Clothing has been one of the three basic human needs since the beginning of our species. From clothing purpose the use of textile has progressively extended to household and domestic applications. The textile was also used for technical applications such as sailcloth, tent, protective garments, ropes, etc., which leveraged the textile properties to create a technical performance advantage.
Smart textiles are defined as textiles that can sense and react to environmental conditions or stimuli, from mechanical, thermal, magnetic, chemical, electrical, or other sources. They are able to sense and respond to external conditions (stimuli) in a predetermined way. Interactive textiles are a relatively new discipline in the textile sector. They are active materials that have sensing and actuation properties. The expressions of “smart” and “intelligent” textiles or “wearable electronic” textiles are commonly used interchangeably.
Smart textiles have applications in medical, sports, personal protective equipment, geo-protection, military, and aerospace sectors, where sensing and monitoring are already used and would only be made more efficient if integrated with textiles. The development of wearable monitoring systems is already having an effect on healthcare in the form of “Telemedicine”. Wearable devices allow physiological signals to be continuously monitored during normal daily activities
Their potential is enormous. one could think of smart clothing that makes us feel comfortable at all times, during any activity and in any environmental conditions, a suit that protects and monitors, that warns in case of danger and even helps to treat diseases and injuries. Such clothing could be used from the moment we are born till the end of our life. Some of the more important efforts include applications that Aid in patient health monitoring through sensor embedded garments that track and record biometric data, helps to improve athletic performance both by analyzing sensor data and adapting to changing conditions. So as to improve performance over the time. Provides environmental sensing and communication technologies for military defense and other security personals.
Our armed forces and first responders are carrying more electronic equipment than ever before and because the dangers and they face do not diminish, there is an increasing emphasis on keeping them as safe as possible. In extreme environmental conditions and hazardous situations there is a need for real time information technology to increase the protection and survivability of the people working in those conditions.
The requirements for such situations are to monitor vital signs and ease injuries while also monitoring environment hazards such as toxic gases. Wearable technologies will enable new capabilities for situational and performance monitoring of service personnel. For example, the location of soldiers and emergency service personnel can be tracked in real-time with great precision, improving safety and success rates in high-risk operations. In addition to this, physiological monitoring will allow us to keep track of levels of stress and fatigue in individuals. Wireless communication to a central unit allows medics to conduct remote triage of casualties to help them respond more rapidly and safely. Improvements in performance and additional capabilities would be of immense assistance within professions such as the defense forces and emergency response services.
These textiles help to regulate body temperature, control muscle vibrations, and protect from environmental hazards such as radiation.
Constant technological innovations in this market have led to an added range of functionalities and capabilities to smart textiles used in the military sector. Smart textiles are being integrated with adaptive insulation property to enhance warmth in military clothing, sleeping bags, and blankets. Also, manufacturers are developing smart textiles that have the potential for physiological and locational monitoring and energy harvesting.
Smart textiles and materials
Three components must be present in smart textiles. i.e. sensors, actuators and controlling units. Smart textiles integrate a high level of intelligence and can be classified into three subgroups: passive, active, and very smart or intelligent smart textiles. They can be made by incorporating electronic materials, conductive polymers, encapsulated phase change materials, shape memory polymers and materials, and other electronic sensors and communication equipment. Smart textiles include conductive materials such as silver, copper, nickel. Other components may be fiber optics, thermochromic dyes, miniaturized electronic items etc. However, the entire smart textile system could have specific function building blocks such as sensor, actuator, interconnection, a controlling unit, communication device, and power supply.
