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  • Featured in Physics
  • Open Access

Particle Sweeping and Collection by Active and Living Filaments

R. Sinaasappel1,*, K. R. Prathyusha2,*, H. Tuazon2, E. Mirzahossein1, P. Illien3, S. Bhamla2,†, and A. Deblais1,‡

  • *These authors contributed equally to this work.
  • †Contact author: saadb@chbe.gatech.edu
  • ‡Contact author: a.deblais@uva.nl
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Phys. Rev. X 16, 011003 – Published 5 January, 2026

DOI: https://doi.org/10.1103/yxp1-t43g

Abstract

Biological and robotic systems often operate in confined environments where materials must be gathered without centralized control. Inspired by the effective collection strategies of aquatic worms (Lumbriculus variegatus and Tubifex tubifex), we investigate how active filaments autonomously aggregate dispersed non-Brownian passive particles. We study this process across four platforms: living worms, a robotic chain, Brownian dynamics simulations of active polymers, and a coarse-grained toy model. We show that aggregation emerges from repeated contact and body deformation—effectively, a sweeping or brooming motion—and demonstrate that clustering dynamics are governed by filament length and bending stiffness. Across systems, particle gathering follows a shared aggregation-fragmentation process, where the steady-state cluster size approximately follows a quadratic increase with the effective width of the path cleared by the filament W relative to the domain size D. This scaling provides a minimal geometric baseline for comparison across active filamentous systems. We find that filament flexibility modulates W, enabling more flexible filaments to sweep larger areas and collect more particles. These results establish a unifying framework for understanding how shape and flexibility influence transport and organization in active filament systems and filamentous robots.

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Worm-Inspired Active Filaments Sweep Disorder into Order

Published 5 January, 2026

The ability of single active filaments to cluster smaller particles could inspire new materials for building soft robots that perform biological functions.

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Many living systems can gather scattered particles without external control, yet how they do so remains unclear. We investigate this self-organized aggregation using active filaments—flexible, moving filaments—that interact with passive particles. Across living, robotic, and simulated systems, we find that particle gathering happens through repeated contact and body bending, which sweep particles together much like a broom. The resulting cluster size depends mainly on the filament’s length and flexibility, revealing a simple geometric rule that connects all these systems.

To uncover this rule, we study three kinds of active filaments: living worms, a meter-scale robotic chain, and computer simulations. In confined circular arenas, we track how a single filament sweeps passive particles along its path, driving cycles of gathering and breakup until a steady pattern forms. By systematically varying filament flexibility and length, we find that longer and more flexible filaments collect larger clusters. Despite their differences in scale and composition, all three systems follow the same overall trend, showing that a common physical mechanism underlies the aggregation process.

This unified framework shows that the geometry of a filament’s motion controls how efficiently it can gather surrounding particles. Understanding this relationship not only clarifies how organisms such as aquatic worms reshape their environments but also points the way toward new designs in soft robotics. By tuning flexibility or body shape, engineers could create robotic systems that autonomously collect, organize, or manipulate materials in complex environments.

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Phys. Rev. X 16, 011003– Published 5 January, 2026
  • Received 13 June 2025
  • Accepted 28 October 2025
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