Researchers are developing new ways for fabric to respond to human and environmental stimuli.
By Jamie Swedberg
Remember those color-changing T-shirts in the late 1980s? The fibers in the shirts were bonded with microcapsules of thermochromic pigment that changed hue when it was exposed to heat. The idea was that friends could leave their handprints on you. In practice, however, wearers usually just ended up with different-colored underarms.
Interactive textiles have come a long way since then. One of this summer’s biggest high-tech fashion news items was a collaboration between Barbara Layne, the director of Studio subTela at Hexagram-Concordia in Montreal, Canada and Janis Jefferies, artistic director of the Digital Studios at Goldsmiths College in London, U.K. Their handcrafted, one-of-a-kind project, called Wearable Absence, is a set of clothes fitted with sensors that detect heart rate and skin conductivity, then respond to the wearer’s physical state by playing back data files from memory.
“The garments use wireless technologies and bio-sensing devices to activate a rich online database of image and sound that stream through the garments,” says Layne. “An archive of video, audio, still images and text files dedicated to a particular absent person is triggered by the body of the wearer. For example, if your pulse is fast, your temperature is elevated, and your hands are moist, the garment might determine that you are nervous and automatically download a file (such as a song or text) by your absent person that might calm you down.”
That’s a radical evolution. But fashion isn’t the only area in which interactive textiles have progressed. Researchers all over the globe are designing textiles that respond to their environment. These futuristic fabrics have the potential to change the way we communicate, heal the sick, respond to emergencies and generate power. In the past few years, old and problematic ways of making fabrics “smart” have fallen by the wayside, and new ones have been adopted.
A game changer
A decade ago, televisions and computer screens were bulky cathode ray tubes. Now almost all of them are liquid crystal displays and much slimmer and lighter than their predecessors. But they’re still clumsy and fragile compared to what they could be, says Benjamin Wiley, assistant professor of chemistry at Duke University, Durham, N.C.
Transparent conductive coatings for things like LCD displays and touch panels are usually made out of a film of indium tin oxide (ITO), used because it’s conductive and mostly transparent, but it’s also brittle and expensive. In particular, it has to be applied in a vacuum from a vapor phase, which drives up the expense.
But Wiley and his team have a new idea. “We make copper nanowires,” he says. “You can think of them as small sticks made of copper. Copper is relatively cheap, widely used in wiring and can be sprayed from a solution.”
Copper isn’t inherently transparent, he says, but it is so conductive that it can be applied as a microscopic mesh over a surface, leaving 90 percent of the space unblocked. The result is about 85 percent transparency. A copper nanowire mesh can be applied for about one dollar per square meter, 1/30 the cost of an ITO film and a fraction of the cost of silver ink.
The other attribute that makes copper nanowires special is flexibility. When sprayed on a bendable fabric or membrane (currently, the team is using PET because it’s cheap, clear and flexible), copper nanowire mesh can be rolled or crumpled with no change in conductivity at all. And that, Wiley says, is what’s going to change the game.
In the near future, he believes, manufacturers will be able to produce flexible product packaging and signage with moving displays. Technically, this has been possible for a while, but only with pricey silver inks or an ITO film. Now, it may be commercially viable.
“I’ve seen marketing [research] that says if you have something flashing, it increases your sales by 30 percent,” he notes. “This is going to make it more affordable to do that.”
Is a roll-up flatscreen TV on the horizon too? Wiley doesn’t see why not. The current technology, using ITO, can only bend a bit before it breaks, but copper nanowire mesh bends readily. As long as the other components, such as transistors, are attached in a flexible manner, there’s no reason a copper nanowire television screen couldn’t be toted in a yoga mat bag.
Wiping out infection
Battling bacterial infection in a hospital setting is a particularly difficult problem. You can spray everything with alcohol and surround patients with antibacterial fabrics, but all the bad bacteria won’t be eradicated. Worse, applying antibacterial substances indiscriminately makes the surviving bad bacteria more resistant. Methicillin-resistant Staphylococcus aureus (MRSA) infection is responsible for hundreds of disease outbreaks each year, and is becoming resistant to increasing numbers of disinfectants and antiseptics. Not only that, but antibacterials can destroy beneficial bacteria, leaving room for bad microorganisms to swoop in later.
Toby Jenkins, a researcher at the University of Bath, U.K., and part of a European consortium of 11 academic and clinical partners, is working on a prototype for a wound dressing containing nanocapsules that specifically target only hostile bacteria, using their own strength against them.
“We went back to school and said, ‘What is it that makes some bacteria toxic and some not?’” he says. “To a certain extent it can be generalized, at least for Staphylococcus aureus and Pseudomonas aeruginosa, that it’s because they secrete toxins which cause damage to the surrounding tissue. It’s not the bacteria themselves eating the healthy cells; it’s the toxins that they secrete that are actually killing the cells.”
