Techlink :: Tech Practice :: Soft Materials

So long tennis racket; goodbye cricket bat. Last year, a team of Australian researchers announced they had created an 'air guitar' that actually makes music. CSIRO's 'wearable instrument shirt' consists of a shirt with a sensors embedded in it, which pick up the movements made when a wearer picks chords and strums his or her imaginary instrument. Custom software translates the movements into a signal which is wirelessly relayed to a computer for audio generation (no leads to cramp the player's style.) It may not be exactly what the music world needs right now and it takes the fun out of playing your tennis racket with your teeth, but it does point the way to just how strange the world of technical textiles have become.

Textiles have actually been at the forefront of technological development for a while: weaving was the first industry to be fully mechanised and was the catalyst to the Industrial Revolution. The invention of nylon in 1937 led to the synthetic revolution of the 1950s and 60s. But today, the new fibres and textiles being created through advances in electronics, chemistry and, more recently, nanotechnology are taking textiles into realms way beyond their conventional applications of protection and fashion.

In the 1990's, the electronic industry was revolutionised. Devices of all sorts became smaller and more powerful than ever before. The public's growing dependence on mobile devices created a need for lightweight electronic equipment. Because textiles are strong, flexible, lightweight and able to conform to almost any shape, it seemed logical to marry textiles with electronics to produce revolutionary new products to meet this demand.

Electronically conductive textiles were produced by using thin wires of various metals in woven and knit constructions. Semi-conductive fabrics were produced by impregnating knit, woven or nonwoven fabrics with carbon or metal powders. These fabrics were used in a variety of applications but they worked passively. By the late 1990's, it was apparent that a whole new genre of textile products was a possibility – fabrics that had an electrical network integrated into their structure that would interact actively with the surrounding environment. The conductive network within a fabric could be designed to sense, respond and adjust to stimuli such as pressure, temperature, or an electrical charge. The new interactive fabrics were termed "smart textiles." These, in theory at least, would allow clothing to become communications devices in their own right and allow wearers to unplug from wires and use smart textiles to gather information and then disperse that information through wireless communications. Just one application of the technology would be the remote monitoring of patients. Vital data could be captured through gowns and then beamed wirelessly to a doctor, a hospital, a family member or wherever it needed to go.

Among the first to produce commercial electronic apparel were Dutch electronics giant Phillips NV, the European division of Levi Strauss & Co. and Massimo Osti, an Italian designer. In 2000 they introduced their Industrial Clothing Design Plus (ICD+) apparel line. The line included four jacket styles, each equipped with a microphone, remote controller, mobile phone, an earphone and a MP3 player. Retailing for US$600 and up, the jackets had limited commercial success. Contributing to this lack of success was the need to remove a garment's electrical componentry before it could be washed.

Phillips NV continues to invest in the development of wearable electronics- designing working prototypes that incorporate conductive textiles, fabric switches, fabric wiring, fabric stretch sensors, high-sensitivity fabric antennas and flexible electro-luminescent displays. Phillips has also developed apparel that features embedded GPS systems, mobile phones and digital cameras.

More recently, textile research and development company Canesis, has led the field. The company - a subsidiary of Canesis Network Ltd (formerly the Wool Research Organisation of New Zealand) - pioneered the development of the Softswitch, a fabric-based switch and pressure sensing technology. Softswitch is a washable and flexible textile composite fabric that acts as a switch under finger pressure. Burton Snowboard was one of the first apparel companies to use the technology. A Burton jacket which uses a Softswitch sleeve panel to control an integrated Sony MiniDisc personal stereo was named by TIME Magazine as "one of the coolest inventions of 2002".

Canesis subsequently teamed up with Australian Wool Innovation (AWI) to develop a heating system totally comprised of textile based materials. Unlike earlier heating systems that incorporate stiff, heavy wires, the system feels and drapes like a conventional textile, and is durable and washable. The heating system is currently being incorporated into socks as well as interior products such as upholstery and blankets.

