The microbots are highly flexible and are able to swim through fluids and change their shape in response to their environment, meaning they can squeeze through narrow blood vessels without slowing down or being difficult to maneuver. The bots are made of minute hydrogel nanocomposites which contain magnetic nanoparticles, so they can be controlled through the use of an electromagnetic field.

https://www.digitaltrends.com/cool-tech/adaptive-microbots-drug-delivery/