Diffusion in crowded colloids of particles cyclically changing their shapes

TL;DR

This paper introduces a model of active colloids with cyclic shape changes that, despite not propelling themselves, significantly influence diffusion and structural relaxation, mimicking biological cytoplasm behavior.

Contribution

It presents a novel model of non-propelling active colloids with cyclic shape changes and analyzes their impact on diffusion and glass transition behavior.

Findings

Active shape-changing particles fluidize the colloid.

Passive colloids behave as glasses.

Model aligns with experimental observations in cells.

Abstract

A simple model of an active colloid consisting of dumbbell-shaped particles that cyclically change their length without propelling themselves is proposed and analyzed. At nanoscales, it represents an idealization for bacterial cytoplasm or for a biomembrane with active protein inclusions. Our numerical simulations demonstrate that non-equilibrium conformational activity of particles can strongly affect diffusion and structural relaxation: while a passive colloid behaves as a glass, it gets progressively fluidized when the activity is turned on. Qualitatively, this agrees with experimental results on optical tracking of probe particles in bacterial and yeast cells where metabolism-induced fluidization of cytoplasm was observed.