Researchers demonstrate 3-D printing technology to improve comfort, durability of ‘smart wearables’

(Press-News.org) Imagine a T-shirt that could monitor your heart rate or blood pressure. Or a pair of socks that could provide feedback on your running stride.

It may be closer than you think, with new research from Washington State University demonstrating a particular 3-D ink printing method for so-called smart fabrics that continue to perform well after repeated washings and abrasion tests. The research, published in the journal ACS Omega, represents a breakthrough in smart fabric comfort and durability, as well as using a process that is more environmentally friendly.

Hang Liu, a textile researcher at WSU and the corresponding author of the paper, said that the bulk of research in the field so far has focused on building technological functions into fabrics, without attention to the way fabrics might feel, fit, and endure through regular use and maintenance, such as washing.

“The materials used, or the technology used, generally produce very rigid or stiff fabrics,” said Liu, an associate professor in the Department of Apparel, Merchandising, Design and Textiles. “If you are wearing a T-shirt with 3-D printed material, for example, for sensing purposes, you want this shirt to fit snugly on your body, and be flexible and soft. If it is stiff, it will not be comfortable and the sensing performance will be compromised.”

Initial methods of developing smart wearables involved gluing, weaving or sewing functional components such as conductive threads or sensors into fabrics. Newer approaches involving printing have shown promise, but have still faced problems with comfort and maintenance.

Liu’s team used direct ink writing 3-D printing technology to print solutions of polybutylene succinate – a biodegradable polyester that is compatible with natural fibers – containing carbon nanotubes onto two types of fabric. The printed fabrics showed excellent electrical conductivity, mechanical strength, gauge factor and stability under repeated strains, and the solution’s ability to penetrate and bond with fibers gave the fabrics an enhanced washability and resistance to abrasion.

They tested printed fabrics for tensile strength, electrical conductivity, their ability to function as motion sensors, and other qualities. They found the fabrics continued to perform well after 20 cycles of washing and drying, and the surfaces did not scratch or crack after 200 cycles of abrasion testing or 500 cycles of tensile cyclic testing.

The team also used a biodegradable, nontoxic solvent, Cyrene, for processing, which is more environmentally friendly than commonly used toxic solvents.

Smart fabrics are an emerging trend, offering the promise of clothing items that can perform some of the same tasks as smart watches and other such devices. The technology has the potential for applications in health care, for first responders, in the military and for athletes.

The study was a part of the doctoral dissertation of one of Liu’s students, Zihui Zhao, who was the lead author. Liu has been working on various elements of smart fabrics for several years; she developed a fiber with the flexibility of cotton and the electrical conductivity of a polymer that could have use in wearable tech, as detailed in a paper published in 2023.

The most recent work on 3-D printing focused on the ability of fabrics to sense and monitor information; developing functional smart wearables will also require power source and data transmission technologies.

“This is only one part of the whole smart system,” Liu said.

The research was funded in part by a grant from the National Science Foundation.

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