Symposium MD6 : Electronic Textiles

We have developed a new continuous nano micromachining process of fiber substrates with electromechanical functions and large area integration process by weaving of functional fibers to realize meter-scale large-area flexible devices without the use of large sheet substrate.
Conventional MEMS technologies utilizing the microfabrication equipment based on semiconductor manufacturing process, however, may not be suitable for large area MEMS devices manufacturing, because vacuum process equipment for large-area devices is too expensive, and large-area substrates are difficult to be handled and too costly. Our proposed process can offer large area devices with low cost machining tools because nano/micro film deposition and patterning area for fiber is small and automatic weaving of meter-wide textile is commonly available.
The developed continuous processing of fiber is composed of die-coating to form organic functional materials including P3HT, PVDF, PEDOT PSS, PMMA, 3-D photolithography to pattern MEMS structure, chip mounting to integrate silicon devices on fibers. On our die coating system, fiber-type substrates are moved continuously with supplier and winder, and are coated by solution with the coating tool called “die”. Hundreds of nanometer thick functional films for semiconductor devices are formed by our analysis and design of die and by pressure control of the solution. Our 3-D photolithography technology for a high resolution micro process on a fiber mainly comprises the 3-D exposure module and spray deposition of thin resist film on the fiber. 3-D exposure module with long service life, low cost, narrow print gap and thus high resolution is fabricated by the wet etching of a quartz substrate and the projection exposure method. Thin 1 um thick resist is sprayed on the fiber substrates by tuning viscosity and volatility of the resist systematically. The chip-mounting system for the fiber substrate moves the flexible ribbon with power lines and flexible printed circuit board tapes by using the reel winding machines and mounts the LEDs and other chips after dispensing the solders on the fiber substrates.
The developed automatic weaving machine can weave resultant functional fibers by defining the position of the functional fibers precisely with a linear actuator and an alignment camera. The weaving machine is 1.2 m wide and has two rapiers to weave not only polyester fibers but also functional fibers. Since cross-shaped alignment marks are patterned on the functional fiber substrates, the rapier of functional fibers grasps and moves the fiber for detecting the alignment mark for fixing the position of the fiber. Then, it weave the functional fibers between the open spaces between the warps. The 1.2 m-wide electronic textile including LED array fabric, touch sensors, and solar cells is woven continuously with our looming machine, which leads to variety of meter-scale large-area electronic textile.

Garment-based mobile health monitoring systems necessitate the fabrication of stretchable, body conformable, and washable interconnect designs to maintain electronic system functionality during daily activity of the users. Conductive ink printing is an inexpensive route to fabricate electrically conductive interconnects on textiles, but suffers from reliability issues when a conductive trace is directly printed on the fabric surface due to surface roughness of the fabric. To overcome these challenges, a heat lamination approach is introduced, by which ink-based interconnects can be ironed upon the garment. In this work, meandering lines are embedded within stretchable thermoplastic polyurethane (TPU) films via screen-printing and then encapsulated with a stretchable TPU layer. Afterwards, the stretchable conductive printed lines are ‘ironed’ onto a knit fabric. The structure-property relationships and cost analysis of these structures are investigated in terms of the meandering line design (arm length, curvature, line width). The influence of the mechanical behavior of underlying knit fabric upon which the encapsulated interconnect is placed is also defined. Electromechanical and washing tests are performed to test the durability factors. When the encapsulated interconnects are strained up to 40% with a single uniaxial stretching, it results in a resistance change (∆R/R) of 0.29. Their electrical functionalities are maintained when they are exposed to 100 washing cycles, and 1000 tensile oscillation cycles with 20% strain (10% pre-straining and 10% cycling strain). The e-textile approach provided by this work, allows for a unique retro-fitting approach personalization of the e-textile product.

Fiber actuators that generate large strain with high specific power are promising for novel wearable devices. Recently, Haines et. al. (Science 343, 868 (2014)) reported coiled fiber actuators with highly specific power, driven by the thermal strain of crystalline polymers; however, it required temperatures up to 200°C, making it unsuitable for wearable devices. In this paper, we propose a new coiled fiber actuator, based on linear-low density polyethylene(LLDPE). It can be operated by temperatures as low as 60°C driven by resistance heating, using only 20% of the power of previous devices, while generating the same stress of 20 MPa at 10% strain. Thanks to the low driving temperature, the actuator can be combined with common fabrics or stretchable conductive elastomers without thermal degradation, allowing use in wearable systems.
We present the mechanism of large strain on the LLDPE fiber actuator related with structural analysis on the nanostructure of crystalline / non-crystalline morphologies by using SAXS and SPM. From this analysis, we find the fibrils consist of stacked crystalline and non-crystalline periodic structures with weak inter-fibril interactions effectively generate large entropic force along the fibre direction, driving the coiled actuator. Although the extruded and highly drawn LLDPE fiber is a hard crystalline polymer with >2GPa of elastic modulus, after coiling into the helical structure, the LLDPE fiber distorts similar to rubber. Considering with analytical helimorph model we find this contributes to high work efficiency through the thermal strain efficiently multiplied with small heat capacity of coiled fiber.

There is a growing demand for “intelligent environments” or “ambient assisted living” where sensors and actuators that surround people or equipment are constantly exchanging information. Such environments require large area carriers for the electronic components – textile carriers are a good solution due to the large area capability at low cost. They allow the integration of electronic systems in the environment as well as in clothing.
Integrating electronics into textiles is still an emerging field. In the development of smart textiles there is a strong drive to go for integration of electronic components into textiles in high volume manufacturing. Different types of smart fabrics, interconnection technologies, and applications have already been developed. But the technologies reported so far have not yet proven to be suited for reliable mass production.
Novel concepts are required for the use of conductive textiles as sensors or the integration of conventional sensors in fabric. New yarns with well defined properties as well as special fabrication processes for the textile are will be needed to obtain reproducible results.
On different levels integration technologies have already been developed and qualified. For very small components a direct integration of chips into the yarn is possible. Larger and more complex modules require a specific package with contacts that allow the interconnection to the yarn – e.g. crimping, embroidery and adhesive bonding. Another alternative is the integration of stretchable interposers on the fabric. For all these solutions the I/O count is limited – on the one hand due to the limitations of the fabric, on the other hand due to the necessary size of the contacts of the modules. Together the technologies nonetheless build a platform, which allows the realization of a wide range of textile applications.

