Whether a microscopic ring stays still or starts swimming like a motor depends entirely on how it’s knotted.
arXiv · March 17, 2026 · 2603.15591
The Takeaway
Researchers discovered that 'activity'—like the internal forces found in living cells—interacts with the topology of a knot to create motion. Some knots inflate and wander while others tighten up and stay put, meaning the geometry of a knot alone can dictate how a tiny machine moves through its environment.
From the abstract
Nonequilibrium active polymers provide a minimal framework to investigate biopolymers such as DNA and chromatin under the action of molecular motors. Here we study active ring polymers with controlled topology and show that knot type qualitatively determines their nonequilibrium behaviour. We find that activity induces opposite localisation responses in different topological families: torus knots systematically delocalise and inflate, whereas twist knots tighten and remain localised. We trace th