Symposium MA05 : Dynamic Materials and Textiles for Next-Generation Clothing

A wide range of materials and design concepts are now available for microsystems technologies that can softly interface with the human body. The physical properties of these systems – thin, lightweight construction and low modulus, elastic mechanics -- also enable direct integration onto compliant fabric substrates, as thin laminates. Results presented in this talk focus on the combined use of thin, ultralow modulus, cellular silicone materials with elastic, strain-limiting fabrics, to yield soft and flexible, but rugged, wearable platforms for stretchable electronics/microfluidics. Theoretical and experimental studies highlight the mechanics of adhesion and elastic deformation in these systems and provide design rules for engineering artificial fabric structures with optimized properties. Demonstration examples include wireless electronics for measuring hydration state, electrophysiological activity, motion and blood oximetry.

The development of flexible electronics and equipment attracts significant interests in recent years. It is of great importance to explore low cost and scalable preparation approaches for high performance flexible and wearable electronics. Silkworm silk, with five thousand years’ usage history, is a popular natural material for clothes or wearing accessories. In this talk, I will present our work on exploring the application of silk fiber/fabrics in flexible electronics. We demonstrated that carbonized silk fabric with a plain-weave structure, based on its unique N-doped graphitic carbon nanostructure and the macroscale woven structure, could be worked as strain sensors with both of high sensitivity (gauge factor of 9.6 in the strain range of 0%-250% and 37.5 in the range of 250%-500%) and high tolerable strain (more than 500%). The as-obtained sensors have fast response (<30 ms) and high durability (>10,000 cycles). It was demonstrated that such strain sensors could be used for monitoring both of vigorous human motions (such as jumping, marching, jogging, bending and rotation of joints), subtle human motions (such as pulse, facial expression, respiration and phonation) and even sound, and further demonstrated the capture and reconstruction of human body movements with our sensors, showing their superior performance and tremendous potential applications in wearable electronics and intelligent robots. Besides, transparent electronics skins, elastic thermal therapy devices, stretchable wires and stretchable energy devices based on silk materials will also be demonstrated. These strategy paves new ways for the low cost and large scale fabrication of high performance wearable strain sensors.

Refrence：
Chunya Wang, Mingchao Zhang, Kailun Xia, Xueqin Gong, Huimin Wang, Zhe Yin, Baolu Guan, and Yingying Zhang*. Intrinsically Stretchable and Conductive Textile by a Scalable Process for Elastic Wearable Electronics. ACS Appl. Mater. Interfaces 2017, 9 (15), 13331–13338.
Qi Wang, Muqiang Jian, Chunya Wang, Yingying Zhang*. Carbonized silk nanofiber membrane for transparent and sensitive electronic skin. Advanced Functional Materials. 2017, 27,1605657.
Muqiang Jian, Kailun Xia, Qi Wang, Zhe Yin, Huimin Wang, Chunya Wang, Huanhuan Xie, Mingchao Zhang, and Yingying Zhang*. Flexible and Highly Sensitive Pressure Sensors Based on Bionic Hierarchical Structures. Advanced Functional Materials. 2017, 27,1606066.
Mingchao Zhang, Chunya Wang, Huimin Wang, Muqiang Jian, Xiangyang Hao*, Yingying Zhang*. Carbonized Cotton Fabric for High Performance Wearable Strain Sensors Advanced Functional Materials 2017, 27, 1604795.
Chunya Wang, Xiao Li, Enlai Gao, Muqiang Jian, Kailun Xia, Qi Wang, Zhiping Xu, Tianling Ren, Yingying Zhang*. Carbonized Silk Fabric for Ultra-stretchable, Highly Sensitive and Wearable Strain Sensors. Advanced Materials 2016, 28, 6640.

Thermally managing the body’s heat flow is important for working efficiently indoors and outdoors. Power radiated by the human body is in the 7-12 μm Longwave Infrared (LWIR) regime. By using textiles that release heat in warm environments, and trap heat in cold environments, one can work at higher activity levels, and not sweat profusely or lose dexterity, respectively. Saharan ants reflect sunlight and emit infrared (IR) through special fiber-like hairs. We manipulate the IR to manage temperature, building on successful temperature-adaptive insulation research with temperature-dependent fiber shape changes.¹

Fibers may absorb/reflect/backscatter LWIR too strongly, keeping a textile-wearer hot in warm climates. We investigate and control heat flow through these fibers and related films. Materials like ultra-high molecular-weight polyethylene absorb less IR radiation, and nano-structured- and micro-fibers alter IR scattering properties, permitting radiative cooling.² New research has shown that nanomaterials can substantially modify blackbody emission, produce unusually large scattering and reduce unwanted IR absorption. We seek fibers that expand and contract in a cephalopod-like fashion to enable a textile with temperature-adaptiveness, perhaps due to fiber-compatible semiconductor-carbon thermoelectric materials with a temperature differential-controllable electrical output.³

We designed, fabricated, and analyzed polymer fibers and films for thermal absorption, emission, and scattering to enable radiative-cooling and heat-trapping textiles. The IR response of films with sub-monolayer nanoparticle arrays enabled design of temperature-responsive fibers. To control the LWIR, we mixed ultra-high-molecular-weight, medium-density, and low-linear-density polyethylene in different ratios in single-filament fibers with diameters in the range of 100 μm. These fibers were melt-extruded in a micro-compounder and incorporated uniformly 5 types of nanoparticles (which were scalable to high volume processes): silica, TiO₂, Si, cephalopod granules, and Ag, with sizes 60 nm, 500 nm, 2 μm, 500 nm, and 120 – 300 nm, respectively; different concentrations and polymer-only fibers were also analyzed. Individual fibers were characterized (composition and surface morphology) and measured with visible light and IR micro-spectrophotometry;1-d stripes of these fibers revealed thermal properties of a textile. We quantified and controlled IR scattering (not just reflectivity/transmission, as has been found in a recent investigation) to understand absorption for models/predictions of thermal transport across fiber arrays into the body. Fibers of a construction-grade polyethylene fibrous fabric were found to have high LWIR transmission, and were a positive control. Si nanoparticles were found to strongly scatter IR.

[1] B. DeCristofano, S. Fossey, et. al., Proc. MRS (2011) 1312.
[2] J. Tong et.al. ACS Photonics 2 (2016) 769.
[3] G. Fernandes et. al., Nanotech. (2012) 135704.

We will discuss design, fabrication and applications of a new family of flexible polymer metamaterials (films and fabrics) with spectrally tailored transmittance, reflectance and absorptance. Starting with our pioneering conceptual proposal of fabrics that are opaque in the visible yet transparent in the infrared (1), we continue exploring textiles that block certain parts of thermal and solar energy spectra and their exciting applications in thermal management of individuals and infrastructure via passive thermal emission (2,3). Passively cooling fabrics are opaque to the eye and reflect sunlight, while simultaneously allowing the body heat to efficiently dissipate via both radiation and convection. In turn, fabrics reflective in the infrared can help in retaining radiative body heat and providing thermal camouflaging. We will report on our on-going efforts in the fabrication and testing of fibers and textiles that – depending on their structural design – provide either passive radiative cooling or infrared signature control. We will also discuss approaches to coloring fabrics while maintaining their transmittance characteristics.
1. J. K. Tong et al., Infrared-transparent visible-opaque fabrics for wearable personal thermal management. ACS Photonics. 2, 769–778 (2015).
2. S. V. Boriskina, Nanoporous fabrics could keep you cool. Science. 353, 986–987 (2016).
3. S.V. Boriskina, et al, Heat is the new light. Optics and Photonics News, 26-33, Nov. (2017).

The field of computational design in architecture commonly focuses the formulation of design tools that facilitate control over the relationships between advanced manufacturing and material structure. This allows for technical efficiencies and design opportunities to be achieved in aligning material, structural and architectural performance. The research discussed here follows this material-driven practice through exploring the architectural potentials that emerge through the use of advanced textile manufacturing technologies, particular through CNC knit manufacturing. More critically, though, this research engages sensorial experience as a driver for the design and engineering of material performance and architectural responsivity. This is explored as a part of the Social Sensory Architectures research project, through the articulation of tent-like textile hybrid structures and their application to the development of skills in motor control and social interaction for children with autism spectrum disorder (ASD).

The ability to formulate and execute patterns of movement, through feedback between motor commands and sensory data, is pivotal to the development of social behaviour. The relationship between movement and its sensory consequence forms an understanding of the intentions of movement and, ultimately, provides the knowledge that allows the interpretation of other people’s gestures. For children with autism,
learning new patterns of movement is most reliant on proprioceptive feedback – sensation from muscle and joint articulation to determine position and orientation of the limbs and body. Visual stimulation has a secondary impact, meaning the non-physical stimuli can often play a less influential role. To synthesise movement and social behaviour, the multi-sensory nature of the playscape prototype is focused most heavily on its tactile qualities. This operates through multiple scales and in the instrumentalisation of elasticity at each scale. One level attends to forming skills for grading of movement, the ability to assess and execute the appropriate amount of pressure needed to
complete a task. Yarn, variegated stitch structure and the calibration of tensile forces generate an increasingly magnified tactile feedback as one pushes on the surfaces to greater depths. Another level of engagement corresponds to movement of the body through space and
time, the proprioceptive and vestibular senses that guide orientation and pace. The calibration of the pre-stressed textiles, laminated GFRP beams and spatial arrangement generates the combined experience of localised pressure at the interaction of the body with the textile and
minimised (though recognisable) deflection at the scale of the entire material system. Elasticity is tailored to satisfy deeper sensations of touch and register fine and gross movements. Correlation with the visual and auditory landscape fosters continual variability and saliency.

