Active billiards: Engineering boundaries for the spatial control of confined active particles

• 成果类型: Article
• 署名作者: Di Leonardo, Roberto; Buzas, Andras; Kelemen, Lorand; Toth, David; Toth, Szilvia Z.; Ormos, Pal; Vizsnyiczai, Gaszton
• 署名单位: Sapienza University Rome; Consiglio Nazionale delle Ricerche (CNR); Istituto di Nanotecnologia (NANOTEC-CNR)
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10747
• DOI: 10.1073/pnas.2426715122
• 发表日期: 2025-09-19
• 关键词: phototaxis

摘要

Unlike gas molecules at equilibrium, the spatial organization of self-propelled particles can be very sensitive to what happens at the boundaries of their container. Understanding the link between boundary phenomena and bulk stationary distributions could enable the design of optimized container shapes for the geometric control of confined active particles. Here, we propose a boundary method based on the flux transfer formalism typical of radiometry problems, where surface elements transmit and receive rays of active particles with infinite persistence length. We demonstrate the power of this boundary method in the case of the swimming microalgae Euglena gracilis trapped in light-defined billiard geometries. Quite surprisingly, we found that Euglena scatters with a nearly Lambertian cosine law, resembling the behavior of blackbody radiation and consequently resulting in nearly uniform distributions inside simple cavity geometries. Nevertheless, leveraging our boundary method, we were able to design a stacked multistage billiard geometry, with a connection scheme between subunits that breaks spatial symmetry and achieves an exponential amplification of cell concentration between its two ends. Our method can be applied to confined active matter in contexts ranging from spatial control and sorting of microorganisms to the design of efficient navigation strategies for microscopic and macroscopic robots.