Canesis has also developed products that "light up." A variety of products including safety apparel, novelty children's wear and textile displays incorporate electro-luminescence (EL) technology. Electro-luminescent materials are flexible and completely integrated into the products. The challenge has been to lay electro-luminescent components directly onto fabrics in such a way that retains the flexibility of the underlying textile. That technology could be used to create wall coverings or drapes that illuminate interiors in new ways.

Other players in the smart textile field include the switching and sensing company Eleksen, who combine fabric structures and microchip technology in a product called ElekTex. The company's products are durable, washable, flexible and 100% fabric. The company is focussing its efforts on high volume consumer devices - current prototypes include soft keyboards for PDAs and floppy mobile phones. They also have their sights set on games controllers, automotive interiors and medical applications. UK-based Gorix specialises in products with temperature controlled systems. Their system contains a low-voltage heating source capable of maintaining constant temperature regardless of the external ambient temperature. Recreational jackets, blankets and beds for animals are just some of the company's products. Recently Gorix developed a heated diving suit which incorporates an advanced heating system. Previously, diving suits were heated by pumping hot water from a support vessel. The patented heating system is comprised of a series of heater pads powered by a stainless steel battery unobtrusively mounted on the diver's air cylinder. Other wearable electronics include clothing that monitors vulnerable individuals such as newborn babies and post-operative heart patients.

Besides the usual issues that need to be considered when developing a product using conventional textiles, a variety of additional issues have to be considered in the design and development of a product made using an electronic textile. For the textile technologist, a host of challenges arise in the weaving room. It is often necessary to cut or weld the yarns within the electrical network. This is done manually, slowing down the loom's running time. Some conductive yarns are in ribbon form. It is critical that the ribbon yarns do not twist during weaving. To avoid this weaving equipment must be modified. Smart textiles are typically made in short runs - and precision and quality are of the utmost importance.

Another challenge is powering the items made from smart fabrics. At present, conventional and rechargeable batteries are used but a number of developments are in the offing. Scientists in Germany have developed synthetic fibres that generate electricity when exposed to light. These fibres could be woven into machine-washable portable solar cells. The downside being clothes using the fibres as a power source wouldn't work in the dark. Another possible approach is to harness the power generated by walking. In 1996, a researcher in the USA wrote a paper about the potential for harvesting the energy generated by walking. By using a special "piezoelectric" shoe insert that flexes with each step, or a flywheel system connected to a small spring in the back of a shoe, five to eight watts could be recovered from each footfall, enough, the paper said, to power a small wearable computer. Sir Trevor Baylis, the British inventor best known for his wind-up-radio, developed a shoe that would charge a mobile phone battery. But before he could develop a market for the idea, the attacks on the World Trade Centre and the subsequent paranoia over security destroyed the market for such shoe-born devices.

Microencapsulated fabrics are among the latest generation of intelligent textiles. Microencapsulation involves encapsulating liquid or solid substances in tiny thin-walled natural or synthetic bubbles. Microspheres gradually release active agents by simple mechanical rubbing, which ruptures the membrane over time.

Encapsulation has allowed moisturisers, therapeutic oils, and insecticides to be incorporated into fabrics. Buzz Off is an encapsulation treatment designed to prevent mosquito bites. Originally developed for the military, Buzz Off uses microspheres containing permethrin, an all-natural insect repellent derived from the chrysanthemum plant, and is now being sold worldwide for cotton fabrics destined for holiday clothing.

Medical application of encapsulation has centred around the delivery of drug treatments through clothing, to patients. One such application involves the delivery of antimicrobial treatments to cut down the bugs causing the hospital super-infection MRSA. The potential of microencapsulation for use in sportswear, underwear and workwear was soon recognised and now it is becoming a common treatment for fashion clothing. The use of microencapsulated antibacterials was encouraged by the difficulty of eliminating bacteria from clothing. One common treatment works by blocking the cell walls of the bacteria and cause them to starve, keeping garments fresh and hygienic.

Micro-encapsulation is also used in thermo-chromic and photo-chromic fabrics, which change colour with changes in temperature or light. The fabrics themselves are not thermo or photo-chromic, but their microencapsulated colourings are. For the time being, thermo-chromic micro-encapsulation is almost entirely limited to the lingerie and swimwear sectors and industrial clothing such as protective and safety clothes.

