The bots have a magnetic iron-oxide exterior that both lets doctors control how quickly they degrade and makes it possible to guide them using magnetic resonance imaging. And since they have naturally fluorescent insides, they're easy to spot. They'd only have to stay in your body as long as necessary, and they'd waste less time getting to those places where they're actually useful.

They should be flexible, too. While the nanobots can be used to deliver medicine to targeted parts of the body, they can also sense environmental changes that reflect an oncoming illness. Diagnoses for certain conditions could be more accurate, especially for parts of the body that are normally hard to reach.

Don't expect to slip these tiny machines into your body any time soon, however. The scientists still want to refine their effectiveness, tracking and compatibility with your body before they start trials in humans. However, their very existence shows that nanorobots should be genuinely practical to make and use. Instead of relying on elaborate creations that have little connection to the natural world, you could use readily available organic materials that are already friendly to your body.