Scale-free wrinkling of cell nuclei and vortex line entanglement of active suspensions
Nicolas Romeo (U. Chicago, USA)
| When |
Feb 20, 2024
from 11:00 to 12:00 |
|---|---|
| Where | Salle des thèses |
| Contact Name | Alexis Poncet |
| Attendees |
Nicolas Romeo |
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Soft and biological matter can display non-trivial forms of order and structure. We will present two examples of geometrically-complex systems that display remarkably robust self-organization, which we rationalize using statistical physics methods.
Our first example is provided by the surface wrinkling of cell nuclei, which has been implicated in disease and cellular aging. We characterize the onset and dynamics of nuclear wrinkling during egg development in the fruit fly: a spectral analysis of three-dimensional high-resolution live-imaging data from several hundred nuclei reveals a robust asymptotic power-law scaling of angular fluctuations consistent with renormalization and scaling predictions from a nonlinear elastic shell model. We further demonstrate that nuclear wrinkling can be reversed through osmotic shock and suppressed by microtubule disruption, providing tunable physical and biological control parameters for probing the mechanical properties of the nuclear envelope.
Our second example will be given by the statistics of vortex line entanglement in 3D active fluids. Over the last decade, substantial progress has been made in understanding the topology of quasi-2D non-equilibrium fluid flows driven by ATP-powered microtubules and microorganisms. By contrast, the topology of 3D active fluid flows still poses interesting open questions. Here, we study the topology of a spherically confined active flow using 3D numerical simulations of a model equation at the scale of typical microfluidic experiments. Our simulations confirm the formation of Beltrami-like bulk flows with spontaneously broken chiral symmetry, which we explicitly connect to the entanglement statistics of vortex lines. Those statistics agree with theoretical predictions from Arnold and a generic entropic argument for chiral random walks. Beyond active suspensions, the tools for the topological characterization of 3D vector fields developed here are applicable to any solenoidal field.