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Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2026,3,17]]},"abstract":"<jats:p>Active filaments are a workhorse for propulsion and actuation across biology, soft robotics, and mechanical metamaterials. However, artificial active rods suffer from limited robustness and adaptivity because they rely on external control, or are tethered to a substrate. Here, we bypass these constraints by demonstrating that nonreciprocal interactions lead to large-scale unidirectional dynamics in free-standing slender structures. By coupling the bending modes of a buckled beam antisymmetrically, we transform the multistable dynamics of elastic snap-through into persistent cycles of shape change. In contrast to the critical point underpinning beam buckling, this transition to self-snapping is mediated by a critical exceptional point, at which bending modes simultaneously become unstable and degenerate. Upon environmental perturbation, our active filaments exploit self-snapping for a range of functionality including crawling, digging, and walking. Our work advances critical exceptional physics as a guiding principle for programming instabilities into functional active materials.<\/jats:p>","DOI":"10.1073\/pnas.2531723123","type":"journal-article","created":{"date-parts":[[2026,3,13]],"date-time":"2026-03-13T17:39:57Z","timestamp":1773423597000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":3,"title":["Nonreciprocal buckling makes active filaments polyfunctional"],"prefix":"10.1073","volume":"123","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4764-1457","authenticated-orcid":false,"given":"Sami C.","family":"Al-Izzi","sequence":"first","affiliation":[{"name":"School of Physics","place":["Sydney, Australia"]},{"name":"University of New South Wales","place":["Sydney, Australia"]},{"name":"Australian Research Council Centre of Excellence for the Mathematical Analysis of Cellular Systems\u2013University of New South Wales Node","place":["Sydney, Australia"]},{"name":"Department of Mathematics","place":["Oslo, Norway"]},{"name":"Faculty of Mathematics and Natural Sciences","place":["Oslo, Norway"]},{"name":"University of Oslo","place":["Oslo, Norway"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yao","family":"Du","sequence":"additional","affiliation":[{"name":"Institute of Physics","place":["Amsterdam, The Netherlands"]},{"name":"Universiteit van Amsterdam","place":["Amsterdam, The Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jonas","family":"Veenstra","sequence":"additional","affiliation":[{"name":"Institute of Physics","place":["Amsterdam, The Netherlands"]},{"name":"Universiteit van Amsterdam","place":["Amsterdam, The Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8544-7658","authenticated-orcid":false,"given":"Richard G.","family":"Morris","sequence":"additional","affiliation":[{"name":"School of 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