Shape memory materials are a part of the smart fabric and wearable technology research movement. One primary shape memory material is the shape memory alloy, SMA. SMAs are a unique material that can transform into a trained or “memorized” shape when a thermal condition is met. This along with many super-elastic material properties, including high power and force to weight ratios, makes them remarkable for actuation in robotics. SMA integration into textiles brings a new outcome of functioning fabric-structures through thermal control. Currently, most SMA research is within the linear scope of actuation due to a hysteresis in the material. However, in previous at low frequencies this hysteresis can be contained through material properties and heat-treatment processes. High frequencies are not always required for textile-integrated applications. Therefore, it is necessary to look into the bending of SMA wires as an actuator to further the research in smart fabrics. This paper presents a study of Ni-Ti-Cu wire as a bending actuator for the medical application of compression textiles. It yields the understanding of how the heat-treatment position effects the outcomes of reaction time, temperature hysteresis, and power consumption. It further looks into how the addition of a braided sleeved to form a SMA yarn effects these outcomes and whether the yarn disrupts the over all control and/or movement of the wire. Proper control and temperature values are achieved by keeping the samples between 60 and 100 mm in length. Samples are tested to a full 180 degrees of motion through joule-heating. Thermal readings, heating and cooling curves, optical distance measurements and images, frequency and power consumption plots are presented in this comprehensive study to enable direct-application based research in smart fabrics and wearable technology.

The massive increase in the number of healthcare monitoring devices for medical and sport applications is creating a large need for wearable sensors. They have to be flexible to conform to the human body, to perform at least as well as common medical sensing devices and to be easily connected with acquisition systems. A novel approach is to directly use the textile as a substrate for sensors, by coating an electroactive material onto the textile. To do so, we adapted a traditional dying process from Japanese kimono fabrication and selectively deposited the conductive polymer PEDOT:PSS into polyester fabric. By using a polyimide-based mask, structures as fine as 0.5 mm were patterned. We then applied this process for fabrication of cutaneous electrodes and study their performances. To promote a better skin contact, we added on top of PEDOT:PSS a layer of ionic liquid gel. We compared our textile-based electrodes with medical ones by measuring cardiac activity (electrocardiography, ECG). Our sensors showed better electrical impedance on skin and were able to detect high quality ECG recordings. Both gel and flexibility of the textile substrate permitted to drastically reduce noise content generated by motion that generally disturbs ECG measurements. Moreover, these electrodes demonstrated long-term stability during 3 days of ECG recordings and after extended ambient storage without any special reconditioning. This work paves the way towards fully integrated sensors on textiles that keep the softness advantages of clothes and show great performances for electrophysiological monitoring.

We have developed MEMS pressure sensor integrated textile by integrating MEMS pressure sensor node into fabric for the application of nursing care of eleders and artificial skin of robot.
High sensitive MEMS pressure sensors are suitable for the elders or robot monitoring, but integrating them into large-area surface of floor, wall, bed sheets, and robotic skins is difficult since the conventional chip mounter can’t mount and wire MEMS sensors on meter-scale large area substrate. Basically, most existing flexible printed circuit board technology offers 25-cm-wide and several-meter-long circuit boards, not several-meters-square ones, because the large area lithography and etching have difficulty tuning the uniformity of photo-resist patterning and etching on large areas and their machining tools are expensive. In addition, the mounters for MEMS chips are designed for PCBs of tens of centimeter and are not suited to meter-scale rolls of PCBs films. To solve this problem, we developed a MEMS pressure sensor integrated textile structure where the MEMS pressure sensor-mounted small piece of PCB with wireless sensor node is firstly connected to the power line-woven ribbon and the ribbons are secondly woven by 1.2 m-wide automatic looming machine.
MEMS pressure sensor consists of Pb(Zr, Ti) O₃ (PZT) microelectromechanical systems (MEMS) force sensors and soft-rubber package. a small MEMS PZT cantilever was used as a sensing element, and it was covered with soft rubber, poly(dimethylsiloxane) (PDMS), to avoid cracking the brittle PZT film when touching the sensor. The sensitivity was adjusted by changing the hardness of the soft rubber package, where hard rubbers lead to high sensitivity, but the sensor is easily cracked. Therefore, a sensor with a Durometer hardness A of 35.6 and force sensitivity of 3.15 pF/N was found to be optimal for human interface sensors to detect human touch of around several N because it has linear sensitivity below 5 N and the bending is small over 5 N, which leads to a highly durable sensor. The sensor node is 5 x 5 mm 300 MHz wireless chip with comparator. The amplifier for MEMS PZT sensor and RF chip is integrated 2 cm x 5 cm flexible circuit board.
The sensor node integrated textile is assembled by a process in which firstly the MEMS sensor -mounted pieces of PCBs are soldered to a 2-cm-wide ribbon with copper power lines, and secondly the resultant ribbons are woven as wefts by using a 1.2-m-wide automatic weaving machine. The power lines are integrated as warps in the woven textile, thus the wires in the ribbon and those in the textile are soldered for constructing electric power lines. When the MEMS sensor detects the pressure, the signal transmits from the sensor node to the PC through 300 MHz wireless communication. This technologies will lead to e-textile-based large area wireless sensor systems.

