Laboratoire de Physique Théorique
Toulouse - UMR 5152

In recent years a great deal of attention has been put on the modelling and understanding of epithelial monolayers freely expanding, as a model system to study morphogenesis, tissue repairing or cancer invasion. These cellular systems show a rich repertoire of dynamic behaviours. In particular, some puzzling observations have revealed the existence of elastic waves at time scales of several hours where one would expect a fluid-like behaviour. In this talk, I will show that these observations can be conciliated through a minimal model of a thin active gel by introducing two sources of activity : traction forces with the environment and intercellular contractile stresses. I will show that the physical model harbours a new periodic oscillatory instability controlled by the acto-myosin machinery. The phase of the stress-strain rate oscillations is not universal, unlike Newtonian fluids, but depends on the material properties of the tissue. I will show that the elastic-like behaviour observed in experiments is an effect due to the intrinsic activity of the system. Near this instability, the system admits a reduced description in the terms of the Complex Ginzburg-Landau equation for which we have derived analytically the mapping with the material parameters, providing a complete characterisation of the dynamical states near criticality, ranging from coherent nonlinear waves to turbulent states. Last, I will apply these results to discuss other observations of these cellular system such as the two modes of expansion of epithelial monolayers depending on the confinement’s width within the context of our theoretical framework.