Energy harvesting chip size comparison and closeup. The radio transmitter onboard is powered by a mammalian ear. (via MIT)
Living creatures are full of energy being converted and transferred continuously. Differences in potential or voltages, cause electrical signals to move from one place to the other within the body. Scientifically speaking, all living things are examples of power. MIT is taking advantage of at least one tiny power plant in the human body.
This biological battery is located in the deep inner mammalian ear where a chamber filled with ions produces a voltage that drives neural signals. Specifically, this chamber is called the cochlea and it consists of membranes with specialized pumping cells that transfer ions from one side of it to the other. Imbalanced sodium and potassium ions, on either side of the membrane, and a distinctive arrangement of these pump cells, converts and amplifies the mechanical energy, in vibrations of the ear drum, into an electrochemical signal that can be processed by the brain.
The team attached an electrode on each side of this membrane in a guinea pig’s ear in the same fashion one would integrate a regular battery. Connected to the electrodes was an ultralow-power radio transmitter chip made by MIT’s microsystems technology laboratories designed to transmit chemical conditions of the inner ear. After implantation, the animal was fully responsive to hearing tests. For the sake of prototyping, the chip was kept outside the ear, but the team states the chip is small enough to find in the cochlea.
A problem with the initial set up was that the voltage inside the cochlea was not enough to get the chip up and running. To solve this, the MLT chip was fitted with simplified power-conversion circuitry that builds up charge from an initial blast of radio waves. Once the chip reaches adequate voltage, the biological battery inside the cochlea can power it.
The applications of this can result in cochlear implants, and hearing aids that are powered by the body. Measuring how this cochlear voltage changes during different diseases or disease states could lead to new methods for diagnosis. Eventually, scientists believe these cochlear-powered implants could provide therapy themselves and fix inner ear problems.
This experiment is being headed by Konstantina Stankovic, otology surgeon at the Massachusetts Eye and Ear Infirmary and graduate student, Andrew Lysaght, from the Harvard-MIT Division of Health Sciences and Technology. Their results were published in the journal of Nature Biotechnology earlier this month, November 2012.
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