In a sense, we already have millions of little robots in our blood keeping us healthy in the form of the various types of cells. While these natural machines do a remarkable job of protecting our bodies from internal harm, sometimes the task is just too great. So researchers are developing teams of tiny troops to send in as reinforcements.

These bloodstream bots come in two sizes: small and smaller. Or micro and nano, to be more scientific about it. In a recent paper published in the Journal of Nanoparticle Research, scientists described how the size of the robots affects their swimming.

It turns out that it is possible for the robots to be too small. The researchers found that veering too far onto the nano end of the spectrum results in robots that are so tiny they can't overcome the random motion of molecules in the blood, known as Brownian motion. As a result, they end up drifting about aimlessly, much the way they do in the video below.

What you're looking at are chains of iron oxide that are primed to self-assemble when exposed to magnetic fields. The researchers found that by manipulating the magnetic fields surrounding the robots, they can control their size.

Once the robots are the right size, the researchers can then also use the magnetic fields to direct their motion. As this video shows, getting the size right allows much better control over the robot's direction.

One potential use for cellular-scale robots like these is to be able to send them in to open clogged blood vessels. As part of this task, they would release anti-coagulant drugs right where they're needed in the vessel.

"The microswimmers are composed of inorganic biodegradable beads so they will not trigger an immune response in the body. And we can adjust their size and surface properties to accurately deal with any type of arterial occlusion," MinJun Kim, a bioengineering professor at Drexel, told FastCoExist.

But the real question on any '90s child's mind is, when will we be able to shrink ourselves so that we can ride in these tiny vehicles to prevent medical crises like the Rugrats did?

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