Researchers have developed a way to print stretchable electronic skins using a normal inkjet or laser printer. In doing so, they are significantly advancing the fabrication of this technology for a number of applications, including human-machine interfaces.
A team of researchers in the United States and Portugal collaborated to develop an approach that patterns a distributed network of sensors and circuits onto a sheet of transfer tattoo paper. It is then fabricated using an ordinary desktop laser printer.
“The significant breakthrough of this work is introduction of a method that allows, for the first time, printing of stretchable e-skins using a normal inkjet or laser printer,” explained Mhmoud Tavakoli, director of the Soft and Printed Microelectroncis Laboratory in the Institute of Systems and Robotics at the University of Coimbra. “This is significantly easier compared to the previous methods.”
|An “electronic” skin filled with circuits has been manufactured using common printing technology, making it easier to fabricate for myriad applications including virtual reality, prosthetics, and wearable health monitors. (Image source: ACS Applied Materials and Interfaces/University of Coimbra)|
Mimic The Human Touch
E-skins—which are, as their name implies, electronic, synthetic versions that mimic the feel and sense of touch of human skin—can be useful for a number of next-generation applications, including prosthetic devices, wearable health monitors, robotics, and virtual reality.
One major challenge researchers have encountered to develop them is how to transfer ultra-thin electrical circuits onto complex 3D surfaces while allowing the electronics to be bendable and stretchable enough for full movement.
“Human skin has a million receptors,” Tavakoli explained. “If we want to make something similar to the human skin, we need methods that are able to print or pattern many sensors over a substrate which is elastic, similar to the human skin.”
Taking Several Steps
The method he and his team devised involves a several-step process. First, researchers patterned the circuits onto the paper. They then coated the template with silver paste, which adhered only to the printed toner ink. On top of the silver paste, they deposited a gallium–indium liquid metal alloy that increased the electrical conductivity and flexibility of the circuit. Finally, they added external electronics, such as microchips, with a conductive “glue” made of vertically aligned magnetic particles embedded in a polyvinyl alcohol gel.
“Using a novel sintering method based on gallium indium liquid metal alloy, printed circuits developed by this method become instantly stretchable and conductive,” Tavakoli told Design News. “They do not need to go to an oven for high-temperature sintering. Therefore, the printing technique is compatible with a wide range of heat-sensitive material.”
The team demonstrated the success of its method by transferring the electronic tattoo to various objects and showing several different applications. They were able to use it to control a robotic prosthetic arm, monitor human skeletal muscle activity, and incorporate proximity sensors into a 3D model of a hand. Researchers published a paper on their work in the ACS journal Applied Materials and Interfaces.
The team already has patented the technology and aims to license it for various applications, Tavakoli said. In the meantime, they also plan to do further research to optimize printing techniques and inks that would allow robust, low-cost, and scalable production of e-skins, he said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.
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