Symposium SB10 : Electronic Textiles

The beginning of the 1990s marked the dawn of research into smart textiles. At this time, Mark Weiser and his colleagues at Xerox PARC introduced their vision of a computational environment embedded seamlessly into our lives. The vision of Ubiquitous Computing proposed a world in which “computers disappear into our everyday environments and weave themselves into our daily lives without being noticed”. While smart textiles were initially mainly influenced by the military and existing wearable technologies, consumer and healthcare markets have since become major driving forces. Today, textiles make up an essential and indispensable part of our daily lives. Since they are generally lightweight and highly flexible, they are applicable in a wide range of applications. In combination with electronic components, textiles can be enhanced with several additional capabilities ranging from sensing and actuation to lighting and information display. This opens the door to many novel application areas. As stated by Ivan Poupyrev, the leader of the Project Jacquard team at Google, “if you can hide or weave interactivity and input devices into the materials, that will be the first step to making computers and computing invisibly integrated into objects, materials and clothing”.
Within the project TextileUX, we aim to take the next step in realizing Mark Weiser’s vision. We strongly believe that smart textiles can thoroughly augment any object and provide new and exciting features that are difficult or impossible to realize with other solutions. The goal is to create an interactive textile sensor capable of sensing touch gestures and deformation input in real-time. The underlying principle is similar to a Force Sensing Resistor (FSR) that has been used for over thirty years. A typical FSR device is a continuous electrical switch whose electric conductance gradually increases as external force is applied. In one common configuration, two conductors are placed into mutual contact via a semi-conductive material. Most of these sensors, though common, generally detect only a single touch. Resistive array-based multi-touch sensors have a flat form factor, are inherently inexpensive, use little power, and can continuously measure applied force. Researchers have transferred this basic principle into the field of pressure-sensitive fabrics in the form of textile materials that include an array of vertical and horizontal conductors separated by a semi-conductive layer. We reduce the layer stack to one single layer by transferring the same pressure-sensing principle right into the yarn itself. Our novel yarn comprises a conductive metallic thread with a resistive coating consisting of an organic polymer solution containing conductive carbon-based particles. Once an external force is applied to the resistive yarn, the coating gets compressed, which increases the density of conductive particles in the coating and corresponds to a change in resistance of the coating. In the case where two coated yarns overlap each other, the change in resistance can be measured by applying voltage to one yarn and measuring the voltage drop across the other one. The same principle can also be achieved by overlapping a resistive-coated yarn with an off the-shelf conductive yarn. This simple principle opens up a wide array of possibilities for the design of interactive textiles.

The recent rapid advance and eagerness of portable consumer electronics stimulate the development of functional elements towards being lightweight, flexible, and wearable. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Key building blocks of navigation and position tracking devices are magnetic field sensors.
Although there is a remarkable progress in the field of shapeable magnetoelectronics [1], there is no technology available that can enable sensitivities to geomagnetic fields of 50 µT and, ultimately, magnetic fields of smaller than 1 µT in a mechanically compliant form factor. If available, these devices would contribute greatly to the realization of high-performance on-skin interactive electronics [2-5] and point of care applications [6,7].
Here, we will present technological platforms allowing to realize not only mechanically imperceptible electronic skins, which enable perception of the geomagnetic field (e-skin compasses) [8], but also enable sensitivities down to ultra-small fields of sub-50 nT [9]. We demonstrate that e-skin compasses allow humans to orient with respect to earth’s magnetic field ubiquitously. Furthermore, biomagnetic orientation enables novel interactive devices for virtual and augmented reality applications. We showcase this by realizing touchless control of virtual units in a game engine using omnidirectional magnetosensitive skins.

[1] D. Makarov et al., Applied Physics Reviews 3, 011101 (2016).
[2] G. S. Canon Bermudez et al., Science Advances 4, eaao2623 (2018).
[3] M. Melzer et al., Nature Communications 6, 6080 (2015).
[4] M. Melzer et al., Advanced Materials 27, 1274 (2015).
[5] N. Münzenrieder et al., Advanced Electronic Materials 2, 1600188 (2016).
[6] G. Lin et al., Lab Chip 14, 4050 (2014).
[7] G. Lin et al., Lab Chip 17, 1884 (2017).
[8] G. S. Canon Bermudez et al., Nature Electronics 1, 589 (2018).
[9] P. N. Granell et al., npj Flexible Electronics 3, 3 (2019).

Stable and reliable textile electronics require precise tools for the integration of active electronic components. Most printed circuit boards are manufactured using hard materials such as metals, glasses, and semiconductors, which often fail to provide a flexible foundation for textile applications. Polymer-based fibers, which exhibit flexible mechanical properties provide a promising alternative material choice for flexible electronics. Electronic textiles produced from multimaterial fibers could be designed to integrate multiple functionalities while providing the required mechanical stability owed to built-in packaging and insulation. Electronic fabrics based on such fibers can further be integrated into apparel or used for medical or situational monitoring.
As a flexible analog to a breadboard, we demonstrate self-patterned planar fiber structures with push-in electrical connectors. Self-patterned fibers contain 24 to 1000 electrodes (5 µm in thickness), for straightforward assembly of on-fiber electronics. While the thickness of these self-patterned fibers is < 50 µm, they can be drawn as long as 500 meters. The patterns along the fiber can be engineered prior to fiber drawing of the macroscopic preform using conventional machining. After deposition of the electrodes on the self-patterned preform, the fibers can be cut to various lengths and stacked to create complex electronic circuits or used as a continuous fiber-electronic board. In addition, the design allows the integration of on-chip connectors similar to USB ports. The electrodes on the self-patterned fiber can be thermally deposited metals (Au, Pt or TiN), and the impedance can be optimized by tuning the metal thickness. After surface mounted electronic components have been placed onto the fiber circuits, these devices can be encapsulated by depositing high-density dielectrics and parylene C or polymeric coatings. Such fibers are expected to find a broad range of applications in textile electronics, sensors, and structural health monitoring.

The design and control over bespoke means of advanced manufacturing has become ubiquitous within the field of architecture. A designer’s proficiency in orchestrating the means of production, through crafting design-specific fabrication techniques, links directly to the level of technical specificity that is possible for the assembly, form and responsivity of an architectural system. In the most experimental cases, this approach is deployed in order to finely tailor the ambient relationships between the architectural system and its environment – embedding responsivity to atmospheric factors such as light, temperature and humidity. The on-going research discussed here, titled Social Sensory Architectures, looks to further such access to advanced manufacturing by exploring the influences of architectural environment on human behavior. Particularly, the research addresses architecture’s imposition on social function for individuals with the neurodevelopmental disorder of autism, where a sensorial hyper-awareness can commonly drive anxiety and maladaptive behavior.

In this research, novel uses of industrial knit manufacturing are leveraged to create sensorially-reactive architectural environments intended to access an individual’s beneficial spectrum of hyper-awareness towards sensory stimuli. The common immutability of an architectural environment poses a diminished capacity for an individual’s development due to their lack of adaptability towards stressful scenarios – typical for those with autism. Alternatively, proffering an environmental adaptability, particularly towards the tactual modes of stimulation, creates the potential for enhancement of learning, motor and social outcomes. This is done so through tailoring degrees of elasticity across the entire hierarchy of constitutive properties for a manufactured knit textile – fiber, stitch, pattern, interface and structure. As part of a tent-like assembly, which affords a macro-scale degree of deformation and elasticity, the textile serves as a reactive tensile interface. Its operative nature utilizes (i) elastic filaments and the ability to straighten coiled inelastic fibers tailored for responsiveness at the scale of the hand, (ii) the conformable nature of varying stitch types to produce areas of differential pre-stress, and (iii) 3D geometry through which volumetric spatial organizations emerge and manage loading at the scale of the body.

For those with autism, the development of motor skills is commonly delayed and the ability to engage in physical activities increasingly limited with age. The acquisition of motor skills on the same timetable as with peers is critical to social engagement, particularly when centered around play. This linkage between sensorimotor and social behaviors is core to this research, enabling individuals to shape patterns of tactile, proprioceptive and vestibular movement. Through field studies with the sensory-responsive environments, in venues with elementary-age children such as schools, science museums and specialized therapy centers, observational data showed such variability in scales of movement patterns taking place across the entirety of the environment.

Two key capacities were exhibited: (i) the adaptiveness of the responsive environment towards a diversity of sensorial interests across the neurodiverse population that was observed, and (ii) a sustained interest in the exploration, practice and mastery of new movement behaviors allowing for generalization beyond the specific site in which it was mastered. This unfurls the overarching potential for the research, in providing a template for sensorimotor accommodations necessary within more normative architectural conditions. To afford social opportunity within the responsive environment enables the acquisition of the critical adaptive behaviors that allow for more successful engagement in adjacent environments and activities – ones that pose more inflexible sensory and social demands.

Nowadays, the ubiquity of smart technologies and wireless communication networks is stimulating the development of sensing systems able to continuously monitor the human health state and physiological parameters . Local point-of-care medical units or monitoring systems for athletic training performance are two possible examples that would directly profit from such a technology. The crucial bottleneck to establish robust wireless biological sensor networks is the development of new transducer materials capable to effectively convert the biological event (for example concentration changes of chemical markers or a bioelectronic current) into the electronic domain. Semiconducting polymers, such as PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate)) are widely employed in bioelectronical and biosensing applications as they combine two main advantages: (i) they offer electronic as well as ionic conductivity; (ii) they exhibit excellent bio-compatibility and good mechanical properties.
Here, we report a new fully textile biosensing platform that can be directly integrated into fabric, for continuous monitoring of ion chloride concentration and the pH value in biofluids, such as sweat, thus limiting the invasiveness for the wearer. Human sweat contains abundant information about a person’s health status and representing an excellent biofluid for portable, non-invasive chemo-sensing. For instance, chloride content is a precious index for hydration status as well as a consolidated hallmark in newborns diagnosis of cystic fibrosis, while sweat pH is related to hormonal unbalance and lactic acid secretion during physical activity. Our platform consists of PEDOT:PSS-coated threads whose functionalization determines their selective sensing. The ion chloride thread sensor exploits Ag/AgCl nanoparticles that act as a gate electrode embedded into the conductive polymer channel, thus combining an intrinsically amplified response with a simple two terminal electrical connection [1]. The sensor is validated in standard electrolytes and in artificial sweat showing high sensitivity and selectivity demonstrating the reliability of our device.
On the other hand, we synthesize a pH-sensitive composite of PEDOT doped with pH dye Bromothymol Blue to convert pH variation into an electrical signal. The simple two terminal thread sensor gives results similar to the one observed for the devices fabricated onto planar substrates, providing the proof of principle for a wire-shaped sensor that can be easily sewed on clothes for monitoring pH level in sweat.
In conclusion, we demonstrate selective and real-time monitoring of bioanalytes in artificial sweat, validating the implementation of our biosensors in a fully textile electronic device. This approach paves the way for a new generation of smart wearable sensors for medical point of care, effectively fabricated onto non-conventional substrates, such as textiles or single fibres.

[1] I. Gualandi, M. Tessarolo, F. Mariani, T. Cramer, D. Tonelli, E. Scavetta, B. Fraboni, Sensors and Actuators, B (2018) 834-841

Next generation wearable electronics hinges on the development and integration of emerging technologies that can further advance the functionality, user comfort and runtime of devices. Flexibility, conformity and stretchability are commonly addressed in individual textile-based electrochemical devices such as sensors, supercapacitors and batteries, but few works has been reported on the device-level integration of electrochemical energy harvesters and energy storage units. Addressing this issue, we report for the first time of a device-level energy-harvesting and energy-storage hybrid system based on textile-based flexible and stretchable wearable biofuel cells and supercapacitors. The reported all-in-one epidermal device can harvest energy from enzymatic reaction fueled by the abundant lactate from human perspiration. Furthermore, the energy is directly stored into capacitive/pseudocapacitive materials to deliver enhanced and stable output over long period of time. Simple, low-cost and high-throughput screen-printing fabrication is used to deposit customized, screen-printable and stretchable ink composites that exhibit outstanding stability under rigorous mechanical deformations. The continued development of such integrated wearable energy system represents a vital step towards self-powered wearable electronics for healthcare, fitness, security and environmental monitoring applications.

Owing to the merits of mechanical softness and stretchability, stretchable electronics holds promise in many applications including health monitors, medical implants, artificial skins and human-machine interfaces. In general, electronic materials, especially semiconductors, are non-stretchable. Structural designs with special mechanical architectures have been widely adopted to enable the stretchablity in those materials. An alternative route to eliminating the burden of constructing dedicated architectures and the associated sophisticated fabrication processes is to build stretchable electronics from rubbery electronic materials, which have potential toward scalable manufacturing, coherent material and device integration, and large-strain tolerance. Here, I would like to present our recent progress on developing rubbery electronics fully made out from intrinsically stretchable, rubbery composite materials of semiconductors and conductors, which can be scalably manufactured from common and commercial available materials without dedicated and complicated synthesis. Specifically, we build nanofibril organic semiconductor and metallic nanowires percolated in the elastomeric polymer matrix in a composite format for the rubbery semiconductors and conductors, respectively. Employing these rubbery electronic materials, we have achieved fully rubber format devices, including transistors and sensors, logic gates, active matrices, and elastic sensory skin systems etc. The rubbery stretchable electronics holds a wide range of applications, such as artificial skins, biomedical implants, and wearable applications.

Strategies for the selection of materials and manufacturing overwhelmingly dictate e-textile product cost and acceptance into a specific marketplace. Challenges are presented due to the uncertainty in materials selection and then the subsequent need to matching that material within a process to manufacture, which often results in delays in the product development cycle. The goal of this presentation is to outline current best practices and future advancements in materials and manufacturing of e-textiles. From a materials perspective, particular focus will be made on yarn-level design and use of printing strategies, which allow for ‘in process’ formation of e-textile systems. The implication on materials selection and the impact on fabric formation processes will be made based on traditional cut and sew strategies and the evolving whole garment as well as flatbed knitting techniques. Finally, testing strategies will be reviewed for understanding the e-textile at the component and system levels. The future prospective toward more complex e-textile systems will be presented.

Conductive polymers (CPs) display an exceptional set of electrical and optical properties, which in many cases can be tuned to mimic those of inorganic semiconductors and/or metals. Therefore, they have found numerous applications in different technological arenas, such as transparent and flexible conductors in optoelectronics, and as biomaterials, biosensors and tissue engineering substrates in biomedical applications. The fabrication of CPs nanostructures has been investigated comprehensively in recent years, in particular the synthesis of CPs in the form of nanofibers. Unfortunately, producing nanofibers of such CPs has been a challenge faced by several research groups due to the rigid backbone they display. Coaxial electrospinning has been reported as one of the possible approaches that allow the formation of CPs nanofibers. Additionally, recent studies have reported that doping the CPs with certain solvents can improve their charge carriers transport properties; moreover, recent reports have indicated that the addition of metallic and semiconductor nanoparticles into CPs thin films and nanofibers not only improves the electrical charge transport properties of the composite nanofibers, but also bestows on them the property of photocurrent generation when illuminated with the proper light source. In the present study core-shell PEDOT:PSS – PVP nanofibers were synthesized by coaxial electrospinning. These fibers were doped with different solvents (dimethylsulphoxide, isopropyl alcohol, and ethylene glycol) and PbS nanoparticles at different concentrations; additionally, the coaxial electrospinning setup process was inverted in order to exchange the phases comprising the core-shell morphology. The synthesized samples displayed an increment in the conductance of the composite nanofibers, based on a more conjugated structure of the PEDOT:PSS phase, and a better dispersion of the PbS nanoparticles within the nanofibers; this increment was, under certain synthesis conditions, up to three orders of magnitude higher than in the case of the nanofibers with no solvent, nor nanoparticles, added. Photoresponse also showed a clear increment in the value of the photogenerated current as the concentration of the nanoparticles increased. Inverting the arrangement of the core-shell phases in the nanofibers increased the conductance and the photogenerated current in the cases analyzed. These results show novel evidence on the capability of tuning the conductance and photoresponse of composite core-shell nanofibers, based on the doping of the PEDOT:PSS phase with different solvents and PbS nanoparticles, and the arrangement of the core-shell phases.

Abstract not available.

In this talk, we will report recent progress of elastic conductors for electronic textile. First, we have fabricated a metal–elastomer composite with a nanofiber reinforcement. By embedding randomly aligned polymer nanofibers into a silver–fluoroelastomer composite, the elastomer matrix was reinforced and the stress was dissipated by the nanofiber scaffolds. Moreover, combined with the buckled structure, high cyclic durability against repeated stretching was achieved. As a result, a stretchable electrode made from nanofiber-reinforced elastic conductors and wrinkled structures has both excellent cyclic durability and high conductivity, and is stretchable up to 800%. The cyclic degradation (ΔR/R₀) remains at 0.56 after 5000 stretching cycles (50% strain), while initial conductivity and sheet resistance are 9903 Scm^-1 and 0.047 Ωsq^-1, respectively. Finally, we demonstrated a skin-tight multimodal physiological sensing suit using a highly conductive and durable elastic conductor as electrodes and wirings. By wearing the suits, we successfully demonstrated continuous long-term monitoring of electrocardiogram, electromyogram, and motions during weight-lifting exercises without significant degradation of signal quality.

