Optimal systems benefit by having an infrastructure that perfectly marries local supply and demand. The generation of energy resources at the site of their use enhances reliability and minimizes waste. It is for this reason that bioengineers are coming up with new ways to power electronic implants using tricks already inherent in the modality of the implant’s operation — or, in other words, devices that are powered by your body.

Implants for vision which use lasers to stimulate the retina might also deliver power for the signal processing circuitry. Defibrillators for the heart, once huge capacitor banks that would take seconds to charge and leave burn marks on the skin, are now replaced with lower power versions that stimulate with optimized waveforms to restart the heart with less energy. They can now be incorporated into internal pacemakers and possibly draw their power with piezoelectric converters that pick up secondary vibrations. In the brain, where each cell’s function is so tightly coupled to its oxygen and glucose supply that consciousness is dimmed within seconds of its cessation, glucose fuel cells might provide local, demand-optimized power for implants.

Energy harvesting has now reached the human ear. The cochlear implant, though hugely successful, requires a bulky external system to deliver both wireless power and the recorded sound signal to the internal stimulator. An intriguing enhancement would be to develop systems so efficient that all the power necessary for reception of a signal is administered through the signal transmission itself. In other words the charging current is modulated with the signal so that a separate channel becomes superfluous.

That concept is still a long way off, but in the meantime researchers have begun seeking ways to extract power from a battery that is naturally built into the machinery of the ear. The inner ear has no local blood supply, as it would interfere with mechanical response as well as introduce a pulsating source of noise to a system attempting to resolve vibrations many orders of magnitude smaller than that noise. Without energy supplied through blood, the ear chamber relies on the small ion pumps in lining of the chamber to, in effect, pressurize it with positive potassium ions. The ions can then later be released to flow down an electrochemical gradient which acts to amplify and transmit the sound signal to the brain.

Konstantina Stankovic, an otologic (ear) surgeon at the Massachusetts Eye and Ear Infirmary, and others from MIT, have now built a device that could tap into this source and possibly power implants from the inside. They tested the device in guinea pigs, which possess hearing hardware similar in shape and range of function to humans. Electrodes on either side of a natural membrane in the biological battery picked up a fluctuating voltage, and rectified it with power conversion circuitry that was part of an on-board chip. The chip also had a transmitter which relayed a frequency-modulated signal back out to the researchers which gave accurate indication of the inner ear potential.

It generally would take a minute or two for the device to store enough charge to power a transmission so the signals were relayed in brief snatches. The device is still in its infancy and other breakthroughs are needed before we have fully embedded cochlear implants. Accurate sensing of sounds from internal vantage points in the ear or even the mouth have been explored, and may eventually find application within this framework. As we have seen, doing more with less, and paying the piper as he plays, are the new design philosophies that will help deliver biologically miscible solutions to the restorative and augmentative technologies that await us.

Now read: A bionic prosthetic eye that speaks the language of your brain