MEMS and Sensors

New Flexible Sensors Pave the Way For Real “Electronic Skin”

22 November 2015

Researchers from the Department of Chemical Engineering at the Technion – Israel Institute of Technology in Haifa (Israel) have developed materials that can be integrated into flexible electronic devices to “heal” scratches or damages.

This is not the first type of flexible sensor ever developed. The unique technology has been worked on by many groups for use in consumer electronics, robotics, health care and space flight. One important future application could include the creation of ‘electronic skin’ and prosthetic limbs that would allow wearers to actually ‘feel’ changes in their environments.

The problem with flexible sensors is that they can be easily scratched and otherwise damaged, which could destroy their functionality. To combat this, the researchers decided to use a new kind of synthetic polymer with self-healing properties that mimic human skin, which means that e-skin “wounds” could quickly “heal” themselves in less than a day, according to the research.

“The vulnerability of flexible sensors used in real-world applications calls for the development of self-healing properties similar to how human skins heals,” says Professor Hossam Haick, co-developer of the sensor. “Accordingly, we have developed a complete, self-healing device in the form of a bendable and stretchable chemiresistor where every part—no matter where the device is cut or scratched—is self-healing.”

The self-healing, flexible sensor. Image Credit: Department of Chemical Engineering at the Technion – Israel Institute of Technology in Haifa (Israel)The self-healing, flexible sensor. Image Credit: Department of Chemical Engineering at the Technion – Israel Institute of Technology in Haifa (Israel)The sensor has a self-healing substrate, high conductivity electrodes and molecularly modified gold nanoparticles (the gold particles are what allow the cracks to heal and could completely disconnect electrical connectivity).

Once healed, the polymer substrate of the self-healing sensor demonstrates sensitivity to volatile organic compounds (VOCs), with detection capability down to tens of parts per billion. It also demonstrates healability at the extreme temperatures of -20 degrees C to 40 degrees C.

According to the researchers, this property can extend applications of the self-healing sensor to areas of the world with extreme climates—from sub-freezing cold to equatorial heat.

The polymer works fastest when the temperature is between 0 degrees C and 10 degrees C, when moisture condenses and is then absorbed by the substrate. Condensation makes the substrate swell, allowing the polymer chains to begin to flow freely and, in effect, begin “healing.” Once healed, the nonbiological, chemiresistor still has high sensitivity to touch, pressure and strain, which the researchers tested in demanding stretching and bending tests.

“The self-healing sensor raises expectations that flexible devices might someday be self-administered, which increases their reliability,” says co-developer Dr. Tan-Phat Huynh, also of the Technion, whose work focuses on the development of self-healing electronic skin. “One day, the self-healing sensor could serve as a platform for biosensors that monitor human health using electronic skin.”

A paper outlining the characteristics and applications of the unique, self-healing sensor has been published in the current issue of Advanced Materials (2015) (DOI: 10.1002/adma.201504104).

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