Recent work in the field of multimaterial fiber fabrication has produced novel devices that can simultaneously interrogate and modify their ambient surroundings. The production of these fiber-based technologies has relied chiefly on thermal drawing techniques initially developed for the fiber-optic industry. The drawing process begins with the preparation of a preform—a scaled-up model of the final fiber—comprised of one (or more) thermally compatible material(s). The constituent materials of the preform are first compounded or functionalized as needed, then ram extruded and assembled together into the desired structure. Once prepared, the preform is subjected to a thermal profile such that a section of the preform is transformed into a viscous state, pulled under tension, and re-solidified upon exiting the heated zone of the profile. Moreover, in order to account for conservation of mass, the preform must be precisely lowered into and pulled from the thermal profile so as to maintain uniformity in the transverse dimensions of the drawn fiber. Consequently, fabrication of thermally drawn fibers requires highly specialized equipment that can present entry barriers to researchers interested in exploiting the technique—namely, equipment cost, facilities, and training. Additionally, transfer of the technology to industrial-level production is limited by the batch-scale nature of drawing from a finitely-sized preform.

We present here first a remedy to the entry barriers presented by thermal fiber drawing in the form of miniaturized versions of a ram extrusion system and a thermal drawing tower that can be readily operated from a laboratory benchtop with minimal expertise. The machines each occupy a footprint area of 30x30 cm², stand less than one meter in height, and can be constructed at an overall cost of less than $25,000. Using these table-top devices, we present fabrication procedures for producing composite fibers containing a variety of materials including polymers, metals, and soft glasses. The fibers produced with these systems are sufficient for testing hypothesized fiber functionalities and performance without incurring significant material costs or labor. Finally, we present a remedy for technology transfer to industry by introducing commercially-available, specialized fiber extrusion spinning machines that produce multimaterial fibers with complex internal structuring in a one-step process. Well-known in the textiles industry, these machines are continuously fed and thus overcome the limitations of batch-scale manufacturing. Furthermore, we demonstrate the ability of these machines to replicate some of our prior results achieved by thermal drawing.

The emerging of textile-type electronic devices are remarkable, since it is effective for the sensors to be close in contact to the subject in order to measure biometric information with precision. A fabric that can extract electrocardiogram just by putting on has already put into practical use. Researchers devoted their time in developing electronic materials such as a fabric coated with high-conducting resin, a thread dipped to absorb metal powder, as these materials do not interfere with comfort. However, the conductive fibers or thread are not suitable for fine patterning, and it was a barrier in fabricating electrodes and wires with precision. In this work, we have succeeded in printing fine conductive patterns on a cloth with a new conductive ink to realize an elastic conductor that bears high conductivity and strong stretchability. An elastic conductor was fabricated with mixing Ag flakes, a fluorine rubber, and a fluorine surfactant. The new conductive ink bears conductivity even stretched, which is also excellent in durability. The conductivity of a pattern printed with the new ink showed 738 S/cm before stretching, and 182 S/cm after stretching to three times longer at 215%. We have systematically characterize the structures of printed elastic conductors by SEM and AFM in order to elucidate the mechanism of improved conductivities and stretchability by surfactants. We have also manufactured elastic conductor on a fabric used for sportwear, and combined it with a sophisticated organic transistor amplifier circuit to make a prototype wrist supporter type myoelectric sensor. We will also report highly stretchable silver fluoropolymer composite that can be directly printed on textile. This work is financially supported by JST/ERATO Bio-harmonized electronics project.

The ability to integrate electronic devices into textiles has numerous applications in areas ranging from health monitoring to consumer electronics. One necessary requirement for these technologies is the ability of a textile to be electrically conductive. Seamlessly imparting this conductivity into the textile is ideal, however, presently available conductive coatings are opaque and mask the colour and pattern of the textile underneath. Furthermore, many conductive textiles degrade with repeated bending or twisting.

In this work, fabrics are coated with networks of solution-processed silver nanowires. Silver nanowires have been used before to achieve conductive fabrics, but it was not cost effective. A large amount of silver was used since dip-coating resulted in nanowires covering the surface of each individual thread comprising the fabric. We instead transfer print planar meshes of silver nanowires onto the top surface of the fabric only. Although silver is an expensive material, very little of it is used. The nanowire coatings can have sheet resistances of 10 Ω/square while being optically transparent and mechanically flexible. This is an industrially compatible, cost-effective and transparent conductive coating that can be used on a wide range of fabrics.

We report a printing process to additively pattern silver nanowires (AgNWs) with length ranging from ~ 5 μm to ~ 40 μm. Well-defined and uniform features are obtained on different kinds of substrates. Systematic studies are conducted to optimize the printing conditions and to investigate the electrical and electromechanical properties of the printed AgNWs. The performance of the printed features can be tuned by changing the nanowire length. The feature width can be as small as ~ 100 μm when ~ 5 μm nanowires are used, suitable for the applications requiring high resolution. When printed on elastomer substrates, long nanowires exhibit excellent stretchability, showing great potential as interconnects and electrodes for stretchable electronic devices. The ability of directly printing AgNWs will enable various low cost, large area and flexible electronic devices that are otherwise difficult to realize. We further demonstrate a high resolution flexible capacitive pressure sensor array and a “blind display” using the ~ 5 μm and ~ 40 μm nanowires, respectively.

Flexible fabric strain sensors have found wide dynamic applications in smart and wearable electronic measurement systems. In this study, we have experimentally studied the dynamic sensing behavior of flexible fabric strain sensors up to a nominal strain of 70% and a strain rate of 1300/s by using a lab-made measurement system equipped with a novel split tensile device, high speed camera and a voltage divider circuit. The relationship among strain, strain rate and the relative resistance change of fabric strain sensors is described by a modified Cowper Symonds' model or Johnson Cook's model within the range of nominal strain rate from 0.1/s to 1300 /s. The relative resistance change is expressed as a function of the nominal strain ε and the nominal strain rate.

The distributions of local strain in the fabric sensors were determined during the dynamic tensile tests and found to be highly non-uniform. The mechanisms of strain rate effects were discussed with respect to non-uniform and time-dependent changes in tunnelling distances between conductive carbon particles caused by viscoelasticity of the polymer matrix. The obtained results have provided a basis for calibrating the fabric strain sensors in high-speed applications such as in-situ measurement systems of bullet-proof vests.

