Invité direction: Tilman Grunewald, Institut Fresnel, Marseille – « Deciphering biomineralization through in vivo nanodiffraction approaches »

Résumé

Biomineralization is a widely employed strategy to create gossamer yet hard tissues across the whole animal kingdom. In the marine environment, mostly calcium carbonate polymorphs are found. The current understanding of the mineralization process suggests a series of physical and chemical processes that drive ion uptake and crystal formation. 

The role of amorphous calcium carbonate (ACC) as a precursor substance to store ionic concentrates and organic precursors has been highlighted and enabled us to gain further insights into the formation mechanism [1] and the structure of the ACC compounds [2].

While these experiments have significantly advanced our understanding of the biomineralization process, they failed to unravel dynamics of the process, as they relied on post-mortem, static ‘snapshots’ and failed to address the question of the constantly evolving chemistry, involving potentially transient states. 

In vivo approaches are a powerful way to provide spatial, temporal and quantitative information to resolve these questions. In this contribution, we will outline an experimental approach that allows to study the crystallization process in the shell of the pacific oyster Crassostrea gigas with in vivo x-ray nanodiffraction at ID13. By harnessing the power of 4^th generation synchrotron sources, a temporal follow-up with sub-micrometric spatial resolution and quantitative sensitivity to crystalline parameters was achieved. We will focus on the challenges faced during the development of the experiment as well as the process of treating the data and extracting quantitative information on the growth process. 

Our experiments unveil that persistent changes in the strain, the crystallite size and the alignment of crystallites happen as a post-crystallization process. Remarkably, the crystallization process occurs without the presence of the mantle tissue, indicating that the whole process is occurring with minimal direct interference of the animal [3]. These experiments open the door to study a wide host of dynamic processes in vivo and enable us to access a hitherto inaccessible time scale and growth regime. 

References

[1] – J. Duboisset et al., Acta Biomaterialia 142, 194-207 (2022).

[2] – T.A. Grünewald et al., PNAS 119, e2212616119 (2022).

[3] – T.A. Grünewald et al., in revision