Researchers develop ultra-thin, flexible, imperceptible electronic skin
Researchers from Japan and Germany have developed an ultra-thin, flexible, sensitive electronic skin that aims to mimic biological skin with a fully operating set of electronic functional sensors. Researchers hope that electronic skin has potential applications in medicine, such as wearable clinical monitoring devices, with skin-like properties, and transdermal drug delivery.1
“Making artificial skin like that of science fiction movies is a complicated task, as numerous sensors and electronic circuits had to be made flexible and stretchable too, replicating mechanical and perception functionalities of its biological equivalent” explained Dr Daniil Karnaushenko (Institute for Integrative Nanoscience, IFW Dresden).
The thinner the better
One of the main challenges of developing electronic skin that mimics the sophisticated sensing capabilities of biological skin, is packing it full of electronic sensors and circuits while keeping the surface lightweight, thin and stretchable. Karnaushenko and his team developed a functional sensitive device that has a magnetic sensor matrix system integrated with electronic circuits arranged on a soft, reconfigurable surface (as thick as 1/100th of a human hair). “The device was able to accommodate even the tiniest curvatures of human skin”, said Karnaushenko.
Why magnetic sensors?
Electronic skin is not new and in fact other teams have also developed flexible and ultra-thin electronic sensors.2 However, despite the vast progress in the development of imperceptible electronic devices, not many studies have investigated flexible magnetic systems integrated with other magnetic sensors and electronic devices.1 Magnetic systems typically require many sensors arranged on a large surface area. These devices are typically used in industry, commercial applications and robotics to provide position and orientation information to an external controlling device.
“Magnetic sensors are much more robust, and easy to use compared with other types of sensors, such as optical ones. These sensors can be easily protected from the aggressive environment by a plastic film and meanwhile allow operation in a contactless mode, making them perfect candidates for position sensing and control in e-skin applications”, explained Karnaushenko. The group’s device comprises a matrix of magnetic sensors, with an integrated ultra-low power shift register, which automatically scanned the matrix. Extra circuits amplified any electronic signals detected, and switching transistors connected each individual sensor to external testing electronics.
Overcoming obstacles with paste
“However, testing such an imperceptible electronic device becomes a nightmare as any touchdown with a conventional rigid electric probe, such as a simple tungsten needle, made a hole in the contact pad,” said Karnaushenko, “We could not make any reliable electric contact.” But the researchers came up with an elegant and reliable solution for the problem. “We used a conducting silver paste printed or painted on top of testing pads to bind wires between the circuits of e-skin and a rigid external adapter that permits electric testing with conventional equipment.”
The team’s results showed that the use of shift registers (that work by automatically addressing individual sensory signals) had excellent electrical performance, high operating speed at a low voltage (less than 4v). The device’s power consumption is lower than that of conventional designs of thin-film electronics. This high-speed operation together with ultra-low power consumption make this particularly attractive for this type of sensitive electronic skin.
We used a conducting silver paste printed or painted on top of testing pads to bind wires between the circuits of e-skin and a rigid external adapter that permits electric testing with conventional equipment.
Showing the importance of multidisciplinary groups, the research team is made up of scientists from Germany and Japan in fields, from chemistry, physics, electrical engineering, mechanics, material science and surface science. “This particular project covered several disciplines as we faced challenges associated with the choice of materials, circuit design, microfabrication and testing,” said Karnaushenko.
The group want to increase the density of sensors in their next prototype, they are aiming for a few sensors in each square millimeter by using other thin-film electronics. The team also want to integrate new sensors that can detect temperature and pressure. Karnaushenko thinks this type of research could have medical applications in implants, prosthetics and soft robotics. “Biological bodies are not persistent in shape such as a beating heart or a breathing chest. Examining dynamics of this movement could be accomplished with e-skin technology that could provide clinicians with medically valuable information”, said Karnaushenko.
Zhong M, et al. Advanced electronic skin devices for healthcare applications. J Master Chem B 2019; 7: 173-197.
Kondo M, et al. Imperceptible magnetic sensor matrix system integrated with organic driver and amplifier circuits. Sci Adv 2020; 6: eaay6094.