Soft matter physics studies complex fluids : polymers, amphiphilic molecules, liquid crystals... This is a new and highly relevant approach for studying the physical properties of many living systems : cells, tissues, bacterial suspensions, cancer tumor growth. The molecules involved are the same, and the orders of magnitude of mechanical properties are similar. However, biological systems have two important characteristics : specific interactions and the fact that they are not in equilibrium and consume energy on a local scale. Living systems therefore fall within the scope of what is known as " active matter ".

The research activity of the Soft Matter and Biophysics Chair uses ideas from soft matter physics to provide a theoretical description of the physical properties of living systems. The general framework is that of active matter theory. The issues studied range from general properties of active matter to questions of direct relevance to biology : active turbulence, orientation defects in cell monolayers, cancer tissue growth, cell motility, cilia beating, study of the parameters that determine cell and nucleus volumes.

The aim of the lecture is to show how soft matter theory in general, and active matter theory in particular, enable a quantitative description of biological systems from cell to tissue. After a lecture devoted to the hydrodynamic theory of active matter, the 2020 and 2021 lectures discuss tissue physics both at the local cell scale (vertex models) and at the global tissue scale, at which an active hydrodynamic theory can be built that couples mechanical properties to tissue growth.