Active droplet driven by a collective motion of enclosed microswimmers.

Active fluids containing self-propelled particles are relevant for applications such as self-mixing, micropumping, and targeted drug delivery. With a confined boundary, active fluids can generate bulk flow inside the system, which has the potential to create self-propelled active matter. In this study, we propose that an active droplet is driven by a collective motion of enclosed microswimmers. We show that the droplet migrates via the flow field generated by the enclosed microswimmers; moreover, the locomotion direction depends on the swimming mode of these internal particles. The locomotion mechanism of the droplet can be well explained by interfacial velocity, and the locomotion velocity shows good agreement with the Lighthill-Blake theory. These findings are essential to understand the interplay between the motion of self-propelled particles and the bulk motion response of active matter.