Three-dimensional Ptychography for Crystal Coherence analysis in calcareous Biominerals – 3D-PtyCCoBio

3D-PtyCCoBio is a 4-year fundamental project, aiming at exploring the calcareous crystalline structures produced by living organisms. While these calcareous crystals present a wide variety of shapes at the macroscopic and microscopic scales, associated to various organic materials, the most recent observations evidence a nanoscale structure which is common to all crystallizing organisms, underlying a generic biomineralization process. In addition, biomineral nanostructures seemingly exhibit extended crystalline coherence in spite of organic material occluded within the crystal. Providing a nanoscale description of the crystalline lattice (morphology, coherence) is a keystep in understanding calcareous biocrystal formation, which none of the existing nano-characterization tools is able to achieve. We propose to reveal the 3D structure of selected biominerals, using an innovative characterization tool developed in the framework of this project: the x-ray Bragg Ptychography. Ptychography is a lens-less coherent microscopy method, recently demonstrated with x-rays for the imaging of amorphous systems. Instead of lenses, iterative algorithms are used to retrieve the complex-value of the scattered wavefield from intensity (only) measurements. We want to further develop this microscopy method to the Bragg geometry case, in order to probe the crystalline part of the biominerals. In addition to the 3D image of the crystalline structure with a nanoscale resolution and micrometer large field of view, the method is expected to be sensitive to the phase relation within the crystal, giving thereby the possibility to evidence the expected crystal coherence. In parallel, in vitro precipitation experiments will be performed so as to provide comparative biomimetic samples for ptychography and to define a truly biomimetic system. Kinetics studies of the production of these synthetic biocrystals will constitute a major input to the biomineralization model.
Our strategy consists in first demonstrating the Bragg ptychography method with visible light on home-designed optical set-up and model samples before applying x-ray Bragg ptychography on native and biomimetic crystals using coherent x-rays at third generation synchrotron facilities. In addition to its strong impact for the biomaterial community, 3D-PtyCCoBio will contribute to the development of a new nano-characterization tool highly desirable to address major materials nanoscience issues.
3D-PtyCCoBio is based on a partnership composed of 9 well-established researchers and one engineer, and gathers three complementary expertises: optics, biology and materials nanoscience. The Institut Fresnel team (Partner #1) is an expert in the field of digital microscopy methods both with x-rays and visible light. The IDES team (Partner #2) is highly experienced in the microstructural analysis and morphogenesis of biominerals. The LIONS team (Partner #3) is an expert in the field of biomimetic models and x-ray measurements.