There have been growing interests in multi-functional wearable electronic textiles (e-textiles) due to their potential applications in sportswear, military uniforms, environmental monitoring and health care. Currently, metal inks based on Ag, Cu or Au are most commonly used materials due to their higher electrical conductivity. However, metal inks are very expensive, toxic and not-biocompatible; oxidise rapidly and require higher sintering temperature. Graphene, a single atom thick two-dimensional closely packed honeycomb lattice of sp² carbon allotropes, is considered to be one of the most promising materials for fabricating flexible wearable electronics due to its unique physical and chemical properties such as large surface area, record thermal conductivity, excellent mechanical strength and superior electronic mobility. In addition, graphene-based inks such as reduced graphene-oxide (rGO) can produce durable, washable and potentially more environmental friendly e-textiles due to the hydrogen bonding between hydroxyl groups in cotton and residual oxygen containing groups in reduced graphene oxide (rGO). Recent studies have shown promise for fabricating next generation graphene-based e-textiles. However, these are based on time and materials consuming multiple dip and dry or vacuum filtration techniques, graphene/metal composite inks, higher post reduction temperature and the use of toxic reducing agents such as hydriodic acid, sodium borohydride and hydrazine. Here we report a simple, scalable and environmental friendly process of manufacturing next generation multi-functional graphene-based wearable e-textiles. We use a simple pad dry technique to produce graphene-based conductive textiles, which could potentially produce textiles at very high commercial production rate (150 m/min). The graphene e-textiles thus produced are durable, washable and flexible with enhanced tensile properties. We demonstrate multifunctional uses of these graphene e-textiles such as flexible supercapacitors, heating elements and various sensors.

The fast development of wearable sensors has been promoted by the broad needs for real-time monitoring the metabolism, bodily functions non-invasively and the air quality in the environment by aging populations, soldiers, working professionals, etc. Interests in many wearables electronic sensors, which started with high expectations, however have seen a decrease over time, due to the needs of frequent charging of batteries in practical usage. Wearable colorimetric sensors, using optical read-out signals under ambient light without any electronic components, become highly advantageous. However, creating conventional dye- or chemical-based colorimetric sensors with high sensitivity and selectivity usually requires complicated synthesis process. Here we report an adaptive colorimetric sensing platform based on a bulk structure of covalently bonded hydrogel thin film-substrate system. The dynamic coloration arises from the interference of reflected light on air-hydrogel and hydrogel-substrate interfaces, and can be flexibly tuned in a broad spectral range. External stimuli from the analytes can rapidly change the thickness of the hydrogel film, resulting in an instant color change. We have built theoretical models that capture the key chemo-mechano-optical process occurring in the dynamic materials, mainly the mechanics of the chemical-induced hydrogel volume phase change and the interference-based coloration governed by 2ndcosθ = mλ, showing good agreement with experimental results. The soft and high stretchable robust synthetic hydrogel materials can form a highly compliant contact to human epidermis and has good self-recovery capability, as an ideal candidate for soft matrices of wearable devices. Also, this colorimetric sensing platform allows for in situ quantitative analysis by naked eye or camera via analysis app, as a wireless wearable sensing component for the next-generation textile. Moreover, we have shown this customizabile adaptive platform can detect a large variety of analytes including cations for hydration and other physiologic metabolic state monitoring, Cu²⁺ for Wilson's disease prescreening, glucose for diabetes monitoring, and sulfur dioxide and nitrogen dioxide for air quality detecting. This sensing platform showed a high performance on the sensitivity and response time. The limit of detection for Cu²⁺ could reach as low as 10.0 pM with only 1-2 second. Such high performance is attributed by this unique chemo-mechano-optical signal transduction mechanism, which effectively amplifies the nm-scale hydrogel thickness change to a greater and more detectable optical spectrum change. This will lead to a broad platform of a new class of wearable sensors with superior performance at low cost.

An electronic textile and wearable electronic have attractive much attention, because it is effective for the sensors to be close in contact to the subject in order to measure biometric information with precision. Thus, stretchable wires that are compatible with fabric substrate are intensively studied. In particular, printable elastic conductors are expected to play an important role to fabricate large-area stretchable sensor/actuator networks on fabric and elastomeric substrates. In this presentation, we report recent progress of printable elastic conductor for smart apparel and wearable electronics applications. Our elastic conductors are fabricated by mixing Ag flakes with the typical sizes of a few micrometers, fluorine rubbers, and surfactant. Containing. We found that Ag nanoparticles are formed in situ after printing and annealing processes. Our printable elastic composites exhibit conductivity of 935 S cm-1 when stretched up to 400%. Ag nanoparticle formation, which is the key to achieve a drastic improvement of conductivity, is controlled by the surfactant, heating processes, and elastomer molecular weight. Fully printed sensor networks with elastic conductors are demonstrated for e-textile and wearable electronic applications.

The development of wearable chemical sensors is receiving a great deal of attention in view of achieving active, non-invasive and continuous monitoring of physiological parameters for healthcare applications. In this scenario, Organic Electrochemical Transistors (OECTs) are emerging devices displaying peculiar features that are very appealing for the design of fully integrated wearable sensors. This contribution wants to show two strategies based on OECTs with the aim to realise high throughput wearable sensors that could be comfortably worn thanks to the suitable mechanical features of the material of choice (flexibility, light weight and stretchability).
Firstly, we describe the development of a fully textile, wearable chemical sensor based on an OECTs entirely made of the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) for biomarkers detection [1]. The active polymer patterns are deposited into the fabric by screen printing processes, thus allowing the device to actually “disappear” into it. We demonstrate the reliability of the proposed textile OECTs as platforms for developing chemical sensors capable to detect in real-time various redox active molecules (adrenaline, dopamine and ascorbic acid). To this aim their performance was assessed in two different experimental contexts: i) ideal operation conditions (i.e. totally dipped in an electrolyte solution); ii) real-life operation conditions (i.e. by sequentially adding few drops of an electrolyte solution onto one side of the textile sensor). The OECTs response has also been recorded in artificial sweat, assessing how these sensors can be reliably used for the detection of biomarkers in body fluids.
Furthermore, inspired by OECTs technology, we propose a new approach based on an innovative material that allows operating with an only two terminals device, while maintaining the amplification provided by a transistor configuration. To this end, design and synthesis of a novel composite material based on Ag/AgCl nanoparticles (NPs) and PEDOT:PSS have been carried out to integrate the transduction features of Ag/AgCl into the semiconducting polymer. We have fabricated a wearable sensor by directly depositing Ag/AgCl NPs on a cotton yarn, previously modified with PEDOT:PSS, and assessed its performance as chloride sensor. The single-fiber textile sensor exhibits a logarithmic response to increasing Cl^- concentration and its reliability was assessed by comparison with a planar sensor. Finally, no interference was observed for the Cl^- determination when different chemical compounds were added to the sample at their typical concentration in human perspiration.

Reference
[1] I. Gualandi, M. Marzocchi, A. Achilli, D. Cavedale, A. Bonfiglio, B. Fraboni, Scientific Reports, 2016, 6, 33637.

New materials are required for the fabrication of advanced multifunctional garments that allow high moisture vapor transport rates (MVTR) while blocking toxic chemicals and biothreats. In particular, for in-the-field personnel protection from chemical and biological (CB) agents, smart dynamic materials are highly desirable that exhibit a reversible, CB-triggered, rapid transition from a breathable state to a protective state. High breathability is a critical requirement for protective clothing to prevent heat-stress and exhaustion. Current protective military ensembles cannot meet the critical demand of simultaneous high comfort and protection, and provide a passive rather than active response to the environmental threat.
Toward the realization of this new paradigm of adaptive protection, we are developing a chemical threat responsive material based on a surface-functionalized carbon-nanotube (CNT)-membrane, in which vertically-aligned CNTs function as the only pores in an otherwise impermeable, polymeric film. Response to the threat is designed to be triggered by direct chemical warfare agent (CWA) attack to the functional groups at the membrane surface, upon which the membrane switches from a highly breathable state in no-threat environment to a protective state by closing the CNT pore entrance to CWA permeation.
To demonstrate this concept, we first fabricated membranes with sub 5-nm CNT pores and quantified their breathability and rejection properties before functionalization with CWA-responsive polymers. Our results show that these membranes provide MVTR up to 11,000 gr/m²day, thus exceeding state-of-art breathable fabrics (eVent, GoreTex, etc.) even if the moisture conductive pores are only a few nm wide. Complete rejection of 3-nm charged dyes, 5-nm uncharged gold nanoparticles, and ~40-60-nm Dengue virus from aqueous solutions during filtration tests demonstrates that our CNT membranes provide a high degree of protection from bio-threats by size exclusion [1].
Then, we covalently grafted actuating polymers responsive to G-agent simulants to the surface of these CNT membranes. Upon exposure to simulants, these membranes switch from a breathable state with MVTR> 4,000 gr/m²day to a protective state with MVTR> 1,000 gr/m²day. Initial permeation tests reveal that simulant transport is also reduced by 90% in the protective state. Finally, we demonstrated that a simple liquid base treatment reopens the CNT pores effectively and that regenerated membranes can be re-used for multiple cycles without performance loss.
These results suggest that CNT membranes functionalized with CWA-responsive, actuating polymers could indeed combine on-demand protection with high breathability in a single multifunctional material, and achieve the goal of a lighter, cooler, smarter protection of military and civilian personnel in CB contaminated environments.

