Michael Phelps: Faster than a nano-swimmer but won’t fit in your veins Francois Xavier Marit/AFP/Getty Images

It’s no Michael Phelps, but this tiny magnetic robot swims the front crawl at 10 micrometres per second. It would take about two months for the bot to swim the length of an Olympic swimming pool – in that time, Phelps could swim over 200,000 lengths. But the nano-swimmer is fast for its size, and it’s strong enough to pass through more viscous liquids, like blood, to deliver medicine from inside your veins.

The front crawl is the fastest way for humans to swim. So Tianlong Li at the Harbin Institute of Technology in China and his colleagues built their swimming robot to mimic that motion.

Each nano-swimmer is 5 micrometres long and has three main parts, connected together like sausage links by two silver hinges. Its gold body is flanked by two magnetic arms made of nickel, and applying a magnetic field to the tiny robot makes the arms move.


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As the researchers switch the magnetic field’s direction back and forth, it causes the arms of the nano-swimmer to rotate and propel it forward, just like the arms of a human swimmer doing the front crawl.

“It’s exciting due to its speed and its really small size, just about the same size as a blood vessel,” says Eric Diller at the University of Toronto in Canada who researches micro-robots. “It’s small enough basically to go anywhere within the body.”

Because bodily fluids are more viscous and difficult to swim through than water, the researchers also tested their nano-swimmers in serum. The bots were only able to swim 5.5 micrometres per second, but that’s still faster than many other similar mini-machines.

For targeted medicine delivery without invasive procedures, these nano-swimmers could be coated with medicine and injected into the bloodstream, where their trajectories could be roughly steered by external magnetic fields.

Since they are so small, just one nano-swimmer wouldn’t be able to carry enough medicine to actually help. “Maybe a thousand of them would be necessary,” says Diller. “There’s no way to keep track of all of them, so there are a lot of questions about safety and toxicity.”

The next generation of these tiny machines will have to be made from biodegradable materials before they can be used in the bloodstream. But, Diller says that for less complicated areas in the human body like the urinary tract or the eyeballs, clinical trials could begin within the next five to 10 years. Injecting a single swimmer into an eyeball, where it could deliver medication directly to the retina and then be removed, would be much less complicated than letting a swarm of them swim throughout the entire circulatory system.

We don’t know how fast Michael Phelps could swim through blood – thankfully, his recent race against a great white shark didn’t provide a testing ground. But since you can’t inject him into your bloodstream, these nano-swimmers will have to do.

Journal reference: Nano Letters, DOI: 10.1021/acs.nanolett.7b02383

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We corrected the comparison to a human swimmer’s world-record time.