Medical Devices Could Be Powered by Body’s Natural Battery

A new study demonstrates that endocochlear potential (EP), a battery-like electrochemical gradient found in and actively maintained by the inner ear, could power implantable electronic devices.

Researchers from the Massachusetts Institute of Technology (MIT; Cambridge, USA), the Massachusetts Eye and Ear Infirmary (MEEI; Boston, USA), and Harvard University (Boston, MA, USA) demonstrated for the first time that this EP could power implantable electronic devices, without impairing hearing. The devices could monitor biological activity or responses to therapies in people with hearing or balance impairments, and might eventually even deliver therapies themselves.


The researchers designed an anatomically sized, ultra-low quiescent-power energy harvester chip that was integrated with a wireless sensor capable of monitoring the EP itself. The researchers succeeded in extracting a minimum of 1.12 nW from the EP of a guinea pig for up to 5 hours, enabling a 2.4 GHz radio to transmit measurement of the EP every 40-360 seconds. After the implantation, the guinea pigs responded normally to hearing tests, and the devices were able to wirelessly transmit data about the chemical conditions of the ear to an external receiver. The study was published on November 8, 2012, in Nature Biotechnology.

“We have known for 60 years that this battery exists and that it’s really important for normal hearing, but nobody has attempted to use this battery to power useful electronics,” said study coauthor Konstantina Stankovic, an otologic surgeon at MEEI. “With future optimization of electrode design, we envision using the biologic battery in the inner ear to power chemical and molecular sensors, or drug-delivery actuators for diagnosis and therapy of hearing loss and other disorders.”

The ear converts the vibrations of the eardrum into an electrochemical signal that can be processed by the brain; the biological battery is the source of that signal’s current. Located in the cochlea, the battery chamber is divided by a membrane, some of whose cells are specialized to pump ions. An imbalance of potassium and sodium ions on opposite sides of the membrane, together with the particular arrangement of the pumps, creates the electrical voltage.

Related Links:
Massachusetts Institute of Technology
Massachusetts Eye and Ear Infirmary
Harvard University