Editors' ChoiceMedical Devices

Ear Power: Batteries Now Included

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Science Translational Medicine  28 Nov 2012:
Vol. 4, Issue 162, pp. 162ec215
DOI: 10.1126/scitranslmed.3005333

A necessity for many small, surgically implanted electronic devices is battery power. The lifespan of any battery is finite, imposing limits on its use in the body. Mercier and colleagues capitalized on the natural electrochemical gradient of the inner ear to power an electronic device without a battery.

In the inner ear of mammals, there is an electrochemical gradient called the endocochlear potential (EP). The EP is well known to be a critical component that drives the conversion of sound to auditory nerve pulses. Mercier et al. used the EP to power a specially designed “endoelectronic” microchip from electrodes positioned in the perilymph and endolymph in the inner ear of a guinea pig.The power generated was sufficient to measure the EP in real time and transmit these measurements via a 2.4-GHz radio every 40 to 360 s. Overall, the microchip extracted a minimum of ~1 nW for this short 5-hour experiment. The impact of this device upon auditory function was also examined. Threshold decibel responses were nearly the same across all frequencies compared to measurements taken before the insertion of the electrodes.

Before such technology can be used to power ear-implanted devices (or nearby implants in the brain, nerves, or arteries), the device would need to become independently operated. The current device required a “kick start” of external power because the power provided by EP is so low. Also, no current medical device could be sufficiently powered by the low amount of power generated in this study. Nonetheless, the clinical benefits of using battery-free implanted devices, which would eliminate the size and maintenance associated with a battery, are abundant.

P. P. Mercier, A. C. Lysaght, S. Bandyopadhyay, A. P. Chandrakasan, K. M. Stankovic. Energy extraction from the biologic battery in the inner ear. Nat. Biotechnol., published online 8 November 2012 (10.1038/nbt.2394). [Abstract]

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