Researchers from Carnegie Mellon University's College of Engineering and the Institute of Systems and Robotics of the University of Coimbra, Portugal have developed a simple, efficient method to make robust, highly flexible, tattoo-like circuits for use in wearable computing. The low-cost process adds trace amounts of an electrically-conductive, liquid metal alloy to tattoo paper that adheres to human skin. These ultrathin tattoos can be applied easily with water, the same way one would apply a child's decorative tattoo with a damp sponge. For more information see the IDTechEx report on Electronic Skin Patches 2018-2028.
Other tattoo-like electronics either require complex fabrication techniques inside a cleanroom or lack the material performance required for stretchable digital circuit functionality on skin.
Carmel Majidi, an associate professor of mechanical engineering and the director of the Soft Machines Lab at Carnegie Mellon, and Mahmoud Tavakoli, the director of the Soft and Printed Microelectronics Laboratory at the University of Coimbra, teamed up to develop methods for direct printing of stretchable electronic circuits. Their collaboration succeeded.
"This is a breakthrough in the printed electronics area," said Tavakoli. "We showed for the first time that inkjet-printed patterns of silver nano particles can be sintered at room temperature using the gallium indium alloy. Removing the need for high temperature sintering makes our technique compatible with thin-film and heat sensitive substrates."
In addition to low-cost processing, these tattoos provide other advantages. Because they have mechanical properties similar tolightweight fabrics, they remain functional under bending, folding, twisting, and strains above 30% (which is the typical stretchability of human skin). They can conform and adhere to highly curved 3D surfaces, like a model of a human brain or a lemon.
Applications for ultrathin, compliant tattoos include epidermal biomonitoring, soft robotics, flexible displays, and 3D-transferable printed electronics.
The findings were published in Advanced Materials in a paper titled "EGaIn‐Assisted Room‐Temperature Sintering of Silver Nanoparticles for Stretchable, Inkjet‐Printed, Thin‐Film Electronics."
Source and top image: Carnegie Mellon University