Fig. 1. Robotic functions, fabrication, and characterization of PBs.

(A) Schematic illustration of PBs performing robotic functions. (B) Fabrication process of a PB. A cuboid ice with side lengths of (2, 5.42, and 7.5) mm is coated with PTFE particles. When the ice melts, a PB is formed. Scale bar, 2 mm. (C) Experimentally measured particle mass versus volume of PBs and liquid marbles (LMs). Inset shows calculated surface area versus volume of PBs and LMs based on their geometries. (D) Experimentally measured maximum compression force (MCF) before bursting versus the aspect ratio (AR) of liquid-particle composites. Each point corresponds to the average of five measurements and error bars to SDs. Insets: Initial bottom view images of the composites. Scale bar, 5 mm. (E) Experimentally measured critical height causing liquid-particle composites to burst. Each composite (D and E) consists of an internal liquid with a volume of 75 mm³. (F) Schematic illustration of a PB propelled by the acoustic radiation force from the ultrasonic transducer. (G) Acoustic radiation force as a function of the distance from the transducer to a sphere. (H) Velocity profile of the PB propelled by an acoustic radiation force. PBs are initially located at a distance d = 40 mm (red) and d = 50 mm (blue) from the transducer. (I) Ice shapes used to make PBs with the identical water volume of 75 mm³ but different surface areas.