Fig. 3. Self-assembly and propulsion of ellipsoidal microbubbles.

a Schematic and image sequence depicting the microbubbles crawling in the z-direction and squeezing into the narrow slit when exposed to ultrasound. These microbubbles then self-assemble into train-like arrangements. The arrows indicate the direction of movement of ellipsoidal microbubbles. b Image series demonstrating propulsion of the bubble train, translating left-to-right in the narrow slit. c Plot of the translational velocities (v_y) of microbubbles moving along the narrow slit in the y-direction.