Post doc position in Mechanics of pressurized cellular solids

Mimosa Pudica moves its foliage when touched in less than a second by changing turgor pressure in pulvinus cells. Pulvinus tissue consists of flexible thin-walled parenchyma cells organised around a core of vascular pipes (xylem/phloem for water/sap transport), see fig 1. The selective change of cell turgor pressure allows, for instance, the contraction of the upper pulvinus (flacid cells) and expansion (turgid cells) of the lower one, achieving leaf motion by bending.

The research goal is to elucidate the mechanical properties of pressurized cellular solids. The research has two aims:

1. Cell level: The goal is to determine Young modulus of pressurized cellular solids from an energetic analysis of a single cell considering a periodic lattice. The macroscopic Young’s modulus will be characterized both in the linear and non linear regimes considering thinning of cellular elastic walls and strain hardening material. This research will be complemented with numerical simulations (finite elements) to obtain the prefactor of the scaling laws found analytically.
2. Tissue level: The goal is to find the macroscopic mechanical properties (Anisotropic Young modulus and Poisson coefficient) depending on the pressurisation pattern considered. The modelling will be done considering a 3D array of cells with on and off cells similar to a 3D array of springs in parallel and series. The refined modelling will consider cells with a continuum of pressures.
3. The model will be compared to (i) controlled idealized lab prototypes (50 to 200 cells). And (ii) to living plant pulvinus (Mimosa Pudica).

FUNDING : ANR MExP