Electric eel inspires research team to develop implantable battery

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The electric eel has inspired researchers at the University of Fribourg, the University of Michigan, and the University of California San Diego, to develop a novel power source and suggest their work could enable self-powered batteries for biological applications such as pacemakers.

According to the team, integration of technology into living organisms requires some form of power source that is biocompatible, flexible and able to draw energy from inside a biological system. Generating electricity inside the body, they say, would eliminate the need for replacement surgery in some cases and could provide sustained power for wearable devices such as electrically active contact lenses with an integrated display.

The researchers began by reverse-engineering the eel’s electric organ, which is made up of long and thin cells called electrocytes. These span 80% of the eel’s body in parallel stacks and generate a small voltage almost simultaneously by allowing sodium ions to rush into one side of the cell and potassium ions out on the other side of the cell. Together, these cells can generate up to 600V.

The team, led by Fribourg Professor Michael Mayer, designed a power source that generates electricity based on the salinity difference between compartments of fresh and salt water separated by ion-selective membranes. By arranging hundreds of these compartments and membranes in a repeat sequence, it was possible to generate 110V.

Each component is made of a hydrogel that can be assembled on clear plastic sheets using a commercial 3D printer. Like the eel, the power source has individual compartments with small capacities, so the voltages must be triggered at the same time. While the eel does this using its nervous system, the researchers achieved this by bringing all the cells into contact simultaneously, using a strategy originally developed to unfold solar panels in space.

The results are still far from matching the capacities of the eel. According to Mayer, the major challenge will be to tap into the body’s metabolic energy, for example by mobilizing ion differences in zones such as the stomach fluids, or by converting mechanical muscle energy to electrical energy, which could then be stored and released from an artificial electric organ.

The researchers are now working to improve the efficiency of their design.