The knifefish Electrophorus electricus, better known as the electric eel, can generate electricity to stun its prey thanks to specialized organs that generate power via ion flux—no batteries required. The structure of these organs provided a jolt of inspiration to researchers led by Michael Mayer of the Adolphe Merkle Institute at the University of Fribourg, who wanted to create a soft power source. The electric eel’s organs contain thousands of alternating compartments containing either potassium or sodium ions separated by membranes that keep the ions apart. When the knifefish charges up, the membranes let the ions flow, creating a burst of power. To create ion gradients in their system, Mayer and colleagues used three-dimensional printing to pattern a substrate with alternating spots of hydrogels loaded with either sodium chloride or pure water (shown in red and blue, respectively). On a different substrate, they dotted cation-selective and anion-selective hydrogels (shown in green and yellow, respectively). When overlaid, the system of dots creates a conductive pathway that can generate up to 110 V (Nature 2017, DOI: 10.1038/nature24670). The researchers note that because the materials are biocompatible, they have the potential to power implantable medical devices, such as pacemakers. “To get there, we are looking for talented Ph.D. students and postdocs,” Mayer says.