Scientists at North Carolina State University have been able to print layers of electrically conductive ink on polyester fabric to make an e-textile that could be used to make wearable devices in future. Since the process can be done at room temperature in normal atmospheric conditions, inkjet printing may offer a simpler way of making electronic textiles.

The scientists said the findings suggest they could extend the techniques common in the flexible electronic to textile manufacturing. The findings are reported in the journal ACS Applied Materials & Interfaces.

“Inkjet printing is a rapidly advancing new technology that’s used in flexible electronics to make films used in cellphone displays and other devices,” said Jesse S Jur, professor of textile engineering, chemistry and science at NC State, who led the study. “We think this printing method, which uses materials and processes that are common in both the electronics and textiles industries, also shows promise for making e-textiles for wearable devices.”

In the study, the scientists described how they used a Fujifilm Dimatix inkjet printer to create a durable and flexible e-textile material, what they did to reliably create the e-textile, and its properties. Part of their challenge was to find the right composition of materials so the liquid ink would not seep through the porous surface of the textile materials and lose its ability to conduct electricity.

“Printing e-textiles has been a very big challenge for the e-textile industry,” said Inhwan Kim, a former graduate student at NC State and one of the team members which carried out the research. “We wanted to build a structure layer by layer, which has not been done on a textile layer with inkjet printing. It was a big struggle for us to find the right material composition.”

The scientists created the e-textile by printing layers of electrically conductive silver ink like a sandwich around layers of two liquid materials, which acted as insulators. They printed those sandwich layers on top of a woven polyester fabric. After they printed the layers of silver ink and insulating materials – made of urethane-acrylate, and poly(4-vinylphenol) – they monitored the surface of the material using a microscope. They found that the chemical properties of the insulating materials, as well as of the textile yarns, were important to maintaining the ability of the liquid silver ink to conduct electricity, and prevent it from penetrating through the porous fabric.

“We wanted a robust insulation layer in the middle, but we wanted to keep it as thin as possible to have the entire structure thin, and have the electric performance as high as possible,” Kim said. “Also, if they are too bulky, people will not want to wear them.”

The team evaluated the electrical performance of the e-textile after bending the material multiple times. It tested more than 100 cycles of bending, finding the e-textile didn’t lose its electrical performance. In future work, the team wants to improve the materials’ electrical performance compared to e-textiles created using methods that require special facilities and atmospheric conditions, as well as increase the material’s breathability.

Eventually, the team intends to use the printing method to create an e-textile that could be used in wearable electronics such as biomedical devices that could track heart rate, or used as a battery to store power for electronic devices.

“We were able to coat the ink on the fabric in a multi-layer material that’s both durable and flexible,” Kim said. “The beauty of this is, we did everything with an inkjet printer – we didn’t use any lamination or other methodologies.”