Control of Bacterial Turbulence

Active fluids are liquids that contain tiny objects capable of propelling themselves, such as swimming bacteria, microscopic algae, or specially designed artificial particles. Active fluids are often seen in nature, from schools of fish and flocks of birds to groups of cells. When many of these movers interact with each other, they can spontaneously form large, constantly changing flow patterns that are large compared with the size of the individual particles. These swirling motions have been widely studied, but researchers still have limited ability to guide or control them. The lack of control has restricted the use of active fluids in many promising technologies. This project will develop new ways to direct and control these dynamic fluid motions by combining two complementary approaches: designing the behavior of the individual particles and applying carefully chosen external influences to guide their collective motion. By learning how to reliably control these active systems, this project will improve the understanding of how complex patterns emerge in nature and open new opportunities to create advanced materials and intelligent fluids whose properties can be adjusted on demand. These capabilities could lead to applications in areas such as targeted drug delivery, soft robotics, and advanced manufacturing. Bacterial suspensions will serve as a model active fluid system in this study. Control of the collective dynamics of bacterial suspensions, the so-called bacterial turbulence, will be achieved through the synergistic integration of a bottom-up approach, in which the swimming behavior of individual bacteria is precisely tuned on demand, and a top-down approach, in which collective bacterial motion is guided through large-scale geometric confinement. Building on the research team's prior work and strong preliminary results, the project will substantially expand the experimental toolbox for controlling and manipulating the collective dynamics of active fluids. This integrated control framework will provide an unprecedented opportunity to investigate the fundamental physics of bacterial turbulence, including its onset, nonlinear dynamics, and energy cascade mechanisms. The experimental platform will also enable the development of a novel optorheological fluid with dynamically tunable viscosity, opening new avenues for designing adaptive and responsive soft materials. This award will contribute to undergraduate curriculum development in fluid mechanics and support science and engineering outreach activities for preschool-aged children at the University of Minnesota Child Development Center. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.