So Jenkins and his team adopted a “Trojan horse” strategy. Using artificial cell membranes, they created nanocapsules that look, from the point of view of bacteria, like a healthy cell. When they are infected, they even behave like healthy human cells, falling apart and releasing what’s inside. But what’s inside isn’t nutritious cellular material; it’s antibiotic and a color-change material to alert medical personnel that an infection is present.
Currently, about half of the people who die from severe burns die because their wounds have become infected. A Trojan horse wound dressing could stop that infection in its tracks. It could also help people with hard-to-heal wounds such as diabetic ulcers, and wipes containing the molecules could be used to determine whether hospital surfaces are clean.
Jenkins also sees potential for his work to help soldiers in the field. “Both U.S. and U.K. soldiers are in Afghanistan at the moment, and many of them are being horrifically burned in IED attacks,” he says. “It struck us that if we could have these systems that could be applied to soldiers directly after being burned, then at least they could be monitored potentially much more easily, and if the wound becomes infected while they’re being flown back to Germany or the U.K. for treatment, there’s a chance the physicians could intervene at an earlier stage. So that is something we’re potentially quite excited about.”
So far, the nanocapsules have been attached to nonwoven polypropylene in a gel suspension. Jenkins says it’s easy to attach the molecules to fabric; the challenge is doing so in a way that keeps the nanocapsules fresh and effective. He hopes to have the prototype complete in two to three years and within another two to three years, get it through the regulatory process and on the market.
The real magic
All-fabric electronic circuits are the Holy Grail of interactive textiles. It’s one thing to have a jacket with power supplies in the pockets and wires in the sleeves; it’s quite another for the garment itself to contain flexible fabric circuitry.
The issue is that while it’s relatively easy to weave or knit a textile with conductive material in it, it’s hard to connect all the ends in a series and keep the unit from shorting itself out. On a prototype level, it can be done, but Terri Jordon, vice president of business development at Konarka Technologies Inc., Lowell, Mass., says there are other issues.
“Truthfully, the commercialization of that technology is brutal,” says Jordon. “We have the original IP on [a woven photovoltaic cell], but we’re open to anyone who can figure that one out. This is one of those things where you’ve got the core technology, but the magic is going to be in who can take it and make a viable manufacturing process.”
Konarka has decided to go a different route for now. Instead of pursuing woven circuits, it’s putting its energy into flexible multilayer organic photovoltaic (OPV) panels that can be affixed to all kinds of surfaces, including fabrics. These rollable, bendable solar cells called Power Plastic® create clean, portable, green energy that can power anything from a cell phone to electric lights.
“Soldiers need to be lighter; carrying around heavy batteries can definitely hinder them,” Jordon says. “The military are often at remote locations with temporary structures such as tents [that need power]. But Power Plastic also works in consumer-type applications such as handbags, umbrellas and shade structures. Architects go crazy for this stuff.”
One of the limitations of OPV is its life span, which is currently only about three to five years; another is its low efficiency compared to hard solar cells. Konarka has entered into a partnership with Konica Minolta with a goal of attaining 10 percent efficiency and a 10-year life span by the year 2012. That should improve the commercialization potential, and before long, Jordon hopes, people everywhere will power their cell phones and computers via chargers on their jackets or bags.
Printing protective clothing
Proetex, a consortium of 24 European research entities including textile and electronics companies, universities and the Fire Brigade of Paris, is using textile-compatible circuits to create “smart” protective clothing. Lieva Van Langenhove, a professor in the Department of Textiles at the University of Ghent, Belgium, is one of the members.
Van Langenhove and her colleague, Carla Hertleer, have been working with other Proetex researchers to create a smart firefighter suit. The group started with a suit that used traditional electronics, and bit by bit they’ve been replacing the electronics with textile components. One of Van Langenhove and Hertleer’s contributions was a textile antenna. Like Jordon, they found that weaving or knitting the circuits created difficulties.
“Usually we use printing instead because it needs to cover a pretty accurate shape,” Van Langenhove says. “The suit monitors the body parameters: heart rate, respiration rate, but also temperature, heat flux and sweat, and the concentration of salts in the sweat because this indicates risk of dehydration. And then there is an electronic device that captures all the signals, processes it and, via the textile antenna, sends it out together with an integrated GPS system so that the commanding officer can follow up on his crew. We want to warn people before they actually experience a problem. And then in an emergency case, when somebody drops down, for instance, the other people around are informed to go there and help that person.”
Right now the suit is a hybrid of conventional and textile electronics. The antenna and the heart and respiration monitors are fully textile, and the sweat sensor is a hybrid. Other components are wired the old-fashioned way, but will hopefully be replaced in future prototypes.
Other research in the department includes fiber transistors that can be woven into fabric to create a textile computer, and garments to electrostimulate skin and prevent bedsores in hospital patients. One day, they hope these interactive textiles will be manufacturable and launderable so they can be commercialized.
“We first try to get things working, and then we see where it needs to be improved [to make it viable],” Van Langenhove says. “We know, more or less, where the challenges are, but that doesn’t mean there isn’t more to learn.”