糖心TV

Monolayers of cells in tissue and bacterial colonies growing on substrates are ample examples of materials that are continuously driven out of equilibrium by the activity of their constituent elements. One generic property of these active materials is the spontaneous emergence of collective flows which often leads to chaotic flow patterns characterised by swirls, jets, and topological defects in their orientation field [1,2,3]. In this talk I will discuss recent works on cell monolayers and growing bacterial colonies, where we find interesting correlations between liquid crystal-like features of these active systems and their biological functionality.

I will explain our recent finding on the role of topological defects in regulating the morphology of growing cell colonies [2] and represent evidence on spontaneous formation of singularities in cellu- lar alignment in the form of nematic topological defects, as a previously unidentified cause of cell apoptosis and extrusion, suggesting that such defects govern cell fate in epithelial tissues [3]. In ad- dition, I will use theory of active liquid crystals to explain how motility of Pseudomonas aeruginosa bacteria leads to a slower invasion of bacteria colonies, which are individually faster. Moreover, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems [4]. By confining an active nematic fluid within a channel, we find a regular motion of disclinations, in conjunction with a well defined and dynamic flow structure. As pairs of moving disclinations travel through the channel, they continually exchange partners producing a dynamic ordered state, reminiscent of Ceilidh dancing [5]. I will show that this state is an intermediate state governing the transition to meso-scale turbulence in living fluids and that the transition belongs to the directed percolation universality class [6].