Flexible electronics and wearable textiles are of high interest for functional devices including health monitoring and other display applications. Haptics technology enables the appreciation of functional surfaces for interfacing with the human sensory function. The use of 3D printing to create prototypes and devices from elastomeric and polymeric materials has appended the design functionality for new materials including uses in biomedical devices enabling rapid development. New opportunities for multi-materials and composites are possible. The processability and functionality of thermosets and elastomers make it a challenge to employ using most 3D printing methods for polymer additive manufacturing. This is more evident with the choices of 3D printing methodologies (fused deposition modeling - FDM, stereolithographic apparatus -SLA, selective laser sintering- SLS, and viscous solution printing - VSP) which can make use of blended or formulated compositions. We have demonstrated the 3D printing of biomedical grade thermoplastic polyurethanes (TPU), epoxy, silicones, and rubberized epoxies to demonstrate flexible and wearable objects and devices. 4D printing allows the design of new materials and applications based on integrating the chemistry of conversion with the printing mode. In this talk, we will demonstrate the fabrication of multi-materials including thermosets and thermoset elastomers with concept objects and elastomeric actuators. This is based on the use of biomedical grade TPU melts and extruded viscous solutions. Other works based on the use of SLA, SLS, FDM, towards high strength epoxy, silicones, and nanocomposite materials will be discussed.

Fibers that are capable of harvesting various mechanical energy via triboelectric effect are excellent power units for wearable electronics, especially for smart textiles. However, the fabrication of highly stretchable and soft fibers for the realization of truly conformal, elastic and durable textiles with high triboelectric outputs remains still challenging. Here, a large-scale fabrication of inherently stretchable and soft triboelectric fibers with engineered architectures, for a dual function of energy harvesting and self-powered mechanical sensing, is demonstrated. We take advantage of the rheological behavior of the selected thermoplastic elastomer and employ the one-step thermal drawing process for the large-scale production of uniform triboelectric fibers (Advanced Materials 2018, 30, 1707251). The resulting fibers can sustain large strains of up to around 560% and maintain high electrical outputs, regardless of long-term extreme deformations and extended environmental exposure. By exploiting the particular attributes of the thermal drawing process, we optimized the outputs by introducing textured pattern to the triboelectric fiber surface (Advanced Functional Materials 2017, 27, 1605935). The versatility of this unique fiber enables its facile integration into a soft, elastic and machine-washable triboelectric textile with excellent electrical outputs of ~490 V (triggered by hand tapping), which are even higher than two-dimensional planar triboelectric nanogenerators with similar dimensions. With the drawing process being simple and scalable, it opens the possibilities for the practical implementation of self-powered multi-functional smart fibers and large-area textiles.

Advances in artificial muscles have demonstrated high power-to-mass ratio, work capacity, energy density, and work efficiency, challenging traditional actuators. Recently, thermally actuated fiber-based artificial muscles, capable of lifting more than 650 times their weight, have demonstrated strain programmability and the ability to transduce electrical signals in response to contraction and relaxation, similar to biological muscles. Expanding the palette of the suitable driving stimuli to include electrical, thermal, photonic, hydraulic, and pneumatic will pave way for applications of these fiber-based devices in smart textiles, implantable sensors, wearable electronics, and prosthetics.
Here, we report on a class of fiber-based artificial muscles that can be actuated by a broadband illumination with wavelengths spanning 10-400 nm. These photo-actuated artificial muscles are manufactured using thermal-drawing process, and consist of polymer bimorph structures of cyclic olefin copolymer elastomer (COCe) and carbon loaded polyethylene (CPE) as the low and high thermal expansion materials, respectively. CPE further serves as a UV absorbing material. To amplify the actuation capacity of the thermally drawn fibers, we transformed them into coiled structures via cold drawing, arriving at cross-sectional dimensions of 300×470 µm². We demonstrate the weight lifting capacity of the photo-actuated fibers using a 324 nm light emitting diode with an energy density of 1 mW/mm². Photo-actuated fiber muscles can be actuated using a single LED, potentially enabling the remotely controlled operation and further expanding the domain of utility of these miniature devices.

The phenomenon of self-healing, an intrinsic nature of human skin, has inspired those who focus on interdisciplinary field of biomimetics, robotics, and wearable electronics to pursue humanlike electronic skin systems that offer the opportunity to realize future healthcare and wearable robotics. Specifically, developments of intrinsically stretchable and self-healable conductors are significantly desirable for interfacing with active electronic modules with taking advantages of reliable reuse and low power consumption even after mechanical damages. However, it is still difficult to simultaneously achieve high stretchability and high conductibity and autonomous self-healability, due to limited materials strategies.
Here, we describe electrically and mechanically self-healable composite conductor with ultra-stretchability, fabricated by simply mixing conducting nano-/micro-materials (Ag flakes) with a tough self-healing polymer (SHP, PDMS-4,4’-methylenebis(phenyl urea) (MPU)_0.4-isophorone bisurea units (IU)_0.6). The conductibity of our self-healable composite conductor is as high as 1137 S cm^-1 even under 3500% tensile strain, and more interestingly, it gradually increased to 3086 S cm^-1 over 60 hrs under 3500% strain. Such unprecedented phenomenon, termed “electrical self-boosting”, result from a synergy effect: an efficient strain energy dissipation of SHP and self-alignment and rearrangement of Ag flakes with spontaneously assembled AgNPs in response to dynamic nature of the strained polymer matrix. This dynamic behaviors of Ag flakes-AgNPs in a stretch mode is confirmed by using micro computed tomography (μ-CT), in-situ scanning electron microscope (SEM), and transmission electron microscope (TEM).
Furthermore, we found that a double-layered conducting structure formed using a self-bonding process shows extremely reliable stretching endurance performances over 1000 cycles at 50% strain owing to its homogeneous conducting interface located on the neutral mechanical plane. Finally, we successfully demonstrated that electromyogram (EMG) signals can be measured in real-time by a flexible wireless bio-integrated system using our conductor and transmitted to a prosthetic robot hand to control various hand motions after making a complete cut and self-healing. Our dynamic stretchable and self-healable composite conductor is highly applicable to the robust interactive human-machine interfaces.

Conductive elastic fabrics are desirable in wearable electronics and related applications. Here, we report a highly elastic conductive polyamide/lycra knitted fabric using intrinsically conductive polymer poly (3, 4-ethylenedioxythiophene) (PEDOT) blended with polyelectrolyte poly (styrene sulfonate) (PSS) by easily scalable coating and immersion methods. We investigated the effects of these two methods of treatments on uniformity, electromechanical property, stretchability, and durability. Different grades of waterborne polyurethanes (PU) were employed in different concentrations to improve the coating and adhesion of the PEDOT:PSS on the fabric. The immersion method gave better uniform treatment, higher conductivity, and durability against stretching and cyclic stretching than the coating method. The surface resistance increased from ~1.7 and ~6.4 Ω/sq at 0% PU to ~3.7 and ~12.6 Ω/sq at 50% PU for immersion and coating methods, respectively. The treatment methods as well as the acidic PEDOT:PSS did not affect the mechanical properties of the fabric and the fabric showed high strain at break of ~650% and remain conductive until break. The resistance increased only by a small amount when samples were stretched for 10 cycles at 100% strain and the samples show good durability against 10 domestic laundry washing cycles.

In recent decades, microfluidics has emerged as a game changer in the field of clinical diagnostics. These in-situ, on-site microfluidic portable devices have a great potential to substitute traditional analytical labs. However, the complex fabrication techniques (photolithography, etching and printing) used to make microchannels, as well as complex pumping system to drive fluids, are a potential barrier for the development of practical microfluidic devices. In a simpler approach, textile substrates (in the form of fibres, yarns or fabric) which have an inherent ability to create microchannels and wicking properties that facilitate fluid movement provides the potential for a far simpler approach than the microfluidic chip. In this work multi-yarn textile assemblies, that are either knitted or braided, have been investigated as a potential electrofluidics separation platforms. These provide an open surface accessible separation platform, which contrast conventional closed glass capillaries or chips, where direct access to sample zone during separation is nearly impossible. In this work, braided structures made from a range of commercially available fibers have been investigated for; the electrophoretic separation of different analytes through capillary zone electrophoresis; the preconcentration of analyte through Isotachophoresis and selective delivery of analyte through their transport and separation in bifurcated and trifurcated braided structures. This channelled textile platform can be successfully used for the separation of complex mixtures of chemical and biological samples. The developed technology will provide significant new inverted-microfluidic capabilities in bioanalysis, proteomics and rapid clinical diagnostics.

Macroscale, flexible electronics are now of great interests in the human-interactive application. In fact, low-cost device fabrications such as printing technique have been proposed. For the practical applications as human-interaction devices, reliability and washability as well as economic fabrication method are key parameters. However, most of reports have not covered all important requirements due to difficulties to fabricate the devices. To address this challenge, we demonstrate textile-based tactile pressure sensor sheet with high reliability and washability as well as the sensitivity and threshold pressure analyses. To simplify the fabrication method and structure, Ag threads or printed conductive polymer (PEDOT:PSS) are used for the resistive sensing materials.
Ag thread and standard thread were sewn in the two linen textiles by using a commercial sewing machine. After sewing the threads, a mesh sheet was sandwiched by the linen sheets. For the electrical connection between the textile sensors and measurement equipment, Ag coated Velcro strap was used. One side of the Velcro strap was sewn on the linen sheets using the Ag thread continued with the sensor area. Another side of Velcro strap was sewn on a PET film, where Ag electrodes were screen-printed. Using this Velcro strap, textile sensor sheet and read-out circuit can be readily connected and disconnected, which allows it to wash the sensor sheets without having special water-proof coating over the equipment. For the sensing mechanism, by applying tactile pressure, Ag threads are contacted through the mesh holes. After contacting the electrodes, then contact resistance changes as a function of applied pressure due to rough surface of Ag thread.
Mesh thickness and diameter size dependences for the pressure sensor were characterized to control the detectable tactile pressure range. Detactable threshold pressure was varied from 1 kPa to 1 MPa depending on the number of mesh sheets (i.e. thickness: 1 – 5 sheets) and diameter (0.5 – 3.0 mm) of mesh. This indicates that this can detect the pressure difference by monitoring the resistance change, and the threshold pressure can be tuned by mesh sheet thickness and diameter of mesh size. It is also confirmed that real-time pressure can be measured with relative fast response less than 0.5 s.
Next, reliability and washability were analyzed. The results indicate the limitation of repeatable measurement cycles. Depending on the applied pressure, this limitation is varied. However, it is found that the limitation can be estimated with line fitting of the results. For human body pressure monitoring on a bed, the pressure distribution is ~5 kPa. For this body pressure monitoring, the sensor sheet shows high reliability >250,000 cycles.
Without using any water-proof coating or packaging, this sensor sheet can be washable using a standard washing machine with detergent. Output resistance does not change even after 2 times washing processes.
Finally, as proof-of-concepts, real-time monitoring of derriere and foot pressure distributions and respiration were conducted by placing the sheet under body. Based on the results, this simple device structure can be used for the tactile pressure sensor sheet with high reliability and washability.
This study proposes the high reliable and washable tactile pressure sensor textiles. We confirmed that this platform can be used for the pressure distribution monitoring including respiration.

Electronic textile (E-textile) seems to offer more comfortability for daily clothing compared to flexible planar electronic devices developed on film-type substrates. Because the geometric structure of the textile itself is woven bundles of yarns or fibers, it is extremely difficult to achieve such devices by silicon-based technology in growing, deposition, and etching process that are well-developed in the planar geometry. In this study, we focused on the development of coating process to allow strong interfacial adhesion and cohesion of the conductive dyes. For example, surface modification of the textile surface (cotton in this case) with (3-aminopropyl)trimethoxysilane (APTMS) enhances the interfacial adhesion on the textile surface. Layer-by-layer coating of the mixture of PEDOT:PSS:Ag nanowires as for the negatively charged conductive dye and chitosan as the positively charged counterpart enriches cohesion among the layers by using ionic interaction. To control the line width and penetration depth of the conductive dye during coating process, we also used stencil masks that can undergo conformal wrapping to the woven surface by printing linear polymer such as acrylonitrile-butadiene-styrene using 3D printer or laminating a premade mask film at high temperature above glass transition temperature. Viscosity modulation of the conductive dye also controls penetration depth; higher viscosity induces shallow depth. Additional coating of a PTFE protecting layer dramatically improves mechanical durability of printed circuit in harsh environmental conditions. To demonstrate the feasibility of our printed circuit textile, we successfully developed a joule heater and electro-thermochromic display with seven-segment digit pattern for electronic textile application.

Textile electronics are increasingly becoming an important field of research. One of the key features of smart textiles is the ability to control core body temperature in different weather conditions. Particularly, the idea of battling cold weather conditions using self-heated textile is intriguing. It can be done in for various applications like in jackets for military personnel who fight in cold climate conditions, in hand gloves for skiers [1], for heat therapy for certain medical conditions and so on. A power supply, bus bars for sending the currents, heating elements and a carrier to assist the heating elements are needed for such heated wearable textiles [2]. Another important aspect is that the heating element needs to be flexible and stretchable since it is used in textiles. This work presents the idea of using space-filling fractal curves based heating elements in textiles. Because heating elements are based on metal coils, they are the most large-area and expensive component of a self-heating wearable. However, decreasing metal spacing or metal length in coils leads to non-uniform temperature distribution. Hence, a cost-effective and efficient heater should have uniform temperature distribution while having minimum metal consumption. The geometry of the heater plays a crucial role in its uniformity and average temperature (T_µ). We modelled space-filling fractal curves as geometries for heaters and observed that they are on par with the typical double-spiral heat-pad in terms of temperature uniformity, while being cost-effective due to optimal distribution of metal. This work presents modelling of fractal curves based on Peano curve, Hilbert curve and Moore curve of different orders, as micro-heaters. To make the metal coil designs stretchable, sharp edges in the geometries were modified into smooth arcs. Further, to compare them in an efficient way, a constant power of 2 W was maintained across all the geometries and the heating elements were restricted to an area of 30 mm x 30 mm. Finite element analysis (FEA) results showed that heating elements based on Hilbert & Moore curves of order-4 and Peano curve of order-3 outperformed double-spiral heating element in terms of temperature uniformity while being cost-effective, i.e., using lesser metal coil length (all the curves were assumed to have the same metal width and thickness). Heaters based on Hilbert & Moore curves of order-4, Peano curve of order -3 were observed to have a temperature non-uniformity () of 4.4%, 4.3% and 2.2% respectively, whereas double-spiral had non-uniformity of 5.8%. The average temperature was lower by 10 K for Hilbert and Moore order -4 and 50 K for Peano order -3. Further, heaters one fractal order lower than these, i.e., Hilbert & Moore of order -3 and Peano of order -2, gave the same average temperature as double spiral heaters, while using only half the length of the double-spiral, thus promising significant reduction in metal consumption. Hilbert and Moore order -3, Peano order-2 were observed to have a non-uniformity of 11.7%, 11.6% and 7.24%, respectively, which makes them slightly more non-uniform compared to the double-spiral heater, but with only half the metal consumption. With many fractal patterns to choose from, space-filling fractal curves can provide very good performance heating elements for smart, self-heating textile applications.

References
[1] Zhang, L., Baima, M. and Andrew, T.L., 2017. Transforming commercial textiles and threads into sewable and weavable electric heaters. ACS applied materials & interfaces, 9(37), pp.32299-32307.
[2] Wiezlak, W. and Zielinski, J., 1993. Clothing heated with textile heating elements. International Journal of Clothing Science and Technology, 5(5), pp.9-23.

Graphene-based electronic textiles have recently been recognized as a promising flexible materials and devices for smart fabrics and next-generation wearable electronics due to their many advantages such as good electrical conductivity, mechanical strength, chemical stability, softness, light weight. In addition, they can be produced at low cost, easily cut, and assembled into diverse flexible substrates in various form by simple approaches such as sewing and weaving. In these reasons, a variety of wearable devices have been developed including textiles transistors, thread like solar cells, fabric type nanogenerators, yarn like chemical and physical sensors, etc. Among these devices, threat and fabric type photodetectors have gained importance for applications in biomedical imaging, environmental sensing, fire monitoring, etc. However, processing challenges for improving their poor performances and complicated fabrication process have so far precluded the realization of diverse wearable electronic devices. Here we report a facile solution strategies to fabricate the high performance graphene electronic textiles composed of reduced graphene oxide (RGO) and commercial cotton yarns by simple dipping and chemical reduction and investigate the broadest photoresponses from the ultraviolet upto the infrared in various deformations such as bending and stretching. The as-prepared RGO yarns showed good basic properties including including electrical conductivity (~1.0 S/cm) and mechanical stability (1,000 cycles), as well as a UV photoresponsivity of 1.31 mA/W (flat) and 1.0 mA/W (bent) and response times of 5 s/6 s (flat) and 6 s/7 s (bent). Using our high-performance RGO textiles, we successfully fabricate wearable optoelectronic systems that can be integrated with garments for continuous ultraviolet radiation.

Wearable IoT devices and sensors have been featured recently, therefore stretchable interconnects and devices are required to develop. In this research, we have developed an advanced fabrication method of stretchable interconnects that corrugated copper (Cu) foil attaches to a pre-stretched elastomer substrate. Fabricated interconnects applying our method showed >200% stretchability stably. We also applied our method to stretchable electrical circuits.

There are two types of methods to fabricate stretchable interconnects: using conducting inks such as a mixture of metal nanowires or carbon nanotubes with thermoplastic polyurethane resin (TPU) or fluorine rubber, and processing metal film into a wavy shape (vertical or horizontal wavy structure). Stretchable vertical-wavy-shaped metal interconnects are getting attractive because the conductivity is smaller by one order of magnitude to that of the above mentioned inks. Wagner et al. (2004) made stretchable thin-film conductors by metallizing a pre-stretched elastomer membrane with Au, and reported that fabricated conductors showed 10-100% stretchability. But the stretchability was unstable, that is, it varied widely in the fabricated samples. Although vertical-wavy interconnects are preferred since they can achieve high density wiring and electrical stability, vertical-wavy-structured interconnects are hard to fabricate in terms of manufacturing stability.

