for skeletons or teeth show a hierarchicalarchitecture, where organic macromolecules and mineral substance form ahybrid composite material with its components inter-weaved on manylength scales. On the nanostructure level brachiopods form hybridcomposite mesocrystals of calcite with occluded organic molecules. Onthe microstructure level several types of materials are produced, onwhich the electron back-scatter diffraction (EBSD) technique givesinsight in texture and architecture. We describe the calcitesingle-crystal fiber composite architecture of the secondary layerinvolving organic matrix membranes, the competitive-growth texture ofthe columnar layer and the nanostructuring of the primary layer. In theoverall skeleton the organic biopolymers provide flexibility and tensilestrength while the mineral provides a high elastic modulus, compressivestrength, hardness and resistance to abrasion. The hierarchicalcomposite architecture, from the nanostructure to the macroscopic levelprovides fracture toughness. The morphogenesis of the biomaterial as awhole and of the mineral crystals is guided by the organic matrix andmost probably involves amorphous calcium carbonate (ACC) precursors. Inthis paper we review the hierarchical architecture of rhynchonelliformbrachiopod shells, which is very distinct from mollusk nacre.