samiali

• Al-Izzi, Sami Cameron; Du, Yao; Veenstra, Jonas; Morris, Richard G.; Souslov, Anton & Carlson, Andreas [Vis alle 8 forfattere av denne artikkelen] (2026). Nonreciprocal buckling makes active filaments polyfunctional. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 123(11). doi: 10.1073/pnas.2531723123. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Janssen, Mathijs Adriaan; Liese, Susanne; Al-Izzi, Sami Cameron & Carlson, Andreas (2024). Stability of a biomembrane tube covered with proteins. Physical Review E (PRE). ISSN 2470-0045. 109(4). doi: 10.1103/PhysRevE.109.044403. Fulltekst i vitenarkiv Vis sammendrag

  Membrane tubes are essential structural features in cells that facilitate biomaterial transport and inter- and intracellular signaling. The shape of these tubes can be regulated by the proteins that surround and adhere to them. We study the stability of a biomembrane tube coated with proteins by combining linear stability analysis, out-of-equilibrium hydrodynamic calculations, and numerical solutions of a Helfrich-like membrane model. Our analysis demonstrates that both long- and short-wavelength perturbations can destabilize the tubes. Numerical simulations confirm the derived linear stability criteria and yield the nonlinearly perturbed vesicle shapes. Our study highlights the interplay between membrane shape and protein density, where the shape instability concurs with a redistribution of proteins into a banded pattern.

• Al-Izzi, Sami Cameron & Alexander, Gareth P. (2023). Chiral active membranes: Odd mechanics, spontaneous flows, and shape instabilities. Physical Review Research (PRResearch). 5(4). doi: 10.1103/PhysRevResearch.5.043227. Fulltekst i vitenarkiv Vis sammendrag

  Living systems are chiral on multiple scales, from constituent biopolymers to large scale morphology, and their active mechanics is both driven by chiral components and serves to generate chiral morphologies. We describe the mechanics of active fluid membranes in coordinate-free form, with focus on chiral contributions to the stress. These generate geometric “odd elastic” forces in response to mean curvature gradients but directed perpendicularly. As a result, they induce tangential membrane flows that circulate around maxima and minima of membrane curvature. When the normal viscous force amplifies perturbations the membrane shape can become linearly unstable giving rise to shape instabilities controlled by an active Scriven-Love number. We describe examples for spheroids, membranes tubes, and helicoids, discussing the relevance and predictions such examples make for a variety of biological systems from the subcellular to tissue level.

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