Persistence of strain in motor-filament assemblies

TL;DR

This paper develops a mean field theory to understand how active motor forces and filament elasticity determine a characteristic persistence length over which active strain decays in motor-filament assemblies, relevant to biological structures.

Contribution

It introduces a theoretical framework linking motor activity, filament extensibility, and passive resistance to define active strain persistence length in ordered systems.

Findings

Active motor forces create a finite decay length of strain.

Filament extensibility and passive resistance influence strain decay.

The theory generalizes thermal persistence to active biological systems.

Abstract

Crosslinked semi-flexible and flexible filaments that are actively deformed by molecular motors occur in various natural settings, such as the ordered eukaryotic flagellum, and the disordered cytoskeleton. The deformation of these composite systems is driven by active motor forces and resisted by passive filament elasticity, and structural constraints due to permanent cross-links. Using a mean field theory for a one-dimensional ordered system, we show that the combination of motor activity and finite filament extensibility yields a characteristic persistence length scale over which active strain decays. This decay length is set by the ability of motors to respond to combination of the weak extensional elasticity, passive shear resistance and the viscoelastic properties of the motor assembly, and generalizes the notion of persistence in purely thermal filaments to active systems.