There are two options for controlling a robot inside of the human body: Either you try and build some sort of intricate and tiny robot submarine with self contained propulsion and navigation, which would be really really hard to do, or you just make the robot with a tiny bit of something that responds to magnetic fields, and control it externally with some big magnets. The latter approach is vastly less complicated, but it has one major drawback, which is that it’s very hard to manage multiple robots.
Here’s the problem: Magnetic fields, being fields, aren’t easily constrained to specific areas. Realistically, if you’re using something like a clinical MRI scanner to create a magnetic field, whatever gradient you give the field will affect everything inside of the MRI, whether you’ve got one single microbot or a vast swarm of them. If you want two different robots to do two different things, you’re out of luck.
One potential way of getting around this is by making each of your robots slightly different, such that consistent control inputs have inconsistent effects on each robot. But for homogenous robots, it’s much more difficult. In a paper published today in Science Robotics, researchers from Philips, in Hamburg, Germany, describe a technique that can use magnetic fields to selectively actuate individual microbots, or individual components of a robot, even if they’re all made of the same stuff and located within the same field.