The implants are powered by radio frequency waves that can safely pass through human tissue. The waves are able to power devices that are 10 cm deep in tissue from 1 meter away.
“Even though these tiny implantable devices have no batteries, we can now communicate with them from a distance outside the body. This opens up entirely new types of medical applications,” Fadel Adib, assistant professor in MIT’s Media Lab and senior author on the study, said in a press release.
Since the devices don’t need a battery, they can be made tiny. The researchers tested a prototype that was about the size of a grain of rice, but they hope to make the devices smaller in the future.
“Having the capacity to communicate with these systems without the need for a battery would be a significant advance. These devices could be compatible with sensing conditions as well as aiding in the delivery of a drug,” Giovanni Traverso, an author on the study, said.
Ingestible or implantable medical devices can give doctors a new way of diagnosing, monitoring and treating different diseases. Implantable electrodes in the brain that deliver an electrical current are used for deep brain stimulation. Traditionally, the electrodes are controlled by a pacemaker-like device that is implanted under the skin. The pacemaker-like device could be completely eliminated if wireless power can be implemented.
Other implanted medical devices like pacemakers have their own batteries that take up a lot of space on the device and have a limited lifespan. Adib has been working on wirelessly powering implantable device with radio waves emitted by antennas outside of the body. Until this study, it had been difficult to have a wireless system like that because radio waves dissipate as they pass through the body, which means they’re too weak to supply enough power to the device.
The researchers developed a system called In Vivo Networking (IVN) that relies on an array of antennas that emit radio waves of different frequencies. The radio waves overlap and combine in different ways as they travel and at certain points, 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 in time these are going to reach their highs at the same time. When they reach their highs at the same time, they are able to overcome the energy threshold needed to power the device,” Adib said.
Using the new system means that researchers don’t need to know the exact location of the sensor in the body since the power gets transmitted over a large area. It also means that they are able to power more than one device at a time. When the sensors receive a burst of power, they are also receiving a signal that tells them to relay information back to the antenna. The researchers suggest that the signal could be used to stimulate the release of a drug, a burst of electricity or a pulse of light.
The researchers tested the system in pigs and showed that they could send power from up to a meter outside of the body to a sensor that was 10 cm deep in the body. If the sensors were implanted closer to the surface of the skin, they could be powered up to 38 meters away from the body.
“There’s currently a tradeoff between how deep you can go and how far you can go outside the body.” Adib said.
The researchers are working on creating a more efficient power delivery and further developing the system to transfer the power over greater distances. The technology also has the potential to improve RFID applications in other areas like inventory control, retail analytics and “smart” environments.
The research was funded by the Media Lab Consortium and the National Institutes of Health.