Learning from Electric Eels

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Biomimicry may be considered a science of emulation in which engineers build systems for human use based on the way nature builds its systems. This science looks at nature in a new way, focusing not on what humans can extract from nature but rather what they can learn from nature.

In 2008 researchers at Yale University developed tiny artificial cells for the purpose of powering medical implant devices. They used the energy-generating cells called electrocytes in electric eels as their model. The chemical engineer Jian Xu explained, “The electric eel is very efficient at generating electricity. It can generate more electricity than a lot of electrical devices.” (A clue to this ability lies in the eel’s biological name, Electrophorus electricus.) The engineering team’s problems in generating energy the same way as an eel does were twofold: understanding how the electrocyte works and learning to build a similar electrical device.

Electric eels have three different energy-generating systems: two high-voltage systems are used for defense and for stunning prey and a low-voltage system helps in navigation. Disc-shaped electrocytes run all three of these systems. The electrocytes stack up like a series of watch batteries in the eel’s organs so that when each fires and produces a low to moderate amount of energy, the cumulative effect is a large energy pulse.

Non-firing electrocytes hold a negative charge inside the cell by constantly pumping positive sodium ions (Na+) out and allowing positive potassium ions (K+) to naturally diffuse out through the cell membrane. An ion is an element missing electrons or possessing extra electrons. To fire the electroctyes the eel’s brain sends a message to nerve cells, which stimulate one side of each electrocyte. The side of the electrocyte receiving this nerve impulse becomes stimulated in a process called depolarization. The nerve-side of the electrocyte becomes depolarized an instant before the far side of the electrocyte depolarizes. This occurrence leads to a temporary one-way flow of ions or an electrical charge. The eel’s charge of up to 600 volts comes from the synchronized depolarization of about 200,000 electrocytes.

Yale’s researchers built small discs based on the electrocyte’s depolarization action, which they called a “bio-battery.” The quarter-inch- (0.64-cm) thick bio-batteries contain the following two components: (1) artificial membranes based on the electrocyte membrane that sets up inside-outside charge differences, plus (2) proteins that mimic the ion channels in real membranes. So far, the artificial electrocytes have been made to generate 30–40 percent more power than the natural electrocyte. The researchers plan to line up the bio-batteries in several stacks of about a dozen to produce enough electricity to power medical prostheses such as retinal implants.

Though these plans and devices are scarcely off the drawing board, tiny power generators have opened similar possibilities for using bacterial cells or even mitochondria—the energy-generating component of eukaryotic cells—as mini–power plants. The task involves only the willingness to apply basic engineering concepts to designs produced by nature.