Textiles are ubiquitous in many applications, spanning fashion, furnishings, automotive, aerospace, military and medical applications. Adding electronic functionality to textiles, either directly via electronic yarns or indirectly via printing or integration adds further value to the key textile qualities of comfort, protection and aesthetic. Unlike more familiar forms of wearable technology, electronic textiles and smart textiles don’t require PCBs or other cumbersome hardware components, as sensors and circuits are integrated directly into a garment or coating.
The introduction of sensors into textiles, either individually or in arrays provides scope to develop novel sensor devices, materials and fabrication methods. Researchers in South Korea used flexible, self-healing threads to devise a sweat monitoring sensor. Attached to a headband, the carbon fiber thread embedded in a self-healing polymer matrix forms a wearable sensor that can accurately measure potassium and sodium ions. California Institute of Technology researchers have also engineered a wearable sweat sensor, fabricated by laser etching a plastic sheet to form a 3D graphene structure with tiny pores in which sweat can be analyzed for cortisol as an indicator of stress level. The device might be applied to monitor conditions such as anxiety, post-traumatic stress disorder and depression, all of which are correlated with changes in cortisol levels. For extraterrestrial use, the sensor is being incorporated into a system for monitoring the stress and anxiety of NASA astronauts.
Smart materials are also manifesting themselves in the physical environment, as with the SprayableTech system that lets users create room-sized interactive surfaces with sensors and displays. The technology developed at MIT uses airbrushing of functional inks, incorporating copper, dielectric, phosphorus, copper bus and clear conductor layers enables various displays, such as interactive sofas with embedded sensors to control appliances and personal electronics, and sensors for adjusting lighting and temperature through walls.
Fiber-shaped sensors invented by the Swiss Federal Institute of Technology Lausanne can detect different kinds of fabric deformation like stretching, pressure and torque at the same time. Envisioned for integration with clothing or artificial intelligence (AI)-powered textiles, the elastomeric fibers are synthesized with an optical fiber fabrication process applied to unusual materials such as elastomers or liquid metals that serve as the conductors. The resulting soft, stretchable liquid metal transmission device combines high mechanical flexibility with powerful electronic performance.
A smart shirt that measures lung function by sensing movements in the chest and abdomen has proven accurate when compared to traditional testing equipment. Hexoskin uses textile-embedded respiratory inductance plethysmography thoracic and abdominal sensors to monitor respiratory health, and a three-axis accelerometer to monitor daily and sleep activities. The technology is now being combined with AI/machine learning software to better assess the risk of COVID-19 patients recovering at home.
Finally, sensor materials destined for inclusion in wearable devices may not become smarter with a dash of wine or coffee but they will become more durable and flexible. Repeated bending often leads to conductivity loss due to microcracks formation in the metal coating layer, which is undesirable for flexible conductors. The addition of tannic acid extracted from the aforementioned liquids to conductive textile‐based tactile sensors improved the mechanical properties and service life of cotton and other substrate materials.