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

TL;DR

This paper presents a theoretical framework explaining how biological systems actively regulate the viscous length scale of the cellular cortex, linking activity to mechanical properties and matching experimental observations.

Contribution

It introduces a coarse-grained hydrodynamic theory incorporating activity, revealing a universal inverse relationship between activity and the viscous length scale.

Findings

Viscous length scale inversely proportional to activity

Theory matches experimental data across diverse systems

Provides a mechanistic understanding of cellular rigidity regulation

Abstract

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 $\ell$. Cells actively regulate $\ell$ via the activity of force generating molecules, such as myosin II. Here we develop a general theory for such systems through 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 $\ell$, 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 show good agreement.