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Flexible Carbon Nanotube Composite Coatings for Fibers to Enable Smart Textiles

Researchers from the University of Delaware have been working to create futuristic smart textiles by developing flexible carbon nanotube composite coatings on a broad range of fibers including nylon, cotton and wool.

Sagar Doshi (left) and Erik Thostenson test an elbow sleeve outfitted with one of their novel sensors. (Image credit: University of Delaware)

The findings of the study have been published in the ACS Sensors journal, demonstrating the ability to measure an extremely broad range of pressure—from the slight touch of a fingertip to being driven over by a forklift.

This sensing technology can be coated on the fabric used for making future “smart garments,” where the sensors can be stitched into clothing or slipped into the soles of shoes for the detection of human motion.

The impressive sensing capability of this flexible, light, breathable fabric coating is due to the carbon nanotubes. By squeezing the material, large electrical variations in the fabric can be easily measured.

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

Nerve-form electrically conductive nanocomposite coatings are developed on the fibers through electrophoretic deposition (EPD) of polyethyleneimine functionalized carbon nanotubes.

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

At present, scientists have been able to integrate these sensors into the fabric in a way superior to existing techniques for making smart textiles. Current methods, such as plating fibers with knitting or metal fiber and metal strands together, can reduce the comfort and durability of fabrics, stated Thostenson, who directs UD’s Multifunctional Composites Laboratory. The nanocomposite coating created by Thostenson’s team is flexible and comfortable to touch and has been tested on a wide variety of synthetic and natural fibers, such as nylon, Kevlar, Spandex, wool and polyester. The thickness of the coatings is only 250–750 nm, which is about 0.25%–0.75% of the thickness of a piece of paper, and would only add around 1 g of weight to a typical garment or shoe. Moreover, the materials used to develop the sensor coating are low-cost and environmentally friendly, as they can be processed at ambient temperature with water as a solvent.

Exploring Future Applications

One prospective application of the sensor-coated fabric is the measurement of the forces on people’s feet when they walk. This data can be used by clinicians to evaluate the imbalances following injury or help prevent injury in athletes. For example, Thostenson’s research team has collaborated with Jill Higginson, professor of mechanical engineering and director of the Neuromuscular Biomechanics Lab at UD, and her team as part of a pilot project funded by Delaware INBRE. Their aim is to verify the way these sensors, upon being slipped into footwear, compare to biomechanical lab techniques such as motion capture and instrumented treadmills.

At the time of lab testing, people are conscious of the fact that they are being observed; however, outside the lab, their behavior could be different.

One of our ideas is that we could utilize these novel textiles outside of a laboratory setting—walking down the street, at home, wherever,” stated Thostenson.

The lead author of the paper is Sagar Doshi, who is a doctoral student in mechanical engineering at UD. He was involved in developing the sensors, optimizing their sensitivity, testing their mechanical characteristics, and incorporating them into shoes and sandals. He has worn the sensors in preliminary tests, and thus far the sensors gather data that compares well with the data gathered by a force plate—a laboratory device with a price of 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,” stated Doshi. “This data could be analyzed later by researchers or therapists to assess performance and ultimately bring down the cost of healthcare.”

This technology could also be promising for post-surgical recovery, sports medicine applications, and for the evaluation of movement disorders in pediatric populations.

It can be challenging to collect movement data in children over a period of time and in a realistic context,” stated Robert Akins, Director of the Center for Pediatric Clinical Research and Development at the Nemours–Alfred I. duPont Hospital for Children in Wilmington and affiliated professor of materials science and engineering, biomedical engineering and biological sciences at UD. “Thin, flexible, highly sensitive sensors like these could help physical therapists and doctors assess a child’s mobility remotely, meaning that clinicians could collect more data, and possibly better data, in a cost-effective way that requires fewer visits to the clinic than current methods do.”

Interdisciplinary collaboration is vital for the development of prospective applications, and at UD engineers have a unique chance of working with faculty and students from the College of Health Sciences on UD’s Science, Technology and Advanced Research (STAR) Campus.

As engineers, we develop new materials and sensors but we don’t always understand the key problems that doctors, physical therapists and patients are facing,” stated Doshi. “We collaborate with them to work on the problems they are facing and either direct them to an existing solution or create an innovative solution to solve that problem.”

Thostenson’s research team also employs nanotube-based sensors for other applications like structural health monitoring.

We’ve been working with carbon nanotubes and nanotube-based composite sensors for a long time,” stated Thostenson, who is affiliated with the faculty at UD’s Center for Composite Materials (UD-CCM). Through collaboration with scientists in civil engineering, his team has pioneered the creation of flexible nanotube sensors to assist in the detection of cracks in bridges and different types of large-scale structures. “One of the things that has always intrigued me about composites is that we design them at varying lengths of scale, all the way from the macroscopic part geometries, an airplane or an airplane wing or part of a car, to the fabric structure or fiber level. Then, the nanoscale reinforcements like carbon nanotubes and graphene give us another level to tailor the material structural and functional properties. Although our research may be fundamental, there is always an eye towards applications. UD-CCM has a long history of translating fundamental research discoveries in the laboratory to commercial products through UD-CCM’s industrial consortium.”

The U.S. National Science Foundation (NSF) CAREER Program and the Delaware INBRE program with a grant from NIH-NIGMS (P20-GM103446) and the State of Delaware have supported this study.

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