New “smart clothing” uses conductive nanotube thread to continuously monitor the heart.
Researchers sewed the fibers into athletic wear to monitor the heart rate and take a continual electrocardiogram (EKG) of the wearer.
The fibers are just as conductive as metal wires, but washable, comfortable, and far less likely to break when a body is in motion.
On the whole, the enhanced shirt 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 EKGs.
“The shirt has to be snug against the chest,” says Lauren Taylor, a graduate student at Rice University and lead author of the study in Nano Letters. “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 note the nanotube fibers are soft and flexible, and 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 them.
The fibers provide not only steady electrical contact with the wearer’s skin but also serve as electrodes to connect electronics like Bluetooth transmitters to relay data to a smartphone or connect to a Holter monitor that can be stowed in a user’s pocket, Taylor says.
Zigzag gives nanotube thread its stretch
The lab of Matteo Pasquali, a professor of chemical and biomolecular engineering, of chemistry, and of materials science and nanoengineering, introduced carbon nanotube fiber in 2013.
Since then the 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.
The original nanotube filaments, at about 22 microns wide, were too thin for a sewing machine to handle. Taylor says the researchers used a rope-maker 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,” says 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 says it’s possible to adjust the zigzag pattern to account for how much a shirt or other fabric is likely to stretch. Taylor says the team is working with Mehdi Razavi and his colleagues at the Texas Heart Institute to figure out how to maximize contact with the skin.
Better than Kevlar
Fibers woven into fabric can also be used to embed antennas or LEDs, according to the researchers. Minor modifications to the fibers’ geometry and associated electronics could eventually allow clothing to monitor vital signs, force exertion, or respiratory rate.
Taylor notes 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 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,” she says.
“We see that, after two decades of development in labs worldwide, this material works in more and more applications,” Pasquali says. “Because of the combination of conductivity, good contact with the skin, biocompatibility, and softness, carbon nanotube threads are a natural component for wearables.”
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, Pasquali says.
“We’re in the same situation as solar cells were a few decades ago,” Pasquali says. “We need application leaders that can provide a pull for scaling up production and increasing efficiency.”
Additional coauthors are from the University of Pennsylvania and Rice. The US Air Force, the American Heart Association, the Robert A. Welch Foundation, the Department of Energy, the Department of Defense, and a Riki Kobayashi Fellowship from the Rice Department of Chemical and Biomolecular Engineering funded the work.
Source: Rice University