Seminar by Amin Doostmohammadi – University of Copenhagen

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Seminar by Amin Doostmohammadi

From Dancing Topological Defects to Active Turbulence in Biological Matter

The spontaneous emergence of collective flows is a generic property of active fluids and often leads to chaotic flow patterns characterised by swirls, jets, and topological disclinations in their orientation field. I will discuss our recent finding on the role of topological defects in regulating the morphology of growing cell colonies. I will present evidence on spontaneous formation of singularities in cellular 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. 

Moreover, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems. 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. 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. Finally, I will discuss means of exploiting meso-scale turbulence to produce useful mechanical power in microfluidic applications.