Smart textiles are revolutionizing the textile industry by combining technology into fabric to give clothing new abilities including communication, transformation, and energy conduction. The advent of electroluminescent fibers, which emit light in response to an applied electric field, has opened the door for fabric-integrated emissive displays in textiles. However, there have been few technical publications over the past few years about the performance of these light emitting fibers inside a garment. In this work, electroluminescent fibers in a knitted textile are evaluated under a range of operating conditions to determine how the illuminance and lifetime of the fiber is affected by voltage, frequency, stress, and strain. This data is used to develop guidelines for predicting the lifetime of the fiber inside the knitted structure based on the range of operating conditions. The effect of environmental factors like humidity, moisture, ambient light, and temperature on the performance and safety of the device will be discussed as they relate to the practical applications of this technology. The electroluminescent fibers used in this work were prepared using a 3D printed extrusion method for depositing a solution processed electroluminescent device structure onto a fiber substrate.

Due to the low mechanical properties of electrospun nonwoven fabrics, they cannot be used in most applications even though they have unique properties such as small fiber diameter, high surface area, high porosity and small pore size. The addition of CNTs into polymer electrospun fibers has attracted many researchers, due the CNTs’ high mechanical, electrical and multifunctional properties. However, this method has been generally unsuccessful due to difficulty of dispersion, low volume (or weight) content, and short length required of the CNTs. In order to address these limitations and improve final nanofiber nonwoven properties, a novel processing technique was developed and presented here. CNT – polymer hybrid nonwoven fabrics were created by simultaneously winding continuous sheets of millimeter long CNTs (drawn from aligned CNT arrays) onto an electrically grounded mandrel which served as the collector for the electrospun fibers. This technology overcomes the numerous physical and mechanical limitations of traditional electrospun nonwovens, and is promising for some of the most demanding nanofiber applications. The mass fraction of CNTs in the hybrid fabrics can be easily controlled by adjusting the take up speed of the rotating mandrel during the process. Hybrid fabrics with CNT weight fractions of approximately 15%, 30% and 60% were prepared in this way. The hybrid fabrics show extremely high strength, small pore size, high specific surface area and electrical conductivity. Once the samples were prepared, two additional steps, consolidating under pressure and heated calendaring, were applied to understand the effects on the properties. The hybrid fabric with 15% CNTs showed 15x higher strength than the control electrospun fabric. The 30% CNT consolidated hybrid fabric showed 21x and the 30% CNT calendared hybrid fabric exhibited strength that was 49x higher than the control sample. All the hybrid fabrics showed high electrical conductivity of up to 205 S/cm. The aerosol filtration properties were examined and consolidated hybrid fabrics with a thickness of 20 microns and areal density of 8 g/m² exhibited ultra low particulate (ULPA) filter properties. The barrier performance of the hybrid fabrics for protection against chemical solutions was also investigated. The hybrid fabrics showed very good water vapor permeability and also demonstrated super hydrophobicity and high levels of oleophobicity after a plasma fluoropolymer functionalization.

Printed organic field-effect transitors (OFETs) have been considered for many novel applications towards large area and flexible electronics [1], since they can enable pervasive integration of electronic functionalities in all sorts of appliances, their portability and wearability. Applications are countless: from personal devices (e.g. wearable health monitoring devices) to large-area sensors (e.g. electronic skin, bio-medical devices), and smart tagging of products with radio-frequency identification tags. It is no doubt that a huge driving force comes from flexible and/or rollable displays deployable on demand, to be integrated with portable and wearable devices. However, printed OFETs fabricated with scalable tools fail to achieve the minimum speed required for example to drive high-resolution displays or to read the signal from a real-time imager, where a transition frequency (f_T), i.e. the highest device operative frequency, above 10 MHz is required. In this work we present effective strategies to increase f_T in polymer and polymer-hybrids based devices by combining only printing and laser-based direct-writing techniques.[2] In particular, we demonstrate the possibility to achieve MHz operation in all-organic transistors on plastic foils, where short channels are ablated by a fs-laser. Moreover, we show that fs-laser sintering is another very promising approach for fast direct-written devices, with the possibility of achieving 10 - 20 MHz regime already with an OFET mobility in the range of ~ 1 cm²/Vs thanks to the drastically reduced capacitive parasitism. Further improvements towards even faster wearable polymer and hybrid electronics, suited to build wireless body area networks, will be discussed.

[1] M. Caironi and Y.-Y. Noh (eds.), Flexible and Large Area Electronics, Wiley, 2015, ISBN: 978-3-527-33639-5
[2] S.G. Bucella, M. Caironi et al., Nature Communications 2015, 6, 8394

A growing interest is focused on the development of new wearable technology for physiological monitoring, to obtain a novel class of personalized point-of-care devices that could be integrated into the daily life of a patient in the form of wireless body sensors. Although most of the research efforts are converged on the production of miniaturized wearable appliances based on relatively mature technologies, such as motion tracking, a remarkable ability would be the chemical sensing of bio-markers in body fluids. Several wearable sensors, mainly based on an electrochemical transduction, have been developed, however they often require the implantation of electrodes and the use of a relatively bulky read-out electronics. To overcome these drawbacks a good solution is the monitoring of biomarkers in sweat through wearable sensors that are developed within the textile.. Recently, the potentiality of textile Organic electrochemical transistors (OECTs) for the detection of ions and adrenaline has been shown [Coppedè et al., J. Mater. Chem. B, 2 (2014) 5620], but the sensing process should be studied in depth in order to control and fully exploit their properties and performance .
This contribution reports on the huge potential of OECTs as wearable chemical sensors for the detection of bio-compounds in sweat. In an OECT the current flowing in the channel (a stripe of conductive polymer) can be modulated through the voltage applied to the gate electrode by electrochemical reactions that take place in an electrolytic solution. Since the device is the combination of a sensitive element and an amplifier, OECTs directly amplify the electro-chemical signals. These transistors are made by screen printing on different textiles and they exhibit very appealing features for wearable sensors: 1) the operating potentials are very low (< 1 V), a key point considering that the device must be placed in direct contact with skin; 2) since the current used as signal is quite high (~ 1 mA), it requires a simple readout electronics ; 3) the absorbed power is very low (~ 10^-4 W); 4) it can be deformed without observing a degradation of its electrical features. Moreover the stability of the OECT we have developed has been assesed under washing conditions. The potentialities of the here described OECT as a sensor were tested using different redox active bio-molecules (adrenaline, dopamine and ascorbic acid). All tested analytes react with PEDOT:PSS by extracting charge carriers from the transistor channel and leading to a logarithmic decrease of the drain current for increasing concentration. The OECTs sensing capability has been assessed in two different experimental contexts: i) totally dipped in an electrolyte solution, to evaluate their performance in the ideal operation; ii) in air, by sequentially adding few drops of electrolyte solution in the sensing area in order to simulate the exposure of the fabric to human sweat in real applications.

