Call it another case of science fiction becoming scientific fact. Researchers have long dreamed of developing tiny robots that could roam about inside our bodies, delivering drugs with unprecedented precision, and hunting down and destroying cancer cells.
We’re not there yet, but we’re getting close. Last month scientists from China’s National Center for Nanoscience and Technology (NCNT) and Arizona State University said they had developed robots a few hundred nanometers across — there are 25 million nanometers in an inch — and when they injected them into the bloodstream of mice, the nanorobots could shrink tumors by blocking their blood supply.
The nanorobots were made from sheets of DNA rolled into tubes containing a blood-clotting drug. On the outside, the researchers placed a small DNA molecule that binds with a protein found only in tumors. When the bots reached tumors, this molecule attached to the protein, triggering the DNA tube to unroll and release the drug.
Most cancer drugs typically have nasty side effects because they can’t distinguish between cancer cells and healthy ones. The researchers showed that the nanorobots only targeted the tumors and didn’t cause clotting elsewhere in the body. They say this offers a promising future of cancer treatments free of side effects.
Such a device is very different from the human-scale bots that build our cars and vacuum our floors. But Guangjun Nie, one of the NCNT professors who developed the nanorobots, points out that they are able to sense their environment, navigate, and carry out mechanical tasks just like large robots.
The researchers are working with a biotech firm to commercialize the cancer-fighting nanobots. And Nie says this is just a taste of what DNA nanorobots could do.
“What we call nanorobots are the next generation of nanomedicines because they give you much better control and can be made to work like a machine,” he says. "In the future we will demonstrate even more scenarios for our nanorobots from monitoring disease, to finding tissue damage, curing cancer and maybe even finding and destroying plaques in our blood vessels."
Taking cues from sci-fi
The idea of tiny disease-fighting machines working inside the human body can be traced at least as far back as the 1966 release of the movie “Fantastic Voyage,” in which a submarine and its crew were shrunk down and injected into a scientist’s body to remove a dangerous blood clot.
In real life, of course, it’s not so easy to shrink machines, much less humans. Computer chips, electric motors, and batteries are typically too bulky to operate in blood vessels or between cells.
But being able access hard-to-reach areas of our bodies could have profound implications for medicine, so scientists are scrambling to find ways to power and control inside-the-body bots.
In addition to boosting the effectiveness and lessening the side effects of powerful drugs, nanorobots loitering in our bloodstream could act as early warning systems for disease. And tiny wireless surgical tools could let doctors perform medical procedures without cutting people open.
Eric Diller, an assistant professor of mechanical engineering at the University of Toronto in Canada, is working on this last problem. He’s developing robots just under a millimeter across that are built from elastic polymers filled with magnetic particles that can be dragged through fluids and triggered to grasp objects.
These tiny bots are controlled by precise magnetic fields generated by an array of electromagnets. The robots could eventually be used to collect tissue biopsies or carry drug capsules inside the body, says Diller.
His lab has yet to test the devices in animals, but researchers at ETH Zurich, in Switzerland, have already tested a similar magnetically guided microbot in the eye of a rabbit, using it to puncture a blood vessel with its needle-like tip. The ultimate goal, Diller says, is to create a suite of wirelessly powered surgical tools.
"Instead of having an open wound site we would like to be able to inject surgical tools,” he says. "We could do non-invasive, not just minimally invasive, procedures with no external cuts and without the complications that come from surgery."
Probably the most developed and versatile approach to microscopic medical robots uses so-called “nanomotors” and “micromotors.” These are tiny particles, tubes, or wires made from materials like gold, magnesium, and carbon. They either propel themselves using fuels found in the body — such as stomach acid or water — or are dragged or pushed around by magnetic fields or ultrasound waves.
Researchers have shown that these devices can precisely navigate to disease sites and can even penetrate deep into diseased tissue to deliver drugs more efficiently. When combined with biosensors like enzymes or antibodies, they can create much more sensitive ways to detect chemical signals of disease, because their movement means they bump into other molecules more frequently.
By the same principle, combining them with nanosponges that absorb toxins could someday create tiny robots that efficiently mop up harmful substances in the body.
Dr. Joseph Wang, a professor of nanoengineering at the University of California, San Diego, is one of the pioneers of this field. Last August, his lab demonstrated that micromotors loaded with antibiotics and powered by stomach acid could treat stomach infections in mice more effectively than taking the drug by itself.
"We just dump the motors in the stomach and they just swim autonomously," he said. "It's like taking a pill and forgetting about it."
Meanwhile, other researchers are looking for ways to harness and redirect the activities of nature’s own tiny machines.
In December, a group at the Leibniz Institute for Solid State and Materials Research in Germany loaded sperm cells with anti-cancer drugs and fitted them with tiny magnetic harnesses. The sperm tails provided propulsion but the harnesses let the researchers guide them using a magnetic field toward mini cervical cancer tumors that had been grown in a petri dish. They killed 87 percent of the tumors’ cells within three days.
And in 2016, a team from Polytechnique Montréal in Canada hijacked bacteria that naturally swim along magnetic field lines, loading them with cancer drugs and using artificial magnetic fields to steer them to tumors in mice.
Eventually, Diller says building in-the-body robots from scratch will give us much greater control over their functionality. But we’re still a long way from being able to mimic nature’s innovations, so for now, these bio-hybrid approaches are a smart idea.
“At this point in time there is a compelling argument for using these organisms that are already functional and trying to modify them to do what our goal is,” he says. “They have much more functionality than the devices we can build today.”