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Dynamic steady states and non-equilibrium phase transitions in active biological matter Schmidt, Christoph


Biological functions rely on ordered structures and intricately controlled collective dynamics. Such order in living systems is typically established and sustained by continuous dissipation of energy, largely through mechano-enzymes. The emergence of ordered patterns of motion is unique to non-equilibrium systems and is a manifestation of dynamic steady states. Many cellular processes, such as cell locomotion or division, also require transitions between different steady states. We found that model acto-myosin cortices, created in water-in-oil emulsion droplets using Xenopus egg extract, self-organize into three non-equilibrium steady states as a function of network cross-linking by -actinin. The different states arise from a subtle interaction between mechanical percolation of the actin network and myosin-generated stresses. All states show distinct dynamic order. Marginally percolated state display strong velocity fluctuations with long spatial correlations. High connectivity causes structural phase separation. We tracked flow patterns in the model acto-myosin cortices with IR-fluorescent single-walled carbon nanotubes.

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