Adhesion via electrostatic astriction, termed electroadhesion, allows for residue free, controlled, and reversible joining of various substrate materials. However, since electroadhesion strength scales quadratically with the applied voltage and is limited by the dielectric strength of the insulating material, all current electroadhesive devices operate above 1 kilovolt. This high voltage operation prohibits safe use of electroadhesion in biomedical applications.

We first investigate the dielectric strength of polycarbonate film as a function of the thickness. We find that although above 1 millimeter in thickness the dielectric strength of polycarbonate is steady at 50 volts per micron, we achieve upwards of 200 volts per micron with thicknesses on the order of 1 micron. Leveraging our unique top down thermal reduction process for creating multimaterial fibers, we demonstrate the ability to simply and cheaply fabricate kilometers of fiber device with micron and nanometer thick dielectric layers. The increased dielectric strength achieved easily with the thermal reduction process allows us to obtain significant adhesion strengths of 3.5 millinewtons per square centimeter at biosafe voltages of less than 50 volts.

Here we report on the design of a fiber device structure that combines electroadhesion with ultrasound transduction capabilities. A piezoelectric layer of PVDF-TrFE poled to the beta phase is sandwiched between conductive polyethylene plates. The conductive polyethylene is wrapped around the sides to form the electroadhesion conductive electrodes on the outside of the fiber. A layer of polycarbonate film covers the electrodes and provides the insulating dielectric while BiSn metal wires inside the fiber provide conductivity along the length of the fiber. Since air-polycarbonate interfaces reflect nearly all acoustic power in the ultrasound regime, above 1 megahertz, ultrasound coupling gel is often used to eliminate the air gap between the transducer and the substrate. Electroadhesion integrated into the piezoelectric fiber allows the device to dynamically adhere to the desired surface for increased signal to noise ratio without the aid of a coupling gel. This comprehensive fiber device can be weaved into a patient’s clothes to periodically adhere to and measure target areas throughout the day without the need for an attending medical professional.

Fabrication of transparent conductors that are mechanically stretchable is challenging yet essential in developing smart textiles or soft electronic devices such as stretchable displays. So far, indium tin oxide (ITO), the most commonly used transparent conductive materials has been known to hardly exhibit long term stability under mechanical stress, and thus, investigations of novel transparent electrodes in curvilinear stretchable devices have been extensively growing. Ag nanowire (Ag NW) networks are considered one of the strong candidates for stretchable transparent conductors due to their superior transparency and conductivity. Most previous studies have been focusing only on uniaxially stretchable conductors and very few studies have been attempted to create electrodes that are stable under biaxial mechanical deformations.
Here we present novel design of Ag NW network-based transparent conductors that are biaxially stretchable. We have developed a facile method to control the structure of NW networks in an isotropic manner that releases applied strains so that the NWs sustain the conductive nanowire network. Strain tests and cyclic tests showed that samples prepared by our method have high strain tolerance regardless of the direction of stretching while electrodes prepared via pre-straining method have strain tolerance only in the direction of a pre-strained direction. Morphological examinations were intensively performed to analyze the cause of improved electrical stability under biaxial deformation in the developed electrodes.
The prepared NW networks were directly applied to a dielectric elastomer actuator as compliant electrodes. As the actuator repeatedly expands and contracts isotropically under applied voltages, it requires compliant electrodes to be also stretchable in all directions. Our biaxially stretchable electrodes resulted in superior cyclic stability and greater expansion when involved in actuators. We anticipate our findings could potentially be applied to other metal NWs for stretchable optoelectronic applications.

The development of point of care biosensors is of fundamental importance towards the detection of cardiac diseases. The need for early detection of cardiac arrest has propelled the need for wearable biosensors. The current technology in the field of wearable sensors is focused towards monitoring the physiological parameters. The integration of electrochemical biosensors in the wearable textile biosensor is of crucial importance towards improving the quality of life. The conventional method for cardiac disease detection is the analysis of the electrocardiogram. The current trend in the research is inclined towards the point of care testing for spike in the levels of cardiovascular biomarkers.
The goal of our research is the design of a non-faradic label-free flexible textile biosensor to detect the concentration of the cardiovascular biomarkers through electrochemical impedance spectroscopy technique. Our research strategy is focused towards the understanding of biomolecular interactions between a surface functionalized electrode and electrolyte consisting of target biomarkers diluted in the sample buffer. These bimolecular interactions cause changes in the impedance which correlate to the concentration of the target biomarker in the test sample. We have validated our hypothesis that flexible porous substrates provide enhanced signal response compared to rigid substrate biosensors through our experiments.
We have evaluated different choices of electrode material such as Gold and Molybdenum on flexible substrate and our results exhibits linear sensor response over the clinically relevant concentrations for the biomarker detection to ascertain the presence of disease condition. The robustness of the sensor was validated by testing multiple concentrations of the biomolecule and through cross-reactivity experiments. The sensor performance was also evaluated on different buffer media to understand the effect of test medium on the biosensor characteristics.
Thus, the presented flexible textile biosensor resolves the need of robust textile biosensor capable of early detection of cardiovascular diseases.

