Doctors make sure your heart is ticking steadily by taking an electrocardiogram, placing electrodes on your skin to measure your heart’s electric activity. Someday, though, we might be able to take such measurements more precisely from inside our bodies. A team of Japanese scientists has designed an amplifying device that can be implanted into the body to detect even faint cardiac signals—like an internal ECG.

Monitoring our bodies from the inside rather than relying on external instruments allows tracking of individual organs more precisely. However, the human body can be an inhospitable environment for such devices, which must stay attached to the moist, curved surfaces of our organs over long periods of time without degrading.

To create flexible electrodes that can still transmit electricity, the researchers linked a carbon nanotube sheet to a stretchable gel made of cross-linked polyrotoxane molecules, a barbell-shaped polymer. The resulting material was less than a micrometer thick and could bend and flex easily, as reported in Nature Communications.

The researchers fabricated an array of tiny amplifiers on that substrate. They used the electrode/amplifier system to obtain electrical measurements of heart activity like those taken by an ECG. Tests in animals suggested that the device was less invasive and less disruptive in the body than traditional metal electrodes.

“Electric vital signals are very small, so amplifiers to increase these signals are needed,” says Takao Someya, a physicist at the University of Tokyo who led the project.

By using a device implanted into the body, Someya says, “an ECG can be measured with high spatial and temporal resolution simultaneously.” That precision could help doctors not just to identify an organ that is not working properly, but to pinpoint the specific part that is struggling.

Down the road, in vivo monitors like this one would not necessarily have to stand alone. They could also be wired into larger circuits to collect data and then respond to it.

“One vision is that such sensing systems could be connected, in a feedback loop, to stimulating systems, providing increased sophistication in pacemakers, low energy defibrillators and other similar technologies,” says John Rogers, a materials scientist at University of Illinois at Urbana-Champaign who was not involved in the work.

However, the setup has a long way to go before it is ready for real-world use. “One of the challenges is to improve the mechanical durability of the gel while maintaining material softness,” says Someya. It is possible that over time, the gel/nanotube composite could break down inside the body. The system would also need to undergo rigorous tests in humans.

Read the article in Nature Communications.