Geometry and Dynamics of Living Films: from Active Nematics to Morphogenesis of Algal blades

Many living systems—such as epithelial cells and bacterial films at the microscale—exist within thin fluid layers. Theories of active nematics have been successful in describing the instabilities that arise in these systems when confined either to two-dimensional space or to a fully three-dimensional environment.

In the first part of the talk, I construct a theoretical frame work that describes the orientation field, thickness, and shape of an active nematic film embedded in 3 dimensions. I show how introducing a finite thickness modifies the well-known active nematic instabilities and leads to new ones associated with centreline deformations and thickness variations, in both flat and curved geometries. In the second part, I apply these theories—adapted to isotropic thin layers—to describe the growth and shape of the giant unicellular organism Caulerpa.