Abstract

How can a collection of motile cells, each generating contractile nematic stresses in isolation, become an extensile nematic at the tissue level? Understanding this seemingly contradictory experimental observation, which occurs irrespective of whether the tissue is in the liquid or solid states, is not only crucial to our understanding of diverse biological processes, but is also of fundamental interest to soft matter and many-body physics. In this talk, I will discuss how to resolve this cellular to tissue level disconnect in the small fluctuation regime by using analytical theories based on hydrodynamic descriptions of confluent tissues, in both liquid and solid states. Specifically, I will provide analytical and numerical evidence that  a collection of microscopic constituents with no inherently nematic extensile forces can exhibit active extensile nematic behaviour when subject to polar fluctuating forces.