Title: "Self-organization: from active matter to the nervous system"
Abstract:
Large-scale order in materials emerges from local interactions among their constituent components. When the components are passive, they self-assemble into equilibrium structures that are well described by minimizing the free energy. When the components consume energy, detailed balance is broken: the material self-organizes out of equilibrium, and its final structure becomes far more difficult to predict. My work builds experimental systems in which the components can be controlled and the resulting organization measured, so that the two can be connected through theory.
I will first describe three model systems I built during my PhD, which progress from passive self-assembly to active self-organization. Rod-like viruses assemble into fluid membranes whose assembly and disassembly pathways can be observed directly. Adding molecular motors to microtubules creates a three-dimensional active nematic, in which we visualized defect loops forming, streaming through the sample, and annihilating, providing the first experimental test of theory for these materials in three dimensions. Finally, combining this active fluid with liquid–liquid phase separation produces a two-phase fluid with one active phase: droplets split themselves in two, the active phase climbs the walls of its container, and fluctuations of the interface between the phases enabled the direct measurement of active stress.
I will then turn to the most complex self-organizing system: the nervous system. Here too, components organize themselves into large-scale structure. In this case, the components are neurons, and the structure is a set of circuits that produce behavior. Bringing the same approach to the cnidarian Hydra, whose nerve net reassembles from dissociated cells, makes it possible to record every neuron as circuits form and to perturb the molecules that connect them. This work builds the experimental foundation for a research program whose goal is a predictive physical theory of how nervous systems self-organize.”
