Scientists have developed tiny, remote-controlled robots — each no larger than a grain of sand — that can travel through blood vessels to deliver medication directly to targeted areas of the body. The goal is to allow doctors to give precise doses where they’re needed most, while avoiding the harmful side effects that occur when drugs circulate throughout the entire body.

According to Nature, these microrobots are guided by magnetic fields and have already been successfully tested in pigs and sheep. While the system has not yet been tried in humans, researchers say the results are promising because the animals’ blood vessel structures and components are similar to those of people.

Robotic experts at Switzerland’s ETH Zurich described their breakthrough in the journal Science. They designed a tiny gel capsule containing iron oxide particles, which allows the robot to be steered magnetically. Once the capsule reaches its destination and delivers the medication, it dissolves harmlessly.

“Because the vessels in the human brain are so small, there is a limit to how big the capsule can be. The technical challenge is to ensure that a capsule this small also has sufficient magnetic properties,” said robotics researcher and study coauthor Fabian Landers.

To help track the robots during procedures, Landers and his team added nanoparticles of tantalum so the devices can be seen on X-rays. Finding the right material combination took years, but researchers say they now have a magnetic microrobot capable of navigating the body’s roughly 360 arteries and veins.

Bradley Nelson, a mechanical engineer at the Swiss Federal Institute of Technology who co-led the project, noted that one-third of new drugs fail to reach the market because they are too toxic when delivered throughout the body. The microrobot system could solve this problem by delivering tiny amounts of medication directly to specific sites, reducing dangerous side effects. The technology could be used to treat conditions such as stroke, where targeted drugs might break up blockages, or to deliver therapies to brain tumors.

In early laboratory tests, the microrobots achieved a 95% accuracy rate when delivering drugs to the correct location in pigs. The team then moved on to sheep, successfully navigating the animals’ cerebrospinal fluid — a result that suggests the technology could have broad medical applications.

“This complex anatomical environment has enormous potential for further therapeutic interventions, which is why we were so excited that the microrobot was able to find its way in this environment, too,” Landers said.

The achievement is the result of two decades of work to develop materials that allow the robots to be controlled remotely while remaining tiny enough to maneuver through extremely small blood vessels.

“The next step is looking at doing some kind of clinical trials with this in humans,” Landers added.