Researchers at Harvard and the University of Chicago used "electrochemically active ink" and a custom 3D printer to print microbatteries smaller than a single grain of sand. They reported their breakthrough in the journal Advanced Materials.

So why might we need such small batteries? To power microdevices such as medical implants or insect-like flying robots.

Watch here to see the printing of these batteries in action:

Image and video courtesy of Lewis Research Group, Harvard University