Researchers have developed a new method that uses a common technology for fabricating T-shirts to create a new electrode platform that potentially could make wearable electronics more affordable to manufacture.
A team from Washington State University has demonstrated that they can make electrodes using a screen-printing process to fabricate a flexible, durable circuit pattern. This pattern then can be transferred to fabric and worn directly on human skin as a platform for various electronics such as those for health or fitness monitoring, researchers said.
The goal of the research was to facilitate the fabrication of flexible, wearable electronics, lowering production costs and making the overall process more convenient, said one of the researchers, Jong-Hoon Kim, associate professor at the WSU Vancouver’s School of Engineering and Computer Science. “That’s why we focused on screen printing: it’s easy to use," he said. "It has a simple setup, and it is suitable for mass production.”
Benefits of Screen Printing for Wearable Electronics
Screen printing is a process in which ink is transferred through a mesh screen onto a substrate where certain parts are blocked by a stencil, resulting in imprinted designs. While screen printing is used in some commercial manufacturing of wearable electronics, most also require expensive processes and clean rooms, researchers said.
Creating a process that relies wholly on screen printing to develop durable circuits for wearables then has distinct advantages for manufacturers and ultimately consumers because it can drive costs of these products down, they said.
In their specific research, researchers used a multi-step process to layer polymer and metal inks to create a serpentine electrode structure. They detail their process in a paper in the journal ACS Applied Materials and Interfaces. "The screen printing of the polyimide (PI) layer enables facile, low-cost, scalable, high-throughput manufacturing," researchers wrote in the paper's abstract. "PI mixed with poly(ethylene glycol) exhibits a shear-thinning behavior, significantly improving the printability of PI. The premixed Ag/AgCl ink is then used for conductive layer printing."
The resulting pattern appears delicate but produces durable electrodes that can be stretched by 30 percent and bend to 180 degrees without breaking, researchers reported.
Proving the Concept of Wearable Electronics
Researchers printed multiple electrodes onto a pre-treated glass slide, which could then be peeled off and transferred onto fabric or other material. After printing the electrodes, they were transferred onto an adhesive fabric that volunteers wore directly on their skin.
Combined with a flexible printed circuit, the wearable performed real-time wireless electrocardiogram monitoring with a custom developed algorithm that can calculate accurate heart rates, respiratory rates, and heart-rate variability metrics for arrhythmia detection, researchers wrote.
While researchers tested their electrodes on ECG monitoring, the screen-printing process they developed can also create electrodes for a range of uses, including those that power smart watches or fitness trackers, Kim said.
The team is currently working to expand their technology platform to print various electrodes as well as entire electronic chips. They even are eyeing the potential printing of whole circuit boards using the technology, he said.