In recent years, the integration of electronics in textiles has gained increasing attention worldwide. Many industry driven projects have already been started in this area on national as well as on European level. In order to enable industrial manufacturing of wearable smart textiles it is necessary to develop modular concepts as well as integration processes suitable for high volume production. By introducing new concepts for textile substrates, electronic packaging as well as textile-integrated sensors and actuators, more comprehensive smart textile systems will be possible.
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. For these applications sensors can be textile based but also miniaturized conventional sensors can be required. Different polymers and metals can be used as yarns, printable pastes or foils to realize a broad range of measurement principles. While the performance of textile and polymer sensors cannot compete with conventional sensors, the mechanical properties of these materials allow completely new applications, e.g. in strain measurements.
The mechanical reliability is essential for smart textiles. Especially different degrees of stretchability and drapeability have to be achieved while maintaining the sensor properties. This presentation describes and compares different technological approaches for conductor integration sensor and actuator integration in textiles. It also introduces a new technology for Textile Circuit Boards with improved mechanical and electrical performances by embedding structured conductive textiles into a matrix of thin thermoplastic elastomers films. This new approach also allows the realization of actuators.

Closed-cell foams are widely applied as the material of choice for thermal insulation, which is essential for the thermal management of buildings, organisms, and many industrial processes. Foam insulation is often comprised of a polymeric matrix with dispersed, closed cells that are filled with an insulating gas. We develop and demonstrate a processing technique for replacing the typical fill gas with a variety of high-molecular-weight, superior insulating gases for significantly improved insulation. We focus on neoprene foam, which is a closed-cell synthetic rubber foam with a thermal conductivity of 0.050-0.060 W/m-K. With our processing technique, we achieve a thermal conductivity of as low as 0.031 W/m-K for neoprene foams, the lowest value that has been measured for neoprene foams to date. We show that this reduction in thermal conductivity can be accurately predicted by analytical models and numerical simulations. A simple Fickian diffusion model describes the processing technique and agrees well with experimental data. Finally, we demonstrate that similar reductions in thermal conductivity can be realized for neoprene in the form factor of a wetsuit using our simple charging procedure. Whereas conventional wetsuits allow divers to spend only 15-30 minutes in cold water (<10 °C) before they become vulnerable to hypothermia, the results in this work could enable divers to safely spend 2-3 hours in the water.

Metal oxide nanoparticles are important for a variety of applications including catalysis, photocatalysis, gas filtration, gas sensing, and improving the physical properties of materials. The development of methodologies to fabricate textiles covered with metal oxide nanoparticles has potential benefits for Soldier protection. Previous investigations using bi-component melt extrusion were conducted to explore the ability to incorporate metal oxide nanoparticles within polypropylene (PP) fibers. That effort showed that only relatively small concentrations of metal oxide nanoparticles are on the surface of the PP fibers and that these particles are inactive for adsorption and photocatalysis. Based on those findings, a new effort is underway which focuses on the fundamental research to understand and optimize surface segregation and diffusion of metal oxide nanoparticles within polymer films and fibers. Success of this research has the potential to lead to methods to extrude blends of polymers and metal oxide particles such that the extruded fibers have surfaces that are decorated with high concentrations of active particles. Scanning electron microscopy and surface science techniques are being used to understand how parameters such as the nature of the polymer, the type and shape of the nanoparticles, and temperature affect surface segregation of metal oxide nanoparticles in polymeric fibers and films. Annealing techniques were used in an attempt to affect surface segregation in PP fibers containing ca. 3 wt. % ZnO nanorods and nanospheres. Annealing at temperatures as high as 140^°C did not result in appreciable migration of the nanoparticles to the periphery of the fiber. The reason for this lack of surface segregation may likely be due to the high molecular weight of the polymer, with the long chains impeding particle mobility. Based on these findings, surface segregation studies of ZnO nanospheres in low molecular weight PP films is currently being investigated. The amount of surface segregation, as determined by X-ray photoelectron spectroscopy (XPS), was found to depend on the annealing atmosphere, with greater oxygen content leading to greater surface segregation. XPS revealed that the PP surface was partially oxidized upon heating in oxygen-containing atmospheres, resulting in carboxylate groups that helped drive the segregation.

Fiber membranes with unique functionalities has been developed to spur both academy and industry in filtration, clothing, and bio-medical fields. Now, many researches are aiming to fabricate multi-functional membranes for advanced applications. Bonding several functional membranes provides a facile way to fabricate a multi-functional membrane with high engineering and commercial values. The adhesives for bonding fiber membranes require both strong bonding characteristic and minimal effect on the structures and functionalities, because the functionalities of fiber membranes mainly comes from the base materials, coatings, porous structure, and dimensions, etc. Moreover, most commercialized adhesives with high bond strength and high water resistance are often derived from depleting petrochemical resources, which involves volatile organic compounds or other toxic compounds and causes environmental problems. In addition, as many functional membranes are used in biomedical applications, developing environmentally friendly and biocompatible adhesives are strongly required. Therefore, the development of natural and abundant source adhesives possessing excellent bonding characteristics is an industrial challenge and an important edge of the research field of adhesives. Here, we used chitosan as an adhesive for bonding several membranes into a multi-layered membrane. Chitosan is natural abundant bio-polymer obtained by alkaline deacetylation of chitin, abundant in crustaceans or insects. Chitosan is biocompatible as it has chemical structure of β-(1-4)-linked D-glucosamine and N-acetyl-D-glucosamine. Use of commercialized adhesives for bonding fiber membrane would result in loss of their original structure, porosity, and functionalities. However, novel chitosan bonding technique combined with vacuum filtration process enables to keep the structure, porosity, and functionalities of fiber membrane with minimal changes. In details, chitosan solution was applied on a fiber membrane and the membrane was filtered by aid of vacuum filtration, which lead to allocate chitosan on the interconnected area among the fibers. Post cross-linking process by using glutaraldehyde was applied to enhance the bonding strength and water resistance of adhesives. The tensile strength of adhesive was 0.7040 N/mm, which was about 4 times stronger than the tensile strength of a polypropylene membrane (0.1697 N/mm). Chitosan bonded multi-layer membrane retained their original flexibility and hydrophilicity. The novel chitosan bonding technique allows to fabricate multi-layer (up to 5 layers), multi-scale (fiber dia. From hundred nanometer to sub micron), multi-functional (air and water filter, drug delivery, antiadhesive) membrane. Due to its fast and facile bonding process, this technique will spur the development of multi-functional membranes.

Ultrafine electrospun fibers have been utilized in numerous applications including tissue scaffolding, energy storage, sensing, and water treatment. However, randomly oriented nonwoven fiber mats from conventional electrospinning can be easily tear apart, limiting their broader uses and scaling up. To make it mechanically strong, electrospinning set up was modified in order to align and group single fibers together as a yarn which is knittable, and can be prepared in wide range of complex structures. In this work, continuous electrospun yarns were prepared by electrospinning of Polycaprolactone (PCL) from 2 spinnerets spun toward a rotating funnel. The polymer jets were solidified and assembled at the funnel before it was continuously withdrawn as a long fiber bundle. Beside the setup component position, solvent type was found to have a large effect on polymer jet stability and continuous process of yarn manufacturing. The tensile strength of obtained PCL yarn was significantly higher than that of PCL nonwoven mat, and it could be hand-braided, indicating their potential as a knittable yarn. Plying was applied to PCL yarn to achieve a better mechanical performance, and we found that PCL cords was strong and comparable to commercial yarns. We successfully knitted PCL cords by a computerized knitting machine, fabricated fabrics entirely from nanofibers. With high surface area, high porosity and nanoroughness, these fabrics can enhance functionalities leading to novel wearable technologies such health monitor and energy storage cloth. Furthermore, with a modification of electrospinning setup, we produced core-sheath yarns by inserting a commercial yarn as a core. It provides mechanical robustness which would bring the nanotechnology to human scales.

