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From Active Nematics on Tori to Fire Ants in the Rheometer
We will discuss recent results with different types of active materials. We will begin by looking at active nematics on toroidal surfaces. We will illustrate defect unbinding and defect-curvature coupling, consistent with theoretical expectations for inactive ordered materials arranged on the surface a torus. In our experiments, however, the number of defects is far larger than what one would expect for inactive nematics. We will then change gears and discuss the viscoelastic properties of fire ant aggregations, emphasizing the role of effective packing fraction and activity. Here, also, we find that the data seems consistent with expectations from linear response theory, which applies to inactive matter close to equilibrium. Note, by contrast, that fire ant aggregations are inherently far from equilibrium. To end, we will present preliminary data on how the toroidal geometry affects epithelial cell behavior. We will discuss how we make toroidal hydrogels, how they swell and how cells proliferate when placed on top of them.