Research Probes Possibilities for Liquid-Metal-Coated Textiles
Conductive textiles may represent the next frontier for wearables.
China and Korea-based researchers with Advanced Materials Technologies are testing the creation of conductive fabrics by dip-coating material with liquid metal particles. The textiles can be made into conduits for electricity by compressing them with a patterned mold to create conductive circuits on the fabric face.
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According to the group’s investigations and testing, conductive textiles could have a number of applications and benefits. They could serve as “circuit interconnects, Joule heaters, and flexible electrodes to measure ECG signals,” the researchers wrote. What’s more, liquid metal-coated textiles provide antimicrobial protection against certain strains of bacteria that cause common skin and soft tissue infections.
Coating with gallium-based liquid metals is a simple process due to the silvery-white metal’s low melting point, they wrote. The liquid metal demonstrates electrical and thermal conductivity, nearly zero vapor pressure—meaning that it has a low propensity to change into a gaseous state—and low toxicity. Liquid metals are especially versatile, and the researchers said they are particularly suited to potential applications in “soft-robotics, wearable electronics, and health monitoring systems.”
Unlike solid metals, liquid metals can be administered to fabrics and patterned at room temperature. This means that circuits made from liquid metals can be achieved through 3D-printing, injection and mixing liquid metals into polymers to form composite materials. Most work thus far has focused on depositing liquid metals onto non-porous surfaces like films, but permeability helps promote breathability to avoid skin irritation or inflammation, a key criteria for wearables. The researchers experimented with coating particles of liquid metal directly onto textiles, “which has the appeal of not blocking the pores of the textile.” Textiles can be coated and subsequently cut and maintain their conductivity and antibacterial properties, otherwise known as autonomous healing, the testing showed.
The researchers tested a liquid-metal-coated textile’s ability to conduct heat on a wearer’s body, powered by two AA batteries. It took about 15 seconds for the fabric to heat up to a maximum temperature of about 107 degrees, and the fabric cooled to an ambient temperature within 20 seconds. Another experiment showed that the liquid-coated textile could function as a permeable electrode for biopotential measurements, or electric signals generated by the body’s physiological processes. The testing showed that liquid-textile-based electrodes performed as well as conventional gel-based electrodes, like those that are applied to the arms of patients in hospitals. Moreover, the textiles proved more breathable than the traditional gel electrodes, leading to greater comfort for the wearer over a long period of time.
Next, the researchers moved on to testing the antibacterial properties of the liquid-metal-coated textiles.
“This study demonstrated that the simple [liquid metal] coatings can provide the protection for the textile from harmful bacterial contamination,” they wrote—a feature that’s particularly advantageous for preventing bacteria contamination of wearable devices that could potentially lead to infections or unpleasant body odor. The antimicrobial properties of the coated materials were tested against two of the most pervasive strains of bacteria that cause healthcare-related infections. Compared against an uncoated control textile, the coated textiles were effective in preventing the spread of both. Receiving multiple liquid-metal coating dips added to their efficacy—for example, textiles that received two dips in the liquid metal suspension were found to inhibit the growth of bacteria by 84 percent, and five dips eliminated 90 percent of bacteria growth.
“Such simple coatings provide a route to convert otherwise insulating textiles into electrical circuits with the ability to autonomously heal and provide antimicrobial properties,” the researchers concluded.