Researchers at the University of Wollongong in Australia and the University of Texas at Dallas in the US have made stretchy, electrically conductive textiles based on Spandex and carbon nanotubes. The composite yarns, which are knitted together, could be used to make actuators and sensors for use in artificial muscles and smart clothing.

Materials that expand and contract in response to some form of stimulus could be useful as actuators or artificial muscle fibres for robotics or smart textiles. They could also make good sensors for lab-on-a-chip devices.

Now, a team led by Javad Foroughi in Wollongong has come up with a knitting technique to produce electrically conducting 3D yarns from the stretchy fabric Spandex (SPX) and multi-walled carbon nanotubes (CNTs). The fibres can be highly stretched and so could make excellent sensors and artificial muscles, say the researchers.

Capacity for work

The team made the yarns by continuously feeding commercially available SPX fibres and CNT aerogel sheets drawn from an aligned forest of tubes into a circulating knitting machine. “The CNT/SPX fabric we made can be stretched to over 600% its original length and has an electrical conductivity of between 870–7092 S/m, depending on the amount of tensile strain we apply to it,” explains team-member Geoffrey Spinks. The mechanical and electrical properties of the fabric are also stable over 10,000 cycles of strain and/or bending.”

When a voltage is applied to the stretched yarn, it heats up and contracts by as much as 33%. As a consequence, it generates a mechanical work capacity of up to 0.64 kJ/kg and a maximum specific power output of 1.28 kW/kg, which is much higher than that produced by human skeletal muscles.

We have already demonstrated a knee-sleeve prototype using our technology

Ray Baughman, University of Texas at Dallas

“Our knitted textile has strain-sensing capabilities as well as being porous, and as such could be used in smart clothing, for example, which monitors the wearer’s movements while at the same adjusting garment fit,” explains team-member Ray Baughman. “We have already demonstrated a knee-sleeve prototype using our technology, and such a device might be used to help repair injury after an accident by monitoring and manipulating knee movement.”

The team says that it is now working on using the CNT knitted textile as a wearable antenna as well as in biomedical applications, like knee sleeves and lymph sleeves. “The lymph sleeve, for example, will be developed using lightweight actuating fabric that will detect swelling and then respond by ‘squeezing’ the arm to enhance lymph flow,” explains Foroughi. “We are also investigating the possibility of employing it in artificial-heart muscles for positive support of the right ventricle,” he says.

The SPX/CNT composite yarn is described in ACS Nano.

• A version of this article first appeared on nanotechweb.org