In the United States, thousands of patients are admitted into emergency departments due to work-related musculoskeletal knee injuries, many caused by overexertion from extended period of squatting, heavy lifting, and climbing. Significant structural injuries of the knee often require multiple surgeries and long rehabilitation periods. The postoperative progress made by patients during rehabilitation is largely self-reported, as is the extent of physical strain a worker experiences. Overexertion and inattentive rehabilitation may be prevented through continuous quantitative monitoring of patients’ physical activity and rehabilitation progress. However, systems to actively monitor the biomechanics of a knee throughout the rehabilitation process or workday in a continuous manner are not currently available.
We have developed a device of textile strain sensors integrated into a knee brace to provide this continuous monitoring. Mechanical and electronic characterization of resistive and piezoelectric textile sensors developed for this application will be presented. Prototype devices including biomechanical data and design considerations for comfort and performance will also be presented. Preliminary correlations between strain data and rigorous knee flexion movements will also be discussed with implications for knee injury prevention and recovery monitoring. These developments, while targeted for knee flexion monitoring, can be translated to many common physical ailments including ankles, wrists, elbows, shoulders, and backs.

Metal-Organic-Frameworks (MOFs) are molecular latticework structures composed of organic linking molecules (linkers) bonded with inorganic nodal unites (nodes). We recently developed a computer algorithm that uses grammatical evolution to design, without human supervision, MOFs with kinematically active linkers. In this work we dissect the folding mechanisms employed by the most successful MOFs that the computer designed. Large scale molecular dynamics simulations were performed of MOFs collapsing under pressure and cooperative patterns of linker folding and node rotation identified. By analyzing the patterns of folding we assess the diversity of kinematic strategies that the computer algorithm discovered. We comment on the applicability of this approach to the design of other mechanically active polymers.

Acknowledgments: The authors acknowledge the support of the W.M. Keck Foundation and the National Science Foundation.

In recent years, there has been an increasing demand for fibers and textile materials with integrated sensing and monitoring capabilities. One possible solution for producing multi-functional fibers is near-field electrospinning (NFE). This direct-write fabrication approach enables fast, yet precise positioning of micron-sized fibers for low-cost, scalable manufacturing. In addition, NFE is able to merge the strength and durability of polymers with the additional functionality of emitters for optically active sensing and/or receptors for enhanced selectivity. Here, fluorescent dye-doped polymer fiber sensors that support whispering gallery mode (WGM) resonance within the fiber cross-sections were fabricated and their sensing ability was demonstrated. Dye-doped polymer solutions were mixed, and were rheologically and optically characterized to determine the solution that would produce fibers with high quality (Q) resonance. Fibers were fabricated using NFE to draw fibers onto a substrate from a 25 wt% poly(vinyl) alcohol polymer solution doped with 1.74 mM rhodamine 6G. The substrates were patterned with deep trenches to prevent unwanted optical coupling, thus allowing WGM resonance to occur. The effect of different NFE parameters such as stage speed and applied voltage on fiber diameter was studied. The resulting fibers ranged from 2 to 22 µm in diameter and displayed circular cross sections. Using microphotoluminescence, resonant peaks with high Q factors (Q > 14,000) were measured in the wavelength range of 590 – 640 nm. Using size-dependent mode spacing predicted by finite-difference time domain simulations, the resonances were identified as first order WGMs. Each centimeter of fiber containing several resonators and the likelihood of finding a resonator in a suspended region of fiber was determined to be above 90%. Furthermore, isopropanol vapor sensing experiments confirmed the ability of the electrospun WGM fibers to detect small changes in the surrounding environment. The fibers fabricated here have demonstrated the potential of near field electrospinning to manufacture fibers with incorporated functionality for sensing and monitoring textile applications.

In the field of safety at work, there is the need to develop a system able to monitor the activity of manual workers, in order to prevent serious hands’ injuries during the working activity. In parallel, athletes that use repetitive movements of the hands, i.e. tennis players, may benefit of a technology able to record non-invasively hand motion in real time in order to improve their athletic performance and prevent accidents. Indeed, uncomfortable positions, high force stress, prolonged repetitions or combination of these elements, are risk factors for musculoskeletal disorders.
Actually, the most common methods used to identify the risks’ activities, are based mainly on empirical observations, supported by subjective evaluation or trough video analysis. However, the video method results often complicate and difficult to be interpret. In this context, the recent development of wearable sensor systems for healthcare applications give rise to an innovative alternative. Focusing the attention on the hand injuries, sensors pressure implemented directly on gloves are a promising technology in continuous development.
The main constrain for the proposed applications is to fabricate gloves that can be easily worn, that is imperceptible and does not alter or hinder the normal activity of the hands by worker or athletes. In addition, the pressure sensors have to be opportunely tuned to guarantee high sensitivity in a wide pressure range, to account for all the different hand’s activities.
In this contribution, we report a new generation of textile pressure sensors based on PEDOT:PSS fabricated by screen printing directly on gloves for monitoring hand activity. The architecture and sensor design ensure lightway, robust, thin and non -invasive gloves, which, once worn, do not affect the normal mobility of hands.
Moreover, we carried out a detailed investigation on the PEDOT:PSS piezoelectric behavior and on the working principles of the developed textile pressure sensors, and we demonstrate the ability to tune the operating pressure range simply by changing the conductive ink formulations, leaving the same architecture and structures. The here proposed tunable sensorized gloves pave the way for a new generation of smart textiles in a field, such as the safety in work place, that is in continuous increase of interest.

Cardiovascular diseases and neurological disorders form the majority of diseases that need periodic or constant medical attention. Such continuous monitoring requires non-invasive and imperceptible device to prevent a lack of comfort that would impede continuous wearing. For this reason, smart textiles are currently being considered as a relevant solution. Specific reliability issues related to strain during wearing and washing have to be addressed.
In this work, we focus on the mechanical reliability of fundamental surface mounted devices (such as passives components and microprocessor) on flexible polymeric substrates embedded onto textile. We developed a specific experimental protocol in order to characterize the radius of curvature of the overall bent system down to few hundreds micrometers through optical measurements. At the same time, in-situ electrical characterizations are correlated to mechanical cycling in order to determine the reliability of the device.
This study investigates the mechanical behavior of the electrical interconnection between electronic components and conductive tracks. Different elastic conductive materials are investigated and compared to standard electronic processes (i.e., tin-based alloys soldering, flip-chip). The study also points out 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-thin devices for a comfortable and continuous monitoring.

Wearable electronics have been widely studied to overcome traditional electronic devices which are bulky and rigid. Electronic textiles (e-textiles) are advantageous as they can be used to seamlessly embed electronic devices into clothes. Nevertheless, chemical sensors have not been widely investigated using stretchable conductive fibers despite the usefulness for alerting the users. H₂ gas has been researched as an alternative energy source due to many advantages. However, it has a low ignition energy (0.02 mJ) and a wide flammable range (4~75%) which requires detection of H₂ gas. In this work, palladium nanoparticle (PdNP) and polymer composite is used for stretchable fiber-type H₂ sensor. The fiber is fabricated by simple solution processes. Pd ions are inserted to the outer shell of the polymer fiber due to partial swelling of the polymer, which is later chemically reduced to PdNPs. The fiber is composed with a dense PdNP shell which responds to H₂ gas. The sample shows a -27.3% response at 10% H₂ and -0.43% response at 5 ppm H₂. The sample can detect H₂ gas even under 70% strain. Pure Pd has a lattice constant of , but when it is exposed to H₂, H atoms are incorporated into the surface of the Pd layer resulting in the formation of semiconducting Pd hydride (PdH_x) with a lattice constant of . We confirmed that the PdNP/polymer composite resistance changes under H₂ gas using theoretical calculations, and the volume expansion of the composite can close cracks which leads to shorter electrical paths.

The advent of smart materials systems and devices has revolutionized the world in recent years enhancing the sensing and communication capabilities with the aim of improving the standard of life. Wearable electronics, which combines electronic components into textiles for numerous applications, play a key role in this regard, while being considered a major component in the internet of things (IoT). One of the main challenges for wearable technologies is to ensure their autonomous operation via a renewable energy source, which can ideally be realized by scavenging energy from the surrounding.
Triboelectric nanogenerators (TENGs) convert mechanical movements into electricity via a combination of triboelectric effect and electrostatic induction, and are in the forefront of energy harvesting technologies. [1, 2] TENGs can act as energy harvesters as well as self-powered sensors, with a reputation for high outputs, high efficiency, simple construction, and low cost. [1] However, there is only a limited number of studies conducted on textile based TENG structures which can fulfil the requirements of a wearable system.
Herein, we present a new class of wearable TENGs composed of commonly used textile materials and processing techniques. The active triboelectric materials are deposited on both metallic, and non-metallic conductive core fabrics. The triboelectric layers are modified with different polymers and fibres, using techniques such as core-spinning, dip coating and spray coating. Different surface modification techniques commonly utilized in the textile industry are used to further improve TENG performance. These devices are capable of producing significant outputs, with maximum current density of around 100 µA/m², voltage exceeding 20 V, and a power density of around 10 mW/m² under low frequency periodic contact and separation movements.
In conclusion, this work introduces a new method of constructing efficient textile based wearable TENG structures with a high emphasis on preserving their wearable properties and improving the manufacturability at large scale, encompassing many potential applications.
1. Z.L. Wang, et al. Faraday discuss. 176 (2014) 447-458.
2. Dharmasena et. al., Energy Environ. Sci. 10 (2017), 1801-1811.

