February 29, 2016

Paper Skin Mimics Sensory Functions

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The flexible temperature array was made by drawing a resistor structure with a silver conductive ink pen on sticky note paper. Photograph courtesy of KAUST.

A team of electrical engineers from King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia, has developed a low-cost, paper-based sensor that mimics the sensory functions of human skin. The sensor, called Paper Skin, was made using everyday materials from the kitchen drawer, such as aluminum foil, sticky note paper, sponges, and tape, and can detect external stimuli, including touch, pressure, temperature, acidity and humidity. The team said the sensor performs as well as other artificial skin applications currently being developed while integrating multiple functions using cost-effective materials. Their work has implications for wearable and flexible electronics, such as wireless monitoring of patient health and touch-free computer interfaces, as well as for wound care and prosthetic applications.

“The objective of our work is to use the skin for burn [victims], acid [burn] victims, and...for prosthetic hands, and organs," said Muhammad Mustafa Hussain, PhD, an associate professor of electrical engineering in KAUST’s Computer Electrical Mathematical Science and Engineering Division. "One of the major reasons (in addition to affordability and simplicity), we used paper is [that] it is porous like our natural skin. Previous studies in this area focused on polymeric materials, which are impermeable and cannot mimic the skin textures and porosity important for comfortable experience.”

The team used sticky note paper to detect humidity, sponges and wipes to detect pressure, and aluminum foil to detect motion. Coloring a sticky note with an HB graphite pencil allowed the paper to detect acidity levels, and aluminum foil and conductive silver ink were used to detect temperature differences. The materials were put together into a simple paper-based platform that was then connected to a device that detected changes in electrical conductivity according to external stimuli. Increasing levels of humidity, for example, increased the platform’s ability to store an electrical charge. Exposing the sensor to an acidic solution increased its resistance, while exposing it to an alkaline solution decreased it. Voltage changes were detected with temperature changes. Bringing a finger closer to the platform disturbed its electromagnetic field, decreasing its capacitance. The results of the team’s work was published online February 16 in the journal Advanced Materials Technologies.

The team leveraged the various properties of the materials they used, including their porosity, adsorption, elasticity and dimensions to develop the low-cost sensory platform. They also demonstrated that a single integrated platform could simultaneously detect multiple stimuli in real time.

Several challenges must be overcome before a fully autonomous, flexible, and multifunctional sensory platform becomes commercially achievable, explained Hussain. Wireless interaction with the paper skin needs to be developed. Reliability tests also need to be conducted to assess how long the sensor can last and how good its performance is under severe bending conditions.

“The next stage will be to optimize the sensor’s integration on this platform for applications in medical monitoring systems. The flexible and conformal sensory platform will enable simultaneous real-time monitoring of body vital signs, such as heart rate, blood pressure, breathing patterns, and movement,” Hussain said.

Editor’s note: This story was adapted from materials provided by King Abdullah University of Science and Technology.

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