Overview
Researchers from MIT and Brigham and Women's Hospital have developed a method to power and communicate with implanted medical devices using radio waves instead of batteries. These battery-free devices could deliver drugs, monitor internal conditions, or use electrical current and light to stimulate the brain for therapeutic purposes.
Device size and prototypes
The prototypes can safely traverse body tissue and, without batteries, can be made much smaller. The research prototypes are about the size of a grain of rice, and the team expects further miniaturization is possible.
Remote communication and applications
Fadel Adib, an assistant professor at the MIT Media Lab, said that although these micro-implants lack batteries, they can still communicate remotely from outside the body, enabling new types of medical applications. Implantable devices provide clinicians additional options for diagnosis, monitoring, and treatment.
Resorbable systems under study
Assistant professor Giovanni Traverso said the lab is investigating various bioresorbable systems for drug delivery, vital-sign monitoring, and detecting gastrointestinal motility.
Background on existing implantable devices
Current implantable medical devices, such as pacemakers, include batteries that occupy significant volume and have limited lifetimes. Electrodes implanted in the brain that deliver current are used in deep brain stimulation to treat conditions like Parkinson's disease or epilepsy. Those electrodes are typically controlled by subcutaneously implanted hardware, which could potentially be replaced by a wireless power source.
In vivo network (IVN) approach
Radio waves lose strength when passing through the body and so may not supply sufficient power. To address this, the researchers designed an in vivo network system called IVN. The system uses an array of antennas that emit radio waves at slightly different frequencies. As the waves propagate, they interfere and combine in varying ways; specific locations where wave peaks overlap can concentrate enough energy to power implanted sensors.
Multiple-device powering and signaling
Because the IVN transmits power over a larger area, the researchers do not need to know the exact location of each sensor, and multiple devices can be powered simultaneously. When a sensor receives power, it also receives a command signal instructing it to transmit data back to the antenna. The same signaling can trigger drug release, increase delivered current, or pulse light.
Experimental results
In tests on pigs, the system delivered power from 1 meter outside the body to sensors located 10 centimeters deep. If a sensor is located very close to the skin surface, radio waves could power it from up to 38 meters away.
Future work and broader applications
Adib noted that implant depth affects remote power range, and the team is working to improve power-transfer efficiency and increase range. The technique could also enhance other RFID applications such as inventory control, retail analytics, and smart environments by enabling longer-range object tracking and communication.
Funding and publication
The research was funded by the Media Lab Consortium and the U.S. National Institutes of Health. The paper is scheduled for presentation at the SIGCOMM conference in August.