Energy harvesters with superior energy output are rapidly growing with development of novel organic material such as piezoelectric, thermoelectric and photovoltaic material. By combining these energy harvesters to electrical sensors, the sensor can extract power from environment which makes the sensors self-powered and applicable to the Internet of Things (IoTs). For continuous power source of wearable IoT sensors, ultraflexible organic photovoltaics (OPVs) are the most promising among all existing energy harvesters because of their flexibility, light-weight, and high power output (ref. 1). Also, ultraflexible OPVs are advantageous of textile-compatibility, thereby the area of the power source can be enlarged by applying the textile itself as the platform. Such textile-compatible power source must possess environmental stability in both air and water. Here we show ultraflexible, air/water stable and efficient OPVs based on inverted structure with an active layer of a D–A polymer with quaterthiophene and naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NTz) (PNTz4T) (ref. 2) and [6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM). The device shows high PCE of 7.9% on 1-μm-thick foil after peeled off from supporting glass and remains almost 50% of initial PCE even after 30 days storing in air. Additionally, the freestanding OPV was converted to double-side coated OPV by sandwiching the freestanding OPV with two pre-stretched elastomer, which results simultaneous achievement of stretchability and high stability against water immersion. First, we evaluated mechanical durability of double-side coated OPVs. Even the double-side coated OPV was compressed up to 52%, the device shows stable photovoltaic properties. Additionally, we cyclically compressed the OPVs with 52% compression. After 20 cycles of 52% compression, the PCEs for double-side coated OPV remained at 83%. Second, stability of OPVs against water immersion was examined. While the PCEs for the freestanding OPVs decreased by 20.8% after water immersion for 120 min, those for the double-side coated OPVs only decreased by 5.4%. Now we realize that highly efficient, stretchable, and air/water stable power sources with double-side elastomer coated OPVs. This double-side coated OPVs are promising textile-compatible power sources for future wearable applications (ref. 3).

[Reference 1] Kaltenbrunner, M. et al. Ultrathin and lightweight organic solar cells with high flexibility. Nat. Commun. 3, 770 (2012).
[Reference 2] Vohra, V. et al. Efficient inverted polymer solar cells employing favourable molecular orientation. Nat. Photonics 9, 403–408 (2015).
[Reference 3] Jinno, H. et al. Stretchable and waterproof elastomer-coated organic photovoltaics for washable electronic textile applications. Nat. Energy 2, 780–785 (2017).

It is critically important to develop miniature energy storage and conversion devices in modern electronics, e.g., for portable and wearable electronic facilities. Here a novel family of energy storage and conversion devices as well as their integrated devices in 1D configuration are carefully discussed with unique and promising advantages such as lightweight and weaveable compared with the conventional planar architecture. For the energy storage devices in 1D configuration, electrochemical capacitors, lithium ion batteries, lithium sulfur batteries, lithium air batteries and zinc air batteries are carefully investigated. For the energy conversion devices, dye-sensitized solar cells, polymer solar cells and perovskite solar cells are covered. The main efforts will be made to highlight the recent advancement in the electrode material, device structure and property extension.

The wearable devices and integrated systems has attracted broad interests in the fields of microelectronics, biomedicine and communication. However, the limitations of rigid, bulky and unifunction in traditional devices restricts the further development of flexible, miniaturized and highly-integrated wearable devices. To this end, advances in the textile industry have suggested a useful direction: all the functional units (such as stimuli-responsive devices and energy devices) can be made into a continuous fiber using a melting or all-solution-based process, and they can be woven into various flexible textiles or easily integrated with each other. Therefore, smart and multi-functional textiles can be produced from these fiber-shaped devices.

Herein, a new family of integrated wearable textiles including stimuli-responsive fibers that are the key to become intelligent and wire-shaped energy devices (perovskite solar cells and supercapacitors) that are essential for wearable devices. Through precisely manipulating the hierarchically helical structures, the responsive fibers can generate large, fast and reversible actuations upon the stimuli of electricity, solvents, vapors, visible-light and thermal. Depended on the flexible, robust and conductive properties in aligned carbon nanotubes, solar cells and supercapacitors can be integrated into fiber substrates with flexibility, stretchability and shape memory effect. These devices can be further effectively integrated to absorb and store solar energy simultaneously and meet the requirements of multiple-function and intelligentization in modern electronics.

Recent progress in the field of nanotechnology and functional fibers has led to the fabrication of textiles with advanced functions, including sensing and actuating, processing and storing data, and communicating with nearby electronics. Incorporating these functionalities into textiles necessitates the integration of energy storage devices into garments. Supercapacitors are promising candidates for wearable energy storage applications, as they can charge and discharge for thousands of cycles, meaning that their lifetime can surpass that of a traditional garment.

Many material design challenges are presented when developing electrode materials for textile-based energy storage devices. Not unlike traditional supercapacitors used in static environments, such as in laptop computers, achieving high-capacitance and high-power requires electrode materials with high surface area and electrical conductivity. However, for textile-based devices, which are used in dynamic environments, the electrode materials also need to be flexible and mechanically robust, i.e. capable of withstanding stresses during industrial-scale textile manufacturing and throughout wear. While several researchers have developed fiber-based supercapacitors that exhibit impressive capacitance, to our knowledge, few have demonstrated scalability.

Here, we capitalized on the attractive electrochemical performance of Ti₃C₂ MXene, a two-dimensional titanium carbide, and the high surface area of electrospun nanofibers to develop electrode materials for knitted supercapacitors. We developed a modified electrospinning setup to create and collect meters of twisted bundles of nanofibers, known as nanoyarns. These nanoyarns are composed of over 80,000 fibers, with fiber diameters ranging from 300-800 nm depending on the electrospinning parameters chosen. The nanoyarns are flexible and elastic, reaching a strain-to-failure of 300% for poly(caprolactone) (PCL) yarns. Using this setup, nanoyarns with various architectures, such as core-sheath yarns, can be fabricated from a variety of polymer solutions, including PCL, poly(acrylonitrile), and poly(vinylidene fluoride). After functionalizing the surface of the nanoyarns using oxygen plasma, Ti₃C₂ MXene is incorporated into these yarns through a dipping and drying process, a method that can easily be integrated into industrial-scale yarn manufacturing. Next, these MXene-coated nanofibers are integrated into knitted energy storage devices using industrial and programmable Shima Seiki knitting machines. These devices have the potential to connect with energy harvesting devices and power wearable electronics.

The field of smart textiles has been advancing rapidly over the last decade and has found applications in a variety of industries, including sports, medicine, and military. Of many functions, these smart garments are capable of providing and tracking physiological data, retraining use of impaired limbs, and giving feedback to athletes on their performance. Many smart garments require energy storage devices for operation. However, most smart garments still utilize conventional battery architectures such as coin or pouch cells, which can be uncomfortable and unsafe and also can impose design limitations to the final device. Designing an energy storage device for integration into textiles requires the development of fiber-based electrodes that exhibit high conductivity and promote diffusion of ions.

Carbons, including activated carbon and carbon onions, and 2D metal carbides, such as Ti₃C₂T_x MXene, are promising candidates for achieving the next generation of smart textile energy storage devices thanks to their high specific surface area, high electrochemical activity, and chemical stability. Ti₃C₂T_x MXene, the most widely studied MXene to date, has demonstrated outstanding performance as a freestanding paper electrode, exhibiting excellent cyclability, with no significant change in capacitance reported after 10,000 cycles¹. These properties are attractive for wearable energy storage devices, which require long lifetime and fast charge-discharge rates. As such, researchers are beginning to explore the incorporation of Ti₃C₂T_x MXene into fibers.

Carbons and 2D carbides enable different design approaches to be implemented such as (1) coated textile energy storage, (2) fiber or yarn energy storage, (3) custom textile structures that incorporate energy storage. Each approach has its advantages, for instance, coating pre-existing textiles with energy storing materials helps pre-made garments to be outfitted with new technology at ease. As MXenes are hydrophilic, they can be incorporated into conventional yarns using a simple dipping and drying procedure. This procedure can easily be scaled-up and used in industrial-scale textile manufacturing processes. On the other hand, fibers and yarns that can act as energy storage devices can be woven or knitted into full fabrics enabling integration into many different kinds of garments. Lastly, custom designing knitted structures that incorporate all the components of energy storage devices give engineers the advantage to design fabrics with specified power and energy densities. In this talk, recent advancements in the field will be presented regarding integration of carbon and 2D carbides into smart textiles structures, as well as potential challenges facing the field of wearable energy storage.

References
1. Ghidiu, M., Lukatskaya, M. R., Zhao, M.-Q., Gogotsi, Y. & Barsoum, M. W. Conductive two-dimensional titanium carbide ‘clay’ with high volumetric capacitance. Nature 516, 78–81 (2014).

Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. Nanogenerators have been developed based on piezoelectric, trioboelectric and pyroelectric effects, aiming at building self-sufficient power sources for mico/nano-systems. Triboelectrification is a universal phenomenon that exists for all of the materials regarding their chemical structure and physical shape. This presentation will focus on the fiber based triboelectric nanogenreators and sensors as flexible power source and motion detection.

