Mechanics of Nonreciprocal Active Filaments

Date: Thu 16th July 2026

Abstract

From venus flytraps to cilia, nature uses the flexing and snapping of slender structures for fast motion and cyclic shape change. Many living filaments are internally energized by active processes, these active filaments are a workhorse for propulsion and actuation across biology and bioinspired engineering. Unravelling the mechanics of these filaments and understanding the wide range of functionalities in this energy-nonconserving setting remains a challenge. This repertoire of functions stems from two ingredients: geometrical slenderness to enable bending, and directed waves to drive cyclic motion. Increasingly mechanical nonreciprocity is being utilized as a design principle and conceptual framework for understanding the latter and it is the coupling of this to geometrically slender structures that we will discuss here.

We develop a geometrically exact theory of nonreciprocal filaments and provide simulations that capture their post-instability nonlinear dynamics [1]. We find that nonreciprocity, when coupled to inertia or pre-stress, amplifies and advects curvature variations. The resulting one-way patterns of shape morphing can then be selected via dissipative interactions with the environment.

We then use a combination of theory and experiments with robotic active beams to show that we can exploit the enhanced sensitivity inherent to exceptional phenomena to engineer filaments that autonomously crawl, dig, and walk [2]. These materials may form the basis for smarter robot bodies that operate without centralized control and are robust, conformal, and scalable. Our work advances critical exceptional physics as a guiding principle for programming instabilities into functional active materials.

References

[1] - Al-Izzi, Binysh, Du, Coulais & Carlson - arXiv:2607.01603

[2] - Al-Izzi et al. PNAS 123 (11) e2531723123 (2026)