3D printing tech improves durability of 'smart wearables'

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 3D ink printing method for so-called smart fabrics that continues 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, 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. If you are wearing a T-shirt with 3D 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,” Liu said.

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 3D printing technology to print solutions of polybutylene succinate — a biodegradable polyester that is compatible with natural fibres — 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 fibres gave the fabrics an enhanced washability and resistance to abrasion.

The researchers 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.

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