Rice University graduate student Lauren Taylor holds up a shirt with carbon nanotube threads that can provide constant monitoring of the wearer’s heart. Photo: Jeff Fitlow/Rice University.
Rice University graduate student Lauren Taylor holds up a shirt with carbon nanotube threads that can provide constant monitoring of the wearer’s heart. Photo: Jeff Fitlow/Rice University.

There’s no need to don uncomfortable smartwatches or chest straps to monitor your heart if your comfy shirt can do a better job. That’s the idea behind 'smart clothing' developed by a Rice University lab, which employed its conductive nanotube thread to weave functionality into regular apparel.

In a paper in Nano Letters, researchers led by Matteo Pasquali reported sewing carbon nanotube fibers into athletic wear for monitoring the heart rate of the wearer and for taking a continual electrocardiogram (EKG). These fibers are just as conductive as metal wires, but washable, comfortable and far less likely to break when a body is in motion, according to the researchers.

On the whole, the shirt they enhanced was better at gathering data than a standard chest-strap monitor. When matched with commercial medical electrode monitors, the carbon nanotube shirt gave slightly better EKGs.

“The shirt has to be snug against the chest,” said Rice graduate student Lauren Taylor, lead author of the paper. “In future studies, we will focus on using denser patches of carbon nanotube threads so there’s more surface area to contact the skin.”

The researchers noted that the nanotube fibers are soft and flexible, while clothing that incorporates them is machine washable. The fibers can be machine-sewn into fabric just like standard thread. The zigzag stitching pattern allows the fabric to stretch without breaking the nanotubes.

The fibers not only provided steady electrical contact with the wearer’s skin but also served as electrodes for connecting electronics like Bluetooth transmitters that can relay data to a smartphone or connect to a Holter monitor stowed in a user’s pocket.

Pasquali’s lab introduced carbon nanotube fiber in 2013. Since then, these fibers, each containing tens of billions of nanotubes, have been studied for use as bridges to repair damaged hearts, as electrical interfaces with the brain, for use in cochlear implants, as flexible antennas, and for automotive and aerospace applications. Their development is also part of the Rice-based Carbon Hub, a multi-university research initiative led by Rice and launched in 2019.

The original nanotube filaments, at about 22µm wide, were too thin for a sewing machine to handle. According to Taylor, a rope-maker was used to create a sewable thread, essentially three bundles of seven filaments each, woven into a size roughly equivalent to regular thread.

“We worked with somebody who sells little machines designed to make ropes for model ships,” explained Taylor, who at first tried to weave the thread by hand, with limited success. “He was able to make us a medium-scale device that does the same.”

She said the zigzag pattern can be adjusted to account for how much a shirt or other fabric is likely to stretch. The team is currently working with Mehdi Razavi and his colleagues at the Texas Heart Institute to figure out how to maximize contact with the skin.

Fibers woven into fabric can also be used to embed antennas or LEDs. Minor modifications to the fibers’ geometry and associated electronics could eventually allow clothing to monitor vital signs, force exertion or respiratory rate.

Other potential uses could include human-machine interfaces for automobiles or soft robotics, as well as antennas, health monitors and ballistic protection in military uniforms. “We demonstrated with a collaborator a few years ago that carbon nanotube fibers are better at dissipating energy on a per-weight basis than Kevlar, and that was without some of the gains that we’ve had since in tensile strength,” Taylor said.

“We see that, after two decades of development in labs worldwide, this material works in more and more applications,” Pasquali said. “Because of the combination of conductivity, good contact with the skin, biocompatibility and softness, carbon nanotube threads are a natural component for wearables.”

He added that the wearable market, although relatively small, could be an entry point for a new generation of sustainable materials derived from hydrocarbons via direct splitting, a process that also produces clean hydrogen. Development of such materials is a focus of the Carbon Hub. “We’re in the same situation as solar cells were a few decades ago. We need application leaders that can provide a pull for scaling up production and increasing efficiency.”

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.