Micro-encapsulation also offers another way of maintaining body heat. Phase-change micro-encapsulation involves encapsulating a paraffin-based phase change material (PCM) in plastic shells. In contrast to the microcapsules used in cosmetic textiles, which must be thin-walled enough to allow for the gradual release of the material within the shell, the shells used for heat retention are hard; to protect the paraffin based substance from wear and tear. The spheres are small – about 1,000 microcapsules can fit on a single pinhead. The PCM is ultra-sensitive to temperature variations: below 37° the PCM remains in its solid state; above this temperature it turns to liquid, storing surplus body heat. When it solidifies again, the PCM releases body heat stored in the plastic shells and distributes it evenly around the body. This re-heating effect can last several hours. Fabrics containing PCM microcapsules are capable of storing at least 10 times more heat than untreated products.

But of all the new technologies being applied to textiles, nanotechnology is generating the most excitement. Nanotechnology is science and technology done at the nth degree of minuteness - the scale of atoms and molecules. It's the use of materials and devices so small that nothing can be built any smaller. Nanomaterials are between 0.1nm (nanometre) and 100nm long. A nanometre is one billionth of a metre (10-9m). Which, to most people means nothing at all. A nanometre is to us what a glass marble is to the Earth. By way of comparison - most atoms are 0.1 to 0.2nm wide, strands of DNA are around 2nm wide, red blood cells are around 7000nm in diameter, and human hairs are typically 80,000 nm across. It is the scale which the basic functions of the biological world operate at.

At scales below 100nm the weird quantum effects of the atomic world start to take hold, changing the optical, electronic or magnetic qualities of materials in unpredictable ways. Nano-scale materials can show physical and chemical properties different to those shown by larger particles of the same material. The relatively larger surface area of the smaller particles, compared to their volume, makes them much more chemically reactive than larger pieces. Silver, popular in jewellery because it is unreactive and tarnishes slowly, shows unique catalytic properties at the nanoscale. Nanoparticles of silver are being incorporated directly into wound dressings because they show strong antibacterial properties. The same approach has been taken to produce socks and shoe liners, which combat smelly feet.

In 1951, the Ealing Studios in Britain made "The Man in the White Suit". The film is a satirical comedy starring Alec Guinness (later Sir Alec Guinness) who plays a brilliant young researcher working in a textile mill, who invents a yarn which repels dirt and never wears out. He has a suit made out of the fabric, which is brilliant white because it cannot be dyed. He is lauded as a genius until both management and the trade unions realise the consequence of his invention - once their customers have purchased enough cloth, demand will crash and put the textile industry out of business. In a weird "life-imitates-art" turn of events, one of the first application of nanotechnology to textiles was the development of spill-proof, self-cleaning trousers.

A self-cleaning cotton fabric known as Nano-Care was developed and is marketed by American company Nanotex, and stain-resistant jeans and khakis made from the material have been available from American firms Gap, Eddie Bauer and Lee Jeans since 2001. Nano-Care fabrics are created by modifying the structure of the cylindrical cotton fibres making up the fabric. At the nano scale, cotton fibres look like tree trunks. Using nanotechniques, these tree trunks are covered in a fuzz of minute whiskers, which creates a cushion of air around the fibers. When water hits the fabric, it beads on the points of the whiskers; the beads compress the air in the cavities between the whiskers creating extra buoyancy. In technical terms, the fabric has been rendered super-non wettable or superhydrophobic. The whiskers also create fewer points of contact for dirt. When water is applied to soiled fabric, the dirt adheres to the water far better than it adheres to the textile surface and is carried off with the water as it beads up and rolls off the surface of the fabric.

The concept of "self-cleaning" is based on the leaves of the lotus plant. While the self-cleaning abilities of the lotus plant were recognised thousands of years ago – Buddhists venerate the plant because it can grow out of a muddy pond in pristine beauty – the reason why water and dirt skitter off a lotus leaf like drops of mercury, the so-called Lotus-Effect, only became apparent with the advent of the scanning electron microscope. These instruments revealed that the surface of a lotus leaf is rough at the micro-and nanolevels – just like nano-care fabrics, and, just like nano-care fabrics, this roughness means water doesn't spread, but rather forms highly spherical globules. Dirt, which has a greater affinity for water than the surface of the leaf, is simply washed off when it rains. The development of nano-care fabric is a good example of biomimicry: taking a leaf from natures book and applying its properties, perfected over millions of years, to the man-made world.