The amalgamation of electronics with clothing has revolutionized the textile industry and became a precursor to the evolution of smart textiles. Traditional smart fabrics, such as metallic silk, organza, stainless steel filament, meta-clad aramid fiber, conductive polymer fiber, conductive polymer coating, and special carbon fibers are used for manufacturing the fabric sensors, while conductive yarn, conductive rubber, and conductive ink have been developed into sensors or used as an interconnection substrate. Researchers have already integrated materials such as metallic, optical fibers, and conductive polymers into the textile structure, thus supplying electrical conductivity, sensing, and data transmission capabilities to smart textiles. Organic polymers may provide a solution to overcome the stiffness of inorganic crystals such as silicon. Researchers are focusing on dual-channel data transfer capable fibers, color-changing fibers, and fibers that can store electricity and are developing the ability to create wearable power sources for military applications. The development of power source textiles and connectors in body armor and similar fabrics are crucial to creating a system with extreme reliability and user-friendliness. Such developments are expected to propel the market growth during the forecast period
Electrical conductive textiles are used in many applications of smart textile materials. However conventional textile materials are usually insulating materials, where they cannot be used directly for smart textile applications that require electrical conductivity. It is possible to obtain electrically conductive textiles by integrating metallic wires, conductive polymers, or other conductive compounds into the textile structure at different stages, such as fiber construction, yarn spinning, or fabric creation stages.
Another application of smart textiles is Textile electrodes that play an important role within a variety of medical applications such as sensors and or actuators. A vital part of textile electrodes are conductive yarns or fabrics integrated in the clothing directly, ensuring mobility. Advantages of textile electrodes are its ductility, flexibility, conductivity, functionality for muscle and nerve stimulation as well as surveillance of body signals such as EMG and ECG.
Nanotechnology is being increasingly used to impart special functionality into fibers such as water and stain resistance, UV protection, and anti-bacterial.
Globally, smart textiles were manufactured using woven or knitting technologies, however, with recent advancements, electronics conductive inks can be printed on textiles.
The success of inkjet printing for printed electronics has been attributed to the emergence of functional printable inks with different nanoscale sizes and structures. Based on their constituents, conductive inks can be categorized into three-dimensional nanostructured materials as nanoparticles, nanowires, nanotubes or they may exhibit plate-like shapes.
The printable ink has a wide range of choices such as conductive, semi-conductive, and dielectric inks. The conductive inks can be prepared from conductive metal nano-particles and micro-particles. The semi-conductive inks can be prepared from metal-oxides, organic polymers, and inorganic semiconductors. The dielectric inks are organic polymers in solvents, organic polymer thermosets or ceramic-filled organic polymers. Therefore, the functional conductive inks can be developed from metals, metal oxides, conductive polymers, organometallic inks, graphene, carbon nanotubes, and a mixture of the different inks.
Some examples of the conductive inks employed for the development of conductive textile are reactive silver, graphene ink, and carbon nanotube, etc. For instance, Liang et al. used a silver nanoparticle-based conductive ink that was configured with poly(styrene-block-ethylene-ran-butylene-block styrene) to develop a skin-inspired ultra-sensitive pressure sensor
Carbon-Based Conductive Materials
As the need for conductive textiles gains importance, carbon-based materials such as graphene, carbon nanotube (CNT), carbon black, graphene oxide, and reduced graphene oxides have been investigated to develop electrically conductive textiles. These carbon materials are preferable for producing conductive textiles as most of them are relatively inexpensive, and they are corrosion-resistant and flexible. In graphene-based polyester conductive fabric was developed and used for bio-potential monitoring applications. Rahman and Mieno have also developed an electro-conductive cotton textile by multiple dip-coating of the cotton fabric in a multi-walled carbon nanotubes solution.
Intrinsically Conductive Polymers
At present, intrinsically conductive polymers are widely used in the development of electro-conductive textiles. Traditional organic polymers are electrical insulators or semiconductors, so the discovery of conductive polymers in the 1970s, opened a new opportunity to produce electro-conductive textiles. Conductive polymers are polymers that contain a conjugated molecular structure that is having alternative single and double bonds between carbon atoms. They can combine the electrical property of metals or semiconductors with the benefit of conventional polymers such as price, structural diversity, flexibility, and durability, which makes them an ideal choice for textile-based electrodes.
