Smart shirt: Rice University graduate student Lauren Taylor shows a shirt containing carbon nanotube thread that provides constant monitoring of the wearer’s heart. (Courtesy: Jeff Fitlow/Rice University)
Museum collections across the world feature characteristic clothes from different time periods that showcase human history. Such garments can identify a wearer’s country, social status, approximate age and religion. Clothing also provides a historical link to the materials and textile technologies available at the time. Today, researchers envision that clothes’ functionalities could reach beyond fashion, protection and comfort to provide sophisticated biosensing and tracking capabilities.
Electronic clothing aims to combine flexible fabrics – that seamlessly morph with the body’s anatomy – with electronics that can capture signals such as the electrical activity of the heart in electrocardiograms (EKGs). For textile biosensing to succeed, however, the electronics must match the fabric’s flexibility and not affect the material’s thermal and moisture-transfer functions.
To achieve this, researchers in Matteo Pasquali’s laboratory at Rice University fabricated carbon nanotube-based conductive threads and sewed them into stretchable fabrics. Reporting their findings in Nano Letters, they demonstrate the durability and functionality of textile-based wearables as future health monitoring systems.
The researchers detail a non-invasive continuous monitoring strategy that uses the carbon nanotube electrodes to precisely record the heart’s electrical signals – even after 10 machine washes and 1000 stretching cycles.
“The major challenge with existing commercial hybrid electronic clothing is that the metal alloys used in these fabrics tend to have poor mechanical properties and cannot withstand repeated washing and wear,” explains lead author Lauren Taylor, a former graduate student in Pasquali’s laboratory. “This is where I feel our technology has demonstrated a major breakthrough. Our carbon-based conductive threads have the conductivity necessary for electronics but outstanding mechanical strength with the softness and flexibility of cotton.”
Textile nanomaterials
To form the carbon nanotube threads, Taylor and co-authors wove 21 cylindrical carbon nanotube filaments into a sewable thread, using a custom-built rope-making device. The resulting carbon threads have an electrical conductivity comparable to that of metals, and are soft and mechanically flexible.
The team then sewed 2, 15, 30 and 60 cm lengths of thread into elastic wrist straps, using a zigzag pattern to facilitate fabric stretching. Despite having a larger skin impedance than commercial electrodes, the all-carbon electrodes placed on the wrists could clearly capture the EKG signals used by physicians to assess heart conditions. Moreover, the wrist-mounted textile electrodes could also measure electrical signals generated during muscle activation cycles.
Weaving the fabric of health
Athletic clothing is designed with flexible fabrics that closely contact the skin and facilitate body motion during physical activities. To enable health monitoring using electronic textiles, the authors sewed five 15 cm carbon nanotube electrodes on an existing athletic shirt in a Holter configuration (the electrode placement pattern used in continuous EKG monitoring) to record a complete EKG while the wearer is running, jogging, walking and sitting.
Fitness tracking: Carbon nanotube threads in an athletic shirt could record EKG and heart rate data better than standard chest-strap monitors.
Additional carbon nanotube threads sewn through the shirt connect the electrodes to a Bluetooth monitor located in the back of the neck, which wirelessly transmits the recorded data to a nearby smartphone.
The authors asked three cardiologists to evaluate the quality of blinded EKG signals recorded by the carbon nanotube and commercial electrodes. All agreed that signals from the textile-based electrodes were “slightly better”, due to a better definition of the heart waves.
“When we made the EKG shirt, I had anticipated the advantages in wearability and washability – in essence, convenience. I had not expected that EKG quality would also be superior – that was a bit lucky,” senior author Matteo Pasquali tells Physics World.
Reference: textile clinic