Thus, we propose a new method of bending a Cu film by corrugate process in advance and then attaching it on a pre-stretched substrate in order to shrink corrugated Cu foil further.
The proposal method is as follows:
(1) Corrugating a strip of copper (Cu) foil by a pair of gears to create vertical-wavy structure
(2) Adhering the above processed Cu foil on a pre-stretched Polydimethylsiloxane (PDMS) substrate
(3) Relaxing the pre-stretched PDMS substrate into its initial length to compress the vertical wavy structure
(4) Covering the whole interconnect with PDMS and peeling it off

The elongation rate of a pre-stretch substrate was changed to 0, 25, 50 and 75%, and each sample was prepared. The thickness of Cu foil was 5um. The fabricated samples showed 220% strechability in the case where pre-stretch rate was 75%, while 102% strechability in the case where a PDMS substrate was not stretched in advance. The resistances of all samples were <1 ohm/cm and these fluctuations during stretching were ±0.1 ohm/cm.

In order to consider possibility of higher stretchability if Cu foil thickness is different from 5um, an effect of Cu foil thickness on stretchability was investigated when a PDMS substrate is not stretched beforehand. Cu foil thickness was varied from 2um to 40um. Strechability of vertical-wavy interconnects can be predicted by measuring a wavy shape (pitch, height and angle) of corrugated Cu foil. The actual shapes of fabricated samples were measured and stretchability was predicted from prediction equations. It was assumed that the thinner Cu foil is, the larger stretchability gets because height of waves also is getting high. On the other hand, as the result of the break tests of fabricated samples, the strechability became the highest (73%) when the thickness was 10um. The reason is considered that thinner Cu foil has not enough strength so it broke before it gets flat.

In this study, higher stretchability and lower resistivity than those of previous studies were achieved, so our fabricated interconnects can be useful as stretchable interconnects with high conductivity.
Finally, we demonstrated stretchable LED circuits with our proposal technique. LEDs can be lit in the manufactured circuit with about 50% stretch. Therefore, it is assumed that our proposal technique can be applied to stretchable circuits.

In recent years, the field of wearable technology and Internet-of-Things has attracted a great attention and a large variety of sensors has been developed. Wearable electronics sensors are becoming extremely attractive for several application fields such as medical, healthcare, wellness, sport, entertainment and safety. A very promising platform to realize fully wearable and imperceptible sensors is the “smart textile” one, as fully textile physical or chemical sensors offer unique features in terms of comfort and fitting features.
In this framework, we focused our attention on developing wearable textile pressure sensors operating in a wide linear pressure range. Pressure sensors with high sensitivity in the low pressure range (<10kPa) allow touch detection, very relevant for human-computer interaction and for the development of artificial hands for handling object. Conversely, pressure sensors that operate in high pressure range (up to 100 kPa), can be used to monitor the foot pressure distribution, the hand stress during the movement of heavy weights or to evaluate the cyclist’s pressure pattern on a bicycle saddle.
In this presentation, we report on a new promising class of fully textile pressure sensors based PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate)) [1]. The sensor can be easily fabricated directly on textile fabric by processing from solution and sewing. We report and discuss the sensor working principles, investigated by comparing the effects of macroscopic to nanoscopic variation in the sensor performance [2]. We quantitatively discuss (by analyzing static and dynamic operation mode) how the mechanical properties of several fabrics and the piezoresistive properties of different ink formulations impact on the sensor response. Our results highlight the complexity of the whole system, due to the active role of multiple parameters (e.g. the fabric composition, structure, the polymer formulation, the targeted pressure range, etc.) and suggest a protocol to optimize and tune textile pressure sensors to every kind of application.

[1] J.Saenz-Cogollo, M.Pau, B.Fraboni, A.Bonfiglio “Pressure Mapping Mat for Tele-Home Care Applications” Sensors 16, 365 (2016)
[2] M.Tessarolo, L.Possanzini, E. Campari, R. Bonfiglioli, F.S.Violante, A.Bonfiglio and B.Fraboni “Adaptable pressure textile sensors based on a conductive polymer” Flexible Printed Electronics 3, 034001 (2018)

Textiles present unique material properties in terms of their flexibility and conformability, which are ideal for applications in wearable technology. However, the practical use of textiles as substrates for printed electronics and functional devices presents considerable challenges because of their considerable roughness and intrinsic porosity when compared with polymer films. This is particularly true for inkjet printing where printed drop dimensions are on a scale similar to that of yarns used during textile manufacturing processes, e.g. weaving and knitting. Here we present a study of the use of inkjet printing of a commercial silver nanoparticle ink on plain woven polyester fabrics. The electrical conductivity of the printed silver is shown to be a function of printed drop spacing, number of printed layers, surface hydrophobicity and sintering treatment. To visualize and understand the contribution of these processing parameters on electrical conductivity, computed X-ray micro tomography has been used to characterize silver deposition and transport through the fabric fibre architecture.

In a woven fabric the warp and weft yarns will show different yarn structures, particularly mean fiber spacing and twist, because of the different yarn tension during weaving. This is shown to lead to distinctly different ink penetration behavior with the ink travelling further by capillary forces along the warp fibers than the weft. 3D reconstructions of silver distribution after printing indicates that capillary transport along a fiber yarn is faster than penetration normal to the plane of the weave, hence warp fiber conductivity does not require conductivity in weft fibers. The development of conductivity can be tracked through segmentation to identify regions that are mutually connected demonstrating that the conductivity of the woven textile can be modelled as relatively conductive warp yarns that are interconnected by more percolative structures in the weft yarns.

The conductivity of a yarn can be computed by determining the largest connected silver object in the printed silver and assuming that this represents the conductive pathway. Tomographic reconstructions of silver distribution after printing and sintering are used to interpret the observations that better conductivity is found when printing onto hydrophobically treated (Scotchgard) textiles and when multiply overprinted printed tracks are sintered after each printing pass rather than sintered once after multiple printing.

Functional flexible fabrics with both excellent electrical conductivity and high-performances are increasingly attractive in modern industries. In this study, we report a silver/polyimide fabric (Ag/PIF) composite with high conductivity, heat-resistance, mechanical and fastness properties, which is fabricated by combining an O₂ plasma pretreatment and a spray-assisted electroless plating (SAELP) technique. The O₂ plasma pretreatment can firstly roughen the surface of PIF, induce the oxygen functional groups on PIF and rearrange the imide groups in PIF, which results in a great improvement in the wettability of PIF. The silver nanoparticles (Ag NPs) are deposited on the plasma-treated PIF by the SAELP technique to obtain the Ag/PIF composites. The effects of O₂ plasma treatment and SAELP duration on the Ag/PIF composites are investigated and discussed. The results demonstrate that the Ag NPs are coated on PIF uniformly and densely with surface resistance of 0.1 Ω/sq. The first decomposition temperature of Ag/PIF composites is up to 600 ^oC, indicating the excellent thermal stability of Ag/PIF composites. This work gives a new strategy for fabricating electrically conductive functional fabrics with high-performance properties.

To date, although there has been significant progress in the development of new techniques for emerging EL devices, enabling soft robots, actuators, flexible/stretchable/wearable electronics, and self-healable devices, most of these reported devices have coplanar structures, which require planar electrodes with high transmittance and mechanically durable characteristics as well as stable electrical conductivity, even in the deformed state. Here, we present a textile-fiber-array–embedded flexible composite system capable of producing multiluminescence (electroluminescence (EL) and mechanoluminescence (ML)) on the application of electromechanical stimulus [1]. In our work, we embed a conducting fiber array into a mixture of PDMS and ZnS EL phosphors with parallel orientation, to act as electrodes. Because the EL is generated by the in-plane field, there is no requirement for the light to be transmitted to the electrode, thereby eliminating the requirement of high transmittance. We also found radially distributed electric/optical fields arising from the unique fiber-array configuration, which are beneficial for applications as a uniform plane light source. Furthermore, a patterned device was realized by controlling the embedding depths of fibers, utilizing the vertical and in-plane electric fields simultaneously. We believe that these results can provide a basis for the development of emerging soft display systems.
[1] S. Song, B. Song, C. –H. Cho, S. K. Lim, S. M. Jeong, Submitted

E-textile is a representative technology used in smart clothing, which is an integrated type of fabrics with electronic components to realize wearable computers. In early stage, it was realized by attaching various kinds of electronic devices on clothes. Recently, research is active on inherently textile-like devices such as fiber transistors, piezoelectric temperature sensors, and fiber displays based on yarn-type conductive fibers.[ref] In our previous research on e-textile using conducting yarns, we have succeeded to develop the resistance switching memory devices with normal yarn, coated with aluminum using solution process, and carbon fiber.[ref] This study focuses on change of resistance at the contact between fibers along the strain, and a strain sensor was developed that can be used in smart clothing. The contacts between different yarns for the resistance change were achieved with all in one yarn, comprising aluminum coated yarns, carbon fibers and normal yarns. In this knitted textile, the resistance switching characteristics was shown as confirmed in previous studies. Then, the samples were stretched in both the horizontal and vertical directions to demonstrate a change of on / off resistance ratio. This variation of on/off ratio was verified by the physical and chemical mechanism and a dependence on the contact area was also investigated. On / off resistance ratio decreased when stretched, and restored to the ratio before stretch when the sample was recovered. This characteristic is maintained when stretching and recovery are repeated along the cyclic test. We expect that the textile-type resistance strain sensor developed in this study can be used as a strain sensor/motion sensor by applying to the joint part of clothing.

The concept of wearable technology is currently concerned with products that are more ‘attachable’ than truly wearable. Over the past decade the world’s biggest consumer-product focused corporations have found varying levels of success from their experiments within the industry. These devices generally exist to quantify, socialise or record. They are ‘outward facing’ and share data that contributes to ‘The Internet of Things’. Intuitive interfaces, further development of responsive materials and a deeper understanding of unobtrusive human-centred design or ‘calm’ technology (Weiser, 1993) are all central to the concept of an authentically wearable device.
Using practice-led 2D and 3D design:STEM activities, this research explores the triangular relationship between the user, the device and the environment it exists in, on both a physical and emotional level. Key to this exploration is the understanding that human bodies are kinetic and their needs therefore differ from that of static entities.
As identified, these three factors contribute to the development of effective ‘wearable’ materials used in, on or around the human body. Although the study of ergonomics, anthropometrics and human-centeredness are well explored, challenging them within the context of materials that possess intrinsically responsive behaviours reveals new areas of research. This work describes results of research undertaken at Northumbria’s bio-design STEM Lab to investigate interactive materials with intrinsically responsive behaviours that can be applied to soft stretchable fabrics potentially resulting in artefacts that work in harmony with its user and/or surrounding space to benefit living. The basis for this work and the results of the sensing and response to external stimuli will be highlighted including progress with Weiser’s concept of ‘calm technology’ which is not a burden on the user.

With a forecasted market value higher than 27 billion dollars by 2022, the amount of wearable devices sales will double by that time and obviously continuing to grow. As consumers interest pursues more and more portable electronic devices such as wearables, batteries dimensions and capacity of such devices is a common limitation of their size, weight and life time between charging cycles. Off the grid standalone power harvesting systems that can convert kinetic energy from human motion through piezoelectric and triboelectric effects will soon be a reality capable to meet the requirements of such low power electronics.
In this work, carbon fiber stretch-broken yarn is used as inner electrode for a piezo enhanced triboelectric generator (PETG). The carbon yarn was functionalized with nanostructured ZnO rods grown by a simple solvothermal method and covered with a layer of Polydimethylsiloxane rubber (PDMS) by a novel method that was, to the extent of the authors knowledge, not ever reported in literature and named “in-situ PDMS curing”. The use of a fiber-shaped system and the selection of such materials and methods intends to meet a lightweight, bendable, ecological and sustainable power converter for the widely available and unused energy from body motion, in which the enhancement of power output, as well as the energy conversion mechanisms, were subject of study.

With the increasing importance of electronic textiles as an ideal platform for wearable electronic devices, organic thin-film transistors (OTFTs) comprised of organic or polymeric electronic components have been shown to be a promising component for e-textile applications on account of their flexibility, light weight, and ease of implementation. While the realization of fibrous OTFTs have been demonstrated so far, several critical issues including a low drain current, unstable contact between the semiconductor and source/drain electrodes, and a high operation voltage remains to be addressed. We report herein is a demonstration of high performance fibrous organic transistors with a new device architecture that exceeds the current limitations of fiber OTFTs. A key feature of this work is that the semiconductor channel of the fiber transistor comprises a twist assembly of the source and drain electrode microfibers that are coated by an organic semiconductor. This architecture allows us to not only facilely control the channel dimension of the device by varying the thickness of the semiconductor layer and the twisted length of the two electrode microfibers, but also passivate the device without affecting interconnections with other electrical components. The resulting fibrous organic transistors based on the twist assembly of the microfibers showed a high output current of over -5 mA at a low voltage of -1.3 V and a good on/off current ratio of 10⁵. The electrical properties of the device were maintained even after repeated bending deformation and washing with a strong detergent solution. In this presentation, discussions on a holistic process for the fabrication of this fiber OTFTs and the correlation between the nano-crystalline structure of semiconductor films and the device performance will be included.

To fabricate stretchable electronics devices, wiring parts to connect power supply and devices such as sensors and IC chips is important. There are two types of stretchable wiring: metal thin film and electrically conductive paste. Electrically conductive paste made by dispersing conductive fillers such as silver particles and CNTs into insulating polymer matrices are widely used because it can be fabricated by simple printing method.
The recent papers reported a successful strategy to effectively improve electrical conductivity by using multiple CNTs with different shape. On the other hand, research and development of stretchable conductive paste have mainly been conducted based on discovery and empirical rules. If the modeling of stretchable paste is developed, further research and development of new stretchable can be expected to be promoted.
In this study, to develop a modeling method of mixing multiple types of conductive particles, a mechanical and electrical model to calculate the conductivity of the stretched silver paste mixing micro-flake particles and nano-spherical particles at different blending ratios was suggested.
Here, micro-flake particles and nano-spherical particles are treated as multi-sphere and hypothetical sphere models, respectively.

The calculation steps are descried below.
(1) Generate multi-sphere and hypothetical sphere models in a cubic area. In this paper, volume fraction of silver particles, blending ratio of micro-flake particles and nano-spherical particles, and dimensions of area can be changed. In case of three-dimensional model, the three-dimensional particle distribution was generated by stacking the two-dimensional particle distribution in the normal direction. Moreover, in order to avoid the calculation of the distance between silver particles, the region is divided into small regions to be able to determine the particle distribution without volume intersection.
(2) Update the position of particle distribution following the stretch force to the silver paste, which was calculated by using the finite element method (COMSOL.).
(3) Calculate the electrical resistance between each particle: If the spherical particles obtained by the finite element method are adjacent to each other, it is 1Ω, otherwise ∞Ω.
(4) Calculate the electrical resistance of the entire composite between two parallel plate electrodes by inverse matrix calculation.
In this paper, volume fraction of silver particles was set to 50%, and three-dimensional model was selected. Blending ratio of micro-flake particles and nano-spherical particles was varied from 0 % to 100 % every 10 %.
In calculation, the size of the particles in model was set to Φ 3.5 to 5.5 μm for micro-flake particles and 200 nm for nano silver particles, which was determined from measurement result of real silver particles.
From the above calculation of conductivity, the optimum blending ratio of small particles and large particles when stretch force was applied to silver paste was estimated. As a result of blending large and small particles, the volume resistivity became lower than the result of small or large single silver particle, and the lowest result was obtained when the blending ratio of nano-particles was 50%.
The contact between the particles is classified two types: contact in the conduction direction and contact in the normal direction of the flake particles. In this model, the resistance of contact in the conduction direction was calculated as the same electrical resistance regardless of the particle shape. Therefore, the increase in the volume resistivity of the nano-spherical particles was considered to be caused by the increase in the number of contact points in the conduction direction between the flat plate electrodes sandwiching the particle distribution. On the other hand, the high resistivity in case of using only flake particles seems to be caused by the high resistance value in the normal direction of the flake particles.

Functional textiles received considerable attention both in scientific field and in the market since late 2000s. Thanks to the developments in nanotechnology, functional textiles have been evolving into smart textiles. In addition to powering the smart textiles, improvement of their washing stability has utmost importance. Currently, batteries are used as the energy sources of smart textiles. However, there are cases where batteries do not fulfill the consumer needs. Moreover, integration of batteries onto the conventional clothes without reducing the consumer comfort is almost impossible. As a consequence, self-powered systems using triboelectric nanogenerators (TENGs) are evolved as strong alternatives to battery powered smart textiles. Silver nanowires are known to impart antibacterial activity [1] and heatability [2] to the textiles. In this study, silver nanowire (Ag NW) decorated fabrics are used as current collectors for the realization of wearable TENGs. Thermoplastic polyurethane (TPU) was deposited onto Ag NW decorated textiles and used as both the dielectric and protection layer. Simple dip and drying method was used for the deposition of both Ag NWs and TPU. The overall structure was used as a single electrode for wearable TENGs, where an open circuit voltage and short circuit current of 30 V and 4 µA were measured, respectively. TENGs were connected in series to further improve the output power. TPU overcoating was also demonstrated to enhance the washing stability of the Ag NW decorated fabrics. While the fabrics without TPU coating lost their conductivity after 10 washing cycles, TPU overcoated fabrics kept their conductivity up to 20 washing cycles.
[1] Silver Nanowire Modified Fabrics for Wide Spectrum Antimicrobial Applications, D. Doganay, A. Kanicioglu, S. Coskun, G. Akca, H.E. Unalan, J. Mater. Res. 34 (2019) 500.
[2] Silver Nanowire Decorated Heatable Textiles, D. Doganay, S. Coskun, S. Polat, H. E. Unalan, Nanotechnology 27 (2016) 435201.

