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The latter finding further strengthened the notion that spinodal decomposition is independent of the biological characteristics of the studied organisms, and rather originates from a similar chemical composition and specifically the Mg content, which generally ranges from 14 to 48 mol%. The fact that the nanoparticles were found within six biologically different organisms indicates that this phenomenon is widespread, and it is believed to be even more widespread in biomineralisation. The absence of the high-Mg nanoparticles in the studied organisms whose Mg content was lower than 14 mol% provided further evidence that whether or not spinodal decomposition of an amorphous Mg-calcite precursor takes place prior to crystallisation is determined by the amount of Mg it contains. A summary of all nine studied organisms is presented in Figure 122, and shows their separation into two categories based on their chemical composition and the presence of high-Mg nanoparticles within their skeletons.

The presence of high-Mg nanoparticles within the skeletons was found to serve a mechanical role, assisting the organisms in enhancing the durability of their skeletons against stresses from their natural environments. The formation of Mg-rich nanoprecipitates greatly enhances the hardness of the biomineralised tissues, as was clearly suggested by theoretical calculations. Additionally, the arrangement of the nanoparticles in a layered manner (also observed in previous studies [2,3]) was shown to greatly enhance the fracture toughness of the calcified skeletons.

Altogether, the findings on the mechanical advantages of the studied biogenic structures have great value in understanding nature s biostrategies and in the design or improvement of novel structures with superior mechanical properties.

Fig. 122: The various studied biomineralised tissues divided into two categories based on their Mg content. High-Mg nanoparticles are present only for those with an average Mg content higher than 14 mol%.

PRINCIPAL PUBLICATION AND AUTHORS

High-Mg calcite nanoparticles within a low-Mg calcite matrix: A widespread phenomenon in biomineralization, N. Bianco-Stein (a), I. Polishchuk (a), A. Lang (a), L. Portal (a), C. Dejoie (b), A. Katsman (a), B. Pokroy (a), Proc. Natl. Acad. Sci. 119(16), e21201771199 (2022); https:/doi.org/10.1073/pnas.2120177119 (a) Department of Materials Science and Engineering and the Russell Berrie Nanotechnology Institute, Technion−Israel Institute of Technology, Haifa (Israel) (b) ESRF

REFERENCES

[1] E. Seknazi et al., Nat. Commun. 10, 4559 (2019). [2] N. Bianco-Stein et al., Acta Biomater. 130, 362 (2021). [3] I. Polishchuk et al., Science 358, 1294 (2017).