Scientists at the University of Massachusetts Amherst have invented a way to apply breathable, pliable, metal-free electrodes to fabric and off-the-shelf clothing so it feels good to touch and also transports electricity to power small electronics. That means there may be a lightweight, comfortable jacket generates power to light up a jogger at night.

The research has been carried out a team of scientists led by materials scientist Trisha Andrew and postdoctoral researcher Lu Shuai Zhang. The paper is published in the online edition of Advanced Functional Materials.

Andrew is director of wearable electronics at the Center for Personalised Health Monitoring in UMass Amherst’s Institute of Applied Life Sciences (IALS). Since the basic work was completed, her lab has also made a wearable heart rate monitor with an off-the-shelf fitness bra to which they added eight monitoring electrodes. They will soon test it with volunteers on a treadmill at the IALS human movement facility.

Andrew says, “Our lab works on textile electronics. We aim to build up the materials science so you can give us any garment you want, any fabric, any weave type, and turn it into a conductor. Such conducting textiles can then be built up into sophisticated electronics. One such application is to harvest body motion energy and convert it into electricity in such a way that every time you move, it generates power.”

Powering advanced fabrics that can monitor health data remotely are important to the military and increasingly valued by the health care industry, she notes.

Generating small electric currents through relative movement of layers is called triboelectric charging, explains Andrew, who trained as a polymer chemist and electrical engineer. Materials can become electrically charged as they create friction by moving against a different material, like rubbing a comb on a sweater. “By sandwiching layers of different materials between two conducting electrodes, a few microwatts of power can be generated when we move,” she adds.

The scientists use the vapour deposition method to coat fabrics with a conducting polymer, poly(3,4-ethylenedioxytiophene) also known as PEDOT, to make plain-woven, conducting fabrics that are resistant to stretching and wear and remain stable after washing and ironing. The thickest coating they put down is about 500 nanometres, or about 1/10 the diametre of a human hair, which retains a fabric’s hand feel.

The authors report results of testing electrical conductivity, fabric stability, chemical and mechanical stability of PEDOT films and textile parameter effects on conductivity for 14 fabrics, including five cottons with different weaves, linen and silk from a craft store.

“Our article describes the materials science needed to make these robust conductors. We show them to be stable to washing, rubbing, human sweat and a lot of wear and tear,” Andrew says. PEDOT coating did not change the feel of any fabric as determined by touch with bare hands before and after coating. Coating did not increase fabric weight by more than two per cent. The work was supported by the Air Force Office of Scientific Research.

Until recently textile scientists have tended not to use vapour deposition because of technical difficulties and high cost of scaling up from the laboratory. But over the last 10 years, industries such as carpet manufacturers and mechanical component makers have shown that the technology can be scaled up and remain cost-effective, Andrew and Zhang point out. The invention also overcomes the obstacle of power-generating electronics mounted on plastic or cladded, veneer-like fibres that make garments heavier and/or less flexible than off-the-shelf clothing “no matter how thin or flexible these device arrays are.”

“There is strong motivation to use something that is already familiar, such as cotton/silk thread, fabrics and clothes, and imperceptibly adapting it to a new technological application. This is a huge leap for consumer products, if you don’t have to convince people to wear something different than what they are already wearing,” Andrew adds.

Test results were sometimes a surprise, Andrew notes. “You’d be amazed how much stress your clothes go through until you try to make a coating that will survive a shirt being pulled over the head. The stress can be huge, up to a thousand newtons of force. For comparison, one footstep is equal to about 10 newtons, so it’s yanking hard. If your coating is not stable, a single pull like that will flake it all off. That’s why we had to show that we could bend it, rub it and torture it. That is a very powerful requirement to move forward.” (SV)