With the extensive research of electronic textiles for wearable devices, fibriform organic field-effect transistor is a one of the key components for organizing the electronic circuit into the fabric by weaving the fiber. However, fiber type field-effect transistors have disadvantage of channel dimension since the resolution of printing or deposition techniques on microfibers is primarily restricted by the dimension of the microfibers. Here, we report a new strategy to improve the performance of fibriform OFET where the channel dimension can be readily controllable. Key technology of this work is that single-walled carbon nanotube source and drain (S/D) electrodes with desirable geometry are printed at hydrogel substrate first, then directly transferred to the semiconductor-insulator layer coated Au microfiber. Fine geometry of CNT electrodes was successfully transferred to the microfiber by special rolling process and resulting transistors with wrapped CNT S/D electrodes exhibited a high on/off ratio of ~ 10⁵ and good field effect mobility of 0.73 cm² V⁻¹ s⁻¹. It was confirmed that the fibriform transistors demonstrated on the flexible polyurethane thread also exhibited good electrical performance which was maintained even after bending deformation at different bending radius.

Recently, some forms of polyethylene compounded with nano-particles/micro-particles promise to absorb less infrared radiation by enhancing the forward scattering in the long-wave infrared. By developing such as fibers containing special materials that are infrared transparent and visibly opaque, textiles could be made for clothing which actively cool the body and provide thermal comfort. This technology could have potential in civilian and military applications.
In this study, the nanocomposite fibers comprised of blended ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) with different mass ratios were successfully prepared using a micro-compounder/twin-screw extruder via a two-step process. The first step involved melt-blending UHMWPE powder with TiO2 nanoparticles at 250C for a residence time of 3 minutes; then HDPE pellets were added and mixed with the melt blended TiO2/UHMWPE at 220C for a residence time of 5 minutes. The fibers were produced via melt-spinning through a controllable diameter spinneret and collected on a motorized spool at various speeds. The morphology and thermal properties of the samples were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) techniques. The total reflection and transmission of the blended fibers were measured using the FTIR coupled to an IR integrating sphere. This study showed that the crystallinity and melting temperature of nanocomposites of the blended fibers were found to be significantly increased by decreasing the blended fiber diameter and the IR-transparency of samples was remarkably improved by increasing the draw ratios.

Inkjet printing of functional inks on textiles to embed passive electronics devices and sensors is a novel approach in the space of wearable electronic textiles. Achieving functionality such as conductivity by inkjet printing on textiles is challenged by the porosity and surface roughness of textiles. A novel reliable and conformal inkjet printing process is demonstrated for printing particle-free reactive silver ink on uncoated polyester textile knit, woven, and nonwoven fabrics. The particle-free functional ink can conformally coat individual fibers to create a conductive network within the textile structure without changing the feel, texture, durability, and mechanical behavior of the textile. It is noteworthy that the electrical conductivity of the inkjet-printed conductive coating on pristine polyethylene terephthalate fibers is improved by an order of magnitude by in situ heat-curing of the textile surface during printing as the in situ heat-curing process minimizes the wicking of the ink into the textile structures.
A new approach which combines simultaneous collection of submicron spatial resolution infrared (IR) and Raman spectra was used to help characterize the structures produced. These two complimentary vibrational spectroscopy techniques provide key insights into the identification and distribution of chemical entities on the surface of these textile fibers as a function of deposition and heat curing conditions.

Flexible supercapacitors have been intensively studied as promising power sources for next-generation flexible electronics in many consumer, medical, and military applications, because they are safe, mechanically stable and durable compared with current batteries. However, flexible supercapacitor devices reported so far have not demonstrated mechanical properties that can withstand critical deformations including folding, twisting, and machine washing, which are required for real-world applications. Multifunctional materials that can provide not only mechanical flexibility and strength, but also energy storage capability are desired for practical flexible supercapacitors.

Here we present the design of composite electrodes with exceptional mechanical properties for foldable, twistable, and machine-washable supercapacitors. The composite materials consist of polymer electrolyte as matrix and carbon-based materials as fillers. The polymer electrolyte acts as both ion conductor and binder. The combination of activated carbon fibers and particles serves as both high-surface-area electrodes and reinforcement materials.

Calculations and simulations show that proper volume ratio of the polymer, fibers, and particles results in optimized flexibility, strength, as well as high areal capacitance. The use of carbon fiber with proper length also enables the composite to survive critical mechanical deformations which particle-based electrodes cannot.

The supercapacitor prototypes are constructed using thin composite electrodes and ion-conducting separators. The separator is composed of randomly distributed glass fibers in polymer electrolyte matrix. The electrochemical and mechanical tests demonstrate that the activation of the carbon fiber surface has not only improved the mechanical properties of the laminates, but also greatly increased the surface area of electrodes, which leads to two orders increase in their electrical double-layer capacitance. The prototypes show adjustable areal capacitances of over 10 mF/cm² with thickness and flexibility (flexural rigidity) comparable to wearable fabrics. The electrochemical performance has remained unchanged after repeated folding and twisting tests. Moreover, we sewed the devices onto fabrics and washed them in a washing machine, after which we observed no mechanical damage or capacitance degradation.

In conclusion, we believe that the excellent electrochemical performance, flexibility and mechanical durability make the composite-based flexible supercapacitors promising to power various flexible and wearable electronics. The design rules and results are also applicable to developing other multifunctional devices that require high performance without sacrificing mechanical properties.

Polyacrylonitrile (PAN)/carbon nanotube (CNT) composite fibers have been processed by gel spinning with combined good tensile properties and electrical conductivity. These fibers can potentially be used for smart textiles, electromagnetic interference (EMI) shielding, electrical heating of fabrics, and for making stabilized fibers and carbon fibers via Joule heating. High CNT loading leads to high materials cost. To address this issue, further studies have been done to reduce CNT content in the fiber while also achieving good electrical conductivity and mechanical properties.
Bi-component spinning has been successfully conducted to produce fibers with 100% PAN in the core and 90:10 PAN:CNT weight ratio in the sheath. The overall CNT content in the fiber is about 5 wt%. The processing steps, structure and properties of the fibers will be presented. One important application for these composites fiber is to make carbon fibers. Polyacrylonitrile (PAN)/carbon nanotube (CNT) fibers can be stabilized by applying electric current (Joule heating process), rather than by external heating. Thus, stabilization of PAN/CNT fibers by application of electric current provides a pathway for making carbon fibers with reduced energy consumption. The innovation, opportunity, as well as the scale up challenge for Joule heating, and for flexible electronic applications of this PAN/CNT bi-component fiber technology will be presented and discussed.

Sub-micron diameter metallic wires of long lengths would enable a wide range of applications including electronic textiles, woven batteries to power wearables, sensitive neural electrodes, and low-loss conductors for microwave electronics, among many others. Existing synthesis methods for developing nanowires are often limited to sub-millimeter lengths, or long length fine wires are extruded at high cost. Instead, we use a low-cost, scalable, bottoms-up approach to fabricate small wires by metallizing long lengths of electrospun polymer (PMIA) nanofibers. While we have demonstrated that a wide variety of metals can be deposited onto the PMIA nanofibers by sputter or vapor deposition, electroplating would provide a more cost-effective and scalable deposition approach. Traditional reel-to-reel electroplating is done by connecting electrical leads to the drum that a metalized wire sits on and driving it through a plating solution that has a platinum electrode immersed in it also connected to electrical leads, thus closing the circuit. However, polymer nanofibers in air can easily be disturbed by forces exerted by convection and electrostatic charging, and can also break under low tensile loads, which can make handling the fibers challenging and prevent making an electrical connection through physical contact. Therefore, we developed a contactless electroplating method comprised of at least two isolated fluid streams of plating solution and conductive salt solution which are used to tension and guide the nanofiber. A potential drop across electrodes immersed in the fluids drives current to flow through the bridging conductive nanofiber allowing for contactless electroplating. Using a commercial gold electroplating bath, we demonstrate metallized wires with lengths that are 10³ to 10⁶ times greater than the core diameter. This work was sponsored by the Air Force Research Laboratory (AFRL) and the Defense Advanced Research Agency (DARPA).

Electrospinning is an inexpensive and versatile technique for fabricating micro and nano scaled fibers for varied applications. There have been limited attempts to employ it for the fabrication of a thermochromic device however, and the fabrication for a three component (dye, developer, and solvent) thermochromic system has required the use of a more complicated coaxial electrospinning technique. Herein, we will employ a simple and novel method for creating thermochromic fibers by electrospinning single strands of poly(methyl methacrylate) (PMMA) with embedded thermochromic powder of polymer encapsulated three-component system. Unlike past thermochromic fibers, an unmodified syringe tip can be used for the spinning process and only one flow rate needs to be determined. A solution of solvent (either N-dimethylformamide or chloroform), PMMA, and commercially available black thermochromic powder was created and spun using a custom-made electrospinning apparatus. The effects of solvents, polymer concentration, and thermochromic powder concentration on morphology and thermochromic performance were also investigated to determine the composition for an electrospinning solution with the most consistent structure and most visible color change from black to translucent. These as-developed micro- or nano- fibers will be characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM) imagery to determine surface/interface morphology, energy dispersive X-ray (EDS) spectroscopy to determine the elemental composition, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to analyze thermal properties and Fourier Transform Infrared Spectroscopy (FTIR) to determining the chemical environment. The thermochromic color change behavior with respect to temperature of these electrospun fibers will be observed by modified Ocean Optics’s UV-Vis/CIE spectrophotometer.

Wearable sensors with various sensing functions and lower costs are necessary for practical application. Sensors based on carbon materials with unique physical and chemical properties can be considered alternatives to relatively expensive electronic devices. This project uses a quick and effective dip-dry method to make carbon nanoparticle wearable sensors on cotton fabric, silk, and sponge. The sensors are responsive to various physical stimuli like relative humidity, temperature, strain, and pressure. The sensor can be properly designed to isolate each stimulus from others, allowing precise determination of each property through resistance measurement. The composites formed by carbon nanoparticles and sponge are found to have high sensibility and fast response to pressure and strain, showing potential for wearable sensors.

While the future developments are emphasized towards thinner, lighter and cheaper solutions, flexible electronics are highly promising and expanding the areas of use almost daily. In this manner, smart textiles are considered to be the next generation of textiles with added functions like sensing, controlling, computation etc [1]. Regarding the key role of energy storage systems for wearable electronics, the actual interest of the researchers will be allocated for developing high performance wearable energy storage systems—receiving benefit from foldability and flexibility. In this work, polyol synthesized silver nanowires are used as conductive additives to fabricate conducting textiles via a simple dip and dry method [2]. Cobalt hydroxide (Co(OH)₂) is decorated onto conducting textiles via electrodeposition [3]. A detailed morphological, structural and chemical analysis was performed on the fabricated textile-based electrodes. Electrochemical characteristics of the fabricated textile-based electrodes were investigated through cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. During electrochemical measurements, 3 M KOH aqueous electrolyte was used. Preliminary results showed that the fabricated Co(OH)₂ decorated Ag NW smart textiles have a capacity of 33.7 C.cm^-2 at a current density of 3 mA.cm^-2 within a potential range of -0.2 - 0.6 V. Moreover, an energy efficiency of 65% and a Coulombic efficiency of 87% was obtained. Improved electrochemical stability of the Ag NWs was also noteworthy. Numerous bending cycles were used to determine the mechanical stability of the fabricated textile-based electrodes. Gravimetric analysis is underway to determine the gravimetric capacity of the electrodes.

1.M. Stoppa and A. Chiolerio, "Wearable Electronics and Smart Textiles : A Critical Review", Sensors 2014, 14, pp. 11957-11992
2.D. Doganay, A. Kanicioglu, S. Coskun, G. Akca, H.E. Unalan, " Silver Nanowire Modified Fabrics for Wide Spectrum Antimicrobial Applications", accepted for J. Mater. Res. (2019)
3.M.B. Durukan, R. Yuksel, H. E. Unalan, "Cobalt Oxide Nanoflakes on Single Walled Carbon Nanotube Thin Films for Supercapacitor Electrodes", Electrochimica Acta 2016, 222, pp. 1475-1482

The future of textiles is electronic, with new wearable devices integrated into "smart clothing" systems that will incorporate sensors to detect biometric data, light-emitting devices to display data, and integrated wiring. Powering this next generation of smart clothing is of key importance, making the development of flexible and stretchable energy storage devices that are compatible with textiles particularly urgent. Lithium-ion batteries (LIBs) are one of the most promising power sources because of their high energy density and long cycle life. As a core component, the battery electrode largely dictates the mechanical properties of the entire battery. The electrodes of conventional LIBs are typically fabricated by depositing brittle composite materials on metal foils. These electrodes are vulnerable to mechanical strain, which can cause the delamination and cracking of active materials, and ultimately device failure. Previous work has relied elastomeric materials to improve the mechanical properties of these active materials. Depositing active materials onto a prestrained elastomer to form wavy electrodes, coating 3D porous elastomers, or mixing active materials with elastomers to form stretchable composites are all leading approaches. However, active materials in these systems still experience strain to some extent, which can be problematic for practical use. There is therefore an urgent need to explore new ways to fabricate electrodes with good mechanical properties and that retain functionality under strain for use in stretchable LIBs. In this presentation, we report a new approach that uses textile structures to protect the active materials from strain and subsequent damage. We use a warp-knitted velour fabric structure, which consists of a warp-knitted trellis and a cut pile. Metallizing the fabric using solution-based electroless nickel-immersion gold plating renders it conductive, preparing it for use as a current collector. We then electrolessly deposit copper selectively on the cut pile fibers, and convert the resulting copper film into CuS by reaction with elemental sulfur. This unique preparation method integrates the active material and the current collector into a single piece of velour fabric in a way that protects the CuS from strain when the fabric electrode is elongated. The CuS/Au-coated velour fabric electrode shows stable conductivity to 130% strain, and the conductivity also remains stable through 1000 cycles of 50% strain. We demonstrate its application in LIBs. The electrode exhibited a specific capacity of ~400 mAh/g at 0.5 C with no obvious sign of capacity decay for at least 300 cycles. After 1000 cycles of 50% strain, the electrode still exhibited stable electrochemical performance.

Radiative cooling and heating can play a role in influencing and controlling the temperature of things like shelters, solar cells, and the human body. Personal thermal comfort is an important consideration for helping to maintain optimum physical and cognitive performance in an individual. It has been shown that thermally transparent polymeric films and fibers can theoretically transmit metabolically-generated heat from the body to the environment via passive radiative cooling [1].

In order to compare the heat-trapping or heat-releasing properties of engineered films and fiber swatches, a simulated device for skin temperature was designed. The device consists of a heater operating at constant power output to mimic the heat produced by human skin which is at roughly 34C. High density polyethylene (HDPE) fibers and/or films will be compared to commercially available ones. The fabric and/or film of interest is placed over the “skin” and the temperature differential, delta-T, across the elemental material or monolayer fiber array or film/membrane is measured. This unique capability can directly measure two test samples simultaneously thus allowing for direct comparison under identical environmental conditions to control for changes in factors like air temperature, wind, and humidity. Finally this device can be operated in a vacuum thus removing conduction and convection as cooling or heating pathways.

While the textile industry community employs standardized test methods and instruments for measuring larger end-item textile products, this measurement capability will enable better analysis of early-stage research materials instead of just finished textiles thus allowing for better control, prediction, and understanding of inherent material properties.

Capacitive pressure sensors (CPS) have long been recognized to be an effective component for interaction with electronic devices. The growing interest in the development of flexible and wearable electronics has prompted the interest in flexible sensors. A number of sensor arrays have been demonstrated on bendable and stretchable substrates. In order to enhance design flexibility and scalability in the manufacture of the CPS, we demonstrate orthogonally woven CPS integrated into elastomer substrates. A further advantage of using a combined elastomer and textile structure is the ability to shape the elastomer to maximize change in capacitance in response to proximity, pressure, touch and shear. In this work we focus on proximity and pressure detection. Specifically, 4x4 cross array woven structure consisting of Ag coated Nylon yarns (diameter 0.54 mm, 0.438 Ω/cm) have been developed that cover an area of 5.5 x 5.5 cm. The woven structure was embedded into Ecoflex^TM. Each electrode is composed of 5 parallel Ag coated Nylon yarns, with 4 electrodes interlaced in each direction to form an array of 16 intersection, each sensitive to pressure and proximity. The woven composite assemblies were subjected to light touch and pressure loads. The corresponding capacitances were measured and are similar in response to those of the orthogonal non-interlaced/non-textile structure, including good proximity detection (> 1 cm), pressure detection (0.23 %/kPa) and spatial resolution ~1 cm). The devices operate in bending and during stretch. Next steps include integration in clothing and bedding to enable health monitoring.

Emerging classes of skin-interfaced, wireless biosensors provide breakthrough capabilities in recording of medically relevant information, continuously in real-world situations, outside of hospitals, clinics or laboratories. This talk highlight progress in two areas of this field of research. The first involves systems for vital signs monitoring in neonates, where advanced, battery-free platforms yield clinical-quality data streams that reproduce, and often exceed, the capabilities associated with the current standard of care, even in level four neonatal intensive care units. The second focuses on soft devices that record multimodal mechano-acoustic signatures of underlying body processes from a unique anatomical location, the suprasternal notch. Data streams from a single device can be analyzed to extract precise measurements of heart rate, heart rate variability, respiration rate, respiration rate variability, respiratory sounds (coughing, wheezing, snoring, etc.), swallowing events, audible and sub-audible speech, ambulatory gait, body orientation and others, of wide applicability in health monitoring and clinical care. Demonstrations include comparisons to clinical gold standards for various individual indications, and to full-night polysomnography (PSG) results captured in a hospital sleep lab.

Commercially available electrocardiogram (ECG) electrodes are rigid and require a gel electrolyte to obtain a clear signal. This electrolyte can dry over time leading to a degradation in signal to noise ratio. Furthermore, the lack of airflow to the skin and adhesive can be irritating to the user. This can pose issues for individuals that require continuous monitoring. Here, we present ECG electrodes made with high performance carbon nanotube (CNT) fiber that are suitable for long-term use. The high conductivity of the fiber and low contact impedance between the fiber and skin allow for good transmission of the ECG signal without the use of a gel. Additionally, the CNT fiber has excellent tensile strength and flexibility so it can be sewn into fabric with a standard sewing machine. The woven structure and softness minimizes the irritation caused by recording ECGs. Furthermore, the CNT fiber is robust and chemically inert so that it can be machine washed without losing performance.

