The electric eel has caught the attention of researchers searching for biologically compatible alternatives to batteries as power sources for medical implants and wearables. An international team of engineers designed a transparent electrical device as the first potentially biocompatible artificial electric organ that generates more than 100 V.

Composed of hydrogel and salt, the soft power cells generate electricity at high voltage but low current, likely sufficient to power a pacemaker or other small medical device.

Electric eels sport specialized electrical organs that contain thousands of alternating compartments, each with an excess of either potassium or sodium ions. The compartments are separated by selective membranes that keep the ions separated in the eel's resting state. The membranes allow the ions to flow together and create a burst of power when the eel needs to produce a jolt of electricity.

A similar system engineered in the laboratory used sodium and chloride dissolved in the water-based A 3D bioprinter deposited arrays of gel precursor droplets onto plastic substrates. Alternating high-salinity and low-salinity gels (red and blue gels, respectively) were printed onto one substrate, and alternating cation-selective and anion-selective gels (green and yellow gels, respectively) onto a second substrate. These connect to form a conductive pathway of 612 tetrameric gel cells generating up to 110 volts. Source: Thomas Schroeder/University of Michiganhydrogel. Thousands of salty gel droplets were printed on a plastic sheet, alternating them with hydrogel droplets of pure water to mimic the function of the eel’s compartments. Alternating droplets composed of charge-selective hydrogel and printed onto a second sheet allow either positively charged sodium or negatively charged chloride to pass, excluding the other.

Pressing the two sheets together connects saline and freshwater droplets across the charge-selective droplets in series. As the salty and fresh solutions mix, the charge-selective droplets move the sodium and chloride ions in opposing directions, producing an electric current.

All four droplet types were then alternated in a precise pattern on a flat sheet that had been laser-scored in a Miura pattern, an origami technique used to fold solar panels into satellites at launch. The sheet quickly folded together under pressure, stacking the cells in exactly the right positions.

"The electric organs in eels are incredibly sophisticated; they're far better at generating power than we are," said Michael Mayer, a professor of biophysics at the Adolphe Merkle Institute of the University of Fribourg in Switzerland. "But the important thing for us was to replicate the basics of what's happening."

The researchers believe the technology may one day prove useful for powering implantable or wearable devices without the toxicity, bulk or frequent recharging associated with batteries. It could even lead to bioelectric systems that could generate electricity from naturally occurring processes inside the body.

Researchers from University of Michigan and University of California-San Diego also participated in this project.