Wearable electronic textiles (e-textiles) have become a focus of significant research interest due to their potential applications in sportswear, military uniforms, environmental monitoring and health care. 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.
Smart fabric is a traditional fabric with added interactive functionality such as power generation or storage, sensing, radio frequency functioning, human interface elements and/or assistive technology. There have been enormous efforts in incorporating electronic components to make e-textiles for various applications such as sensors, energy storage devices, transistors and photovoltaic devices.
The past few years have seen the introduction of a number of wearable technologies, from fitness trackers to smart watches but with the increasing use of smart textiles, wearables are set to become ‘disappearables’ as the devices merge with textiles, according to a new report from Cientifica. Unlike today’s ‘wearables’ tomorrow’s devices will be fully integrated into the the garment through the use of conductive fibres, multilayer 3D printed structures and two dimensional materials such as graphene.
With the help of nano-materials, nano-biotechnology, and nano-electronics, electronic components such as actuators, control units, and sensors, are embedded into smart textiles. The textile-based materials, equipped with nanotechnology and electronics, have a major role in the development of high-tech miltary uniforms and materials. Active intelligent textiles ystems, integrated to electronics, have the capacity of improving the combat soldiers performance by sensing, adopting themselves and responding to a situational combat need allowing thecombat soldiers to continue their mission. Meantime, smart technologies aim to help soldiers do everything they need to do with a less number of equipment and a lighter load.
Nanotechnology based smart textiles
Nanotechnology-based textile coating is a combined approach to textile engineering which mainly relies on using nanoscale materials and novel methods to produce smart finishing. Several methods have been introduced to generate smart coatings on textiles including the sol–gel technique, layer-by-layer technique, cross-linking by polymers, and thin film deposition. Nanofibre coating of different metallic and nonmetallic substrates has been intensively considered for sensory and infrastructure purposes.
Second skin protects against chem, bio agents
Recent events such as the COVID-19 pandemic and the use of chemical weapons in the Syria conflict have provided a stark reminder of the plethora of chemical and biological threats that soldiers, medical personnel and first responders face during routine and emergency operations. Personnel safety relies on protective equipment which, unfortunately, still leaves much to be desired. For example, high breathability (i.e., the transfer of water vapor from the wearer’s body to the outside world) is critical in protective military uniforms to prevent heat-stress and exhaustion when soldiers are engaged in missions in contaminated environments. The same materials (adsorbents or barrier layers) that provide protection in current garments also detrimentally inhibit breathability.
To tackle these challenges, a multi-institutional team of researchers led by Lawrence Livermore National Laboratory (LLNL) scientist Francesco Fornasiero has developed a smart, breathable fabric designed to protect the wearer against biological and chemical warfare agents. Material of this type could be used in clinical and medical settings as well. The work was recently published online in Advanced Functional Materials and represents the successful completion of Phase I of the project, which is funded by the Defense Threat Reduction Agency through the Dynamic Multifunctional Materials for a Second Skin “D[MS]2” program.
“We demonstrated a smart material that is both breathable and protective by successfully combining two key elements: a base membrane layer comprising trillions of aligned carbon nanotube pores and a threat-responsive polymer layer grafted onto the membrane surface,” Fornasiero said. These carbon nanotubes (graphitic cylinders with diameters more than 5,000 times smaller than a human hair) could easily transport water molecules through their interiors while also blocking all biological threats, which cannot fit through the tiny pores. This key finding was previously published in Advanced Materials.
The team has shown that the moisture vapor transport rate through carbon nanotubes increases with decreasing tube diameter and, for the smallest pore sizes considered in the study, is so fast that it approaches what one would measure in the bulk gas phase. This trend is surprising and implies that single‐walled carbon nanotubes (SWCNTs) as moisture conductive pores overcome a limiting breathability/protection trade-off displayed by conventional porous materials, according to Fornasiero. Thus, size-sieving selectivity and water-vapor permeability can be simultaneously enhanced by decreasing SWCNT diameters
Contrary to biological agents, chemical threats are smaller and can fit through the nanotube pores. To add protection against chemical hazards, a layer of polymer chains is grown on the material surface, which reversibly collapses in contact with the threat, thus temporarily blocking the pores. “This dynamic layer allows the material to be ‘smart’ in that it provides protection only when and where it is needed,” said Timothy Swager, a collaborator at the Massachusetts Institute of Technology who developed the responsive polymer. These polymers were designed to transition from an extended to a collapsed state in contact with organophosphate threats, such as sarin. “We confirmed that both simulants and live agents trigger the desired volume change,” Swager added.