Smart apparel with embedded self-powered sensors can revolutionize human behavior monitoring by leveraging everyday clothing as the sensing substrate. The key is to inconspicuously integrate sensing elements and portable power sources into garments while maintaining the weight, feel, comfort, function and ruggedness of familiar clothes and fabrics. We use reactive vapor coating to transform commonly-available, mass-produced fabrics, threads or premade garments into a plethora of comfortably-wearable electronic devices by directly coating them with uniform and conformal films of electronically-active conjugated polymers. By carefully choosing the repeat unit structure of the polymer coating, we access a number of fiber- or fabric-based circuit components, including resistors, depletion-mode transistors, diodes, thermistors, and pseudocapacitors. Further, vapor-deposited electronic polymer films are notably wash- and wear-stable and withstand mechanically-demanding textile manufacturing routines, enabling us to use sewing, weaving, knitting or embroidery procedures to create self-powered garment sensors. We will describe our efforts in monitoring heartrate, breathing, joint motion/flexibility, gait and sleep posture using loose electronic garments and highlight collaborative endeavors to combine signal processing, machine learning and human factor integration to predict behavior in selected at-risk populations.

There is nothing more personal than healthcare. Health care must move from its current reactive and disease-centric system to a personalized, predictive, preventative and participatory model with a focus on disease prevention and health promotion. As the world marches into the era of Internet of Things (IoT) and 5G wireless, technology renovation enables industry to offer a more individually tailored approach to healthcare with more successful health outcomes, higher quality and lower costs. However, empowering the utility of IoT enabled technology in personalized health care is still significantly challenged by the shortage of cost-effective and wearable biomedical devices to continuously provide real-time, patient-generated health data. Textiles have been concomitant and playing a vital role in the long history of human civilization. In this talk, I will introduce my research on smart textiles for biomedical monitoring and personalized diagnosis, textile for therapy, and textile power generation as an energy solution for the future wearable medical devices. Lastly, I will briefly introduce an autonomous self-powered textile body area network that seamlessly integrates wearable power sources, self-powered sensors, microcontrollers, and internet connection for revolutionary applications in the future personalized health care and body computing.
References (^# Equal contribution author; * Corresponding author)
[1] J. Chen, Y. Huang, N. Zhang, H. Zou, R. Liu, C. Tao, X. Fan and Z. L. Wang. “Micro-Cable Structured Textile for Simultaneously Harvesting Solar and Mechanical Energy”, Nature Energy, 1, 16138 (2016)
[2] Y. Peng^#, J. Chen^#, A. Y. Song, P. B. Catrysee, P.-C. Hsu, L. Cai, B. Liu, Y. Zhu, G. Zhou, D. S. Wu, H. R. Lee, S. Fan, and Y. Cui. “Nanoporous Polyethylene Microfibres for Large Scale Radiative Cooling Fabric”, Nature Sustainability, 1, 105 (2018)
[3] Z. Zhou, X. Li, K. Meng, Q. He, C. Sun, W. Fan, Z. Lin, E. Fan, X. Tan, J. Yang, J. Chen^*. “Machine Learning Assisted Fully Integrated Stretchable Sensor Arrays for Wearable Sign Language Translation to Voice”. Nature Electronics. In Revision.
[4] J. Chen, D.G. Machanic, D. Lin, B. Zhao, K. Liu, J. Wan, B. Liu, Y. Peng, L. Cai, P.-C Hsu, Z. Yu, S. Fan, Z. Bao, Y. Cui. “Phase Change Enabled Active Personal Thermal Management via a Nanocomposite Textile”. Nature Energy. Under Review.
[5] J. Chen and Z. L. Wang. “Reviving Vibration Energy Harvesting and Self-Powered Sensing by a Triboelectric Nanogenerator”, Joule,1, 480 (2017)

Integration of smart devices into textiles is a key challenge for tomorrow-wearable technologies. On one hand, the electronics should perform diversified computational operations, such as data processing and transmission, with high performances for responsive smart systems. These conditions are only met today by rigid silicone-based systems. On the other hand, clothes are soft, closely fit to the skin and adapt to the human body. The mismatch in mechanical properties between soft substrates and rigid components induces specific reliability issues, especially for wearable systems, as they are subjected to wearing and washing.
In this work, we present a fabrication process of soft and ultra-thin circuit for imperceptible systems, integrating microelectronic silicon-based components. We use a customized stack of thin decorative copper leaf on polymer, which can be assembled and connected through vias for multilayered systems. We consider and study the aforementioned aspects of imperceptibility (wearability), and mechanical robustness through specifically designed bending tests. We investigated the optimization of electrical connection between ultra-soft substrates and rigid components, and the influence of the stack composition in multilayer electronic systems on the overall reliability of the device.
The combination of optimized stack layout and compliant interconnections allow the fabrication of robust and ultra-conformable, imperceptible devices.

Human bodily activities are complex that consists of dynamic motions of different body parts with broad frequency ranges. Despite it has been widely exploited in human bodily motion detections, the possibility of using soft rubber-based stretchable sensors in the detection of full-range of bodily motions from muscle functions up to mass movements have not been well explored. Here, we demonstrate that controlled interfacing of an ultralow modulus graphene network with rubber can lead to a stretchable hybrid elastomer with performance combinations of high sensitivity, large stretchability, similar modulus compliance to the skin and good durability. The resultant sensor allows resistive detection of subtle dynamic skin stretches induced by muscles and large deformation caused by joints motions, which fills the gap for sensing the whole spectrum of human bodily motions via soft flexible electronics.

The recent rise of the so-called flexible electronics has paved the way for the development of flexible systems that can be easily integrated and also directly fabricated onto textiles, and be employed for the monitoring of a different bio/physical parameters. In this presentation we will introduce different technological solutions for the realization of smart wearable systems specifically engineered for biopotential recordings and on-skin sensing applications. The first proposed approach is based on screen printed PEDOT:PSS electrodes which are seamlessly integrated directly onto commercial garments, for the measurement of the ECG signal, coupled with respiration. These 2 measurements allow evaluating the physiological status of patients and subjects as athletes and workers under stressful conditions, in several applications ranging from rehabilitation to the monitoring of athletes performance or subjects at work.

Moreover, we will also show the employments of similar electrodes for EMG applications. These recordings can be used to evaluate muscle performance and fatigue, by means of simple commercial garments where recording electrodes have been seamlessly integrated. Examples of applications in rehabilitation and gesture recognition will be shown.
Textile sensing systems are part of a broader area of devices that, thanks to their mechanical conformability, can be successfully used for the human body monitoring. Also tattoo electronics can offer interesting solutions for this kind of applications. In this presentation, we will discuss comparatively their advantages and drawbacks for the recording of biopotentials and/or different physiological parameters.

Carbon fiber textile has been utilized as flexible supercapacitor electrodes with cost-effective graphene nanoplatelete (GNP) composite as model material for coating the electrodes. This composite is considered to be a new class of carbon nanomatertial with very high intrinsic electrical conductivity in plane and accessible surface area. Carbon nanotubes (CNT) at the concentration 50:50 of CNT to GNP were added to take advantage of the high surface area of the composite of these two carbon nano-materials.
Perfect shape of the voltammetric curves indicates excellent ion transport behavior, good charge propagation and low losses in supercapacitors with GNP/CNT coated electrodes.
The first experimental results without optimization showed promising supercapacitor behavior of the carbon fiber textile with bare pads, better than in the state-of-the art reference [1]. Graphene nanoplatelete – carbon nanotube (50:50) electrode material has improved the capacitance density approximately 10 times.
Carbon fiber textile is promising material for fabrication of electrodes for high-capacitance high-energy density flexible supercapacitors [2].
We have also developed flexible carbon nanotube sensor for applications of moisture detection. A cost-effective sensor that could detect and measure humidity/moisture levels has been developed. Prototype sensor have demonstrated an extremely high sensitivity to water.

H. Zarrin, S. Sy, J. Fu, G. Jiang, K.Kang, Y.-S. Jun, A. Yu, M. Fowler, and Z. Chen. Molecular Functionalization of Graphene Oxide for Next-Generation of Wearable Electronics, ACS Appl. Mater. Interfaces 2016, 8, 25428−25437.
Patent Application No. 62/461,035, filed February 20, 2017.

The rapidly emerging field of soft robotics presents a new opportunity to develop wearable assistive technology optimized for the needs of individuals with residual capacity as well as for augmenting human performance. Unlike their rigid counterparts, soft wearable robots are lightweight, intimately conformal to the body and can more easily fit a range of sizes. The hierarchical structure and flexible/conformal nature of textiles provide an ideal platform to construct these wearable robotic systems. The ability to tune mechanical properties for use in inflatable actuation profiles or to anchor to the body and distribute and route forces through attachment points in cable driven systems. Looking forward, additional functionalities will be embedded into the textile beyond structural needs including sensing, and flexible electronic routing.

The field of electronic textiles (“e-textiles”) is currently growing rapidly, impacting by research and development activities in multiple fields, from physics and mathematics to textiles and power engineering to health, safety, and social sciences. Combining multiple functionalities – from basic warmth and comfort to harvesting power to more focused monitoring and/or protection – is of great interest, but has so far found only limited success. We report on our research to analyze and experimentally demonstrate both heat-releasing and heat-trapping polymer films and simple 1-d arrays of fibers, and discuss enabling both functionalities in different scenarios for both heating and cooling applications, such as for the human body. We discuss the use of a thermally transparent film in some hot weather applications, when it is critical to release heat, and also where it is essential, for cold weather applications, to trap heat at an extremity. We build on earlier results that highlighted the importance of polyethylene, especially high- and ultra-high –weight polyethylene, for heat release and improved thermal conductivity [1] and light-scattering bio-particles in melt-extruded polymer fibers [2]. Using our thermally transparent materials, we observe small decreases (few degrees C) in the temperature of artificial ‘skin’ when constant power density, emulating an exercising person, is applied to a novel system for characterizing both power density and artificial skin temperature, compared to control samples of standard, commercial polymers. Similarly, we report on heat-trapping experiments when the outside temperature is much lower than the temperature of the artificial skin. We discuss how such ‘electromagnetic textiles’ – purely passive but electromagnetically responsive materials – can be controlled actively, using 1) electrical voltage with conductive particles in the fibers 2) magnetic fields using magnetic particles and 3) thermoelectric materials that generate a voltage in response to an engineered thermal differential 4) light-activated scattering. These active controls will enable the fiber’s or film’s heat-trapping or heat-transmitting states to be reconfigured actively (voltage control) or passively (due to temperature or electromagnetic field alone). We predict how future textiles, containing polymer materials with particles similar to those we have studies, will perform, and discuss new applications for electromagnetically-responsive polymers, including protection and color.

[1] J. Tong et. al., “Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management”, ACS Photonics, 2, p. 769 (2015).

[2] A. Kumar et. al., “Natural light-scattering nanoparticles enable visible through short-wave infrared color modulation in cephalopods”, Advanced Optical Materials (2018) 6, 1701369.

Research on smart clothing aspires to seamlessly integrate electronic devices with textiles to add exciting new functionality without losing softness and wearability. In particular, light-emitting e-textiles are an emerging technology with applications in fashion design, interior design, visual merchandizing, and healthcare. At present, light-emitting textiles are mainly realized by sewing discrete, rigid elements like light-emitting diodes (LEDs) or optical fibers into clothing, which reduces softness, stretchability, and wearability. Better integration of device functionality into clothing requires the incorporation of intrinsically stretchable functional materials into the textile structure; however, this fabrication is challenging due to the porous, 3D structures of textiles that present a non-planar surface for fabrication and readily absorb and wick solutions of functional inks. In this presentation, we show that textile structures can instead be exploited to form the basis for a new, textile-centric design approach. We use the open structure of a low-denier nylon and spandex ultrasheer fabric as the framework for a highly stretchable transparent electrode in wearable and stretchable light-emitting devices. We coat the fibers of the ultrasheer fabric with a conformal gold coating using solution-based electroless nickel immersion gold plating, producing a semitransparent, conductive, and highly stretchable textile electrode. Adhering these new textile-based electrodes to a stretchable emissive material produces lightweight, wearable, and washable light-emitting e-textiles that function to 200% strain. Combining the metallization of the ultrasheer textile with low-cost stencil printing of a wax resist provides patterned electrodes to create patterned light-emitting displays; furthermore, incorporating soft-contact lamination in the device fabrication produces light-emitting textiles that exhibit, for the first time, readily changeable patterns of illumination.

Since the development of photonics, towards optoelectronic devices of flexible, rollable, wearable, user-friendly, and robust to improve human-machine interfaces have been progressed rapidly. To integrate these devices onto human body, they are designed to be biocompatible and can withstand mechanical deformation. A large number of demonstrations have been proven for the promising market of wearable photonics and optoelectronics such as flexible photodetectors, stretchable laser systems, artificial electronic skins, and paper-based memory devices. Biocompatibility, high sensitivity, low energy loss, and long-term endurance, are the features to successfully integrate with wearable photonic systems, the flexible and rollable optoelectronic devices. Certainly, there remains a great challenges to achieve the above mentioned benefits with considering the practical applications.

On the other hand, photonic metamaterials provide a large number of potential functionalities that can be used for wearable optoelectronic devices. Metamaterials are designed with sub-wavelength geometries for controlling or tailoring the electromagnetic waves for a variety of functionalities. A distinct class of metamaterials is hyperbolic metamaterial (HMM), which is defined by its hyperbolic iso-frequency curve in momentum space. For light-matter interactions, HMMs have been proven to boost the transition rates for both of the spontaneous and stimulated emission dynamics. Owing to the increased transition rate of the optical gain media, stimulated emission (e.g., laser action) comes along with a strong output power and a reduced lasing threshold. However, these demonstrations have primarily been done on rigid substrates. To fully explore the excellent functionalities of HMM, large degree of flexibility and even rollability are highly desirable, which remains as a challenge issue.

To realize the usefulness of our new design, we demonstrate that the flexible and rollable HMM is able to enhance random laser action, in which light suffers from multiple scattering in between disordered media, thereby strongly enhancing its optical gain. We choose low-dimensional organic-inorganic perovskite nanocrystals (PNCs) as the gain material, which is composed of methyl-ammonium lead bromide (MAPbBr₃) with a bandgap of ~2.3 eV that can achieve a high quantum efficiency up to ~90.5%. Interestingly, the enhanced laser action based on our flexible and rollable HMM maintains superior stable performance even under cyclic bending to curvatures below 1mm. The intensity of laser action is enhanced by 2.5 times as compared to the flat surface. By tuning the thickness of the HMM structure, we have achieved a large enhancement of the density of states and the scattering efficiency. Simulation results based on the scattering efficiency and the dipole-like dynamics confirm an efficient out-coupling. We anticipate that this flexible and rollable HMM structure can serve as a diverse platform for flexible photonic technologies, such as light-emitting devices, wearable optoelectronics, and optical communication.
Acknowledgments
This work was financially supported by the "Advanced Research Center for Green Materials Science and Technology" from The Featured Area Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (107L9006) and the Ministry of Science and Technology in Taiwan (MOST 107-3017-F-002-001).

Developing nimble, shape-adaptable, conformable and widely-implementable energy harvesters with the capability to scavenge multiple renewable and ambient energy sources is highly demanded for distributed, remote, and wearable energy uses to meet the needs of internet of things. Here, we present the first multifunctional and waterproof triboelectric-nanogenerator fabric that can produce electricity from both natural tiny impacts (rains and winds) and body movements, which can not only serve as a flexible, adaptive, wearable, and universal energy collector but also act as a fabric-based self-powered active sensor. The working principle comes from a conjunction of contact triboelectrification and electrostatic induction during contact/separation of internal soft fabrics. The structural/material designs of the smart textile are systematically studied to optimize its performance, and its outputs under different conditions of rains, winds and various body movements are comprehensively investigated. Its applicability is practically demonstrated in various objects and working situations to gather ambient energy. Lastly, a self-powered human-system interface is demonstrated on a garment for remotely controlling a music-player system. The multifunctional yet nimble energy fabric can not only address the long-lasting challenge of waterproof, adaptive, deformable, and universal energy devices for locally accessible energy but also bring a new class for wearable energy and smart fabric articles.

