The nanotube fibres are as conductive as metal wires, but have the advantage of being more flexible, more comfortable against the skin, and much less likely to break when under stress during motion. According to the researchers, the smart 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 more accurate electrocardiogram (ECG) readings.
“The shirt has to be snug against the chest,” said Rice graduate student Lauren Taylor, lead author of the study, which appears 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.”
At around 22 microns wide, the original nanotube filaments created by the Rice team were too small for a sewing machine to work with. In order to create a workable thread, the researchers recruited a specialist who had experience making tiny ropes for model boats. He was able to take three bundles of seven filaments each, weaving them 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 had originally attempted to weave the miniscule threads by hand. “He was able to make us a medium-scale device that does the same.”
Once sown into the garment, the nanotube threads provided not only steady electrical contact with the wearer’s skin but also served as electrodes to connect electronics like Bluetooth transmitters, relaying data to a smartphone or connecting to a Holter monitor that can be stowed in a user’s pocket. Fibres woven into fabric could also be used to embed antennas or LEDs, according to the Rice team. Minor modifications to the thread’s geometry and the associated electronics could eventually allow clothing to monitor vital signs, force exertion or respiratory rate. According to Taylor, other potential uses include soft robotics and ballistic protection in military uniforms.
“We demonstrated 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 of the gains that we’ve had since in tensile strength,” she said.