Nick Williams didn’t ask permission. The graduate student just stuck his pinky finger under the printer and watched it paint two silver lines on his skin. When printing was complete, Williams put a small LED light at one end of the lines and applied voltage to the other. He smiled as the light glowed.
Williams showed the electronically active tattoo to his advisor, Duke University electrical engineer Aaron Franklin. Since Williams barely felt the printing, and the silver washed off with soap and water, they tried it again.