From IEEE Spectrum:
Being able to do this is all about communication, as Professor Nathan Michael discussed today at the IEEE International Conference on Robotics and Automation (ICRA) in Shanghai. As he and fellow researchers Matthew Turpin and Vijay Kumar have discovered, the robots have to not just know exactly where they are, but they also have to broadcast that information to their neighbors to maintain the integrity of the formation. This processing is all done on each individual quadrotor, so there's no all-seeing computer watching everything and telling each robot where to go. The accuracy is impressive: 50 percent of the time the quadrotors are within a mere two centimeters of where they should be.Well, these robots haven't been miniaturized nor tested in blood so they're not ready for atrial fibrillation ablation yet, but it's still fascinating to see what creative minds can develop.
Then again, maybe I'm just reminded of scrubbing bubbles.