Textiles, in combination with advances in materials and design, offer exciting new possibilities for human and environmental interaction, including biometric and touch-based sensing. Previous fabric-based or flexible touch sensors have generally required a large number of sensing electrodes positioned in a dense XY grid configuration and a multitude of wires. This paper investigates the design and manufacturing of a planar (two-dimensional, XY location) touch fabric sensor with only two electrodes (wires) to sense both planar touch and pressure, making it ideal for applications with limited space/complexity for wiring. The proposed knitted structure incorporates a supplementary method of sensing to detect human touch on the fabric surface which offers advantages over previous methods of touch localization through an efficient use of wire connections and sensing materials. This structure is easily manufactured as a single component utilizing flatbed knitting techniques and electrically conductive yarns. The design requires no embedded electronics or solid components in the fabric, which allows the sensor to be flexible and resilient. This paper discusses the design, fabrication, sensing methods, and applications of the fabric sensor in robotics and human-machine interaction, smart garments, and wearables, as well as the highly multidisciplinary approach pursued in developing medical textiles and flexible embedded sensors.

Smart fabrics have gained a great interest especially for applications such as healthcare monitoring during this last decade. Conducting polymers have been recently integrated in textiles as a non-invasive technique to record electrophysiological signal such as electromyography (EMG). PEDOT:PSS is commonly used for its mixed ionic and electronic transport properties that make it an ideal material for interfacing electronics with biology. It is biocompatible and highly conductive when doped with solvents and has been considered as a key material for printed electronics. In this work, we focused on the deposition of highly conducting PEDOT.PSS inks by inkjet printing. We formulated a new PEDOT:PSS ink with an electrical conductivity up to 420 S/cm. Thin-films have been successfully printed on a commercial stretchable fabric, elastane.
To match the electrodes with the electrical requirements to measure EMG, we printed on top of the PEDOT:PSS layer, an ionic liquid gel cured with UV light exposure. We measured the electrode/skin impedance on a healthy volunteer and successfully recorded EMG signal. The performances of those electrodes are in the same range than commercial electrodes. We did not observe significant sensitivity towards temperature and the printed electrode showed a slight change of resistance when stretched. These printed devices exhibit a performance equivalent to state-of-the-art devices. These results demonstrate that inkjet-printing can be used as a facile and low-cost technique to fabricate high quality electrodes for recording human electrophysiological signals on textiles.

Electrically conducting fabrics are unique combinations of an electrically conducting element and flexible fibrous structures. Emerging research is exploring these materials for microwave absorption, resistive heating, electromagnetic interference suppression and sensors. To fabricate conductive textiles, it is important to develop effective methods to uniformly and completely coat the individual filament within a fabric with a conductive material.
The present work highlights a promising solution-phase deposition route for efficient conformal coating of cellulose fibers with metallic copper. An easy one-step reaction between copper precursor and benzyl alcohol in the presence of cellulose fibers leads to dense, continuous and strongly adherent copper coatings on the cellulose fibers. Benzyl alcohol acts as a solvent and reducing agent for Cu²⁺ ions. The present metallization route offers an effective coating without any prefunctionalization of the cellulose fibers.
The conducting fibers processed into paper show electrical sheet resistance of 0.6 ohm over 12 mm. The emphasis of the current investigations is on processing conducting fibers into flexible mat or textile for the development of new electronic functional systems.

Cable-shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as lightweight, small size and bendability. Recently, we demonstrated a novel device architecture to develop an integrated coaxial supercapacitor cable that functions both as electrical cable and energy storage device. In addition, we also demonstrated a coil-type asymmetric supercapacitor electrical cable with enhanced cell operation voltage and extraordinary mechanical-electrochemical stability. Integration of electrical transmission and storage into a cable is unique and first of its kind. Its advantages are apparent in aviation and space exploration where pay loads and related costs are a primary concern. In addition, it can be made in the form of fibers which can be weaved to make energy storing fabrics for wearables.

Assistive robotic exoskeletons traditionally comprise rigid mechanical frames powered by motors or hydraulics. Yet the constraints imposed by each of these components on the size, weight, power consumption and automotility of the exosuit have prevented this technology from becoming a widespread solution for those with impaired mobility. The new field of soft robotics promises an avenue for sidestepping at least some of these issues by creating wearable assistive technologies from flexible shape morphing materials. Such a material capable of contracting in at least one axis could be fashioned to be worn parallel to the users own musculoskeletal system, thus enhancing or even replacing muscle function. Similarly, a material with tunable stiffness could provide support for load bearing activities such as walking.

Here we present an architectured fabric of embedded bimorph actuators that has a repertoire of dynamically controllable behaviors, allowing its shape, flexibility and surface area to be programmed. The chain-mail inspired material comprises two layers of rigid cubic frame elements (CFEs) stacked on top of one another, and an additional layer of internal CFEs interlaced between the two. The material’s flexibility is locally dependent on the dimensions of the internal CFEs relative to those of the external ones, which in turn define the material’s shape and volume. The result is a programmable flexible material.

The material requires a simulation framework for it to be programmed to meet bespoke users needs. We accomplished this using a numerical framework for computing both the passive and actuated forces acting on each individual link of the fabric. The framework then calculates flexibility through a rigid body physics engine and allows for parametric changes in the rigid body geometries as they actuate. We found this method to be significantly faster than traditional finite element multiphysics packages for determining the flexibility of actuating structures, and used the framework to demonstrate how the material’s linear, three-point and torsional flexibilities can be programmed through selectively modulating the internal CFE dimensions.

We validated the concept through a number of static prototypes made from laser sintered nylon, and an actuated prototype using NiTi archwire as a stand in for the ionic polymer metal composite bimorph actuators that we plan to integrate in future work. We show that the simulation framework can predict the dynamic behavior of the physical prototypes. Apart from the applications in the arena of exoskeletons, we believe this work has great potential in addressing the needs of the disabled, injured and the infirm, for mobility aids and smart bandages.