References
Z.L. Wang, L. Lin, J. Chen. S.M. Niu, Y.L. Zi “Triboelectric Nanogenerators”, Springer, 2016. http://www.springer.com/us/book/9783319400389
Z.L. Wang “Triboelectric Nanogenerators as New Energy Technology for Self-Powered Systems and as Active Mechanical and Chemical Sensors”, ACS Nano 7 (2013) 9533-9557.
Z.L. Wang, J. Chen, L. Lin “Progress in triboelectric nanogenertors as new energy technology and self-powered sensors”, Energy & Environmental Sci, 8 (2015) 2250-2282.

Thermoelectric generators (TEGs) are used to generate electricity directly from waste heat. They are promising energy harvesters for independent, small circuits in sensor networks and wearable electronics since heat flux always accompanies human activity. Toward such an energy-harvesting use, there has been an effort in recent years to fabricate flexible, wearable TEGs from organic or organic/inorganic hybrid materials. Their thermoelectric figure of merit (ZT) is increasing year by year. However, in practical operating conditions where ambient air is the only medium for heat dissipation, the efficiency is restricted not only by the ZT value but also by the thickness and thermal conductivity of the device, which influence the temperature difference used for power generation. A total design of materials, device structure and fabrication process for these devices are therefore important to satisfy difficult requirements; thickness must be more than a few millimeters, but the device must be flexible.
Here, we propose a promising design for thickness-controllable, flexible, stretchable, and thermally insulating TEGs, or “thermoelectric fabrics.” [1] Carbon nanotubes (CNT) are spun into thread with binding polymers and p/n-doped to form striped patterns. By sewing the CNT thread into a felt fabric, operation of a prototype thermoelectric fabric by a finger touch is demonstrated, which indicates its potential as an easy-to-use power source for wearable electronics.
[1] M. Ito, T. Koizumi, H. Kojima, T. Saito, and M. Nakamura, J. Mater. Chem. A 5, 12068 (2017).

A novel breathable piezoelectric membrane has been developed by adding zinc oxide (ZnO) to electrospun polyvinylidene fluoride (PVDF) nanofibers. Notable improvements in the piezoelectric response of PVDF membrane was achieved without compromising breathability, conformability, or safety of the material. Three ZnO nanorod addition method was investigated: hydrothermal growth on the fiber surface, fillers in electrospinning solution, and electrospraying on the PVDF membrane surface. PVDF is one of the most frequently used piezoelectric polymers due to its high piezoelectric coefficient values. However, its piezoelectric response requires further improvements for the use of high-performance sensors or energy harvesters. Previous studies have demonstrated piezoelectric ceramic and polymer composites with a remarkably improved piezoelectric constant. However, such composites often lack breathability, and some contain piezoelectric ceramics with heavy metal which limits its use in wearable applications. The said limitations can be alleviated by electrospinning piezoelectric polymers into porous membranes, and by selecting non-toxic piezoelectric ceramics. Unlike many piezoelectric ceramics containing heavy metal, ZnO is a non-toxic material which has been widely used in many fields of applications including cosmetics. The fabrication process is simple and economical due to no additional poling process needed for PVDF membranes after electrospinning in high electric field.

Textile electronics represents the ability to improve wearable device systems by providing a distributed system of electronics in that is undetectable to the wearer. These clothing systems uniquely position themselves toward emerging opportunities in vigilant health monitoring. Primary challenges exist in understanding electronics integration that are durable and comfortable to the user, in addition to manufacturing strategies such that the garment is precisely designed for an individual consumer. This presentation explores principles in strategic textile design for improving the efficacy of biopotential sensors and energy harvesting devices embedded within the garment. For biopotential sensors, the dynamics of human movement results in unwanted artifacts in the measurement, but can be significantly reduced when considering the system of textile materials which form the garment. In a similar way, the mechanical and thermal regions surrounding piezoelectric and thermoelectric device integration are critical to obtaining usable levels of power that enable self-powered wearable systems. Finally, strategies for assessing performance of the textile electronics through human use-case scenarios are reviewed.

A general strategy to eliminate the mechanical strain on nonstretchable electronic materials while being stretched involves the engineering design from special mechanical structures or architectures. 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, high-density device integration, large strain tolerance. In this work, we present the manufacturing of stretchable elastomeric electronics and sensors from all solution processable, scalable and low-cost rubbery semiconductors and conductors without any additional structural design to achieve large mechanical stretchability. We use all commercially available materials as precursors to achieve highly stretchable semiconductors and conductors that can be manufactured in a repeatable and scalable manner and have stable performances under the mechanical stretching. 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. The constructed thin-film transistors from the rubbery semiconductors and conductors achieved a high value of a field-effect mobility for the stretchable organic format of semiconductors and showed a moderate decrease in the mobility under 50% mechanical stretching. Also, stretchable sensors, which include strain, pressure and temperature sensors show reliable sensing capabilities upon the mechanical stretching up to 50%. Furthermore, successful demonstrations of these rubbery electronics as multifunctional artificial robotic skins that can translate hand motions and gestures to provide haptic sensing capabilities present challenging, but still practical potentials for advanced wearable electronic applications.

Transparent electrochromic materials darken with an applied voltage, making them useful in a variety of applications. The optical transitions of electrochromic materials vary with temperature, a phenomenon necessitating consideration when designing for applications with fluctuating temperatures such as variable tint ski goggles. This work explores how the kinetics of optical transitions of one organic electrochromic molecule, ethyl viologen diperchlorate, vary with temperature. Studies have been conducted on the kinetics of optical transitions of ethyl viologen diperchlorate electrochromic devices at room temperature, and they have also been conducted on other electrochromic molecules at different temperatures, however these studies do not contain findings about the temperature effects on the electrochromic transitions of ethyl viologen diperchlorate. This work aims to investigate these temperature effects by measuring the optical transitions of ethyl viologen diperchlorate electrochromic cells at a variety of temperatures and comparing the kinetics at each temperature. Testing reveals that temperature affects the darkness these electrochromic cells can achieve as well as the rate at which they reach this darkness. At lower temperatures the cells take a longer time to transition, yet they reach a darker state. With increasing temperature, these cells transition more quickly, and achieve a lighter fully-darkened state.

Major opportunities for growth of current and future nanotechnologies stands on the convergence of engineered nanomaterials with electronics, photonics, energy and bio-science application areas, and their scale-up manufacturing base. For instance, several examples exist that encompass applications of carbon nanotubes and graphene in flexible, transparent and printable electronics, or applications of quantum-dots in displays and lighting, as well as in higher efficiency solar cells.
At the same time, the research of novel form factors for wearable electronics has brought an opportunity to reinvent electronics and combine it with conventional textile manufacturing by embedding a full set of engineered nanomaterials onto fibre-based electronic, photonic, energy and sensor devices, and finally integrate these through weaving or knitting to develop novel applications of e-textiles in wearables, as well as for energy harvesting and storage, e-skin, large area displays, lighting or interactive surfaces.
The vision of the H2020 EC-funded project 1D-NEON (1D Nanofibre Electro-Optic Networks) is to develop fibre-based smart materials and integrated technology platforms for the manufacturing of high value-added smart textiles, with applications in Large-Area electronics, Energy, Sensing and Soft robotics.
1D-NEON builds on a modular platform where nanomaterials are assembled into five basic fibre components along with textile-based manufacturing processes for integration of e-fibre components into smart products.
Since its start we have created 34 multifunctional, textile-integrated electronic, sensing and photonic functional building blocks that are integrated in a multifunctional demonstrator kit. The demonstrator kit will serve to kick-start industrial applications of e-fibres for smart e-textile applications.
The project brings together 14 partners from 7 European countries active in advanced materials, design platforms, textiles, electronics and photonic sectors.
The talk will review the main challenges of currently available state-of-the art technologies and discuss opportunities to bring innovation into key market sectors of e-textiles, with the help of selected new prototypes and product concept examples generated in 1D-NEON. For instance we will present smart textiles with embedded fibre-energy harvesting and storage, fibre-sensing, fibre-transistor based circuits for sensor front-end, lighting fibres and human-machine interface capabilities developed by the 1D-NEON consortium.

Cephalopods are arguably the most photonically sophisticated marine animals, as they have evolved the ability to alter the color patterning of their skin to blend into their environment and evade predators. This adaptive coloration is facilitated in part by neurally-controlled, muscle-actuated pigment organs known as chromatophores. Until 2014 the chromatophores were thought to be composed solely of homogeneous clusters of chromogenic pigments; however, recent results suggest that they contain high refractive index, luminescing nanostructures that may facilitate the rapid and sophisticated changes exhibited in dermal pigmentation. In this talk, I will describe a method to incorporate chromatophore derived nanostructures into textiles designed to enhance visible color for future wearable applications.

