Johns Hopkins Engineers Develop Millirobots to Treat Heart Infections

Engineers at Johns Hopkins University have developed a pair of magnetic millirobots designed to travel through the body and deliver antibiotics directly to heart tissue infections. Measuring about the size of a pencil tip, the wirelessly guided devices aim to replace weeks of intravenous drug therapy and risky open-heart surgery.

Life-threatening heart tissue infections known as infective endocarditis affect roughly 50,000 people across the United States every year. Standard medical treatment relies on a grueling course of intravenous antibiotics lasting four to six weeks. Because these drugs often dilute significantly before reaching the heart, physicians frequently face a difficult choice between prescribing toxic, high-dose antibiotics or performing invasive open-heart surgery. A team of engineers has proposed a microscopic alternative that bypasses the limitations of traditional drug delivery.

How Two Magnetically Guided Robots Coordinate Inside the Heart

The newly engineered system relies on two distinct magnetically-powered robots called millirobots, each roughly as wide as a pencil tip or matchstick head and about as long as a grain of rice. These miniature machines work in tandem to anchor themselves and dispense medicine precisely where infection takes hold. The first device, designated the needle module, features a tiny barbed tip designed to latch gently onto heart tissue right at the infected site, remaining stationary to act as a permanent docking station during the procedure.

Image from a video showing how tiny robots connect in a phantom heart model — Photo: hub.jhu.edu

Once the needle module secures its position, the second device—known as the drug module—carries liquid medication through the body to dock magnetically with its partner. The drug module then gradually releases its cargo directly onto the target tissue. An external electromagnetic coil system, operating on principles similar to magnetic resonance imaging technology, guides both robots wirelessly from outside the body. Because the external magnetic fields supply all the propulsion, neither robot requires onboard motors or batteries.

Magnetic guidance is exciting because you don’t have to power the robot itself.

Axel Krieger, senior author and medical roboticist at Johns Hopkins University

Having two separate robots instead of one larger mechanism allows the hardware to move through tight cardiovascular spaces. Because the anchoring needle module stays locked in place, the drug module can detach, travel back out, and accept replacement payloads for multiple rounds of treatment.

See How Robots Deliver Medicine Inside the Heart

Laboratory Testing on Phantom Models and Porcine Tissue

To evaluate how the millirobots perform under physiological conditions, the research team constructed artificial heart models using a gel-like material. They pumped liquid through these models to simulate active, pulsating blood flow. In laboratory trials, the robots navigated autonomously, maintaining smooth movement even against simulated fluid resistance. Additional tests on excised pig heart tissue confirmed that the needle module successfully penetrated tissue while the drug module executed clean docking and undocking maneuvers.

Magnetic docking achieved a 100% success rate across reported trials, while undocking succeeded 93% of the time. During release tests, the drug module dispensed 22 microliters of liquid over a three-hour span—an amount smaller than a typical drop of water.

Johns Hopkins Engineers Develop Millirobots to Treat Heart Infections — Photo: ZME Science

Timeline Reductions and Potential Expansion to Cancer Treatment

While conventional intravenous drug regimens demand weeks of continuous administration, the robotic procedure could compress the timeline dramatically.

“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. If everything works well, you go from four to six weeks of treatment to one day or less.”

Anuruddha Bhattacharjee, first author

Beyond clearing cardiac infections, the research team believes the same steerable magnetic platform can be adapted to deliver targeted therapeutics to hard-to-reach malignancies where cancer is actively spreading. Investigators next plan to test the millirobots in more complex phantom heart models that replicate the natural muscle contractions and beating movements of a living organ. The development was supported by the National Science Foundation’s Foundational Research in Robotics CAREER program under award 2144348, with findings published in Advanced Materials Technologies.

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