Construction réelle et virtuelle de modèles biologiques de paroi végétale – ANALOGS

The project proposes a simpler strategy, compared to works done directly on plant cell walls, to progress in a twofold manner : - To gain excellent skills in building cell wall analogs, - towards a multiscale modelling approach capable of prediction. By working jointly on cell wall analogs (real objects) and on multiscale modelling (virtual objects) lies the originality and novelty of the project. Note also that, even in each separate part of this pluridisciplinary approach, the projects proposes innovation regarding the leading-edge of science. The general outlines of the project are summarized as follows : A stepwise construction of plant cell wall analogs (WP1 : elaboration) and a multiscale modelling approach (WP3 : Multiscale modelling), whose aim is to connect the discrete atomistic scale to the continuum scale of films. A whole set of experimental investigation (WP2 : characterisation and measurements) is organised by tasks able to maintain a strong connection between the real and the virtual construction throughout the project. Finally, a supervision work (WP4 : Convergence of real and virtual constructions) will act as a guideline, starting the second year of the project, to maintain consistency between the 3 WP and guarantee that clear conclusions can be drawn from the project. In term of modelling, the objective of this project is to fill the remaining gap between the discrete scale of atoms to the continuous scale of the plant cell walls. Systems studied with the help of molecular dynamics remains very small compared to the complexity of the cell wall and the time scale of the predicted phenomena does not go far beyond a few nanoseconds. In such conditions, a direct scale-up from atomistic scale simulations to macroscopic scale model parameters is not possible to date. To overcome this difficulty, we propose a two steps scaling approach (atom to meso and meso to films). This goal is very challenging, hence innovative, and we think we can succeed in this task for several reasons: - by working on cell wall analogs rather than on biological objects, we are able to control some parameters and, above all, to vary certain parameter. - the project joins the skill of two teams : one goes up from the atomic scale and the other goes down, from the tissue level, - we selected computational methods adapted at each scale (molecular dynamics, coarse grain, MPM), - the proposed strategy clearly tells how the scale will be connected. Besides the understanding of cell wall properties, this project aims to face a critical challenge encounter in nanocomposite fabrication that is the ability to realize materials that allow the transfer of the exceptional mechanical properties (i.e., tensile strength, and Young's modulus) of the nanoscale materials to the macroscale properties of the bulk materials. At this time, this is clearly a very active field of research in organic-inorganic nanocomposites field; however nanocomposites based of biopolymers arising from natural and renewable resources are more seldom. Besides this point, the original way of this project for building up such structure is to consider simultaneously in a concerted manner the intricate geometric and chemical interaction between the components to optimise properties. In order to reach this goal, we will develop integrated approach that is rather a unique including several scales of length from subnanometer to tens of microns with coordinated strategy. Among the bottlenecks that will have to face, full automation of systems and development of special devices for orientation and layered organisation are the most critical. When succeed, strategies initiated in the project will also afford innovative opportunities of elaboration new process of nanocomposite fabrication.