The surprising properties of biominerals
An international study led by the MIT and the University of Wisconsin-Madison, in which several researchers from the MBBM and FOCUS laboratories of the University of Liège participated, reveals the misoriented structure of coral and shell crystals and its key contribution to fracture resistance. This discovery could trigger the development of new bioinspired materials with remarkable fracture toughness obtained using only one single constituent. Those findings have been published in the top-tier journal Advanced Materials.
B
iominerals are organic mineral composites formed by living organisms, such as corals and seashells. Evolution has allowed biominerals to develop fascinating structures that are among the hardest and strongest materials in nature. Understanding biominerals can provide crucial knowledge for developing man-made bioinspired materials and structures with unprecedented properties. Alexandra Tits, Astrid Cantamessa, Laura Müller and Davide Ruffoni from the MBBM lab (Aerospace and Mechanical Engineering Department / School of Engineering) as well as Yann Delaunois and Philippe Compère from the research unit FOCUS (Faculty of Sciences) at ULiège, participated in an international study conducted by the Massachusetts Institute of Technology (MIT) and by the University of Wisconsin-Madison. The researchers discovered that specific biominerals, such as coral skeletons and nacre, share a similar feature: their adjacent crystals are slightly misoriented.
This study revealed that the adjacent crystals in biominerals showed a slight difference in orientation," explains Prof Davide Ruffoni, director of the MBBM laboratory at ULiège, "and we performed a multiscale analysis of the mechanical consequences of crystal misorientation in several species of biominerals. To do this, the researchers combined several methods. Polarisation-dependent contrast imaging (PIC) mapping, which was first performed at the University of Wisconsin-Madison, revealed and quantified crystal misorientation at the nanoscale. Then, nanoscale mechanical characterisation experiments were carried out at the University of Liège to assess the increase in fracture toughness provided by crystal misorientation. "More specifically, the fracture behaviour of the samples was evaluated using nanoindentation, a technique that allows the accurate measurement of force required to induce small cracks, in combination with electron microscopy, which was used to visualise and characterise the cracks," continues Davide Ruffoni. These techniques were then combined with atomic-scale molecular dynamics simulations carried out at MIT to simulate the fracture behaviour at the atomi-length scale. This multimodal and interdisciplinary analysis has shown that slight misorientation-toughening is a universal strategy for building materials with exceptional fracture resistance using only one component, which may also be intrinsically brittle.
“Our discovery can be exploited for the synthesis of new bioinspired materials that require only one component, and that are not limited to specific architectures. These new materials could be fabricated by automatic assembly of organic molecules, polymers, metals or ceramics, well beyond biominerals," says Davide Ruffoni. "This is a new route to design and fabricate next-generation materials breaking the paradigm of engineering composites. Indeed, classical composite materials traditionally combine two dissimilar constituents (e.g. ceramics and polymers) and therefore suffer from a trade-off in the resulting properties. In the future, such high-performance bioinspired materials can be used in several different areas as diverse as aerospace, optics, robotics, catalysis and tissue engineering," he concludes.
Scientific reference
Andrew J. Lew, Cayla A. Stifler, Alexandra Tits, Connor A. Schmidt, Andreas Scholl, Astrid Cantamessa, Laura Müller, Yann Delaunois, Philippe Compère, Davide Ruffoni, Markus J. Buehler, Pupa U. P. A. Gilbert, A Molecular Scale Understanding of Misorientation Toughening in Corals and Seashells, Advanced Materials, 02 March 2023.
Article available in open access: https://doi.org/10.1002/adma.202300373
