Confinement-induced self-organization of self-propelled cell-like "flexicles"

A defining characteristic of living systems is the hierarchical confinement of active components across multiple scales. For instance, during early embryonic development, organelles are enclosed within cells that themselves form a spherical blastula. Building on this idea, we have recently introduced the "flexicle", a minimal model for synthetic, active composite particles composed of self-propelled particles encapsulated within a deformable membrane, that captures the interplay between internal activity and encapsulation. Here, we extend this concept to a higher level of hierarchy by investigating how swarms of flexicles behave under spherical and cylindrical confinement. Using molecular dynamics simulations, we find that flexicles accumulate and self-organize at boundaries, exhibiting rich collective dynamics. Unlike rigid active particles, which cluster at interfaces without coherent motion, flexicles display dynamic behaviors such as spiral formation and collective rotations even at low densities. At higher densities, confinement promotes alignment and collective flow between flexicles, giving rise to emergent chirality reminiscent of phenomena observed in biological tissues. These results establish a foundation for controlling migration and coordination in synthetic cellular systems and for understanding the importance of hierarchy in living materials.