Conductive Polymer Composites
Metal-based conductive textiles have the highest conductivity but are often not flexible enough. While the existing conductive polymers show promising conductivity, their mechanical properties need improvements. This has led to conductive polymeric composites with improved electrical conductivity and mechanical stability. Electrically conductive polymer composites are polymers consisting of single or hybrid conductive fillers such as carbonaceous, metallic, and conducting polymeric particles dispersed in a polymer matrix. They can be produced based on a single polymer or a multi-phase blend depending upon the electrical and mechanical properties required. Conductive polymer composites have been growing steadily and are being exploited for academic and industrial applications. As a result, a lot of conductive polymer composites have been introduced and used in developing conductive textiles.
For instance, PEDOT: PSS-polydimethylsiloxane, PPy-silver nanocomposites, PANI-copper , graphene-PPy, PEDPT:PSS–CNT-Gr have been reported as conductive polymer composites. The conductivity of the polymers can be enhanced by adding organic solvents called dopants, for instance, the conductivity of PEDOT:PSS can be enhanced from one to three orders of magnitude by adding polar organic solvents like ethylene glycol, dimethyl sulfoxide, glycerol. Therefore, these conductive polymers can be used to develop all building blocks of the smart textile system as a wide range of electrical properties could be achieved by playing with the polymer add-on, and the extent of dopant.
Self-growing materials that strengthen in response to force
Hokkaido University researchers have developed a strategy to fabricate materials that become stronger in response to mechanical stress — mimicking skeletal muscle growth. Their findings, published in the journal Science, could pave the way for long-lasting materials that can adapt and strengthen based on surrounding conditions.
The strategy was inspired by the process that makes human skeletal muscles become stronger. As a result of strength training at the gym, for example, muscle fibres break down, encouraging the formation of new, stronger fibres. For this to happen, the muscles must be supplied with amino acids, the building blocks of proteins, which join together and form muscle fibres.
Hokkaido University’s Jian Ping Gong specializes in polymer science. Her research team developed a strategy employing ‘double-network hydrogels’ that emulates the building process of skeletal muscles. Double-network hydrogels are a soft, yet tough material formed of about 85 weight percent water and two types of polymer networks: one rigid and brittle, and the other soft and stretchable. The team placed a double-network hydrogel inside a solution containing molecules, called monomers, which can be joined to form larger compounds called polymers. This solution emulates the role of circulating blood carrying amino acids to skeletal muscles.
Applying tensile force (stretching) to the hydrogel causes some of its rigid and brittle polymer chains to break. This leads to the generation of a chemical species called ‘mechanoradicals’ at the ends of the broken polymer chains. These mechanoradicals can trigger the joining up of the monomer absorbed into the hydrogel from the surrounding solution into a polymer network, strengthening the material.
With successive stretching, more breaking down and building up occurs, similar to what happens with skeletal muscles undergoing strength training. Through this process, the hydrogel’s strength and stiffness improved 1.5 and 23 times respectively, and the weight of the polymers increased by 86%. The team was further able to tailor the material’s response to mechanical force by using a specific monomer that altered the gel’s reaction to heat; heated at high temperatures, the gel’s surface became more water-resistant.
The researchers say their work could help with the development of self-growing gel materials for applications as flexible exosuits for patients with skeletal injuries; these suits would potentially become stronger and more functional the more they are used. Professor Gong explained “Since many types of DN gels have similar mechanical features, this process could be applied to a wide range of gels, expanding the range of potential applications.”
Innovative material for soft sensor could bring new tactile tech
Purdue University researchers have developed a new type of soft and stretchable sensor, called iSoft, which has a wide range of functionality and is unique because it doesn’t need wiring or electronics within the material, said Karthik Ramani, a professor of mechanical engineering at the university and director of the C Design Lab.
Such flexible and wearable sensors are being developed to measure and track body motion, a task made more complex by the human anatomy’s numerous potential contortions. For a wearable sensor to work properly, it must be able to deform accordingly. Unlike some soft sensors developed previously, iSoft can handle continuous contact and also can be easily modified for custom purposes after manufacture. “By continuous, we mean moving on the surface and also pressing all the time such as drawing with a pen, which is difficult to achieve,” Ramani said.
