November 7, 2012
Scientists Use Inner Ear For Battery Power
Lee Rannals for redOrbit.com — Your Universe Online
Researchers reported in the journal Nature Biotechnology that they have found a new way to help power an implantable electronic device in the ear, naturally.
The scientists said they have demonstrated for the first time that they could use the inner ear to help power implantable electronic devices without impairing hearing.
The inner ear in mammals is a chamber filled with ions that produces an electrical potential to drive neural signals. Ultimately, the devices could monitor biological activity in the ears of people with hearing or balance impairments, or responses to therapies.
During experiments, the team implanted electrodes in biological batteries in guinea pigs' ears. Low-power electronic devices were attached to the electrodes.
After implantation, the guinea pigs responded normally to hearing tests, and they were able to wirelessly transmit data about the chemical conditions of the ear to an external receiver.
“In the past, people have thought that the space where the high potential is located is inaccessible for implantable devices, because potentially it´s very dangerous if you encroach on it,” Konstantina Stankovic, an otologic surgeon at Massachusetts Eye and Ear Infirmary, said in a press release. “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.”
The ear is able to convert a mechanical force into an electrochemical signal that can be processed by the brain. 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, along with a certain arrangement of the pumps, helps to create an electrical voltage.
The researchers equipped their chip with an ultra low-power radio transmitter to help send measurements. The chip is capable of running on the biological battery, but it was not an easy task.
The chip includes power-conversion circuitry that gradually builds up charge in a capacitor. They found that the control circuit needed to be simplified to reduce power consumption. Once this was done, the researchers had to get the control circuit up and running.
“In the very beginning, we need to kick-start it,” Anantha Chandrakasan, who heads MIT´s Department of Electrical Engineering and Computer Science, said in a press release. “Once we do that, we can be self-sustaining. The control runs off the output.”
The team implanted electrodes attached to the MTL chip on both sides of the membrane in the biological battery of each guinea pig's ear. During the experiments, the chip remained outside the guinea pig's body.
“The fact that you can generate the power for a low voltage from the cochlea itself raises the possibility of using that as a power source to drive a cochlear implant,” Megerian said in the release. “Imagine if we were able to measure that voltage in various disease states. There would potentially be a diagnostic algorithm for aberrations in that electrical output.”
He said the current technology isn't ready, but if the team is able to tap into the natural power source of the cochlea, it could potentially be a driver behind the amplification technology of the future.