Collective dynamics of soft vesicles containing self-propelling granular rods

Active particles can be used for creating dynamic structures and responsive systems. One effective way to create active particles is to air-fluidize granular particles and such systems can elucidate the underlying physics of more complex systems. In this study, we fabricated rod-like granular that self-propels by the deflecting uplifting airflow in an air-fluidization system and we study how their self-organization interacts with a deformable confinement. By controlling the size, stiffness, and friction of the confinement as well as the number of particles, we observed distinct particle configurations including orbiting, frustration and aligning. By considering such a particle-confinement assembly as an active vesicle, the collective behaviors of multiple interacting vesicles were also studied in a quasi-one-dimensional channel. Under various channel width, wall stiffness, and vesicle configurations, we observed different collective behaviors regarding vesicle shapes, rod configurations and packing patterns.