3D-printed tumbling microrobots successfully deliver targeted medication in vivo

It’s a dream of modern medicine to deliver a custom medication exactly where needed in the body. That dream has taken a step closer to reality – or in this case, a tumble forward. Purdue University researchers have successfully demonstrated a 3D-printed tumbling microrobot navigating to a specific area of the body and delivering a drug payload on command.

David Cappelleri, Professor of Mechanical Engineering and Biomedical Engineering (by courtesy), and Assistant Vice President for Research Innovation, has experimented with mobile microrobots for years. “We use an external magnetic field to tumble over complex topography, such as what you’d encounter inside a human body,” he said. “This enables us to make the robots very small, and control them very precisely.”

The robots need to be small enough to maneuver, but large enough to carry a significant drug payload — and precise enough to deliver it on command. To build such a tiny marvel, Cappelleri turned to the Nanoscribe 3D printer, which had already become famous for printing the world’s smallest drum for Guinness World Records. “This is the only machine on campus that can construct something that small and complex,” Cappelleri said.

Their team designed and 3D-printed a brick-shaped microrobot: 3 millimeters long, 1.5 millimeters wide, 1.5 millimeters high, and capable of carrying up to 20 microliters of medication. A rotating external magnet provided the energy for the microrobot to tumble in any direction, while an attached ultrasound probe enabled the operator to see inside and navigate precisely.

So how do you deploy a drug payload on command, from a robot that tiny? “This turned out to be one of the biggest challenges of the project,” Cappelleri said. “How do we keep the medication safe as the robot travels, and then release it only when we’ve arrived at our destination?”

After considering mechanical approaches, the team came up with a simple solution: a food-safe wax that maintains a watertight seal at body temperature, but melts when its temperature is raised a few degrees. To actuate it, the team used an external focused ultrasonic pulse to melt the wax cap in about 60 seconds, thus releasing the medication from the robot’s reservoir.

Their research has been published in Advanced Robotics Research.