[Ref]
[1] Demonstration video: https://www.youtube.com/watch?v=Py-Gib1VDqQ
[2] Ying-Chih Lai, Y. C. Hsiao , H. M. Wu, Z. L. Wang, Adv.Sci.2019, 6, 1801883
[News]
[1] 1.Advanced Science News:Energy-Harvesting Raincoats
https://www.advancedsciencenews.com/energy-harvesting-raincoats/?fbclid=IwAR1kb5La8dmDlFEN02Efu5jtSPTjUfjaN2Aaa02HRB3LPMnscKYAWvMVMis
[2] 2.Physics World: Waterproof fabric harvests energy from raindrops(20190319)
https://physicsworld.com/a/waterproof-fabric-harvests-energy-from-raindrops/

The ever-growing demand for lightweight portable high-tech devices is evolving into an even more challenging demand for fully wearable devices integrated into clothes. To meet this demand, the emerging wearable optical technologies must combine multiple functionalities, including visual effects, communications features, thermoregulation to maintain personal comfort level, and even self-cleaning and microbial treatment by sunlight. These technologies often require portable or renewable power sources to operate—and the lack of cheap, long-lasting and lightweight sources has proved a big hurdle to wider adoption. Finally, new technologies must meet the global demand for tighter environmental standards to reduce energy and water use and waste during the fabrication process as well as throughout the garments life cycle. They must also provide a clear pathway for recycling and re-using the materials into new fabrics and wearables.
We develop multi-functional materials for wearable technologies, which combine a variety of optical, thermal, mechanical, and biological functionalities, and meet high standards for energy and water saving and sustainability. I will discuss the engineering approaches used in designing and fabricating woven and knitted fabrics out of polyethylene fibers to achieve either passive cooling without breaking a sweat or passive heating without the use of uncomfortable metal films. I will then show how the fiber micro-structuring can be combined with nano-scale engineering via embedding a variety of nano-inclusions to combine thermoregulation-by-radiation-control functionality with structural coloring, unique lateral heat conduction properties, and anti-microbial resistance of new textiles. We embed colorants and anti-microbial agents into fibers and films during their fabrication, which does not require significant water usage, in stark contrast with the standard industrial processes that use 200 liters of water to produce 1 kg of textile, and create large amounts of wastewater contaminating the environment. The new textiles also offer excellent water wicking, dirt-resistant, and fast drying functionalities, offering significant energy and water savings for their maintenance, and can be easily recycled at the end of their lifetime.
Finally, I will discuss how the new fabrics can be further enhanced by incorporating other functional wearable elements, including fibers for optical communication, photo-detectors, and flexible, lightweight, round-the-clock energy harvesters capable of operating in the self-powered regime.
Acknowledgements: This work is supported by the US Army Research Office (via the CCDC Soldier Center and the MIT Institute for Soldier Nanotechnologies), Advanced Functional Fabrics of America (AFFOA), MIT International Science and Technology Initiatives (MISTI), and the UNSW-USA Networks of Excellence.
References:
S.V. Boriskina, An ode to polyethylene, MRS Energy and Sustainability, in press, 2019.
L.M. Lozano, et al, Optical engineering of polymer materials and composites for simultaneous color and thermal management, Opt. Mat. Express, 9(5) 1990-2005, 2019.
S.V. Boriskina, et al, Nanomaterials for the water-energy nexus, MRS Bulletin, 44(1), 59-66, 2019.
A. Ruiz-Clavijo, et al, Full gamut of structural colors in all-dielectric mesoporous network metamaterials, ACS Photonics, 5(6), 2120–2128, 2018.
S.V. Boriskina, et al, Heat is the new light, Optics and Photonics News, 28(11) 26-33, 2017.
S.V. Boriskina, Optics on the go, Optics and Photonics News, 28(9) 34-41, 2017
J.K. Tong, et al, Infrared-transparent visible-opaque fabrics for wearable personal thermal management, ASC Photonics, 2(6), 769–778, 2015.

Solution processing of graphite and other layered materials provides low-cost stretchable inks enabling electronic textile devices [1]. However, the limited quality of the two-dimensional (2d) material inks, the complexity of the layered arrangement, and the lack of a suitable dielectric 2d material ink [2] has impeded the fabrication of active field effect devices on fabric based on fully-printed 2d heterostructures. In this work we demonstrate fully inkjet printed 2d material active heterostructures with graphene, MoS₂ and hexagonal-boron nitride (h-BN) inks, and use them to fabricate all inkjet printed flexible and washable ambipolar, n- and p-type field effect transistors (FETs) on textile, reaching a field effect mobility of μ ~ 105 ± 29 cm² V^-1 s^-1 on polyester fabric, at low operating voltages (< 5 V). The devices maintained their performance even under ∼ 4% tensile strain and showed stable operation for periods up to 2 years, indicating the two-fold role of the h-BN layer as a flexible dielectric and encapsulant. Our 2d material textile FETs are washable up to 20 cycles, which is ideal for textile electronics. The viability of our process for printed and textile electronics is demonstrated by fully inkjet printed electronic circuits, such as reprogrammable volatile memory cells, complementary inverters, and OR logic gates with graphene/h-BN FETs.

References
[1] Torrisi, F. & Carey, T. Nano Today 23, 73 – 96 (2018).
[2] Torrisi, F. & Carey, T.; Samori P. and Palermo, V. Eds., Wiley, Weinheim (2018).
[3] Carey et al. Nature Commun, 8 1202, (2017).

The next generation of wearable sensors, actuators, and power microsystems must maintain a large area density while recovering reversible elastic deformation of at least 30 - 100% macroscopic strain, to match the elasticity of human skin. To achieve this, wearable devices are often fabricated through the “island-plus-bridge” method where an array of active rigid device micro-islands are separated by stretchable serpentine metal interconnects. Serpentines are advantageous for integration into textiles as interconnect structures since they can undergo geometrical reconfigurations to relieve stress under applied strain. Traditional metals with low intrinsic tensile strains (i.e Cu) configured into serpentines with a large amplitude and narrow wavelength are able to achieve large macroscopic strains of tens to hundreds of percent. Replacing these traditional metals with materials that have a larger elastic intrinsic strain may offer a route to create higher area density devices by requiring less serpentine interconnect material to achieve the same macroscopic strains.

Freestanding magnetron sputtered Nickel – Titanium (NiTi) based shape memory alloys (SMA) are attractive for textile and wearable interconnect technologies. They can reversibly recover from unusually large elastic strains (up to 6%) through a temperature induced solid-to-solid phase transformation, compared to 1 % for traditional metals like Cu. When a SMA’s transition temperature is below room temperature, the material is considered to be superelastic, where elastic strain recovery occurs purely upon unloading. Previously, superelastic TiNiCuCo thin-films were demonstrated to be ultra-low fatigue, reversibly deforming through 10 million cycles at a 2% strain [1]. Additionally, superelastic and SMA materials exhibit exceptional mechanical strength and efficient electrical conductivity, making them ideal stretchable electrode material candidates for active serpentine interconnects in various wearable devices.

Here, we present a MEMS compatible fabrication process to fabricate and characterize the stretchable mechanical performance of novel superelastic TiNiCuCo serpentines [2]. Fabricated devices have a serpentine amplitude of 1 mm, wavelength of 1 mm, width (w) between 25 – 75 μm, and film thickness (t) between 20 – 80 μm. We evaluate different mechanical deformation modes for our serpentines where < 1 results in buckling deformation and > 1 results in scissoring deformation [3]. We demonstrate large single strain-to-rupture testing of all devices ranging between 97 - 156% macroscopic strains, superior than those modeled for a Cu system of the same geometry. Preliminary cyclic fatigue testing has demonstrated these serpentine interconnects can survive up to 8000 cycles at a 100% macroscopic strain, with minimal structural and functional fatigue. Future fatigue testing will explore electropolishing of the serpentine structure to exclude any residual defects which is likely to improve the fatigue resistance even further. Overall, our results show superelastic metals may offer a route to increase the stretchability of wearable devices while simultaneously reducing the size and cost of device production.

[1] Chluba, C., Ge, W., de Miranda, R. L., Strobel, J., Kienle, L., Quandt, E., & Wuttig, M. (2015). Ultralow-fatigue shape memory alloy films. Science, 348(6238), 1004-1007.
[2] Lima de Miranda, R., Zamponi, C., & Quandt E. "Micropatterned freestanding superelastic TiNi films." Advanced Engineering Materials 15.1 - 2 (2013): 66-69.
[3] Wang, B, Bao, S., Vinnikova, S., Ghanta, P., & Wang, S. "Buckling analysis in stretchable electronics." npj Flexible Electronics 1.1 (2017): 5.

Composite materials incorporating carbon allotropes are emerging as a powerful technology to manufacture membranes able to impart advanced functions to textiles [1,2]. Body temperature increases under physical effort, and an excessive body warming negatively affects the comfort feeling and the physiological performances [3]. Here, we report an innovative family of advanced nanocomposite membranes for thermal comfort enhancement in functional textiles, based on a thermosetting aliphatic polyurethane (PU) and graphene nanoplatelets (GNPs).

A thorough chemico-physical characterization of GNPs was performed to provide an insight of the thermal properties obtained for the composite materials. The highly crystallographic quality of GNPs, obtained via physical-mechanical processes, was revealed by Raman spectroscopy (I_D/I_G = 0.127) [4]. TEM and AFM analyses assessed that about 85% of the analyzed GNPs possessed a thickness lower than 10 graphene planes. These results confirmed the suitability of the produced GNPs for the fabrication of highly performant membranes in terms of thermal conductivity.
The GNPs were then loaded into the PU matrix (5 and 10% w/w) by conventional industrial mixing process. The obtained composites were characterised after coupling with cotton fabrics, via hot-melt process. SEM micrographs showed that graphene nanoplatelets were homogeneously distributed in the PU matrix, with a preferential alignment parallel to the matrix plane, maintaining the original dimensions. Crystalline phases present in the composites were evaluated by X-ray diffraction: two peaks around 2θ = 26.48° and 54.78°, corresponding to the characteristic peaks of GNPs, were clearly present in the diffraction patterns of PU-GNPs composites. Moreover, the intensity of these peaks increased by increasing the GNPs loading [5].
Thermal characterization was performed on the composite membranes as a function of the filler percentage. In-plane thermal conductivity of the pristine PU membranes and PU-GNPs membranes was measured, showing that thermal conductivity improved (up to 471 %) by increasing the percentage of GNPs. An appropriate designed forearm manikin device was used as phantom to evaluate the thermal conductivity and thermal dissipation of the developed membranes, mimicking the possible in vivo condition [6]. PU-GNPs membranes were demonstrated to improve the thermal dissipation, lowering the internal temperature of the phantom compared to pristine PU membranes (-1.2 °C for 10% GNPs-loaded membranes).

This study provides a new approach for the design of innovative membranes suitable for sport and technical textiles, with significant performance improvement in thermal comfort.


References:
[1] Kuilla et al., Prog Polym Sci (2010)
[2] Stankovich et al., Nature (2006)
[3] González-Alonso et al., J Appl Physiol (1999)
[4] Dresselhaus et al., Nano Lett (2010)
[5] Verma et al., Compos Part B Eng (2017)
[6] Brauer et al., Acta Anaesthesiol Scand (2002)

Smart apparels capable of tracking the wearer’s gait and motion have the potential to revolutionize human behavior sensing and personalized health monitoring by transforming everyday clothing into sensors. The ability to measure motion at individual joints can enable many applications. For example, the knee and ankle joints are important to monitor gait disorders that can occur due to neurological causes like Dementia and Parkinson’s, as well as non-neurological causes such as Osteoarthritis, intoxication, and medications (e.g. sedatives). However, existing sensing techniques typically rely on sewing or inserting traditional hard sensors (such as inertial measurement units and piezoelectric buttons) into tight-fitting garments to obtain sufficient signal to noise, making it uncomfortable to wear and limiting the technology to niche applications in lab settings.
Here, we describe an approach to leverage the unique properties of textiles and garments themselves to enable entirely new ways to sense motion using clothing. Specifically, a garment folds, compresses, twists, and stretches as a wearer moves, and, by conformally applying an imperceptible electronic polymer coating directly onto the textile surface, we demonstrate the ability to transduce these mechanical deformations into an electrical signal. We use a solvent-free vapor coating technique developed in our lab to conformally deposit an electronic polymer film followed by an insulating polymer encapsulant onto mass-produced fabrics or garments. Vapor coated samples retain the weight, feel and flexibility of the starting fabrics and garments. Our polymer coatings simply impart electronic functionality to a previously insulating substrate, thus providing a handle to detect changes as the fabrics/garments bend, compress or twist during movement. Notably, vapor deposited polymer coatings are sweat repellant and stable to machine washing, ironing, and mechanical abrasion.
Vapor coated compression socks and elbow sleeves, in particular, serve as resistive strain sensors that produce a unique signal pattern (resistance change) for each specific joint motion. The special knitting pattern of these garments imparts multiaxial strain sensitivity to the sensor, and their tight fitting design maintains constant body contact during motion, limiting spurious noise. The high stretchability of the commercial fabric used in compression socks and elbow sleeves allows for a large range of dynamic motions (axial, bending and torsional strain) to be captured without the need for adaptive circuitry or sophisticated signal processing routines. Because vapor-deposited electronic polymer films are conformal and pinhole-free, a linear resistance change is created while a subject is wearing the compression sock or elbow sleeve, even at large strains (>100%), which is a notable advance over reported movement sensors. Moreover, since vapor deposited coatings are automatically grafted onto the surface of the fabric, repeated and varied mechanical deformations do not deadhere, delaminate or realign the electronic polymer coating over time, meaning that signal hysteresis and stretching fatigue are not observed. Lastly, due to the direct and tight-fitting contact of the vapor coated compression sock with skin, this structure also boasts the ability to record ECG data, which can be correlated with joint motion. All these prominent properties empower wide-spread applications in gait detection and human performance monitoring.

Developing new textile devices is a sequence of trial and error. This iterative process is largely due to a lack of modeling tools that are paramount for predicting properties like electronic conductivity and mechanical performance. In comparison, other industries, such as automotive and aerospace, rely on a digital design environment before fabrication to study the effects of geometry and architecture on device performance. As this kind of engineering system does not exist for textiles, studying the effects of these parameters, including knit architecture, geometry, and loop pattern, on device performance has been underexplored.
We have developed a novel bicontinuous helicoid lattice system for modeling yarn pathways within the knit structure that can begin to address this challenge. This lattice is based on established principles, with the surfaces of the lattice mathematically defined. This allows the path of the yarn to be known at each distinct point throughout the structure, defined by its relationship to the lattice surface, providing an understanding of the complex three dimensionality of the knit textile structure. With the helicoid lattice, we can model how stitch pattern changes lead to loop deformations in the resulting fabric structures. This includes the effects of knit and purl stitch combinations and the deformations these patterns can create, leading to variable surface geometries. The model was originally developed to understand the deformation mechanisms that occur within the knit structure and produce a self-folding effect. Through this understanding, we can see how loop architecture informs device performance in a variety of textile applications, including electronic textiles, where design of non-planar structures can be used to enhance functionality.
Specifically, in the design of textile supercapacitors we explored the effect of knit structure on device performance. Recent literature on the development of fiber and yarn supercapacitors demonstrate high capacitance and energy density at short lengths only (<4 cm), with reduced performance at longer lengths due to high resistance. For this reason, knitted electrodes are a promising new architecture of textile energy storage devices; yarn electrodes are manipulated into interconnected loop structures, providing multiple pathways for electron transport. One of the inherent challenges of knit supercapacitors is that the spacing between electrodes is significantly larger than that of planar microsupercapacitors, and it is well known that the narrower the spacing between electrodes, the better the rate capability, power response, and energy density of a device.
In this work, methods to minimize the electrode spacing were explored by exploiting the fundamental loop structure of knitted textiles. Using the bicontinous helicoid lattice model to inform design decisions, specific loop structures were chosen to control the device geometry and optimize electrochemical performance. By tuning the knit structure, the spacing between electrodes decreased by more than a factor of 4 and the capacitance increased by almost a factor of 2 at low scan rates.

Photolithographic defined films play an important role in modern optoelectronics and are crucial for the development of advanced organic thin-film transistors (OTFTs). Here, we explore a facile photoresist-free photopatterning method for natural carbohydrates and their use as OTFT gate dielectrics and passive for flexible transistors. The effect of the cross-linkable unit chemical structure on the crosslinking chemistry and dielectric strength of the corresponding films was explored by investigating cinnamate-functionalized carbohydrates from monomeric (glucose) to dimeric (sucrose) to polymeric (cellulose) backbones. UV-illumination of cinnamate ester of these carbohydrates leads to [2+2] cycloaddition and thus the formation of robust crosslinked dielectric films in the irradiated areas. Using propylene glycol monomethyl ether acetate as solvent/developer, patterned dielectric films with micrometer size features can be fabricated. P- and N-type OTFTs were successfully demonstrated using unpatterned/patterned crosslinked films as the gate dielectric and pentacene and N,N’-1H, 1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDIF-CN2) as the p- and n-channel semiconducting layer, respectively. Furthermore, implementation of these materials on elastomers enable good performance and mechanical flexibility. Our results demonstrate that natural-derived polymer gate dielectrics, which are soluble and patternable using bio-mass derived solvents, are crucial for the realization of a more sustainable flexible OTFT technology.

Textile-based light-emitting devices, one of the more promising approaches for cutting-edge wearable electronics, have been developed in a variety forms. They can be fabricated directly on fabric, or on individual strands of the fiber itself. Among these approaches, fiber-based light-emitting devices possess many structural advantages including flexibility, breathability and light weight, that make them promising candidates for future wearable displays.[1-2]
So far, most fiber-based light-emitting device studies have focused on fabricating a single device. However, it is essential that light-emitting devices are capable of displaying composite information. High efficiency is also a very important characteristic for functional textile displays. Here, we introduce fiber-based phosphorescent organic light-emitting diodes (fiber phOLEDs) which exhibit the impressive current efficiency (CE) of over 20 cd/A, the highest CE value ever reported. This work also proposes an addressable structure which allows multiple emitting-cells to emit light from a strand of fiber.
The fiber phOLEDs are based on a dip-coating process strategy developed in our previous work proposing organic light-emitting fibers.[2] First, to obtain a higher CE than achieved in our previous work [2], we used a phosphorescent dopant material, tris(2-phenylpyridine)-iridium(III) (Ir(ppy)₃), which can achieve 100% internal quantum efficiency (IQE). However, Sophisticated structures to control the excitons were needed to take advantage of the 100% IQE because the exciton lifetime is so long. The Ir(ppy)₃ based emitting layer (EML) was therefore designed to not only take charge balance into consideration, using co-host materials, but also the appropriate concentration for avoiding aggregation of the solution. Also, a high triplet energy hole transport layer (HTL) was inserted between the EML and Al anode layer for exciton confinement. These sophisticated structures on the thin fiber resulted in the outstanding CE value of over 20 cd/A, along with a sufficient level of luminance, over 3000 cd/m². Next, to make them addressable, an array structure composed of the fiber phOLEDs and Al-deposited fibers was prepared. The layer next to the dip-coated EML was deposited by vacuum thermal evaporation as a series of striped patterns on one side of the fiber, to form multiple emitting–cells on a strand of fiber. Then, each Al-deposited fiber was contacted to the patterned layer. Initially, when we simply placed the fibers on this array structure, there were problems with short circuits and instability. To solve these problems, we introduced contact regions that were inserted between the EML and the patterned layers. No incidental damage was observed in this array structure. As a result, each emitting-cell of the high efficiency fiber phOLED can be reliably addressed.
The resulting fiber phOLED is addressable and highly efficient and exhibits the characteristics required for textile displays, including flexibility, weavability and a reasonable level of brightness. We expect that these strategies will take us a step closer to functional textile displays that can provide visual information.

