Researchers at the Georgia Institute of Technology have created a new type of tiny 3D-printed robot that moves by harnessing the vibration from piezoelectric actuators, ultrasound sources or even tiny speakers. The size of the world's smallest ant, these "micro-bristle-bots" could sense changes in the environment and swarm together to move materials--or perhaps one day repair injuries inside the human body. Prototypes of the robot respond to different vibration frequencies depending on their configurations, which allows researchers to control individual bots by adjusting the vibration. Though they are only 2 millimeters long, the bots can cover four times their own length in a second. The micro-bristle-bots consist of a piezoelectric actuator glued onto a polymer body that is 3D printed using two-photon polymerization lithography (TPP).