Ibec Seminar. Silke Henkes
Mechanochemical feedback in model epithelial tissues
Silke Henkes, Leiden Institute of Physics, Leiden University
In the development of animals, tissues self-organise starting from a single cell into layers, shapes and patterns. This active mechanical process operates beyond the theoretical framework of reaction-diffusion equations such as Turing patterns. At the same time, combining active driving with careful mechanical design of a system is distinct route to pattern formation and artificial functionality.
Here I will show how two types of active driving interacts with mechanics: First, for polar active materials where cells crawl on a substrate, even with only uncorrelated activity, elasticity leads to
the emergence of mesoscopic space-time correlations. I will show how this explains the ‘fingering instability’ at the edge of MDCK epithelial cell sheets as long lived active correlations. If we add alignment to generate a flocking state, and cell division and death, we model corneal epithelial cells well. We are then able to simulate the whole curved corneal epithelium, and show that an inflow of cells from the limbus generates a stable spiral flow pattern with a +1 topological defect at the centre.
Second, mechanochemical stress feedback in cell-cell junctions arises from the catch bond dynamics of the actomyosin cortex. It allows a junction to generate a contractile force that can overcome external pulling and thus allow for an active rearrangement or T1. In vertex and continuum models, for strong enough feedback this gives rise to convergence-extension flows where the flow is opposite the direction of mechanical polarisation, effectively generating a negative viscosity state.