Textiles and clothing have been a staple of human existence for millennia, yet the basic structure and functionality of textile fibers and yarns has remained unchanged. While color and appearance are essential characteristics of a textile, an advancement in the fabrication of yarns that allows for user-controlled dynamic changes to the color or appearance of a garment has been lacking. Touch-activated and photosensitive pigments have been used in textiles, but these technologies are passive and cannot be controlled by the user. The technology described here allows the owner to control both when and in what pattern the fabric color-change takes place. In addition, the manufacturing process is compatible with mass-producing the user-controlled, color-changing yarns.
The yarn fabrication utilizes a fiber spinning system that can produce either monofilament or multifilament yarns. For products requiring a more robust fabric, larger-diameter monofilament yarns with a coarser weave are suitable. Such yarns are produced using a thread-coater attachment to encapsulate a metal wire inside a polymer sheath impregnated with thermochromic pigment. Conversely, products such as shirts requiring yarns that are more flexible and soft against the skin comprise multifilament yarns of much smaller-diameter individual fibers. Embedding a metal wire in a multifilament fiber spinning process has not been realized to date. Our collaboration with Hills, Inc., has led to the design of a liquid metal-injection system to be combined with fiber spinning. The new system injects molten tin into each of 19 filaments being spun simultaneously into a single yarn.
The color change is distinct from garments containing LEDs that emit light in various colors. The pigment itself changes its optical absorption to appear a different color. The thermochromic color-change is induced by a temperature change in the inner metal wire of each filament when current is applied. The temperature required to induce color change is near body temperature and not noticeable by touch. The prototypes already developed either use a simple push button to activate the battery pack or are wirelessly activated via a smart-phone app over Wi-Fi. The app allows the user to choose from different activation patterns of stripes that appear in the fabric continuously. The power requirements are mitigated by a large hysteresis in the activation temperature of the pigment and the temperature at which there is full color return.
This technology enables a never-before seen capability: user-controlled, dynamic color and pattern change in large-area woven and sewn textiles and fabrics with wide-ranging applications from clothing and accessories to furniture and fixed-installation housing and business décor. The ability to activate through Wi-Fi opens up possibilities for the textiles to be part of the ‘Internet of Things.’ Furthermore, this technology is scalable to mass-production levels for wide-scale market adoption.

The emergence of wearable technology has revitalized interest in smart, integrated garment. In fact several smart shirts have already existed for over 20 years without mass adoption. This talk looks to discuss the various barriers that have limited the use of smart, integrated clothing to high price niche application and PR generating exercises. While we will discuss technical barriers such as materials, durability and interconnect we will also discuss way in which we case better identify and target end use cases that the provide true value to consumers that that stretch beyond tech junkies and first adopters into a lasting community of long term users.

The Internet-of-Things (IoT), the interconnecting of everyday devices and objects embedded with electronics, software, and sensors and enabling them to send and receive data, has accelerated the demand for development of wearable technologies that can be used to enhance or monitor the human body and respond to various environments, such as fitness trackers and smart clothing. Concomitant with IoT advancements, smart textile technologies are increasing in popularity because they offer the potential to combine real-time personal communication with convenient portability and can detect and react to environmental variations in light intensity, temperature, and pollution levels when integrated into clothing. For example, smart clothing could become warmer in order to keep the wearer warm when the environment is too cold, and vice versa. Light-emitting textiles are also getting increased attention as they can be used in high-visibility outfits for personal safety, such as for joggers in dark areas, pedestrians at night, and for attractive signaling that enables mutual recognition or new forms of communication.
Here, we integrated zinc sulfide-embedded polydimethylsiloxane into a mechanoluminescent fiber that can be used as a wearable light-emitting textile.[1] The fiber is made robust by increasing the strength of the binding of the mechanoluminescent materials with a chemically treated cross-shaped fiber frame and employing an adhesive layer for encapsulation. This prevents irregular failure induced by the creation of defects (e.g., crevice, bubble) and stable mechanoluminescence behavior has been achieved for over one hundred thousand cycles. Further, by incorporating an encapsulating layer, the mechanoluminescent fiber is highly resistant to water and detergent. A mechanoluminescent fabric made by weaving mechanoluminescent fibers, and which is potentially adaptable to wearable light-emitting fabrics powered solely by human motions such as body movement and muscle stretching, has also been developed. From an application perspective, the mechanoluminescent fibers are promising candidates particularly for wearable displays in high-visibility outfits for personal safety because of their sensing and display functions. Battery-free, human motion-powered mechanoluminescent textile is expected to enable environmentally friendly and sustainable light, and paves the way for new approaches to wearable devices that reduce energy waste.

[1] S. M. Jeong, S. Song, H. –J. Seo, W. M. Choi, S. –H. Hwang, S. K. Lim, Advanced Sustainable Systems 1, 1700126 (2017).

Wearable technology and smart clothing are poised to revolutionize our living environment. Smart accessories such as smartwatches, smart wristbands are gaining their popularity in the consumer market. We have also seen accelerated developments in other smart wearable devices such as smart chest band for monitoring and communicating vital signs (such as heart rate, breathing, oxygen consumption), smart shoe sole to monitor wearer’s activities and foot pressure distribution, and smart sportswear for monitoring and digitalizing body motion.
The future of wearable technology and smart clothing is however very much dependent on the accuracy and reliability of wearable sensing technologies, the ability of wearable actuators to respond the changes of human conditions and environment, the seamless integration of sensors, actuators, energy storage devices and communication devices in fashionable products without compromising comfort, appearance, and easy-care.
In this presentation, recent developments in smart and multi-functional fibrous materials and clothing, Cornell’s research efforts in this area in particular, will be reviewed. The functions and remaining challenges of these state-of-the-art technologies will be discussed.

Current hazmat suits consist of continuous barrier of materials such as butyl rubber, which passively block penetration of majority of hazardous chemicals. A downside of this system is that it also prevents evaporative cooling, which is the body’s natural thermal regulation process. To address this issue, we have developed an adaptive, “selectively breathable” composite fabric of cotton coated with poly(N,N-butylphenylacrylamide). These polymeric fabrics do not respond to water vapor, which allows for perspiration and regulation of the body temperature. However, when the fabrics come in contact with a range of target chemicals, the polymer coating swells and closes the fabric pores. Here we explore different coating mechanisms both computationally using finite element model and experimentally by imaging the aerosol droplet-polymer interactions. The dynamic swelling characteristics of the polymer, based on a validated finite element model, have been utilized to characterize the fabric in terms of optimum pore size, polymer shape and cross-linking density. Our results provide estimates for optimized fabric designs and its manufacturing.

Commonly-available, mass-produced fabrics, yarns and threads can be transformed into a plethora of wearable, skin-mountable and/or biocompatible electronic devices upon being coated with films of intrinsically conducting polymers, such as poly(3,4-ethylenedioxythiophene). Tremendous variation in the surface morphology of conjugated polymer-coated fibers can be observed with different coating or processing conditions. In turn, the morphology of the conjugated polymer active layer determines electrical performance and, most importantly, device ruggedness. I will discuss our lab’s efforts in using reactive vapor coating to create electronically-active textiles. Vapor coating allows for a conjugated polymer to be directly formed on any textile or fiber substrate in the vapor phase, without the need for detergents, fixing agents or surface pretreatments, which can reduce the overall number of steps involved in current textile manufacturing routines and curtail the significant solvent use associated with textile production. Further, vapor coating yields uniform and conformal films on fiber/fabric surfaces and produces conductive materials without any insulating moieties. Selected technologies created by vapor coating fabrics/yarns will be described, including touch-sensitive textiles for interactive electronics; smart elbow braces for movement sensing; textile triboelectric generators that convert small body motions into stored energy; wear-, wash- and ironing-resistant conductive cloths that generate heat with a small applied voltage; and thread/yarn supercapacitors that can be sewed or knitted into garments for wearable and portable energy storage.

The integration of complex functionalities within fibers and fabrics is at the heart of the technological turn the Textile industry has to take. Many strategies are being developed to functionalize fibers and textiles via a direct and selective coating of the already made fiber and fabric. An alternative strategy relies on thermally drawing a fiber from a preform that already contains the desired functional materials within a cladding. This approach enables to realize fiber-integrated devices with complex architectures and functionalities, at the scalability traditionally associated with optical fibers. Thus far however, the cladding materials have been made out of rigid thermoplastic or glasses that could not respond to mechanical external stimuli. In particular, they can only be deformed elastically by strains of a few percent, preventing any monitoring of deformation or pressure by multi-material fibers. More over, biodegradability of some polymers have not been exploited to make multi-material fiber responding to their surrounding by releasing substances in a controlled way.
In this presentation, we will show how we can provide fibers with novel structures and materials that can respond to any mechanical stimulations. We will first show how we can structure a fiber with rigid yet bendable domains to act as a distributed pressure sensor. We will then show how we can expand the map of materials compatible with the thermal drawing process, by looking at the required rheological and microstructural attributes at a deeper level. This analysis will point us towards some thermoplastic elastomers that can be thermally drawn with similar rheology as their thermoplastic counterparts, hence enabling the fabrication of stretchable multi-material fibers. We will show a variety of configurations where optical and electronic fibers can sense and differentiate pressure, strains or shear in a reliable and robust way. Finally, we will show how our analysis also enabled us to identify biodegradable polymers compatible with the thermal drawing process. We will demonstrate fibers with complex microstructures that can be tailored to deliver different substances at controlled times. These advances in fiber architectures and materials opens novel opportunities for fiber-based devices in the fields of stretchable optics and electronics, health care and drug release, and smart textiles.