Unlike conventional water-repellent coatings, the new coating, is permanently bonded onto the fibers of the fabric and will not wash off. And unlike the material in Man in the White Suit, today's self-cleaning fabrics can be made in any color, since the treatment is applied after the fabric has been dyed.

While the range of possible applications of the Lotus-Effect is in inverse proportion to its elemental simplicity, the technology does have its weaknesses. If someone comes along and puts their fingerprint on the material it doesn't function properly on that spot again until the smudge is removed. A lotus leaf repairs itself because it has tiny wax crystals that grow back. Man-made textiles don't have this capacity for self-repair...yet.

Recently, some success has been had in creating fibres directly from nanomaterials themselves. One of nanotechnology's building blocks are tiny, super-strong rolls of carbon atoms known as carbon nanotubes or CNTs. CNTs have a range of unique properties – including the ability to conduct electricity and heat. Although they were first synthesised in 1991, technologists have only recently worked out how to produce yarns made solely from CNTs, opening the door to the production of strong, light, flexible and smart clothing materials. Seventeen times tougher than the Kevlar used for bulletproof vests and six times lighter and twice as strong as steel wire of the same weight and length, CNT fabrics have obvious military applications. In the US, researchers are looking to use the fibres to create body armour. One avenue being explored is using material woven from hollow CNT fibres which have been filled with nanometre-scale magnetic particles. In the presence of a magnetic field generated by, say, a hand-held device, the beads line up, stiffening the fabric to 50 times its normal state.

Creating new fibres and modifying existing ones, both natural and man-made, through the use of nanotechnology offers huge potential to precisely engineer fibres for specific roles. It's likely that in the future combinations of technologies will be used; nanotechnology will be used to refine other approaches, such as micro-encapsulation or electronics. Technology will enable manufacturers to mix and match the capabilities of a variety of fibres and fabrics. Conventionally, there has been a divide between everyday textiles and their cousins – the technical textiles. Technical textiles are materials and products whose performances are more important than their decorative value – such as firefighter and military uniforms, filters and the strong fabrics used by the construction, aerospace, marine industries. Today a convergence between the two is occurring.

The future seems to offer boundless promise for the world of textiles. But enthusiasm about this potential should be tempered by the awareness that sometimes good technology can turn bad or have unforeseen consequences. At the end of Man in the White Suit, Sir Alec Guinness, glowing like a firefly, is hounded through the dark alleys of some grim northern milltown by a baying mob of workers whose jobs are threatened by the new technology. Eventually he gets bailed up in a doorway. As the crowd advances, his suit suddenly begins to dissolve. Whether it's Guiness's sweat that's the problem isn't apparent, but whatever, the chemical structure of the fibre is obviously flawed and the mob, sensing this, rips the suit to pieces.

In November, the US Environmental Protection Agency decided to regulate consumer items made with nanoparticles of silver, because of fears about unanticipated environmental risks. Besides textiles such as bandages and shoe liners, tiny particles of bacteria-killing silver are used in a range of other products including food-storage containers, air fresheners, and washing machines; environmentalists fear the growing amounts of nanosilver washed down drains may be killing beneficial bacteria and aquatic organisms and pose risks to human health. The development of futuristic textiles must, like any other technological project be carried out with all the possible social and environmental consequences in mind.

In early January 2007 State-owned science company AgResearch became the official owner of Lincoln-based Canesis Network's research and development assets which focus on wool and other innovative textiles.

AgResearch is forging a commercial direction for its new Textiles Group, aiming for high fashion garments and warm carpet applications for manufacturers. The textiles unit was working on confidential product development including a new form of protective but breathable outer wear for one apparel maker. General manager Dr Robert Finch said, "That sort of research and development work by around 70 staff would ultimately reward the wool producer at the farm gate."