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Nucleation intermediate in calcareous biocrystallization

Contact: CHEVALLARD Corinne, , corinne.chevallard@cea.fr, +33 1 69 08 52 23
Summary:
The study of mineralization in living organisms, or "biomineralization", will be conducted by developing physico-chemical model systems. The experiments will focus on calcareous biocrystallization, and will test the hypothesis of a liquid-liquid phase separation in the biogenic process of crystal nucleation.
Possibility of continuation in PhD: Oui
Deadline for application:27/04/2018

Full description:
Living organisms are able to produce mineralized structures, or "hard tissues" (teeth, bones, exoskeletons, etc.), the shape and mechanical properties of which are fully adapted to the targeted biological functionality [1]. The fine understanding of the biomineralization mechanisms is actively being sought because it is a prerequisite for the development of bio-inspired pathways of synthesis allowing the development of new materials with very low energy input. Three characteristic features of calcareous biomineralization seem to emerge: (i) the precipitation of the mineral phase is always carried out under the control of organic macromolecules [1]; (ii) an amorphous mineral phase could appear transiently and would explain the observed complex morphologies [2]; (iii) all calcareous biocrystals exhibit a nanostructuring in the form of an assembly of granules, with a spheroidal shape and a characteristic size ranging from 50 to 500 nm [3].
We propose to use a physicochemical perspective to understand the generic mechanisms of biomineralization [4]. One current hypothesis is that, even before crystal nucleation, a liquid-liquid phase separation could generate a mineral-enriched liquid intermediate that would solidify and produce amorphous "granules". The subsequent assembly and crystallization of these granules would lead to the biocrystal in its final state, with a crystalline coherence extended to a few granules.
During this internship, we will test this hypothesis by implementing calcium carbonate mineralization experiments in the presence of organic macromolecules, for which a liquid-liquid phase separation is expected [5]. We will first try to specify the experimental conditions allowing the development of such a phase separation, in particular carrying out titration experiments of carbonated solutions by calcium solutions, and monitoring the calcium concentration at the same time using a suitable ion electrode. When conditions will be identified, we will synthesize crystals under these supposedly biomimetic conditions and we will collect the crystals formed for characterization using laboratory techniques (optical microscopies, IR / Raman spectroscopies, X-ray diffraction) and comparison with the calcareous biocrystals. Here the use of a microfluidic device allowing fast and reproducible mixing of the reactive species will be considered.
This internship will take place within the framework of a European project (3D-BIOMAT, ERC consolidator grant) developed in collaboration with physicists of the Fresnel Institute (UMR 7249, Marseille) and biologists of the IFREMER laboratory of French Polynesia. The obtained results will help in formulating a physicochemical model of calcareous biocrystallization, the ultimate goal of this project.

[1] H.A. Lowenstam and S. Weiner, On Biomineralization (New York), 1989.
[2] L. Addadi, et al., Z. Kristallogr., 227: 711, 2012.
[3] Y. Dauphin, Mineral. Mag., 72: 243, 2008.
[4] Y.-H. Tseng, et al., CrystEngComm, 16: 561, 2014.
[5] L. B. Gower, D. J. Odom, J. Cryst. Growth, 210: 719, 2000.
Technics/methods used during the internship:
Chemical titrations and ion selective measurements (ion selective electrodes). Optical microscopy (birefringence), electron (SEM, TEM) and infrared / Raman spectroscopies, X-ray scattering / diffraction.

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