Magnetically guided millirobots deliver targeted drugs to beating hearts

Johns Hopkins University engineers have created robots the size of a pencil tip intended to travel through the body to deliver medicine to infections inside a beating heart.

The bots, designed to replace risky open-heart surgery and ineffective IV-drug therapy to treat life-threatening heart infections, could also be used to less invasively and more precisely treat other hard-to-reach diseases including cancer.

"With just a little pinprick, you insert a micro robot and do a procedure without infection or blood loss. And you don't need to have a surgeon operating it to get the drugs robustly, safely and efficiently to the right place," said senior author Axel Krieger, a medical roboticist known for creating robots that perform surgery without human help. "There's a lot of areas beyond heart infections where this kind of targeted drug therapy and these kinds of steerable robots could play a major role. It's really the frontier of surgical robotics."

The work is newly published in Advanced Material Technologies.

Each year about 50,000 people in the United States contract endocarditis, a heart tissue infection. The typical treatment is a weeks-long course of intravenous antibiotics, which often fails because the drugs are too diluted by the time they reach the heart. Doctors are then left with two risky choices- prescribing more and higher doses of antibiotics, which can be toxic, or extremely risky open-heart surgery.

To get the drugs directly to the infected heart tissue, the team developed magnetically-powered robots called "millirobots," because of their size-they're as wide as a pencil tip or a matchstick head, and about as long as a grain of rice.

The robots work in pairs. There's one the team calls the needle module, which gently latches onto heart tissue right at the infected site. There it serves as a docking station, waiting right on the beating heart for the drug module. The drug module carries medicine to the docking station where it magnetically docks and slowly releases the antibiotics right where they're most needed.

Both robots are magnetic and guided wirelessly by an external electromagnetic coil system, that works like an MRI machine.

Having two tiny robots instead of one larger one allows the device to reach tight spots in the body. The needle can remain docked while the drug module is replaced allowing for repeat doses of medicine if needed.

Magnetic guidance is exciting because you don't have to power the robot itself. It doesn't carry batteries and motors. The drugs can be delivered safely, with technology like the gradients and fields in an MRI. But instead of for using it for imaging, it drives the millirobots."

Axel Krieger, Senior Author

The researchers successfully tested the robots on phantom heart models that closely mimic a human heart, and on real porcine heart tissue. The robots traveled smoothly and autonomously, even against simulated blood flow.

"We can just inject a robot with a little pill into your vein where it travels to the site, right to where we really need to deliver the drugs, and it's minimally invasive," said first author Anuruddha Bhattacharjee, a former Johns Hopkins postdoctoral student who is now an assistant professor at University of Alabama at Birmingham.

In addition to eliminating the need for open-heart surgery, drug treatment with the robots could take hours instead of weeks.

"Usually if you do IV drug treatment, you need four to six weeks of therapy. But with these robots the entire procedure might take 10 minutes-maybe an hour if you want to do a couple rounds," Bhattacharjee said. "If everything works well, you go from four to six weeks of treatment to one day or less."

The team also believes the robots would also be helpful delivering targeted medications to fight cancer where it's spreading.

The researchers next plan to test the robots in more realistic phantom hearts, with muscle contraction and the beating movement of a real heart.