Devices that monitor inner ear activity could eventually be powered by the ear itself, according to research detailed in the current issue of the journal Nature Biotechnology by scientists from MIT, Massachusetts Eye and Ear Infirmary (MEEI), and the Harvard-MIT Division of Health Sciences and Technology (HST).
They say that for decades we have known the inner ear houses its own natural battery, but this is the first demonstration of its ability to power something external without compromising hearing.
"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," said Konstantina Stankovic, an otologic surgeon at MEEI, in a news 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."
First, a reality check: we're nowhere near being able to rely on our ears to power most devices we hold close to them -- i.e. iPods and smartphones. Nor are the researchers claiming that they were able to power current devices, such as cochlear implants, via this natural battery.
What they have demonstrated in experiments on guinea pigs (actual, literal guinea pigs) is that the tiny, low-power devices they attached to electrodes implanted in the animals' ears were able to wirelessly transmit data about the chemical conditions of the ear to an external receiver, and that the guinea pigs still responded normally to hearing tests.
The ear's cochlea houses a biological battery chamber divided by a membrane, some of whose cells pump ions. Because potassium and sodium ions on opposite sides of the membrane are not in balance, an electrical voltage results.
The trick isn't so much harvesting the power, it's developing devices with such a tiny power demand that they can rely on the low and fluctuating voltage. Because of this fluctuation, and because a device can only harvest a fraction of this power if hearing is to remain intact, the team says it would take between 40 seconds and 4 minutes to amass sufficient charge simply to power their chip's radio transmitter.
Still, it's a start.
"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," said Cliff Megerian, chairman of the otolaryngology department at Case Western Reserve University and not affiliated with the research. "I'm not ready to say that the present iteration of this technology is ready, [but]... if we could tap into the natural power source of the cochlea, it could potentially be a driver behind the amplification technology of the future."