Fiber-based wearable electronics has gathered great interests as a ideal platforms with conformable wearing sensation. Ultimately, to realize weaving-based e-textile system development of the functional fibers integrated with electronic component has been required. To date, organic field-effect transistors (OFETs) based on wire or fiber-shaped substrate have been demonstrated, however the devices were formed at one side of the fiber due to limited coating technology of functional materials. In this work, we have demonstrated the polymer dielectric/organic semiconductor core-shell fibers by die-coating of polymer/semiconductor blend solution. Using the die-coating method, the uniform coating film was obtained unlike with dip-coating method. Vertical phase-separation of the blend solution realized polymer dielectric (inside) /semiconductor (outside) bilyers wrapped fibers in a one-step coating process. The resulting OFET devices exhibited the charge-mobility comparable to that of the device based on a flat substate. The transistor performances at each position surrounding the coaxial fiber were almost identical, indicating the uniform core-shell structure of the fiber. Furthermore, the fibreform OFET integrated with condunting threads as a source and drain electrodes was successfully demonstrated. This presentation will provide significant advancement in semiconducting fiber and its application to texile system, which can motivate other researchers to carry out further investigations.

Recently, wearable smart devices or system have been spotlighted significantly in a large variety of industrial application areas, due to their significance in the emerging electronic field. In order to apply to various electronic components in a fiber textile, electronic components are attached in wearable clothes such as light emitting diode embedded t-shirt for electronic textiles (e-textile). Due to this ability, numerous research groups considered fiber-embedded wearable electronics to be new brand of flexible multifunctional fabric electronics and thus have studied and developed the integration of wearable devices such as fiber-embedded electrolyte-gated field-effect transistors (FETs), fiber organic light emitting diodes (OLED), and fiber integrated circuits. In most of these cases, however, organic materials are used for the device fabrication mainly due to their low-temperature processibility in order to use a low-thermal-budget polymer fiber as a substrate. Although lots of organic electronics have shown their possibilities for fiber-type electronic devices, their performance is thought to be still unsatisfactory for the applications in consumer electronics level e-textile systems. Hence, for realizing high-performance and reliable e-textiles, functional fibers based on inorganic materials and their corresponding fabrication technologies should to be developed. In several inorganic materials candidates, metal oxide materials are considered to be more competitive than other material systems because their electrical and mechanical properties are easily tuned and a variety of conformal deposition methods are available from vapour deposition to solution processing.
In this work, we demonstrate a simple and facile route to achieve high-performance metal-oxide-based F-FETs by using fabrication processes which are compatible with the current microelectronic fabrication. Particularly, solution-processing combined with low-temperature photochemical activation were used to obtain dense and reliable metal-oxide dielectric and semiconducting layers on a cylindrical shape fiber substrate. Using these processes, high mobility indium oxide (InOx) and indium gallium zinc oxide (IGZO) F-FETs were successfully realized, having electrical performances comparable to those fabricated on a planar substrate such as an extremely low leakage current density of ~10^-7 A/cm² and a high breakdown field of 4.1 MV/cm. Furthermore, the indium oxide F-FETs, which are photochemically activated at a low temperature, showed a field-effect mobility and on/off ratio of 3.9 cm²/V-s and >10⁶, respectively, which we believe are among the highest performance fiber-type FETs reported to date.

In the last decade, a large number of wearable devices have emerged. Wearable electronics is a viable solution for a large number of monitoring tasks, for several reasons: textiles are generally low cost, flexible, versatile materials and the idea of monitoring several bioparameters by means of devices embedded in textiles is especially attracting for the inherent unobtrusivity of these materials.
However the first attempts of monitoring electronic systems have been mainly based on the idea of integrating electronics into clothes exploiting the extreme miniaturization ability expressed by traditional electronic materials. Now it is the time of addressing a new approach, i.e. to focus on the direct integration of electronic functions into textiles, thanks to the employment of conductive polymers and technologies at the nanosize.
We have first developed a reliable method for making a common textile fibre electrically conductive, and starting from this milestone, we have developed several new functions, going from fibered transistors, to sensors. In this talk we will give a panoramic view of all these functions and of the possible future perspectives of this technology.
As an example, a fully textile pressure sensing platform will be presented. Textiles represent ideal materials to measure the pressure distribution between any surface and the human body due (among other things) to their inherent light-weight, flexibility and the possibility to fabricate them with low cost processes. At the moment, the few existing textile pressure sensors imply the use of multilayered configurations of fabrics and films that limits the minimum thickness of the devices, are not cost effective or both. We developed a new type of piezoresistive textile sensor made of a piece of standard lightweight 100% cotton fabric treated with a conductive polymer at the crossing point of two silver coated yarns stitched on it. Our approach allows having a large number of sensing elements arranged in a matrix configuration while dealing with a relatively simple fabrication process that involve only sewing (embroidering) a single layer of fabric and stamping (printing or drop-casting) on it spots of a polymeric solution. The sensitivity of our sensors can be defined by adjusting the mixture of the conductive polymer solution. Our prototypes typically have working ranges from few kilo Pascals to few mega Pascals. Applications of this technology can range from touch sensors in gloves and plantar pressure sensors in socks or insoles to pressure sensitive carpets and smart furniture.

