Technion sensor brings ‘electronic skin’ closer to reality

The new sensor is comprised of a self-healing substrate, high conductivity electrodes and molecularly modified gold nanoparticles.

November 18, 2015 22:02
3 minute read.

A TECHNION RESEARCHER shows off a new kind of synthetic ‘self-healing’ sensor that mimics the ability of human skin to repair itself. (. (photo credit: Courtesy)

A new kind of synthetic polymer has been used at the Technion-Israel Institute of Technology to develop a ‘self-healing’ flexible sensor that mimics the ability of human skin to repair itself. According to chemical engineers at the Haifa institute, future applications could include the creation of self-healing ‘electronic skin’ and prosthetic limbs that make it possible for wearers to “feel” changes in their environment.

Flexible sensors have been developed for use in consumer electronics, robotics, health care and space flight.

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One problem with existing flexible sensors, however, is that they can easily be scratched and otherwise damaged, potentially destroying their functionality.

Technion engineers who were inspired by the healing properties in human skin have developed materials that can be integrated into flexible devices to “heal” incidental scratches or damaging cuts that might reduce their efficacy.

The advancement, using a new kind of synthetic polymer (a large molecule composed of many repeated smaller molecules) has self-healing properties including the ability of “e-skin wounds” to quickly “heal” in less than a day.

Self-healing sensor co-developer Prof. Hossam Haick, who headed the team, has just published a paper outlining the characteristics and applications of the unique sensor in the journal Advanced Materials.

“The vulnerability of flexible sensors used in real-world applications calls for the development of self-healing properties similar to how human skin heals,” he said. “Accordingly, we have developed a complete, self-healing device in the form of a bendable and stretchable chemi-resistor where every part – no matter where the device is cut or scratched – is self-healing.”

The new sensor is comprised of a self-healing substrate, high conductivity electrodes and molecularly modified gold nanoparticles. “The gold particles on top of the substrate and between the self-healing electrodes are able to “heal” cracks that could completely disconnect electrical connectivity,” said Haick, 40, an Israeli-Arab scientist and engineer who was born in Nazareth.

He is well known for his invention of the “Electronic Nose” that is widely used for sniffing out disease biomarkers.

A graduate of Ben-Gurion University, the Technion and the Weizmann Institute, Haick also did a postdoctoral fellowship at the California Institute of Technology. He has made many contributions in multidisciplinary fields such as nanotechnology, nanosensors and molecular electronics.

Once healed, the polymer substrate of the self-healing sensor demonstrates sensitivity to volatile organic compounds (VOCs), with detection capability of ten parts per billion. It also demonstrates superior healability at the extreme temperatures of -20 degrees C to 40 degrees C. This property, said the researchers, can extend applications of the self-healing sensor to areas of the world with extreme climates. From sub-freezing cold to equatorial heat, the self-healing sensor is stable in its environment.

The healing polymer works most rapidly, said the researchers, when the temperature is between 0 degrees and 10 degrees Celsius and 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 non-biological, chemi-resistor still has high sensitivity to touch, pressure and strain, which the researchers tested in demanding stretching and bending tests.

Another unique feature is that the electrode resistance increases after healing and can survive 20 times or more cutting/healing cycles than before healing.

Essentially, healing makes the sensor even stronger. The researchers noted in their paper that “the healing efficiency of this chemi-resistor is so high that the sensor survived several cuttings at random positions.”

The researchers are currently experimenting with carbon-based self-healing composites and self-healing transistors.

“The self-healing sensor raises expectations that flexible devices might someday be self administered, thus increasing their reliability,” explained 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.”

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