Abstract
We develop a minimal model to describe growing dense active matter such as biological tissues, bacterial colonies and biofilms, that are driven by a competition between particle division and steric repulsion. We provide a detailed numerical analysis of collective and single particle dynamics. We show that the microscopic dynamics can be understood as the superposition of an affine radial component due to the global growth, and of a more complex non-affine component which displays features typical of driven soft glassy materials, such as aging, compressed exponential decay of time correlation functions, and a crossover from superdiffusive behaviour at short scales to subdiffusive behaviour at larger scales. This analogy emerges because particle division at the microscale leads to a global expansion which then plays a role analogous to shear flow in soft driven glasses. We conclude that growing dense active matter and sheared dense suspensions can generically be described by the same underlying physics.
Highlights
Nonequilibrium physical systems can be divided into two categories: active and externally driven matter
We develop a minimal model to describe growing dense active matter such as biological tissues, bacterial colonies, and biofilms, which are driven by a competition between particle division and steric repulsion
We argue below that this simple intuition does not account for the dynamic behavior seen in growing active matter, where the global expansion itself plays a key physical role in the fluidization of the material
Summary
Nonequilibrium physical systems can be divided into two categories: active and externally driven matter. We argue below that this simple intuition does not account for the dynamic behavior seen in growing active matter, where the global expansion itself plays a key physical role in the fluidization of the material. We shall propose an analogy with glassy materials [45], but we will provide evidence that growing active matter resembles glassy materials that are externally driven at large scale, such as sheared colloidal suspensions [10,11] To reach this conclusion, we show that the single-particle dynamics should be decomposed into two distinct components. The radial growth rate plays, the same role as the global shear rate in sheared dense suspensions [10,11] This suggests that both growing active matter and externally driven soft glassy matter are described by the same underlying physics. VI we discuss our results and offer some perspectives for future work
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