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Lecture

Structural organization and dynamic phase transformations of the ultra-hard magnetic biominerals in chiton radula teeth

Monday (19.03.2018)
14:40 - 15:00
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Nature provides many archetypes of highly ordered systems, some of these biomaterials are known for their remarkable mechanical properties. An amazing example of biomaterials is the tooth of chitons. The fully mineralized chiton teeth display remarkable functional properties such as outstanding fracture toughness, wear resistance and has the highest reported hardness among known biominerals. The excellence functional properties of the resulting mineral composites can be attributed to the buried organic-inorganic interfaces at multiple hierarchical levels and the highly mineralized inorganic content (ca. 70 wt. %). They are hardened by the inclusion of magnetite nanoparticles into a protein-polysaccharide fibrous matrix.

In the present work we have done several characterization experiments on the chiton radula teeth by using SEM, TEM, SANS and SAXS/WAXS. By such methods, nanoscale structure changing over macroscopic length scales is pivotal to understanding the function of hierarchically organized tissues and materials. They are allowed to spatially resolve and quantify the material's ultrastructure orientation in a nanoscale context. From the investigation, the micro focus SAXS/WAXS tomography reveals two-dimensional structure maps of chitin fibres in the surrounding magnetite minerals in the tooth of chiton. In a fully mineralized tooth, the magnetite nanocrystals are aligned parallel to the cusp’s surface along its contours. The arrangement and orientation of this ultrastructure impart the tooth with wear resistance and crack resistance. Further, we explore the magnetite mineralization kinetics which can be found in teeth with different mineralized states. The SAXS/WAXS results demonstrate that the dynamic phase transformations that occur during mineralization. In the different mineralized state, the metal ions and minerals probably show different functional roles in controlling fibre orientation and organic matrix–mineral interactions. We aimed to provide a novel insight establishing a direct relation between the hierarchical structure and the mineralized particles/organic matrix producing such highly and optimized sophisticated materials properties. These structural and mineralization mechanism are compared with the synthetic samples. The comparative studies of the structural features will help to optimize the materials structure for improved mechanical performance.

Speaker:
Dr. Baohu Wu
Heinz Maier-Leibnitz Zentrum
Additional Authors:
  • Christian Debus
    University of Konstanz
  • Dr. Damien Faivre
    Max Planck Institute of Colloids and Interfaces
  • Dr. Dietmar Schwahn
    Technical University of Munich
  • Prof. Dr. Dirk Zahn
    Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
  • Prof. Dr. Helmut Cölfen
    University of Konstanz
  • Dr. Vitaliy Pipich
    Forschungszentrum Jülich GmbH