What a Feeling: Researchers Improve Process to Produce Electronic Skin

Scientific development could be used for human-machine interactions, including prosthetics and wearable health monitors.

Developing an artificial sense of touch could have tremendous implications for robotics, prosthetic devices, wearable health monitors, and virtual reality. The technology behind this quest has taken a leap forward with production of electronic skin using, in part, circuits printed onto tattoo transfer paper with an ordinary desktop laser printer.  

The process resulted in an ultrathin, stretchable electronic skin that could be used for a variety of human-machine interactions, according to a study published in the scientific journal, ACS Applied Materials & Interfaces.

Researchers demonstrated multiple applications of the new method, such as controlling a robot prosthetic arm, monitoring human skeletal muscle activity, and incorporating proximity sensors into a 3D model of a hand, according to a news release and captured in a video. In combination with other innovations, this electronic skin could provide the missing element needed for other medical advancements.

Production of electronic skin is not new. "A major challenge is transferring ultrathin electrical circuits onto complex 3D surfaces and then having the electronics be bendable and stretchable enough to allow movement," according to a news release. "Some scientists have developed flexible 'electronic tattoos' for this purpose, but their production is typically slow, expensive, and requires clean-room fabrication methods such as photolithography."

The scientists involved in this latest endeavor, including lead authors Mahmoud Tavakoli of University of Coimbra in Coimbra, Portugal, Carmel Majidi of Carnegie Mellon University in Pittsburgh, and their colleagues, wanted to develop a fast, simple, and inexpensive method for producing thin-film circuits with integrated microelectronics.

The results of their work were reported in the October 19 issue of the American Chemical Society's scientific journal. The video provides a quick overview of the process:

• Researchers pattern a circuit template onto a sheet of transfer tattoo paper with an ordinary desktop laser printer
   
• They code the template with silver paste, which sticks only to the printer toner ink
   
• They wipe away the excess silver
   
• A gallium indium liquid metal alloy is deposited on top of the silver paste, increasing the flexibility and electrical conductivity of the circuit
   
• Finally, they add external electronics, such as microchips, with a silver epoxy or a conductive glue made of vertically aligned, magnetic particles embedded in a polyvinyl alcohol gel

To transfer the electronic tattoo to 3D objects, such as a prosthetic hand, they immerse the object into a tub of water along with the circuit that was built on the tattoo transfer paper. The paper backing separates from the circuit in the water, enabling the researchers to mold the circuit to the contours of the hand.

The authors received funding from the Foundation of Science and Technology of Portugal, through the Carnegie Mellon University Portugal Program.