Acknowledgments
This work was supported by LG Display under LGD-KAIST Incubation Program and the Technology Innovation Program (20000489, Interactive fiber based wearable display platforms for clothing displays) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).
References
[1] Zhang, Zhitao, et al. Nature Photonics, 2015, pp. 233–38
[2] Kwon, Seonil, et al. Nano Letters, 2018, pp. 347–56

Leaving in the era of the Fourth Industrial Revolution provides the opportunities of taking wearable technology and design to a whole new level .The increase dreliance on creativity across industries and interdisciplinary creative work in fields such asf ashion, science and technology, sets the balance and the boundaries,used as a metaphor to describe ,,creativityin terms of crossing or pushing out a .... Bogartz (1994).. The fusion of smart textile materials and wearable computing technology are introducing a shift in textile, from a passive to a dynamic behaviour: active smart textiles and ultra-smart textiles. The ultra-smart textiles perform similarly to a human brain, with reasoning, cognition, and activating capabilities or a second smart skin.
The recent urge in the design and development of biosensors for health care and wellness engineering is pushing the boundaries of material and technological processes for new kinds of material modification and manipulation,with emphasis on sustainability. The aim of this research is to propose and to open up new opportunities and challenges of the next-generation e-heathy monitoring,in collaboration with one of the most forward moving field: Fashion. Also to push the boundaries of what makes smart fabric technology revolutionary based not only on its ability to communicate, transform, but also to grow or naturally fabricate. Proposing another fold of opportunities - one where technology meets craft and craft meets science and art , while sustainable materials are also a key factor.To propose the next generation of wearables by implementing electrophysiology Interfaces by mechanically Interlocking of conducting polymer and silk fibroin to develop new applications for monitoring, diagnosing, displaying and preventing.
Textiles of today are materials with applications in almost all everyday activities.Fibres, yarns, and other structures with added-value functionality have been developed for a range of applications textile materials and the textile has become an important platform for high-tech innovations.
The projects developed and introduced in this paper followed a design approach by fusing stechnology, science and nature, introducing new innovative hybrid fabrics explorations that requires the understanding of: the what (the purpose of the concept); the how (the used bio and tech); the where (the context in which the product is used) and finally the wearability issues connected to the role of trans materials and technology in human body, changing and perception.

Keywords: wearable technology, textiles, bio, science, nature, Silk Fibroin

We demonstrated an innovative, flexible yarn-based biobattery that generates green electricity from bacterial respiration. The battery can be easily scaled up by controlling the length of the yarn of a single battery or connecting multiple yarns in series. Bacterial cells in the yarn break down the organic fuels (e.g. glucose and lactic acid) and transfer the produced electrons to the electrode, providing power for external applications. The yarn-based biobattery was knotted into a bracelet by connecting three battery units in series, generating the current density of 0.33mA/cm³. Furthermore, this proposed biobattery can be woven or embroidered into a large smart fabric, potentially providing hundreds of milliamperes for powering actual wearable electronics. The ever-increasing worldwide efforts in developing renewable energy sources and reducing environmental footprint are among the greatest challenges faced by mankind. Although there are great potential and innovations in large-scale alternative energy technologies (e.g., wind and solar), the small-scale applications are still powered by batteries that may cause environmental and economic burdens with their recycling and replacement. In addition, electronic products such as wearable devices are becoming more powerful and smaller in size, and work in closer contact with the human body. The conventional energy storage and harvesting devices (e.g., lithium-ion batteries and photovoltaic cells) fail to meet flexible and environmental requirements for the next generation of electronics and micro-/nanosystems (MNSs). Hence, various emerging energy-harvesting technics have been proposed as a power source by using organic-photovoltaic, thermoelectric, electromagnetic, and piezoelectric/triboelectric principles. The biochemical energy harvesting devices (or biobatteries), notwithstanding being the least explored, have three major advantages. First, the biofuels that can be utilized for electricity generation are readily available in sweat, saliva, urine, and even in common beverages. Second, they are capable of continuously generating electricity independent from lights or motions. Last, the devices are easily disposable and cost-effective. However, significant challenges remain in the making of flexible, green and scalable biobattery for the energy conversion. The biobattery developed here can not only be readily integrated into wearable electronics or smart textiles, but also be scaled up to revolutionize the power performance for real-world applications. The proposed battery was made by wrapping the functionalized yarns onto a non-conductive cord. Both the anodic and cathodic yarns were treated with the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), making its own yarn conductive while retaining its porosity and hydrophilicity. Furthermore, the cathodic yarn was loaded with a low-overpotential Ag₂O solid electron acceptor and coated with Nafion as a proton exchange membrane (PEM).

The goal of this research was to realize a textile display that could sustain 3 dimensional deformation such as bending, wrinkling, and stretching. We developed a multifunctional next-generation display technology with commercial-level driving voltage, brightness and efficiency characteristics, and a new form factor. There were three fundamental technical components used to fulfill the goal of the research, a Platform, the Display and Encapsulation layer.

(1) Platform: A study of an elastic clothing platform with a flat surface and a stress lowering structure
[Planarization] A planarization study was conducted to form a flat surface on a textile. A sacrificial layer, a planarization layer, an adhesive layer and the textile were formed on the glass, and then the sacrificial layer was simply removed by deionized water. Previous studies have performed planarization by attaching a plastic film to the textile, and used a very thick planarization layer of several tens of, hundreds of micrometers.[1, 2] However, the planarization layer in this work was only 0.5 micrometers.
[Stress-lowering structure] Flexible and stretchable features of textiles produce very high strain and stress as well. Accordingly, this work studied a platform between the planarization layer and the textile by introducing a 'stress–buffer' layer. The stress–buffer also functioned as the adhesive layer, and significantly reduced mechanical strain and stress, and had the advantage of enhancing durability.
[Improvement of applicability] A stress–buffer that was capable of hardening at room temperature was used to prevent any deformation and distortion by heating. This research developed a fabrication process that can be applied to any textile including cotton, linen, wool, leather, etc.

(2) Display: Low temperature process (below 150 degrees Celsius) OLED display
[Textile-based OLED] To realize the clothing-shaped full-color display, red, green and blue OLEDs were fabricated on the textile platform. The textile–based R, G, B OLEDs had almost the same luminance and efficacy as glass-based OLEDs.
[Low temperature processed display backplane] Thin film transistors (TFTs) typically require a high temperature heating. This causes serious damage to the textile such as twisting and burning. Since a heat treatment is necessary to repair interface damage on the insulator produced by plasma during sputtering, a TFT fabrication method was investigated to avoid plasma damage and chemical deposition of the insulator.

(3) Encapsulation: Washable encapsulation with water-blocking ability and flexibility
[Nano-stratified and washable encapsulation] A study using a nano-stratified structure was performed to improve the gas barrier property and mechanical flexibility of the encapsulation. The nano-stratified encapsulation was composed of ultra-thin sub-layers (less than 3nm) fabricated using the ALD(atomic layer deposition) process. The multi-interface system blocked the growth of defects, and as a result, WVTR(water vapor transmission rate) was lowered. The porous structure also contributed to improved flexibility. In addition, the encapsulation layers were formed on a passivation film to block liquids, and then it was integrated with the textile display.[3]

(4) Practical application study of the textile display
[Smart fashion] The developed textile display combines aesthetic elements with smart functions, which means that it not only has functional capability, but can be attractive in the fashion industry. The proposed approach permits OLED displays on shirts, hats, shoes etc.

References
[1] Hu, et al. "Textile–Based Flexible Electroluminescent Devices." Adv. Funct. Mater. 21.2 (2011): 305-311.
[2] De Vos, et al. "A complex multilayer screen-printed electroluminescent watch display on fabric." J. Disp. Technol. 12.12 (2016): 1757–1763.
[3] Jeong, et al. "Textile–based washable polymer solar cells for optoelectronic modules: Toward self-powered smart clothing." Energy Environ. Sci. (2019).

After more than 20 years of development, e-textiles for various applications are gaining increasing attention worldwide. Industry driven application oriented developments are superseding the research oriented projects. This leads to changes in the technological approaches. Manufacturability becomes a more important aspect which leads automatically to a simplification of components and processes. On the other hand the overall systems reach a new complexity in order to be useful in a real life environment.
In order to enable industrial manufacturing of wearable e-textiles it is necessary to develop modular concepts as well as integration processes suitable for high volume production. Only with modules dedicated for textile integration with standardized interfaces it will be possible to realize new systems in short development cycles. These smart modules have to be compatible to allow fast design of new functionalities and even flexible adaptation.
Approaches to integrate electronics on textile ribbons with conductive bus structures instead of aiming to assemble the modules directly on large area textiles are very promising. They reduce complexity and footprint of the assembly equipment while simultaneously reducing the process time. New interconnection processes like thermoplastic non conductive adhesive bonding and ultrasonic welding will allow to reduce cycle times additionally.
From the early stages of smart textile development the monitoring of physiological parameters plays the most important role. Smart textiles for medical applications can cover various aspects: prevention, diagnosis, therapy and rehabilitation. Derived from rehabilitation concepts a new generation of wearable systems which will support patients but also healthy subjects are now aiming at combining the monitoring of movement,muscle activity and other parameters with actuators for active assistance. For most applications sensors can be textile or polymer based but also miniaturized conventional sensors can be required. A broad range of measurement principles can be realized and integrated. In most cases only the combination leads to the data required for optimum control.
The scope of the presentation is the overview and evaluation of technologies for conductor-, electronics-, sensor- and actuator-integration in textiles to meet the requirements of different wearable applications together with manufacturing and reliability aspects.

The development of new composite materials exhibiting both high infrared (IR) emission and good electrical conduction represents a challenging task for those applications where efficient radiative properties and electrical conduction are simultaneously needed as for instance for heat dissipation in conductive yarns and conductive textiles or for the realization of IR thermal detectors.
To this aim, a set of polymeric fibers composed of randomly oriented carbon nanotubes (CNTs) dispersed into a poly(ethylene terephthalate) (PET) matrix host was prepared and investigated [1]. Among the different carbon materials, CNTs were chosen for the uniqueness of their emissive properties in the IR wavelength range. Besides electrical conductivity, in fact, the inclusion of CNTs offer the possibility to increase of the IR emissivity which is usually not straightforward.
The amount of CNTs in the investigated set of samples ranges between 1 and 10 wt%. The effects of the inclusions on electrical and morphological properties were studied by means of electric conductance, scanning electron micrography and white light interferometry investigations, respectively. Finally, the IR emissivity was characterized in the 3.5-5.1 micron spectral range by using the infrared thermography technique under heating regime [2].
The electrical conductivity showed a percolation-like behavior with increasing CNTs content. In particular, an exponential conductivity growth from the pure PET value (~ 10^-18 S/cm) to about 2×10^-3 S/cm was obtained by dispersing 1 wt% of CNTs as the percolation threshold is passed while an almost linear increase was observed in the samples with a larger CNTs concentration. Concerning with IR characterization, experimental results show that emissivity is gradually growing with the amount of dispersed CNTs.
In order to analyze the obtained experimental results, a model based on the Maxwell Garnett mixing rules was adopted to calculate the dielectric permittivity of the polymeric matrix with randomly oriented inclusions. The effective medium data have then been employed to retrieve the absorption cross section for infinitely long cylinders by means of the Mie scattering theory. The experimental data show higher emissivity values with respect to numerical ones, particularly for larger CNTs concentrations. The large values of the experimental emissivity has been ascribed to the emerging of surface roughness when CNTs are included, as evidenced by SEM images and mean surface roughness measurements carried out by WLI analysis. Indeed, the emerging of surface roughness may lead to an increase in the specific surface and, consequently, gives rise to an increase of the IR emissivity due to the larger value of the radiating sample surface.
Concerning with mechanical properties, in order to preserve the flexibility of the bare PET fibers along with the ability to use these fibers to form textures or fabrics, CNTs values should be kept lower than 4-5 wt%. However, experimental results demonstrate that limiting the CNTs content to 5% still allows good electrical conductivity (1.5×10^-3 S/cm) along with IR high emissivity (>0.90).
In conclusions, this study highlights the possibility to get high electrical conductivity values associated to high values of IR emissivity. Such unconventional properties encourage their use for the realization of conductive yarns displaying both high IR emissivity/absorbance and good electrical conduction.

[1] Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis, “Carbon nanotube–polymer composites: Chemistry, processing, mechanical and electrical properties”, Progress in Polymer Science 35, 357–401 (2010).
[2] M.C. Larciprete, S. Paoloni, R. Li Voti, Y.S. Gloy and C. Sibilia, “Infrared radiation characterization of several stainless steel textiles in the 3.5–5.1 μm infrared range”, International Journal of Thermal Science 132, 168-173 (2018).

Electronic textiles (e-textiles) are fabrics that are integrated with electronic elements including sensors, actuators and microcontrollers, and are expected to be applied to not only wearables but also smart sheets, for instance. In order to realize high function e-textiles, we have been developing integration and packaging technologies to integrate silicon or compound semiconductors based microdevices into textiles, such as stretchable interconnect, flexible interposer and spring contact technologies. Continuous manufacturing processes for these have been developed.
Stretchability is frequently required for e-textiles. For instance, since human skin around the elbow or knee joints can be stretched to more than 30%, interconnects of wearable devices need stretchability of 30% or above. Although stretchable interconnects on textile substrates are often realized by printing horseshoe-patterns with use of “stretchable” inks, printing patterns cannot cover stretch as large as 30% and require large surface areas. To realize fine interconnects with stretchability of 30% or above, we have developed vertical wavy Cu stretchable interconnects utilizing micro-corrugation process of Cu foils and embedding in silicon rubber. When Cu foils are shriveled to -30% by micro-corrugation, the interconnects should be stretched to 30% without electric resistance change. The micro-corrugation process is based on the metal foil forming technique where a flat Cu foil is continuously deformed into wavy shape of interconnects between the upper and lower gears. After the process, the wavy machined Cu foils are embedded in silicone rubber to protect them and improve the interconnects’ elasticity. The fabricated wavy Cu interconnects showed stretchability of more than 40%. Using the 0.5-mm-wide interconnects, FPC(flexible printed circuit)-compatible stretchable electric circuit integrated with LEDs was successfully demonstrated.
It could be difficult to integrate “hard” devices such as ICs, optical devices, MEMS sensors and passive elements as they are into “soft” textile substrates. In addition, inflexibility of hard devices causes breaks of e-textiles during use including washing. To overcome the problems, we have developed an interposer of miniature FPC board on which hard devices are mounted. The flexible interposer can be easily integrated on soft textiles. Using the interposer technology, we prototyped large area (1.2 m x 1.2 m) LED array fabric. The interposers with LED and passives can be continuously mounted and soldered on ribbon textiles woven with polyester fibers copper wires. The large area fabric is realized by weaving the LED integrated ribbons and polyester fibers together. These interposers are necessary for re-distribution of interconnects, because it is often difficult to form fine interconnects and bonding pads on textile substrates.
Even though both interconnects and devices are flexible, solid electrical contacts between them may cause breaks of breaks of e-textiles during use. We have developed reel-to-reel continuous fabrication process of flexible contact structures on fibers (cables). The contact structures are hemisphere or bell shaped elastomers coated with PEDOT:PSS. The fabrication process consists of dispensing suitable silicon elastomer and both hydrophilic and hydrophobic PEDOT:PSS coating. It was found that the structure has life time of more than a million deformation cycles. Although the contact structure was developed for the contact between the fibers (cables), it could be effective that this type of flexible spring structure is introduced into joints between interconnects and devices on textie substrates.

The integration of conductive elements in soft material constructs provides attractive opportunities for the realization of diverse electromechanical devices. Flexible pressure sensors, in particular, offer a wide application range in health monitoring and human-machine interaction. However, their implementation in functional textiles is limited because existing devices are usually small, 0-dimensional elements, and pressure mapping is only achieved through arrays of sensors that are difficult to integrate and include many failure-susceptible connections. Here, we demonstrate compressible and electrically conducting fibers for the detection, quantification, and localization of kPa-scale pressures over m²-size surfaces.[1, 2] The scalable thermal drawing technique is employed to co-process polymer composite electrodes within a soft thermoplastic elastomer support into long fibers with customizable architectures. Exerting pressures on the fibers results in the selective and reversible contacting of the electrodes within the fully enclosed structure, thereby generating electrical signals at distinct pressure levels. Moreover, resistance measures can be directly related to pressure positions along the fibers, enabling pressure localization. The fibers act as accurate and robust 1-dimensional pressure sensors, functional over large cycle numbers, variable frequencies of mechanical stimulation, and in humid environments. Their potential in health care is demonstrated by mapping pressures on a gymnastic mat for the monitoring of body posture and motion. The fibers represent a simple, cost-effective, and reliable strategy towards the functionalization of large, flexible surfaces.

References:
[1] A. Leber, A. G. Page, D. Yan, Y. Qu, S. Shadman Yazdi, P. Reis, F. Sorin, under review
[2] Y. Qu, T. Nguyen-Dang, A. G. Page, W. Yan, T. Das Gupta, G. M. Rotaru, R. M. Rossi, V. D. Favrod, N. Bartolomei, F. Sorin, Adv. Mater. 2018, 30, 1707251.

