Nanocomposite coatings turn fabrics into pressure sensors

Engineers are developing smart textiles by integrating flexible nanocomposite coatings on natural and synthetic fibres, an advance that could turn shoes and clothes into pressure sensors.

Sagar Doshi (left) and Erik Thostenson test an elbow sleeve outfitted with one of their novel sensors (credit: Kathy F. Atkinson)

The team at the University of Delaware is said to have demonstrated the ability to measure pressure ranging from the light touch of a fingertip to being driven over by a forklift truck. Their work is reported in ACS Sensors.

Fabric coated with this sensing technology could be used in future “smart garments” where the sensors are inserted into the soles of shoes or stitched into clothing for detecting human motion.

“As a sensor, it’s very sensitive to forces ranging from touch to tons,” said Erik Thostenson, an associate professor in the Departments of Mechanical Engineering and Materials Science and Engineering.

Nerve-like electrically conductive nanocomposite coatings are created on the fibres using electrophoretic deposition (EPD) of polyethyleneimine functionalised carbon nanotubes.

“The films act much like a dye that adds electrical sensing functionality,” said Thostenson. “The EPD process developed in my lab creates this very uniform nanocomposite coating that is strongly bonded to the surface of the fibre. The process is industrially scalable for future applications.”

Researchers can add these sensors to fabric in a way that is claimed to be superior to current methods for making smart textiles.

Existing techniques, such as plating fibres with metal or knitting fibre and metal strands together, can decrease the comfort and durability of fabrics, said Thostenson.

A sensor could be inserted into the sole of a shoe

The flexible nanocomposite coating has been tested on fibres including Kevlar, cotton, wool, nylon, Spandex and polyester. The coatings are 250nm to 750nm thick and would add about a gram of weight to a typical shoe or garment. Moreover, the materials used to make the sensor coating are inexpensive and can be processed at room temperature with water as a solvent.

One potential application of the sensor-coated fabric is to measure forces on people’s feet as they walk. This data could help doctors assess imbalances after injury, or help to prevent injury in athletes.

Sagar Doshi, a doctoral student in mechanical engineering at UD, is the lead author on the paper. He worked on making the sensors, optimising their sensitivity, testing their mechanical properties and integrating them into sandals and shoes.

He has worn the sensors in preliminary tests and found that they collect data that is comparable to that collected by a force plate, a laboratory device that can cost thousands of dollars.

“Because the low-cost sensor is thin and flexible the possibility exists to create custom footwear and other garments with integrated electronics to store data during their day-to-day lives,” Doshi said. “This data could be analysed later by researchers or therapists to assess performance and ultimately bring down the cost of healthcare.”

This technology could also be promising for sports medicine applications, post-surgical recovery, and for assessing movement disorders in children.