Chi Hwan Lee, the Leslie A. Geddes Associate Professor of Biomedical Engineering and associate professor of mechanical engineering, and, by courtesy, of materials engineering, and speech, language and hearing sciences at Purdue University

The phrase “show your true colors” takes on new meaning with light-emitting textiles. These fabrics can produce vibrant lighting effects in sectors like fashion, healthcare and safety wearables and advertising display. But there’s a hitch: Machine embroidery with customized designs and patterns compromises the integrity of the electroluminescent (EL) threads.

A Purdue University research team led by Chi Hwan Lee has overcome that obstacle by developing multicolor electroluminescent threads in blue, green and yellow for use with standard embroidery machines. This enables manufacturers to stitch their decorative designs on consumer fabrics without degrading the textiles’ wear resistance and light-emitting properties.

The breakthrough was unveiled in a paper in the journal Science Advances, titled “Machine embroidery of light-emitting textiles with multicolor electroluminescent threads.”

Light-emitting textiles have undergone a rapid evolution. Initially, light sources such as light-emitting diodes and electroluminescent thin films were directly glued or deposited onto garments, negatively affecting the fabrics flexibility, wearability and washability, not to mention requiring high temperatures and vacuum conditions to be successful. Newer EL threads can be woven or knitted, better enabling large-scale production, but are restricted to simple straight line or rectangular patterns due to the conductive fibers with which they are interwoven.

“Industry needed a flexible tool that would enable it to embed light-emitting textiles directly onto consumer fabric products, ensuring that users could translate their fashionable or customized designs into the clothing without having damaging effects on the textile product itself,” said Lee, the Leslie A. Geddes Associate Professor of Biomedical Engineering and associate professor of mechanical engineering.

A number of compelling differentiators make machine embroidery the most attractive option. The process can produce a range of decorative designs, from simple to intricate, on any kind of fabric, which is difficult to do when you knit or weave. It provides a higher quality stitch than embroidery by hand, and furthermore is faster, more precise and less expensive — exactly the manufacturing advantages needed for commercialization at an acceptable cost.

The challenge Lee took on was to develop a novel EL thread that could withstand the rigors of machine embroidery, with its mandate for threads that exhibit high-tensile strengths, moderate elongation and smooth surface finishes. His solution involved coating an EL layer onto the surface of a conductive, embroiderable thread. A transparent conductive fiber had been prepped in parallel; the researchers accomplished this by coating the nylon fiber with silver nanowires to form a conductive network. Then a transparent, waterproof fabric sealer (Gorilla Glue™) was used to envelop the conductive fiber, to enhance its mechanical durability and protect against oxidation.

Lee’s lab ran the threads through the gamut, using a programmable embroidery machine to craft sample designs like butterflies, stars and grids onto consumer fabrics like towels, T-shirts and rugs — they also embroidered the letter “P” for Purdue onto a flag — at speeds up to 350 stitches per minute.

“Our study machine embroidered the decorative designs on different consumer fabric items across large areas and at high speeds, with a uniform formation of pixels throughout the embroidered pattern — proof of concept that industry will welcome,” said Lee, who also holds courtesy appointments as associate professor of materials engineering and speech, language and hearing sciences at Purdue. “The EL threads were also durable, holding up through everyday processes like folding, stretching and machine washing.”

Lee’s team also embroidered the light-emitting pixels onto a helmet liner for a football helmet with an embedded accelerometer sensor to detect varying levels of impact severity. “Such wearable displays with real-time warning systems are crucial for preventing and managing traumatic brain injury, particularly in collision sports, where over two million individuals experience concussion annually in the United States,” the journal paper explained.

The innovation is remarkable for its utility across such disparate sectors as trendy fashion, advertising, healthcare and others.

“We have demonstrated everything from lighting messages or designs on consumer products through delivering emergency alerts of physical hazards by instantly ‘visualizing’ the measurement data captured by embedded sensors,” Lee said. “Our versatile toolkit for light-emitting textiles enables users to adjust colors, luminescent intensities and pixel positions to satisfy what’s needed across an array of differing applications.”