‘Smart’ shirt keeps tabs on the heart

The researchers, from the George R Brown School of Engineering lab at Rice University, sewed nanotube fibres into athletic wear to monitor the heart rate and take a continual electrocardiogram (ECG) of the wearer.

According to the team, the fibres are just as conductive as metal wires and are washable, comfortable, and far less likely to break when a body is in motion.

They added that the shirt they enhanced was better at gathering data than a standard chest-strap monitor taking live measurements during experiments. When matched with commercial medical electrode monitors, the carbon nanotube shirt gave slightly better ECGs.

“The shirt has to be snug against the chest,” said Rice graduate student Lauren Taylor. “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 research team noted nanotube fibres are flexible, and clothing that incorporates them is machine washable. The fibres can be machine-sewn into fabric just like standard thread, and the zigzag stitching pattern allows the fabric to stretch without breaking them.

According to Taylor, the fibres provided not only steady electrical contact with the wearer’s skin but also served as electrodes to connect electronics such as Bluetooth transmitters to relay data to a smartphone or connect to a Holter monitor that can be stowed in a user’s pocket.

The original nanotube filaments, at about 22 microns wide, were too thin for a sewing machine to handle. Taylor said 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,” said Taylor, who at first tried to weave the thread by hand, with limited success. “He made us a medium-scale device that does the same.”

Taylor added that the zigzag pattern can be adjusted to account for how much a shirt or other fabrics are likely to stretch. She added the team is working with Dr Mehdi Razavi and his colleagues at the Texas Heart Institute to investigate how to maximise contact with the skin.

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

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

Matteo Pasquali, a professor of chemistry and of materials science and nanoengineering, said: “We see that, after two decades of development in labs worldwide, this material works in more and more applications. 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 the wearable market, although relatively small, could be an entry point for a new generation of sustainable materials that can be derived from hydrocarbons via direct splitting, a process that also produces clean hydrogen.

“We’re in the same situation as solar cells were a few decades ago,” Pasquali concluded. “We need application leaders that can provide a pull for scaling up production and increasing efficiency.”