Activity-dependent self-regulation of viscous length scales in biological systems

Abstract

The cellular cortex, which is a highly viscous thin cytoplasmic layer just below the cell membrane, controls the cell's mechanical properties, which can be characterized by a hydrodynamic length scale ℓ. Cells actively regulate ℓ via the activity of force-generating molecules, such as myosin II. Here we develop a general theory for such systems through a coarse-grained hydrodynamic approach including activity in the static description of the system providing an experimentally accessible parameter and elucidate the detailed mechanism of how a living system can actively self-regulate its hydrodynamic length scale, controlling the rigidity of the system. Remarkably, we find that ℓ, as a function of activity, behaves universally and roughly inversely proportional to the activity of the system. Our theory rationalizes a number of experimental findings on diverse systems, and comparison of our theory with existing experimental data shows good agreement.

Enhanced short time peak in four-point dynamic susceptibility in dense active glass-forming liquids

“…[3][4][5][6][7][8] The former is a non-equilibrium system that shows spectacular dynamical properties like large-scale ordering, flocks, swarms, etc., and is one of the current hot topics of research. [9][10][11][12][13][14][15][16][17][18][19][20] Many biological systems are shown to have dynamical properties similar to glass-forming liquids in the presence of active driving. Thus studying the physics of glasses under activity can shed important information regarding the dynamical properties of biologically relevant processes.…”

“…, and is one of the current hot topics of research. 9–20 Many biological systems are shown to have dynamical properties similar to glass-forming liquids in the presence of active driving. Thus studying the physics of glasses under activity can shed important information regarding the dynamical properties of biologically relevant processes.…”

The random first-order transition theory of active glass in the high-activity regime

“…Active glass is a condensed phase of matter with internal sources of active (non-thermal) forces and extremely slow dynamics resembling in many ways the dynamics of passive glass-forming liquids. It has attracted a significant amount of interest as an abstract model for many biological systems [1][2][3][4][5][6][7][8][9], or synthetic soft active matter systems [10][11][12][13], and as a new challenge for non-equilibrium physics [14][15][16][17][18][19]. Realizations of active glass in simulations are mainly in the form of a dense aggregate of interacting particles that are self-propelled; the selfpropulsion appears as random forces applied to each particle, characterized by a force amplitude f 0 and a persistence time τ p [20][21][22][23].…”

Enhanced Phonon Peak in Four-point Dynamic Susceptibility in the Supercooled Active Glass-forming Liquids

“…On the other hand, glassy liquids or supercooled liquids are the systems whose particles start to move collectively with decreasing temperature (increasing density) until they get kinetically trapped near their putative glass transition temperature (density) [3][4][5][6][7][8]. The former is a non-equilibrium system that shows spectacular dynamical properties like largescale ordering, flocks, swarms, etc., and is one of the current hot topics of research [9][10][11][12][13][14][15][16][17][18][19][20]. Many biological systems are shown to have dynamical properties similar to the glass-forming liquids in the presence of active driving.…”