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Multifunctional Layered Magnetite Composites

 

Prof. Dr. Helmut Cölfen, Universität Konstanz, Fachbereich Chemie AG Physikalische Chemie , Universitätsstraße 10 78464 Konstanz

Dr. Damien Faivre, Max-Planck-Institut für Kolloid- und Grenzflächenforschung Wissenschaftspark Golm Abteilung Biomaterialien, Am Mühlenberg 1 14476 Potsdam

Dr. Vitaliy Pipich, Forschungszentrum Jülich GmbH; Jülich Centre for Neutron Science Außenstelle am FRM II c/o Technische Universität München, Lichtenbergstraße 1 85747 Garching

Professor Dr. Dirk Zahn, Friedrich-Alexander-Universität Erlangen-Nürnberg; Computer-Chemie-Centrum, Nägelsbachstraße 25 91052 Erlangen

 
Nature provides a variety of archetypes of highly ordered systems, of which many biomaterials are known for their remarkable mechanical properties. Nacre is one of these biominerals combining both stiffness and hardness. Its hierarchical structuring of highly organized crystal platelet layers separated by thin layers of organic material is responsible for the extraordinary fracture resistance. Another class of biominerals are magnetite incorporated chiton teeth, which are harder than any other known biomineral. Apart from that there are simple organisms, namely magnetotactic bacteria that can mineralize nano-sized magnetite particles and arrange them in chains which lead to coupling of the magnetic dipoles.
Inspired by these biogenic design concepts, we aim to develop biomimetic composite structures with the fracture resistance of nacre, the hardness and wear resistance of chiton teeth and the extraordinary magnetization of the magnetite chains in the magnetotactic bacteria all combined in one and the same material.


 
As a scaffold for the organic-inorganic hybrid material the demineralized organic chitin matrix of nacre is used. The scaffold will be filled with gelatin gel as a mimic for the natural silk hydrogel, a scheme of the synthetic concept can be seen in image A). In this gel matrix, magnetic nanoparticles will be synthesized with and without the control of nucleator peptides derived from studies of proteins responsible for magnetite synthesis in magnetotactic bacteria (see image B). The combination of a nacre-like structure including a mimic of chiton teeth can lead to a fracture resistant as well as wear resistant material with interesting magnetic properties due to the coupling of the magnetic dipoles. The materials are characterized in terms of structure and physical properties. Small-angle neutron scattering (SANS) is used for studying the individual components structure (shape and size) of hybrid materials on the length scale of 10 to 1000 Å. In particular, SANS structural characterization is employed for the elucidation of the magnetite formation mechanism via the bio inspired in-situ mineralization.
 

 
To reach a deeper understanding of the magnetite nanoparticle nucleation mechanisms theoretical studies of the magnetite-collagen and magnetite-chitin systems are performed. We aggregate single FeII/III(OH)2/3 clusters successively to collagen/chitin (C,E) to understand the role of organic proteins in building up a hierarchical composite structure. We found the Fe2+ and Fe3+ to bind via saltbridges and the Fex+(OH)x clusters to carbonyl and hydroxyl groups of the protein without distorting the organic matrix and observed the iron clusters to aggregate (D,F) on the collagen/chitin. From that we conclude that both organic matrices show to act as nucleation seeds to iron hydroxide aggregation in the precursor stage and will further intergrow with the magnetite nanoparticles at the precursor stage.