The technology features an electrical impedance tomography – or EIT – technique to estimate changes of resistance distribution on the sensor caused by ﬁngertip contact. The system also uses an algorithm the team developed called a dynamic baseline update for EIT that compensates for “rebound elasticity,” which normally causes a signal delay while the elastomer returns to its original shape. These baseline updates are triggered by ﬁngertip contact and movement detections.
The sensor is a thin, rubbery sheet with electrodes around the periphery. It harnesses a material called carbon-ﬁlled silicone rubber, a non-toxic piezoresistive material that has been widely explored in research for various types of low-cost sensors.
“However, the limitations in interactions have been mainly due to a rebound elasticity of the material, which causes a slow-recovery of the sensing signals after material deformations,” Ramani said.
Squid Skin Inspires Creation Of Next-Generation Space Blanket
Drawing design inspiration from the skin of stealthy sea creatures, engineers at the University of California, Irvine have developed a next-generation, adaptive space blanket that gives users the ability to control their temperature. The innovation is detailed in a study published in April 2019 in Nature Communications.
“Ultra-lightweight space blankets have been around for decades – you see marathon runners wrapping themselves in them to prevent the loss of body heat after a race – but the key drawback is that the material is static,” said co-author Alon Gorodetsky, UCI associate professor of chemical & biomolecular engineering. “We’ve made a version with changeable properties so you can regulate how much heat is trapped or released.”
The UCI researchers took design cues from various species of squids, octopuses and cuttlefish that use their adaptive, dynamic skin to thrive in aquatic environments. A cephalopod’s unique ability to camouflage itself by rapidly changing color is due, in part, to skin cells called chromatophores that can instantly change from minute points to flattened disks.
“We use a similar concept in our work, where we have a layer of these tiny metal ‘islands’ that border each other,” said lead author Erica Leung, a UCI graduate student in chemical & biomolecular engineering. “In the relaxed state, the islands are bunched together and the material reflects and traps heat, like a traditional Mylar space blanket. When the material is stretched, the islands spread apart, allowing infrared radiation to go through and heat to escape.”
Gorodetsky said he has many more applications in mind for the novel material: as reflective inserts in buildings to provide an insulation layer that adapts to different environmental conditions; to fabricate tents that would be exceptionally good at keeping occupants comfortable outdoors; and to effectively manage the temperature of valuable electronic components.
Clothing would be a particularly fitting application for the new, bio-inspired material, according to Gorodetsky, who collaborates on research projects with counterparts at athletic apparel manufacturer Under Armour Inc. “The temperature at which people are comfortable in an office is slightly different for everyone. Where one person might be fine at 70 degrees, the person at the next desk over might prefer 75 degrees,” he said. “Our invention could lead to clothing that adjusts to suit the comfort of each person indoors. This could result in potential savings of 30 to 40 percent on heating and air conditioning energy use.”
And those marathon runners who wrap themselves in space blankets might be able to type in a number on a garment-integrated user interface to achieve the desired level of thermal comfort, optimizing performance during races and recovery afterward. Other benefits Leung mentioned include the material’s light weight, ease and low cost of manufacturing, and durability. She noted that it can be stretched and returned to its original state thousands of times.
Materials chemists tap body heat to power ‘smart garments’
Many wearable biosensors, data transmitters and similar tech advances for personalized health monitoring have now been “creatively miniaturized,” says materials chemist Trisha Andrew at the University of Massachusetts Amherst, but they require a lot of energy, and power sources can be bulky and heavy. Now she and her Ph.D. student Linden Allison report that they have developed a fabric that can harvest body heat to power small wearable microelectronics such as activity trackers.
Andrew and Allison explain that in theory, body heat can produce power by taking advantage of the difference between body temperature and ambient cooler air, a “thermoelectric” effect. Materials with high electrical conductivity and low thermal conductivity can move electrical charge from a warm region toward a cooler one in this way. Some research has shown that small amounts of power can be harvested from a human body over an eight-hour workday, but the special materials needed at present are either very expensive, toxic or inefficient, they point out. Andrew says, “What we have developed is a way to inexpensively vapor-print biocompatible, flexible and lightweight polymer films made of everyday, abundant materials onto cotton fabrics that have high enough thermoelectric properties to yield fairly high thermal voltage, enough to power a small device.”
