The physics of active polymers and filaments

Abstract

Active matter agents consume internal energy or extract energy from the environment for locomotion and force generation. Already rather generic models, such as ensembles of active Brownian particles, exhibit phenomena, which are absent at equilibrium, in particular motility-induced phase separation and collective motion. Further intriguing nonequilibrium effects emerge in assemblies of bound active agents as in linear polymers or filaments. The interplay of activity and conformational degrees of freedom gives rise to novel structural and dynamical features of individual polymers as well as in interacting ensembles. Such outof-equilibrium polymers are an integral part of living matter, ranging from biological cells with filaments propelled by motor proteins in the cytoskeleton, and RNA/DNA in the transcription process, to long swarming bacteria and worms such as Proteus mirabilis and Caenorhabditis elegans, respectively. Even artificial active polymers have been synthesized. The emergent properties of active polymers or filaments depend on the coupling of the active process to their conformational degrees of freedom, aspects which are addressed in this article. The theoretical models for tangentially and isotropically self-propelled or active-bath driven polymers are presented, both in presence and absence of hydrodynamic interactions. The consequences for their conformational and dynamical properties are examined, emphasizing the strong influence of the coupling between activity and hydrodynamic interactions. Particular features of emerging phenomena, induced by steric and hydrodynamic interactions, are highlighted. Various important, yet theoretically unexplored, aspects are featured and future challenges are discussed.

Vesicle shape transformations driven by confined active filaments

“…Active matter has played a key role in developing the physical paradigm, through studying minimal biological systems and theoretical models inspired by them (e.g. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]).…”

“…Model: We simulate a system of N fil active filaments confined within an elastic vesicle, which has radius R ves in its undeformed state. We represent active filaments using a modified version of the model in Joshi, et al [86], in which each filament is a nearly-inextensible, semiflexible chain of M beads of diameter σ [12]. Bonded beads interact through an expanded FENE potential [87], while non-bonded beads interact through a purely repulsive expanded Weeks-Chandler-Andersen (eWCA) potential [88] with strength .…”