Electronic tattoos used in Health monitoring are being developed under the CMU Portugal Entrepreneurial Research Initiative (ERI) Stretchtonics

A team of researchers from the Institute of Systems and Robotics of the University of Coimbra in Portugal led by Mahmoud Tavakoli and from the director of the Soft Machines Lab from the Carnegie Mellon University’s College of Engineering led by Carmel Majidi, have developed a simple, low cost, rapid and efficient method to produce stretchable, flexible and easy to apply electronic tattoos using an inkjet printer. These ultrathin electronic e-skins have broad applications ranging from health monitoring to touch control panels in cars.

The tattoos are being developed under the Strechtonics * project, one of the Entrepreneurial Research Initiatives (ERIs) of the Carnegie Mellon Portugal Program (CMU Portugal), funded by the Fundação para a Ciência Tecnologia (FCT) and coordinated by Professor Aníbal Traça de Almeida from the University of Coimbra.

Mahmoud Tavakoli, the director of the Soft and Printed Microelectronics Laboratory at the University of Coimbra, (SPM-UC), explained that the team found a low cost process to make robust, highly flexible and electrically-conductive circuits with a regular inkjet printer: “these tattoos are easily printed and transferred to any surface. The method is really simple: the circuit is designed on the computer and 10 minutes later we have our circuit printed. You just need a printer, conductive inks and some liquid metal.”

These ultrathin tattoos, can be applied easily with water, the same way one would apply a temporary tattoo with a sponge. Until now, the existing options to produce tattoo-like electronics, either required complex fabrication techniques such as lithography technique which is performed inside a cleanroom or lacked the required performance for stretchable digital circuit functionality on skin. When applied, they allow continuous monitoring of the user’s health through factors such as muscular activity, body temperature, heart rate, brain activity, or even emotions. To date, these tattoos have also proven, according to Mahmoud Tavakoli, to be effective in checking muscle activity: “we placed an electronic tattoo on the forearm of a person with a prosthetic hand and proved that it is possible to control it using muscle signals received by tattoos. By putting the tattoo on the right muscle, it lets you know when it is activated and if the hand closes or opens.”

Although the use of printing circuits with a 2D printer is not new, these circuits used to lose conductivity when stretched. According to the researcher “this is the first time that a method allows to print stretchable circuits with a traditional inkjet printer at room temperature, by taking advantage of the gallium indium alloy. Removing the need for high temperature sintering makes our technique compatible with different types of plastic and that allowed us to create these ultrathin circuits These small circuits are made of nano silver particles coated with liquid metal and can be stretched to twice their size without losing conductivity.”

In the future, the main objective will be to insert these tattoos into the skin and the human body: “for example for people with spinal cord injuries who cannot walk, the idea is to find a way to get these tattoos into the spinal cord to stimulate and reactivate the nerves so that they walk again,” says Mahmoud Tavakoli.

Since these tattoos can adapt and adhere to highly curved 3D surfaces, they can be used in many different technologies, for example, in cars. The tattoos would be able to activate the various functions of the touch panel, such as the volume of the radio or the temperature of the car.

The results of this method were published in Advanced Materials e ACS applied materials and interfaces in 2018 and some of the applications developed within this project were patented in 2017.

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About the Strechtonics Project

The Strechtonics project was launched in 2014 as one of the Entrepreneurial Research Initiatives (ERIs) supported by the Carnegie Mellon Portugal and funded by the Fundação para a Ciência e Tecnologia (FCT). This initiative developed in a collaboration between the Institute of Systems and Robotics of the University of Coimbra and Carnegie Mellon University, and is focused on 3D printing for the development of electronic skin (“e-skin”), as stretchable as human skin. More on our website.