For this work, the researchers took advantage of the naturally low heat transport properties of wool and cotton to create thermoelectric garments that can maintain a temperature gradient across an electronic device known as a thermopile, which converts heat to electrical energy even over long periods of continuous wear. This is a practical consideration to insure that the conductive material is going to be electrically, mechanically and thermally stable over time, Andrew notes.
Specifically, they created their all-fabric thermopile by vapor-printing a conducing polymer known as persistently p-doped poly(3,4-ethylenedioxythiophene) (PEDOT-Cl) onto one tight-weave and one medium-weave form of commercial cotton fabric. They then integrated this thermopile into a specially designed, wearable band that generates thermo-voltages greater than 20 milliVolts when worn on the hand.
Using a thermal camera, they established that the wrist, palm and upper arms of volunteers radiated the most heat, so Andrew and Allison produced stretchy knitted bands of thermoelectric fabric that can be worn in these areas. The air-exposed outer side of the band is insulated from body heat by yarn thickness, while only the uncoated side of the thermopile contacts the skin to reduce the risk of allergic reaction to PEDOT-CI, they point out.
The researchers note that perspiration significantly increased the thermovoltage output of the stretchy armband, which was not surprising, as damp cotton is known to be a better heat conductor than dry fabrics, they observe. They were able to turn off heat transfer at will by inserting a heat-reflective plastic layer between the wearer’s skin and the band, as well.
Overall, they say, “We show that the reactive vapor coating process creates mechanically-rugged fabric thermopiles” with “notably-high thermoelectric power factors” at low temperature differentials compared to traditionally produced devices. “Further, we describe best practices for naturally integrating thermopiles into garments, which allow for significant temperature gradients to be maintained across the thermopile despite continuous wear.”
Engineers create programmable silk-based materials with embedded, pre-designed functions
Tufts University engineers have created a new format of solids made from silk protein that can be preprogrammed with biological, chemical, or optical functions, such as mechanical components that change color with strain, deliver drugs, or respond to light, according to a paper published online this week in Proceedings of the National Academy of Sciences (PNAS).
To develop these materials, the engineers began with silk cocoons and dissolved the silk fibers in a solution to create water suspensions of proteins, which were then re-assembled in solid block forms. They manipulated the bulk materials with water-soluble molecules to create multiple solid forms, from the nano- to the micro-scale, that have embedded, pre-designed functions.
For example, the researchers created a surgical pin that changes color as it nears its mechanical limits and is about to fail, functional screws that can be heated on demand in response to infrared light, and a biocompatible component that enables the sustained release of bioactive agents, such as enzymes.
Silk’s unique crystalline structure makes it one of nature’s toughest materials. Fibroin, an insoluble protein found in silk, has a remarkable ability to protect other materials while being fully biocompatible and biodegradable.“Structural proteins are the building blocks of nature,” Omenetto said. “Silk, in particular, possesses compelling properties,” including its durability and biocompatibility. “We usually experience silk as a fibrillar material,” Omenetto said, “but this format comes from the spinning process to which the protein undergoes in the spinneret of caterpillars and spiders
“The ability to embed functional elements in biopolymers, control their self-assembly, and modify their ultimate form creates significant opportunities for bio-inspired fabrication of high-performing multifunctional materials,” said senior and corresponding study author Fiorenzo G. Omenetto, Ph.D
Materials with Intelligence
Researchers from School of Computer Science and Informatics at UCD Dublin and the Centre for Adaptive Wireless Systems at Cork IT, Ireland, are starting to explore the tools and techniques we need in order to build ‘augmented materials’ which combine sensing, actuation and processing into the fabric of built objects.The researchers are using Ireland’s Tyndall National Institute’s 2.5cm-on-a-side motes, which are being reduced to a 1cm form and beyond, making them realistic for embedded use.”
