Nacre is an interesting example for natural organic-inorganic hybrid materials. It consists of layered aragonite tablets providing strength, surrounded by a chitin/protein matrix, adding elasticity to the material. This hybrid structure makes nacre 3000 times more fracture resistant than aragonite itself, which makes up approx. 95 % of this structure. Another astonishing biomaterial is the chiton tooth. The tooth’s shell is formed by magnetite nanoparticles embedded into a protein/polysaccharide gel matrix, showing very high abrasion resistance and the highest hardness and stiffness among the known biominerals, being for example three times harder than human tooth enamel. 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.
To combine the advantageous properties of these biominerals, we established a synthesis method to infiltrate a demineralized nacre chitin scaffold with gelatin and consecutively mineralize the gelatin hydrogel with magnetite nanoparticles of adjustable size. This hybrid material exhibits the layered “brick-mortar” structure seen in nacre, showing anisotropic mechanical and magnetic properties. To further improve the mechanical properties of the materials we add a filler mineral to increase the inorganics content. Ordering of the magnetic particles can also be shown to increase hardness and stiffness. To allow upscaling of our approach, we are investigating a substitute for the natural chitin scaffold by freeze-casting of chitosan.
The work shown here is part of the SPP1569 project “Multifunctional layered magnetic composites” and focuses on the synthesis and mechanical investigations of the project.