Collective behavior of "flexicles"

In recent years the functionality of synthetic active microparticles has edged even closer to that of their biological counterparts. However, we still lack the understanding needed to recreate at the microscale key features of autonomous behavior exhibited by microorganisms or swarms of macroscopic robots. In this study, we propose a model for a three-dimensional deformable cellular composite particle consisting of self-propelled rod-shaped colloids confined within a flexible vesicle - a superstructure we call a "flexicle". Using molecular dynamics simulations, we investigate the collective behavior of dense systems comprised of many flexicles. We show that individual flexicles exhibit shape changes upon collisions with other flexicles that lead to rearrangement of the internal active rods that slow the flexicle motion significantly. This shape deformability gives rise to a diverse set of motility-induced phase separation phenomena and the spontaneous flow of flexicles akin to the migration of cells in dense tissues. Our findings establish a foundation for designing responsive cell-like active particles and developing strategies for controlling swarm migration and other autonomous swarm behaviors at cellular and colloidal scales.