This is a flexible array of LEDs mounted on paper. Hand-drawn silver ink lines form the interconnects between the LEDs.

Two professors from the University of Illinois; one specializing in materials science, the other in electrical engineering, have combined their talents to take the idea of printing circuits onto non-standard materials one step further by developing a conductive ink that can be used in a traditional rollerball ink pen to draw circuits by hand onto paper and other porous materials. In their paper published in Advanced Materials, team leads Jennifer Lewis, Jennifer Bernhard and colleagues describe how they were able to make a type of ink from silver nanoparticles that would remain a liquid while in the pen, but would dry like regular ink once applied. The pen could was then used to draw a functioning LCD display and an antenna.