Steering Microbots
Bacteria-based robots swim through blood vessels

Source: “Flagellated Bacterial Nanorobots for Medical Interventions in the Human Body”
Sylvain Martel et al.
IEEE 2008 Biorobotics Conference, October 19-22, 2008, Scottsdale, AZ

Results: Researchers have coupled swimming bacteria to 150-nanometer-wide beads, creating tiny robots that can be steered inside blood vessels using magnetic fields controlled with a modified magnetic resonance imaging (MRI) device. The MRI can also be used to track the robots.

Why it matters: The tech­nology could provide a new way to deliver drugs directly to tumors. The bacteria would swim through the bloodstream bearing drug-coated nanoparticles; doctors could use MRI to direct them to a specific site, such as a part of a tumor. At two micrometers in diameter, the bacteria are small enough to fit through the smallest blood vessels in the human body.

Methods: The researchers treated nanoscale polymer beads with an antibody that binds to the bacteria. The bacteria naturally contain magnetic particles and swim in different directions depending on the surrounding magnetic fields. The researchers tested their ability to steer the bacteria by altering magnetic fields around them with a special configuration of electromagnetic coils connected to an MRI. The coils, arranged at right angles to each other, allow the researchers to control the bacteria’s movement in three dimensions. The researchers steered the bacteria in human blood, in rat tumors, and through glass tubes that mimic human blood vessels.

Next steps: The bacteria-propelled devices can’t swim fast enough to traverse the currents in larger blood vessels. So the researchers envision ferrying the microbots through large blood vessels inside larger microparticles they have developed, whose motion can be controlled by a clinical MRI system. Those particles would release the bacteria into the small blood vessels that they are too big to enter themselves.