Our activities in this field deal with the modeling of natural biocomposites like nacre which are formed by the crystallization of calcium carbonate assisted by an organic matrix made of proteins and polysaccharides. A starting point is the understanding of how an organic monolayer is able to induce such a crystallisation and what are the main relevant parameters to master (see our review paper in the Bulletin de la Société Française de Physique, 2006). A way of tackling this difficult problem is to start with model peptides able, like their natural counterparts in nacre, to self-assemble in ß-sheets at an air-water interface. These peptides present a great deal of similarity with amyloid peptides, those molecules which may fold anomalously in the body, causing serious pathologies like Alzheimer's or Parkinson's. We chose such a peptide and studied in detail how it self-assemble at an air-water interface where it does not form fibers like in  bulk, but self-assemble under the form of 2D crystalline structures (Crystalline Amyloid Structures at Interfaces by Lepere M, Chevallard C, Brezesinski G, et al., ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   Volume: 48   Issue: 27   Pages: 5005-5009  (2009) 10.1002/anie.200900922 ). Crystal growth under such a 2D peptidic assembly was studied in Chevalier, N. R.; Chevallard, C.; Goldmann, M.; Brezesinski, G. & Guenoun, P. (2012), 'CaCO3 Mineralization under beta-Sheet Forming Peptide Monolayers', CRYSTAL GROWTH & DESIGN 12(5), 2299-2305. and showed that epitaxy was not enough to orientate crystals.

In fact soluble proteins, usually bearing charges, are believed to drive the crystal growth by forming nanometric glassy precursors. This situation can be also found at a larger spatial scale by adding polyelectrolyte like poly(acrylic acid) to the supersaturated calcium  carbonate bath. One then shows that the crystalline growth starts by a first stage where a glassy film forms at hte air -water interface. From this film, crystal islands grow subsequently (Crystalline Calcium Carbonate Thin Film Formation through Interfacial Growth and Crystallization of Amorphous Microdomains, Pecher J, Guenoun P, Chevallard C, CRYSTAL GROWTH & DESIGN   Volume: 9   Issue: 3   Pages: 1306-1311, MAR 2009 0.1021/cg800251t). Soluble extracts from the true nacre of Pinctada  were shown to be also quite efficient to drive the crystal growth to non-classical pathways and eventually form oriented nanodomains that resemble the ones which compose Nacre tablets (Tseng, Y.-H.; Chevallard, C.; Dauphin, Y. & Guenoun, P., CaCO3 nanostructured crystals induced by nacreous organic extracts CRYSTENGCOMM, {2014}, {16}, {561-569}. An on-going approach is to image at the nanoscale how nanodomains are oriented by cohenrent imaging techniques on synchrotron (ANR project Ptyccobio with I. Fresnel (Marseille), V. Chamard coordinator).

 Another important aspect of biomineralization is the confinement of reactants in organic cavities which become the organic scaffold of nacre. These cavities can be mimicked by polymersomes, polymeric vesicles, whose chemical nature can be tailored at will. Growth in these vesicles can be induced by  inducing permeability of the vesicless walls to reactants like ions. This was the subject of a collaborative program supported by ANR Pnano between our lab, LCPO in Bordeaux and IDES at Orsay. (Nuss, H.; Chevallard, C.; Guenoun, P. & Malloggi, F. (2012), 'Microfluidic trap-and-release system for lab-on-a-chip-based studies on giant vesicles', LAB ON A CHIP 12(24), 5257-5261.)