Wireless devices, implanted deep within the human body, could deliver a drug, monitor patient conditions, or stimulate the brain with electricity or light, thanks to new communications and power-transfer technology developed by Massachusetts Institute of Technology (MIT) researchers and scientists from Brigham and Women’s Hospital.
Radio frequency waves – which can safely pass through human tissues – charged the implants. Without the need for a battery, the devices can be tiny. Researchers tested a prototype about the size of a grain of rice, but they anticipate that it could be made even smaller.
Batteries in current medical devices such as pacemakers occupy most of the space in the product, and they offer limited lifespans. Fadel Adib, an assistant professor in MIT’s Media Lab, envisions much smaller, battery-free devices, and is exploring the possibility of wirelessly powering implantable devices with radio waves emitted by antennas outside the body.
Radio waves tend to dissipate as they pass through the body, becoming too weak to supply enough power. To combat that, researchers devised an In Vivo Networking (IVN) system that relies on an array of antennas that emit radio waves of slightly different frequencies. As the waves travel, they overlap and combine in different ways. At certain points, where the high points of the waves overlap, they can provide enough energy to power an implanted sensor.
“We chose frequencies that are slightly different from each other, and in doing so, we know that at some point these are going to reach their highs at the same time… [to] overcome the energy threshold needed to power the device,” Adib says.
With the new system, researchers don’t need to know the exact location of the sensors in the body, as the power is transmitted across a large area. They can power multiple devices at once. When the sensors receive a burst of power, they also receive a signal telling them to relay information back to the antenna. This signal could also be used to stimulate the release of a drug, a burst of electricity, or a pulse of light.
In tests with pigs, the researchers found they could send power from up to 1m outside the body, to a sensor that was 10cm deep in the body.
If the sensors are located very close to the skin’s surface, they can be powered from up to 38m away.
“There’s currently a tradeoff between how deep you can go and how far you can go outside the body,” Adib says.
Researchers are now working on making the power delivery more efficient and transferring it across greater distances.