Controlled in vivo swimming of a swarm of bacteria-like microrobotic flagella

Precisely controlling the motion of large numbers of microfabricated materials within an organism presents opportunities for the targeted delivery of therapeutic and diagnostic agents en masse. To accomplish this, these structures must be actuated, tracked, and their motion trajectories corrected. We have developed a polymer-magnet structure similar in shape and size to flagellated bacteria, such as motile Escherichia and Salmonella (that we call Artificial Bacterial Flagella; ABFs) and chemically functionalized their surface with various molecules including fluorescent probes. We demonstrate the simultaneous injection of over 100,000 of these “microrobots” into a mouse peritoneal cavity, their subsequent controlled motion using weak rotating magnetic fields (9 mT) external to the animals, whole body in vivo tracking using near infrared fluorescence and the IVIS imaging system, and integrated control within the mouse by wireless means. Since only weak magnetic fields are required for actuation and the feedback provided by in vivo tracking, the approach can be used deep within tissue relatively far from an organism’s surface.