Wearable technology is poised to explode in the next decade. Many new devices will be garments made with advanced textiles engineered to perform specific functions. For these garments to perform as devices, it is essential that new functional fibers and yarns be designed and assembled such that they can be integrated into the textile manufacturing processes. Polymer nanofibers that have very large surface to volume ratios could potentially be used as highly sensitive health sensors that can passively diagnose body fluid. Despite the significant effort in electrospinning of polymer fibers, few have created yarns that can be knitted on industrial knitting machines. The dilemma lies in the balance between functionality and mechanical strength of the fibers/yarns. By continuous manufacturing of meter-long functional yarns from electrospun polymer fibers with embedded chemical receptors, we investigate the fiber assembly morphology, yarn architectures, and post-treatment methods to fine-tune the mechanical strength of fiber/yarns. We knit several fabric prototypes on a 3D digital knitting machine, which can change colors in response to humidity, pH, temperature, and electrolytes.

The integration of conducting and semiconducting architectures within thermally drawn thin and flexible fibers is emerging as a versatile platform for smart sensors and imaging systems, medical and biological probes, and advanced textile. Efficient photodetecting or thermal sensitive fibers in particular could bring a breath of new applications for advanced textiles. Thus far however, fundamental aspects of the microstructure formation and the interplay between microstructure and properties are poorly understood, leading to limited optical, electronic and optoelectronic performances of semiconductor-based fibers. Here, we first compare a regular annealing treatment of the as-drawn fiber with a laser annealing approach to tailor the microstructure of semiconductors in optoelectronic fibers. By judiciously controlling the laser parameters, we are able to fabricate an electrically addressed polycrystalline semiconductor domain with ultra-large grains, controllable crystallization depth as well as preferentially crystallographic orientations that allows the system to have the maximum carrier mobility[1]. We then turn to a simple and robust sonochemical approach applied to the amorphous semiconductor at ambient condition without any elevated temperature. The anisotropic surface energy of crystal planes in an organic solvent enables the controlled phase and orientation of monocrystalline nanowires that grow along the desired axis, directly in intimate contact with built-in electrodes[2]. The resulting nanowire-based fiber devices exhibit an unprecedented combination of excellent optical and optoelectronic properties in terms of light absorption, responsivity, sensitivity and response speed that compare favorably with other reported nanoscale planar devices. Most strikingly, this new approach facilitated high throughput and ultra-large area integration of nanowires into devices without the need for complex contacting procedures in the clean room, demonstrated by the growth of high-performance nanowire-based devices along the fiber length. Furthermore, we have demonstrated the unique capability of the functional fiber for fluorescent imaging based on a single fiber exhibiting simultaneous efficient optical guidance and excellent photodetecting performance. The improved control over the microstructure of the semiconductor in the multi-material fiber platform brings new insight into the field and opens unforeseen opportunities for advanced photodetecting probes and imaging systems, in bioengineering and healthcare, in remote and distributed sensing, energy harvesting, and advanced textiles.
[1] Wei Yan, et al. Microstructure tailoring of selenium-core multimaterial optoelectronic fibers. Optical Materials Express, 7 (2017) 1388. (Editor’s pick)
[2] Wei Yan, et al. Semiconducting nanowire-based optoelectronic fibers. Advanced Materials, 29 (2017) 1700681.

Woven fabrics of para-aramid fibers, such as Kevlar and Twaron, are widely used in body-armor applications, but they are limited to shrapnel and small-caliber ratings. These fibers typically fail due to breakage of hydrogen bonds between polymer chains. Cross-linking solves this issue, but results in fabrics less pliable, less breathable, and less suitable for wearable applications. Herein, we present a simple method to enhance the mechanic and ballistic properties of woven para-aramid fibers without compromising their desirable qualities. First, multiwall, carboxyl-functionalized carbon nanotubes (CNTs) dispersed in toluene are functionalized with toluene diisocyanate (TDI). Then, carboxyl or amine functionalized para-aramid fabrics are treated with the TDI-CNT dispersion, which results in CNT loadings up to 6 wt%. The addition of CNTs produces modest tensile strength increases (~5 %) and significant increases in single yarn pull-out strength (190 %). This behavior is indicative of increased entanglement—greater difficulty in fibers sliding past one another, but not in moving together. The modified fabrics are also subjected to two types of ballistic tests using projectiles of 2.6 g and 215 m/s. Single layers of fabric dissipate up to 80 % more kinetic energy following the addition of CNTs. Similarly, five layers of fabric result in up to 50 % lower back-face deformation of ballistic clay following the addition of CNTs. These significant enhancements not only enable lighter and stronger body armor, but they also expand the potential applicatons of para-aramids.

In the 21st century, consumers are rapidly gaining access to a novel suite of wearable electronic devices such as smart watches and garments. This technology promises both comfort and ease of use, and it also provides a wealth of health-monitoring information. Advances in the field of electronic textiles and recent achievements in organic electronics have enabled the development of new flexible and conformable technologies that can perform the same sensing as current solid state devices, for a fraction of the cost. Such progress relies on the subtle engineering of organic functional materials to model their properties. The potential of using organic ionic and electronic conducting materials in wearable monitoring systems for muscles and the heart has been evaluated. We have shown that electrodes made of such organic materials can lower contact impedance in cutaneous applications with the skin resulting in higher quality recordings compared to metal–based electrodes. Moreover, by combining these materials with textiles we have reduced the mechanical mismatch at the interface with the skin, which enables the recording of electrophysiological activities for long time intervals with an enhanced signal to noise ratio. To do so, we developed different direct patterning techniques allowing the selective deposition of organic electrodes onto fabrics. These results pave the way for the seamless integration of organic electronics and the textile platform to provide low-cost and tailored solutions in interfacing smart devices with the human body.

Traditional textile fabrication technologies, such as weft knitting machines, have existed for over 400 years, providing automated methods of producing textiles both in the form of continuous cloth or as shaped 3D forms. The versatility of this production process is being used as a tool for development of the next generation of fabrics: smart textiles and garment devices. While this platform offers efficiency in production, the design and development stages are lacking the modeling sophistication found in modern manufacturing techniques such as 3D printing and composite fabrication.
In weft knitting specifically, basic building blocks, the knit and purl stitch, can be combined into a limitless number of patterns to produce novel textile structures with tunable properties. The interaction of these two stitch types in varying geometric patterns produces relief structures that self-fold due to yarn relaxation, producing highly dimensional and variable textiles architectures. The complexity and range of forms that can be achieved with this technique lend themselves to a variety of engineering and design applications. Several researchers have begun investigating the use of weft knit structures for textile property enhancement. This has included increased impact resistance, sound absorption and auxetic behavior. The variable dimensionality of these structures combined with new active materials could be applied to smart textile innovations including fabrics with engineered moisture or heat transfer properties, origami-inspired folding structures such as those used in satellite design, and assistive garments that could enhance movement or strength through use of articulated segments. These textiles could also be used to add structural design elements in architecture and interiors. However, before these novel textiles can be efficiently designed and produced, we must develop means of predicting their formation. Current textile modeling software can accurately render stitch patterns and yarns, but cannot provide predictions regarding the physical behavior of the structures due to yarn relaxation. This leaves the design of complex relief structures to the process of trial and error, slowing production and leading to material waste.
Here we investigate methods of predicting the relaxation and self-folding behavior of complex weft knit patterns through study of mechanical properties of basic self-folding structures. On the stitch level, all knit-purl structure designs are produced using combinations of four variations of transition between knit and purl, defined by their relationship to the axis of manufacture. By assigning magnitudes of forces to these fundamental building blocks, we can correlate measured mechanical properties to basic self-folding behavior. In this work, we demonstrate methods of measuring the forces driving self-folding and discuss how this information will be used to predict more complex behaviors.

Over the last decades, there have been numerous efforts in developing wearable computing by using interactive textiles. Most of the related work focuses on integrating sensors for planar touch gestures, and thus do not fully take advantage of the flexible, deformable and tangible material properties of the textile. In this presentation, we describe the design and implementation of a tactile pressure-sensitive textile sensor used for next-generation clothing. We built a textile-based, tactile pressure sensor for measuring the pressure distribution on clothing. The resistive sensing approach of this sensor enables static pressure measurement within a range of 50g to 1000g and a sensor density of 1.66 sensors/inch². This flexible, bi-directional stretchable, non-rigid sensor, which is indistinguishable from non-smart fabrics, consists of three layers of knitted fabric and allows easy integration. The developed measurement electronic and software platform enables real-time processing. Furthermore, we show how this sensor data is used as an enabler for interactions on clothing, which are beyond basic multitouch interactions. Based on the gesture detection algorithm we built, which uses learning-based algorithms, we are able to detect complex 2.5D deformation gestures like folding, twisting or stretching the fabric.
The developed technology platform marks first steps towards imperceptible textile interfaces in next-generation clothing.