Collective Dynamics of Active Filaments*

Gliding filamentous cyanobacteria provide an experimental realization of long, flexible, and self-propelled polymers on surfaces.  In addition, their motion is influenced by direction reversal and responses to light, different from previous studies of active polymers. 

To study the patterns formed by these active polymers, we combine simulations and experiments of cyanobacteria in quasi-2D confinement. We explore the patterns they form by tuning the key physical parameters such as the bending stiffness, activity, and reversal rate at low density of filaments. The simulations demonstrate the existence of various patterns including spirals and clusters displaying collective motion, in agreement with our experimental observations. Stochastic reversals tend to suppress both types of patterns.

At high densities of the filaments, our simulation shows dense swarms of filaments with both polar and nematic order. The long-range nematic and polar order are also confirmed by the experiments. Analysis of the dynamics and mechanics of individual filaments (propulsion, bending, buckling)  allows to fully parameterize the simulations for a quantitative comparison of the patterns.