Led by Manu Mannoor and Sudeep Joshi, a team from New Jersey's Stevens Institute of Technology started with an ordinary, living button mushroom. They proceeded to 3D-print a branched pattern onto its cap, using an electronic ink containing graphene nanoribbons. Next, utilizing a bio-ink containing cyanobacteria, they 3D-printed a spiral pattern over top of the first pattern.
Shining a light on the mushroom caused the bacteria to photosynthesize, producing electrons which passed through their outer membranes. At points on the cap where the bio-ink pattern intersected that of the electronic ink, those electrons were transferred to a conductive network formed by the graphene nanoribbons.
The setup ultimately generated a current of about 65 nanoAmps. While that isn't enough to power a device, it is thought that an array of the mushrooms could illuminate an LED.