“Embedding sensing into a physical substrate has a number of attractions. Each sensor package can sense a number of local variables such as the stress on the material, its orientation in space, its proximity to other materials etc. Combine these sensors into a network and we can construct a global view of the material and its relationships to the real world. Add processing and we have the potential to build materials that “know themselves”, in some sense, and which can react in ways that are far more sophisticated than are possible with simpler, ‘smart’ materials,” write Simon Dobson and Kieran Delaney in ERCIM News.
These materials can be used to warn patients if they are overdoing their exercise recommended by downloaded therapy programme. It is even possible to build materials with variable rigidity so that the cast adapts the support it provides over the course of treatment.
“Augmented materials are in many ways the ideal co-design challenge. The properties of the material determine directly what can be sensed and processed, while software provides capabilities to enhance and complement the material’s underlying physics. A physical phenomenon, such as placing one augmented object on top of another, gives rise to individual sensor readings affecting pressure, orientation and the establishing of new wireless communications links etc. These in turn give rise to a semantic inference that can be used in software to drive high-level responses based on the intention inferred from performing this particular action with these particular objects.”
Smart fabrics made possible by new metal deposition technique: Imperial College London
A multidisciplinary team of researchers from Imperial College London led by Dr. Firat Güder from the Department of Bioengineering have developed an innovative technique to print metals such as silver, gold and platinum onto natural fabrics. They have also shown that the technique could be used to incorporate batteries, wireless technologies and sensors into fabrics like paper and cotton textiles.
Ultimately these technologies could be used for new classes of low-cost medical diagnostic tools, wirelessly powered sticker-sensors to measure air pollution or clothing with health monitoring capabilities. Metals have been printed onto fabrics, but until now the process has essentially coated the fabric with plastic which renders the fabric waterproof and brittle. Published in Advanced Functional Materials, the research paper describes how a new approach would allow metal inks to cover entire fibres rather than simply coating the surface of the fabric.
To coat the fibres, the researchers first covered them in microscopic particles of silicon, and then submerged the material into a solution containing metal ions. This preparatory process, known as SIAM (Si ink-enabled autocatalytic metallization), allows metals to ‘grow’ throughout the material as the ions are deposited on the silicon particles.
This approach coats metal throughout the fabric, allowing paper and textiles to maintain their ability to absorb water and their flexibility alongside providing a large metallic surface. These properties are important to the functioning of many advanced technologies, particularly sensors and batteries, where ions in solution must interact with electrons in metals.
Having proven that the method works, the researchers demonstrated its ability to fabricate the elements required for a number of examples of advanced technologies. For example, they created silver coil antennas on paper, which can be used for data and power transmission in wireless devices such as Oyster cards and contactless payment systems. The team also used the method to deposit silver onto paper and then added zinc onto the same paper to form a battery.
The new approach was also used to produce a range of sensors. This included a paper-based sensor to detect the genetic indicators of a disease that is fatal to grass-eating animals (Johne’s disease) and associated with Crohn’s disease in humans. According to the researchers, sensors fabricated within natural fabrics would be cheaper, easy to store and transport, and ultimately could be used in clothing that monitors health.
“We chose applications from a range of different areas to show how versatile and enabling this approach could be,” said Grell. “It involved a lot of collaboration and we hope we have demonstrated the potential of this method so people who specialise in different areas can then develop these applications.
Grell added: “The beauty of this approach is that it can also combine different technologies to serve a more complex application, for example low-cost sensors can be printed on paper that can then transmit the data they collect through contactless technology. This could be particularly useful in the developing world where diagnostic tests need to be conducted at the point of care, in remote locations and cheaply.”
The affordability of this method was cited as one of its major advantages by the researchers, who demonstrated that when using their approach a coil antenna could cost as little as $0.001 to manufacture, compared to $0.05 using current methods. With the support of Imperial innovations, the team have applied for a patent and are now looking for industry partners. The next step will be to demonstrate the use of the new method in a real-life applications, which will require prototype development, testing and optimising.
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