MIT Physicists Are Designing Microscopic Robots to Walk Inside Our Bodies

How will it feel to have tiny robots tumbling through your veins?

Bacteria are badass navigators. They swim away from toxins and pinpoint nutrients with an innate sense of direction, guided by subtle chemical queues. If we could capture that homing action in the laboratory, physicians might be able to deploy microscopic machines to deliver drugs to specific locations, or scan the entire body for rogue tumors.

But that's the future. This week, physicists at MIT took the first baby steps—or tumbles—toward creating machines that mimic bacteria in motion. Ina study published in the journal Physics Review Letters, researchers paired two microscopic, magnetic beads on an artificial surface. They observed as the beads tumbled or "walked" from areas of low friction to areas of high friction.

Artificial micro walkers tumble away from areas of low-friction (blue), toward high-friction areas (red). Image: Juan Aragones, Josh Steimel, and Alfredo Alexander-Katz

That might not sound terribly exciting, unless you really, really love watching things tumble. But for biologists, high-friction areas mean cell surface receptors—where communication happens and, incidentally, where lots of drugs need to go. The idea is that, in the future, doctors might inject MIT's microscopic machines into a patient, and then let the little bots tumble toward receptor-rich areas, with life-saving medications in tow.

"We can make this thing walk and find regions where certain receptors are being expressed," says Alfredo Alexander-Katz, a biophysicist at MIT and lead author on the study. "It could deliver drugs."

Alexander-Katz says he can customize his tumbling micro-beads to stick to different types of cell surface receptors, depending on the mission at hand. Eventually, the researchers envision an active, autonomous system that could monitor how cells and tissues change in real time. Think chemical sensors—or tumor detectors.

"Today, that's impossible," Alexander-Katz says. "But it would be of great benefit to understand how tissues behave and how tumors develop."

The microscale beads are clever mixtures of polymer and metal, made from inexpensive materials like the polystyrene that's found in plastic cups. "We used off-the-shelf materials," Alexander-Katz says. His team conducted their experiment on a model cell surface, and applied a magnetic field to get the beads rolling.

This is certainly not the first attempt to deliver drugs to specific sites in the body. The entire field of targeted cell therapy is pretty much dedicated to doing just that. But Alexander-Katz stresses that his magnetic beads represent one of the first attempts to mimic bacteria in action. "There's a really big push right now to create active, synthetic systems that mimic biological functions."

The biggest caveat is that, right now, the whole thing basically amounts to a few jittery robo-beads on an artificial surface. The next step, Alexander-Katz says, will be to test his prototype on actual, living cells. Until then, all of the medical applications remain largely theoretical.

However preliminary, other scientists in the field are taking notice. "This is a very interesting and exciting result," Vijay S. Pande, a biomedical scientist at Stanford University who was not involved in the research, wrote in an email.

Pande stressed, however, that it is difficult to know exactly how Alexander-Katz's work might develop over the next few years. One day, will microscopic machines tumble through our bodies to deliver medications? Will cancer detection ultimately fall to a refined great-grandchild of the original micro-walker?

"It's hard to predict how far this will go, but this could open interesting doors to new biologically-inspired materials as well as biomimetic artificial 'living systems'," Pande says. "It will be very exciting to see where this leads in five to 10 years."