This presentation will discuss new materials and components that enable our intrinsically stretchable optical fibers [1] to measure strain while meeting the power and washability requirements of wearables. These threadlike sensors work with high-throughput fabrication methods designed for textiles. However, for wearables, practical requirements must be taken into account.
Coated [1], molded [2], and extruded [3] elastomeric optical fibers are a new low-cost, all-polymer sensor material for measuring wearer activity. They can be applied to fabrics by sewing or adhesives. After their light intensity signals are transformed into electronic signals using optoelectronic sensors, the activity data can be sent over a wireless link for analysis. Because washable, battery-free radios are still under development, a battery/processor/radio communication module that separates from the textile is a popular approach that lets the communication module skip the laundry. Resistive strain sensors and conductive-fiber electrodes for sensing the electrical activity of skeletal muscles (electromyography or EMG) rely on conductive connections to the communication module. For reversibly connecting the communication module to these electrical signal sources, a common solution is a metal snap fastener. Fabric-integrated optical fibers need a similar rugged, quick-connect solution for practical applications. This presentation will cover our approach to making reversible optical connections specifically for wearables using all-polymer components.
All-polymer optical sensors are heat-bondable to synthetic fabrics and do not corrode during washing, in contrast to conductive fibers that corrode in water. However, power consumption for light emitting diode (LED)-driven optical fiber strain sensors is significantly higher (~10 mW) than for resistive strain sensors made from conductive fibers (~0.1 mW). Because the power resources for wearables are so limited, both optical and resistive sensors are turned off when not in use. Even so, the peak power requirements of optical sensors may still prevent their use in lightweight, battery-free energy-harvesting wearables.
Differential absorption in a mismatched fiber pair removes the effect of changing light conditions for optical strain sensors, making it possible to drive them with unknown-intensity ambient light. We have previously investigated process-based methods for modifying the light attenuation coefficient of fibers [4]. Control over optical transmission means one can compare the signal intensity from two parallel fibers with known optical transmission differences and thus subtract out the unknown source light that leaked into the fibers along their path over a surface. This approach will be discussed in the presentation. When sufficient external light is available to make measurements, the LED can be turned off, cutting out the main power-consuming component. The optoelectronic sensor brings power consumption to the resistive sensor level. Unlike resistive sensors, no signal return path is required for textile-embedded fiber pairs that use ambient light. Since textiles increasingly form the skins of soft robots in addition to wearables, new developments here will lead to sensorized surfaces in a wide range of applications.

[1] C. K. Harnett, H. Zhao, and R. F. Shepherd, “Stretchable Optical Fibers: Threads for Strain-Sensitive Textiles,” Adv. Mater. Technol., vol. 2, no. 9, p. 1700087, Sep. 2017.
[2] J. Guo et al., “Highly Stretchable, Strain Sensing Hydrogel Optical Fibers,” Adv. Mater., vol. 28, no. 46, pp. 10244–10249, Dec. 2016.
[3] A. Leber, B. Cholst, J. Sandt, N. Vogel, and M. Kolle, “Stretchable Thermoplastic Elastomer Optical Fibers for Sensing of Extreme Deformations,” Adv. Funct. Mater., p. 1802629, Dec. 2018.
[4] M. Campbell, P. Singh, K. Kate, and C. K. Harnett, “Controlling Thermoplastic Elastomer Optical Properties by Mechanical Processing,” MRS Advances, vol. 4, no. 23, pp. 1341–1347, 2019.

The development of objects of sensorized clothing in the previous years has been the subject of experiences of affixing sensors extraneous to the textile nature of the fabric, maintaining as a principle of stability of the sensors on the skin the containing effect of the pressure of the fabric on the body; compromising the effective wearability, comfort and usability of the sensorized clothin’objects.
In this framework we present a new method of developing a range of fully textile sensorized clothing items, completely wearable, washable and usable in different contexts: work, sport, defense and health.

The use of a new method and the new materials for the production of fully wearable sensorized clothing items changes the scope of application of the monitoring materials of bio-vital parameters in use, from a purely episodic and professional use, to a continuous widely use.
The industrialization of this technology makes it possible to apply these materials to different sectors of clothing: technical, formal and specialist, expanding the concept of clothing from a need for purpose and function, creating a new and different awareness of users with respect to clothing materials and individual well-being.

The classic prerogatives of clothing materials in covering, decorating, protecting and distinguishing the human body and its social function are changed by the use of these materials, in which the functions of the body's purpose (its own performances) are measured and evaluated, analyzing the basic parameters of organized action no longer on time shifts but by introducing indicators of safeguard and individual well-being.

In the framework we will present concrete cases of the application of these materials and wearable technologies in the industrial, health and sport fields.

We developed 5 um thick ultrathin film MEMS piezoresistive strain sensor for wearable human motion sensors. We made the 5 um thick ultrathin film MEMS sensor on polyurethane film and detected human finger motion.
Thin microelectromechanical systems (MEMS) sensors which is made of very thin ( < 5 μm thick) have been expected for the application to healthcare monitoring, infrastructure monitoring, structural health monitoring of infrastructure, automotive, aircrafts, and other transportation equipment. The advantages of thin (<5 μm thick) MEMS devices are highly flexible, long-term stability, high sensor sensitivity and mass productivity because thin film exhibits smaller bending strain than conventional thick MEMS films and silicon-based devices have not be affected by the atomospher without packaging in compared with organic semiconductor devices.
Thin MEMS sensor assembly of releasing thin MEMS film and transferring thin film onto flexible substrate has been, however, difficult. Previous studies on thin MEMS sensor assembly report the surface machining MEMS structure as a thin MEMS film releasing structure with PDMS stamp. But the adhesive force of PDMS is not stable or applicable to industrial use because vacuum suction type chip mounter is commonly used.
In this paper, we developed the mechanical model of ultrathin MEMS sensor separation and optimize the design of MEMS sensors and connection parts to achieve high yield of thin MEMS sensor chip mounting with commercially available chip mounter. In detail, we analyze plastic-scale-model-like assembly of ultrathin MEMS piezo-resistive strain sensor theoretically and experimentally in order to find an optimal design of MEMS sensor chip for high yield assembly. In the plastic-scale-model-like assembly of ultrathin MEMS sensor, MEMS sensor chip consists of ultrathin piezo-resistive sensor parts, disconnect part, and outer frame and its structure is similar to the plastic scale model. The plastic-scale-model like MEMS sensor chip is fabricated through conventional MEMS process. By using commercially available chip mounter, the MEMS sensor is cut and picked up from the outer frame in the similar manner of plastic-scale-model assembly. Then, the MEMS sensor film was placed and released on the desired area of substrate.
In the chip-mounting mechanical model analysis and experiment, if the number and the width of the disconnection parts are decreased to four and 20 μm, the successful rate of the chip mounting increased to 100 % because the shear stress on those parts are concentrated for ease of cutting and the resultant small load on sensor body reduces bending stress on sensor body for avoiding crack of sensor body. Therefore,in case of 1 mm x 5 mm sensor film, the four connecting parts with 20 um width are optimal design for high successful plastic-model like MEMS sensor assembly.
Finally, we made human finger motion sensor by ultrathin MEMS sensors. The stretchable silver paste is patterned on the Polyurethene film (PUfilm) to make electrode. Then, ultrathin MEMS sensor is placed on the electrode and the edge of the MEMS sensor and electrode is connected by silver paste. Then the hot-melt PU film covers the MEMS sensor for avoiding the break of the sensors. The fabricated MEMS sensor on PU film is attached on the glove and the bending of the human finger was detected.

Recently, emerging technologies like 3D-printing has doped the development of flexible electronics to design foldable displays, bioprosthesis, wearable devices, etc.^1,2 Particularly, stretchable microelectronics able to adopt easily complex shapes like emulating the human body have attracted attention for smart textiles^3,4. To achieve the fabrication of such devices, innovative technologies and new designs involving the use of materials with advanced mechanical properties are required⁵. In this work, the fabrication of lithium nickel manganese oxide (LNMO) micropillar electrodes on Al serpentine interconnects that can be stretched up to 70% without structural damaging has been achieved by laser patterning technique⁶. Unlike compact and continuous electrode thin-films, we show that under mechanical strains, arrays of vertical micropillar supported on serpentines are carrying empty spaces that can prevent the formation of cracks and the electrode delamination.
This innovative approach has been used to fabricate a flexible micro-battery for powering a smart contact lens⁷ and garments. The innovative micro battery approach relies on two flexible substrates assembling consisting of polydimethylsiloxane (PDMS) supporting 1 cm² surface area disk of LNMO and LTO serpentine electrodes separated by a gel polymer electrolyte.

Interestingly, the micro battery shows in the first reversible cycle a charge and discharge areal capacities of 1.22 mAh cm⁻² and 1.196 mAh cm⁻², respectively. The coulombic efficiency for the first reversible cycle corresponds to 96.17%. Regarding the cycling performance, the LTO/ polymer/LNMO micro battery has been assessed at fast kinetics for 30 cycles. The micro battery delivers 73.5 µAh cm^-2 at 6C, 47 µAh cm⁻² at 12C and 32 µAh cm⁻² at 20C with a remarkable stability.



REFERENCE
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³ N. Lu and D.-H. Kim, Soft Robot. 1, 53 (2014).
⁴ S. de Mulatier, M. Nasreldin, R. Delattre, M. Ramuz, and T. Djenizian, Adv. Mater. Technol. 3, 1700320 (2018).
⁵ M. Amani, R.A. Burke, R.M. Proie, and M. Dubey, Nanotechnology 26, 115202 (2015).
⁶ M. Nasreldin, R. Delattre, B. Marchiori, M. Ramuz, S. Maria, J.L. de Bougrenet de la Tocnaye, and T. Djenizian, APL Mater. 7, 031507 (2019).
⁷ M. Nasreldin, R. Delattre, M. Ramuz, C. Lahuec, T. Djenizian, and J.-L. de Bougrenet de la Tocnaye, Sensors 19, 2062 (2019).

Wearable electronics have received considerable attention due to their promising application areas such as health care, human-machine interaction, and wearable computers. In a wearable computing system, application of brain-inspired neuromorphic system can be advantageous as it can simultaneously perform data processing and storage with low power consumption, which is an essential requirement for wearable devices that are powered by batteries. However, conventional solid-state based neuromorphic devices have several problems for application to the wearable applications due to their unsuitable mechanical flexibility under bending or folding condition. To solve these drawbacks, we present fiber-based artificial synapses by crossing two yarns coated with reduced graphene oxide [1]. Reduced graphene oxide is synthesized directly on conductive yarns using electrochemical reduction process, which does not require additional toxic reducing agents. The artificial synapse yarns can emulate several essential synaptic functions of biological synapses, including excitatory postsynaptic current, paired-pulse facilitation, and a transition from short-term plasticity to long-term plasticity. Also, we fabricate 2 × 2 cross-point structure using reduced graphene oxide-coated yarn to confirm the feasibility of integration of artificial synapse for wearable neuromorphic systems. We expect that the yarn-based artificial synapses offer a new possibility in development for wearable neuromorphic systems. In this presentation, artificial synapse characteristics for wearable devices will be presented in detail.

[1] Youngjun Park, Myung-Joo Park, and Jang-Sik Lee, Advanced Functional Materials 28, 1804123 (2018)

Wearable sensing technologies have received considerable interests due to the promising use for real-time monitoring of health conditions. The sensing part is typically made into a thin film that guarantees high flexibility with different sensing materials as functional units at different locations. However, a thin-film sensor easily breaks during use because it cannot adapt to the soft or irregular body surfaces, and, moreover, it is not breathable or comfortable for the wearable application. Herein, a new and general strategy of making electrochemical fabric from sensing fiber units is reported. These units efficiently detect a variety of physiological signals such as glucose, Na⁺, K⁺, Ca²⁺, and pH. The electrochemical fabric is highly flexible and maintains structural integrity and detection ability under repeated deformations, including bending and twisting. They demonstrate the capacity to monitor health conditions of human body in real time with high efficacy.

Electronic textiles have integrated life of human being with highly developed electronic devices in an innovative way, enabling wearable electronics for displaying bio-medical information and illuminative textiles for smart fabric or internet-of-things applications. Light-emitting devices on textiles can display bio-medical signals immediately via integrating with health-monitoring devices or notify information using a luminous carpet. Although, in order to realize “real” textile displays, flexibility, lightweight, and breathability are necessary for skin-conformal electronic devices, various prototypes of commercial products still have been focused on rigid silicone-based devices. Recently, many research groups have reported flexible light-emitting devices directly implemented on the fabric or fiber. The alternating current electroluminescent (EL) devices on fiber substrate have been reported, whose device configuration is quite simple compared to other EL devices, however, low power efficiency demands high driving voltage up to hundreds volts, which limits practical use. Organic light-emitting diodes on fabric substrate showed good mechanical properties based on its ultra-thinness, but they have low breathability because of additional planarization layers for evaporation process. In addition, high process temperature in the fabrication causes inevitable deformation in the textile substrate. While, polymer light-emitting diodes (PLEDs) has good advantages of low-voltage operation and low temperature process available. And, since the light-emitting polymer is compatible with solution processes, fiber-shaped PLEDs and the corresponding woven structure can be developed without any breathability loss. Although some papers have already reported fiber-shaped PLEDs, a practical integration with thin-film transistor (TFT) has not been reported yet. Some technical challenges such as low device performances should be also addressed.
In this work, we report development of solution-processed PLEDs on a plastic fiber substrate and its TFT-driven operation for textile displays. Specifically, we fabricated the fiber PLEDs on polyethylene terephthalate (PET) fiber, which is flexible and weavable for textiles. By controlling the condition of dip coating of PET fibers, such as withdrawal speed and coating number, we can obtain poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) anode, which has resistance of 200 ohm/mm for 5 times dip coating. Then, PEDOT:PSS hole-injection layer and SPG-01T emissive layer are successively dip coated. After then, lithium fluoride and aluminum are thermally evaporated for an electron-injection layer and cathode, respectively. The device shows a turn-on voltage of 4.8 V at 1 cd/m², a current efficiency of 4.58 cd/A at 1000 cd/m², and luminance of ~4000 cd/m² at 10 V, enabling low-voltage operation for highly luminous display applications. Finally, we integrated fiber PLEDs with fiber TFTs that are also fabricated by a solution process on a PET fiber, showing the feasibility of our devices in textile displays. The detailed fabrication process and experimental results will be discussed at the conference.
This research was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-IT1801-07. This work was also supported by the OLED (Organic Light-Emitting Diodes) center of Samsung Display Corporation and ISRC (Inter-University Semiconductor Research Center) of Seoul National University.

Thermal regulating textiles play a very important role in providing thermal comfort for human beings in temperature changing environments. The level of thermal comfort depends on the heat exchange between the human body and the surrounding environment. The thermoregulatory effect can be achieved by dispersing microcapsulated phase change materials (PCMs) into the textiles. As these materials have ability to lower the temperature of the body, besides wearing comfort they can improve thermal concealment properties of nowadays defence personnel military camouflage clothing.
Various types of phase change materials (PCM) are currently used in the production of smart materials capable to actively control the temperature of the body. Studying the thermoregulatory effects of PCM treated textiles and their multi-layer assemblies is fundamental for the effective use of such smart thermal functional textiles [1, 2].
In the present work two types of commercially available microcapsules of organic phase change materials were investigated in order to improve the thermo-regulating properties of textile fabric. The first type of PCMs, namely type PCM-A (PCM microcapsules –Mikrathermic P, developed by DEVAN® Chemicals NV, Belgium), demonstrates chemical activity to all kinds of fibres without the use of a binder. The second type of PCMs, type PCM-B (Ito finish PCM microcapsules, LJ Specialities LTD, UK) was embedded into the textile by means of an acrylic binder as cross linking resin.
For samples preparation, the knitted fabric, produced from cotton/PES, intended for contacting layer near the skin, were treated by PCM microcapsules using pad-dry-cure method.
After sample preparation, melting point and latent heat storage capacities (enthalpy ΔH, J/g) of PCM microcapsules and the corresponding treated knitted fabrics were characterized, using differential scanning calorimeter equipped with a nitrogen-based refrigerated cooling system.
The IR emissivity of the PCM-based textiles has been characterized by means of Infrared Thermography according to the ASTM E1933-99a standard method [3] in the contact-free configuration. In the adopted method, a small portion of sample is covered with a thin layer of a reference paint with known emissivity.The textiles samples were placed onto a heating stage, which is also equipped with a Peltier modulus in order to set their temperature below and above phase transition temperature of PCMs. During measurements samples and reference paint were simultaneously imaged by the IR camera, operating in the 3.5-5.1 μm range, and from the resulting thermographic images the infrared (IR) emissivity was characterized before and after PCMs phase transition.
Experimentally obtained data show an emissivity increase with increasing temperature, as a consequence of additives’ phase transition. Furthermore, the emissivity dynamic range (ε_hot-ε_cold) for the three samples containing type-A additives show anti-correlation with melting enthalpy values, i.e. the higher enthalpy corresponds to lower emissivity variation, along the phase transition. The observed features open the way to potential applications such as tunable emissivity smart textiles and pave the way to the design of customized IR shielding textiles, by proper selection of the suitable additives type and amount.

[1] B.A.Ying, Y.L.Kwok, Y.Li, C.Y.Yeung, Q.Y.Zhu, F.Z.Li, “Computational Investigation of Thermoregulatory Effects of Multi-layer PCM Textile Assembly”, Studies in Computational Intelligence (SCI) 55, 235-245 (2007).
[2] D. Celsar, “Influence of Phase-change Materials on Thermo-physiological Comfort in Warm Environment”, Journal of Textiles vol.2013, 757319 (2013).
[3] ASTM E1933-99a, “Standard Test Methods for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers”, American Society for Testing and Materials International, West Conshohocken, PA (1999).