The team showed that the responsive membranes have enough breathability in their open-pore state to meet the sponsor requirements. In the closed state, the threat permeation through the material is dramatically reduced by two orders of magnitude. The demonstrated breathability and smart protection properties of this material are expected to translate in a significantly improved thermal comfort for the user and enable to greatly extend the wear time of protective gears, whether in a hospital or battlefield.
“The safety of warfighters, medical personnel and first responders during prolonged operations in hazardous environments relies on personal protective equipment that not only protects but also can breathe,” said Kendra McCoy, the DTRA program manager overseeing the project. “DTRA Second Skin program is designed to address this need by supporting the development of new materials that adapt autonomously to the environment and maximize both comfort and protection for many hours.” In the next phase of the project, the team will aim to incorporate on-demand protection against additional chemical threats and make the material stretchable for a better body fit, thus more closely mimicking the human skin.
Smart textiles can act as a sensor and also initiate movement in response to a stimulus.
The team from the University of Wollongong, Australia, and the University of Texas in Dallas, USA, have developed an innovative smart material consisting of carbon nanotubes and Lycra fibres can act as a sensor and also initiate movement in response to a stimulus. “Our recent work allowed us to develop smart clothing that simultaneously monitors the wearer’s movements, senses strain and adjusts the garment to support or correct the movement,” explained Javad Foroughi, the project’s lead researcher who works at the Wollongong University’s ARC Centre of Excellence for Electromaterials Science (ACES)
“We have already made intelligent materials as sensors and integrated them into devices such as a knee sleeve that can be used to monitor the movement of the joint, providing valuable data that can be used to create a personalized training or rehabilitation program for the wearer,” said lead researcher Javad Foroughi of ACES. “Our recent work allowed us to develop smart clothing that simultaneously monitors the wearer’s movements, senses strain, and adjusts the garment to support or correct the movement.”
The researchers said the new material, which could be easily manufactured on an industrial scale, has a mechanical work capacity and power output exceeding that of human muscles. The team envisions the technology could be used in robotics or to make sensors for lab-on-chip devices
Graphene-based wearable e-textiles move closer to commercial production
The market for e-textile clothing is forecasted to reach $5 billion by 2027, according to the market research firm IDTechEX. And while graphene is expected to be one of the most prominent materials in wearable e-textiles, currently there is no good way to manufacture graphene-based e-textiles on an industrial scale.
To address this problem, a team of researchers led by Professor Kostya S. Novoselov at The University of Manchester have developed a scalable process to manufacture graphene-based wearable e-textiles on an industrial scale. As they write in their paper published in a recent issue of ACS Nano, the method could allow graphene e-textiles to be manufactured at commercial production rates of 150 meters per minute.
“To be able to produce graphene-based wearable e-textiles in scalable quantity at very high speed is a significant breakthrough for the rapidly growing wearables market,” first author Nazmul Karim at The University of Manchester told Phys.org. “Our simple and cost-effective way of producing multifunctional graphene textiles could easily be scaled up for many real-life applications, such as sportswear, military gear, and medical clothing.”
In the new method, the team has reversed the previous process of coating textiles with graphene-based materials. Traditionally, the textiles are first coated with graphene oxide, and then the graphene oxide is reduced to its functional form of reduced graphene oxide. Instead, here the researchers first reduced the graphene oxide in solution, and then coated the textiles with the reduced form.
By making coating the final step, it becomes possible to use a coating technique called padding, which is currently the most commonly used method of applying functional finishes to textiles in the textile industry. For example, water-repellent and wrinkle-free clothing are often made by padding.
A commercial pad-dry unit can process approximately 150 meters of fabric in just one minute—a huge leap from laboratory methods for coating textiles with graphene that often involve multiple time-consuming steps. As the researchers write in their paper, they believe that using padding to manufacture graphene-based e-textiles will be an important step in moving from R&D-based e-textiles to real-world applications.
In their study, the researchers demonstrated that e-textiles made by a laboratory-scale pad-dry unit exhibited excellent electrical and mechanical characteristics. Tests showed that the reduced graphene oxide forms a uniform coating around the individual cotton fibers, which results in good electric conductivity, tensile strength, breathability, flexibility, and overall comfort of the fabric. The coated fabric also appears to remain electrically conductive after repeated washing cycles.
Graphene-based wearable e-textiles have a variety of potential applications. One possibility, which the researchers demonstrated, is that sensors can be incorporated into the fabric for monitoring physical activity. A sensor mounted on the wrist, for example, can capture mechanical movements such as bending/unbending, stretching/relaxation, and twisting/untwisting. Another possibility is to incorporate flexible heating elements throughout an item of clothing, along with flexible supercapacitors to power them.
“Our future research plan is to look into other 2D materials and utilize their benefits for wearable e-textiles applications,” Karim said. “We are also looking to commercialize these technologies in collaboration with industrial partners.”
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