Abstract

In soft active matter, such as crawling and swimming cells, or active colloids and polymers, active driving interacts with the mechanical properties of the material to form active solids, liquids and everything in between.Here I will present how a generic mesoscopic correlation length emerges from the coupling of uncorrelated but persistent self-propulsion to the elasticity of the underlying material in overdamped dynamics. It can be applied it to an intriguing system of travelling strings made of active colloids, where it explains string propulsion and emergent tangent-tangent corrleations seen in simulation and experiment.Within this framework, we can model epithelial cell sheets with active Brownian dynamics and soft repulsive interactions, and also as a self-propelled Voronoi model. Then uncoordinated cell crawling interacting with mechanics produces characteristic ’swirly’ motion with strong spatiotemporal correlations. We are able to quantitatively match simulations and in-vitro cell sheets made of corneal epithelial cells and MDCK cells. We can also show that these emergent correlations are a good model for the fingering instability at the edge of these sheets. I will conclude with recent results that consider uncorrelated activity that takes the form of internal stresses in the system, which are a frequent feature in morphogenesis.