One of the main challenges in wearable sensors is to conform and wrap over surfaces, accompanying movements in unobtrusive manner. An attractive solution is to use sensing devices based on soft and flexible materials with compliances and extensibilities not allowed by rigid components (e.g. fabrics, elastomers, polymers) that can be embedded into garments for applications in human motion detection, health monitoring and therapeutics[1]. Here, we present a sensorized glove with electrotextiles-based tactile sensors embedded, capable of providing information about contact and forces during grasping and manipulation tasks. Earlier studies address the integration of conductive textiles and/or flexible polymers strain sensors into gloves for motion detection[2]. However, few focus on textile-based tactile sensors embedded into gloves providing information about spatial force distribution[3]. Hence, we propose a glove embedding capacitive tactile sensors able to provide spatial information about normal force up to 20 N, with a resolution in the mN scale. Such sensors, in addition to the low cost and easy fabrication process, have mechanical properties suitable for adaptive and safe interactions with the environment, and can lead to highly sensitive and robust devices[4]. The glove has three sensorized fingers. For the index and middle finger two sensor arrays (each containing four sensors with an area of 15x20 mm²) are located at the distal phalanges, and one sensor (area of 20x20 mm²⁾ is at the proximal phalange. A single sensor (area of 20x30 mm²) is positioned also on the thumb. Each capacitive sensor array is made by a combination of conductive and dielectric layers: one electrode layer (with four channels) of 150 μm thick non-stretchable copper/tin coated textile (Zelt, Mindsets Ltd), a ground layer and a shield layer of stretchable fabric made of silver-plated nylon fibers (Electrolycra, Mindsets Ltd.), and silicone elastomeric dielectric films with thickness from 100 to 300 μm (i.e., Ecoflex 0010, Smooth-On; Fluorosilicone, Dow Corning 730). The sensors’ electronics is integrated in a 300 μm thick PCB on the dorsal side of each finger, to perform differential measurements (i.e. reducing the influence of parasitic capacitances[5]). Finally, data are acquired by a PIC32 microcontroller, integrated on a PCB on the dorsal side of the glove.
References
[1] Yamada et al., “A stretchable carbon nanotube strain sensor for human-motion detection”, Nat. Nanotech., 2011
[2] Akerfeldt et al., “Textile sensing glove with piezoelectric PVDF fibers and printed electrodes of PEDOT:PSS”, Textile Res. Journal, 2015
[3] Lee et al., “Conductive fiber-based ultrasensitive textile pressure sensor for wearable electronics”, Adv. Mat. 2015
[4] Viry et al., “Flexible three-axial force sensor for soft and highly sensitive artificial touch”, Adv. Mat., 2014
[5] Lucarotti et al., “Revealing bending and force in a soft body through a plant root inspired approach”, Sci. Rep., 2015

The issue to monitor human psycho-physical condition in noninvasive way, with wearable bio chemical sensor, through the real time test of physiological fluids, like sweat, need at least two strategic conditions to be realized. At first the device should be really wearable and noninvasive, in a way that is not disturbing the daily life of the patients, then the device should absorb the fluids when they are produced. To reach this goal, we realized an electrochemical chemical sensor built directly on a textile fiber of natural cotton. A specific functionalization allows the creation of a fully wearable device, which could not be felt by the user, and it is able to naturally absorb the fluids to be tested, during any sports or physical activity. The device maintains flexibility, ease of preparation, low cost and biocompatibility [1]. Moreover it exploits a transistor architecture, which allows a high gain in transconductance and opens to different possible configuration measurements [2].Herein we applied conductive organic material on a natural textile surface, which being sensible to positive ions in the fluids, act as a wearable electrochemical transistor. In particular, the cotton sensors have been used to monitor saline concentration in human sweat and to control dehydration of the patients [3]. Then a selective detection of specific molecules as neurotransmitters have been tested. Adrenaline has been selectively revealed with respect to saline concentration. The sensing works through an oxidation process using nano-Pt electrode with formation adrenaline-quinone and then of adrenochrome [4]. The oxidation of adrenaline has been studied with UV-Visible absorbance in different conditions: in air, in presence of silver and of platinum working electrode. Then, with a fine control of the reaction at the electrodes, on the kinetic of sensing and using specific functionalization (enzymes), it is possible to reveal Tyrosine, Dopamine and Phenylalanine, with high selectivity with respect to other interferents. The detection of human neurotransmitters is very important, because it allows to monitor psycho-physical condition, preventing critical conditions like panic or heart attack. With an in-situ and non-invasive approach, the proposed selective biosensors can monitor human performances (hydration and stress), and thus, could find large applications in sports, health care and working safety.
References:
[1] M. Nikolou, et al. Chem. Rec. 8, 13 (2008). [2] G. Malliaras et al. Nature Communications 4, Article number: 2133 [3] G. Tarabella et al., J. Mater. Chem., 2012, 22, 23830 [4] N. Coppedè et al. J. Mater. Chem. B, 2014,2, 5620-5626

The study of on-body energy harvesting is most often focused on improving and optimizing the energy harvester. However, other factors play a critical factor in the energy harvesting integration techniques of the harvester to close-to body materials of the wearable device. In addition, one must recognize the wide array of human factors and ergonomic factors that lead a variation of the energy harvesting. In this work, key affecting variables at varying on-body locations are investigated for commercial thermoelectric generators (TEGs) integrated within a textile-based wearable platform. For this study, a headband and an armband is demonstrated with five TEGs connected in series in a flexible form factor via Pyralux®. These platforms enable comparison of the amount of energy harvested from the forehead versus the upper arm during various external conditions and movement profiles, e.g. running, walking, and stationary for periods of up to 60 minutes. During these tests, ambient temperature, ambient humidity, accelerometry, and instantaneous power are recorded live during the activity and correlated to the energy harvested. Human factors such as skin temperature and application pressure were also analyzed. Our analysis demonstrates that vigorous movement can generate over 100 µW of instantaneous power from the headband and up to 35 µW from the armband. During the stationary movement profile, the instantaneous power levels of both the headband and the armband decreased to a negligible value. Our studies show that for higher intensities of movement, air convection on the cool side of the TEG is the dominating variable whereas the temperature gradient has a significant effect when the subject is stationary. This work demonstrates key materials and design factors in on-body thermoelectric energy allows for a strategic approach to improving the integration of the TEGs.

There is a growing demand for soft robots that can interact and work closely with humans. Such robots need to be compliant, lightweight and equipped with silent and soft actuators. Electroactive polymers such as conducting polymers (CPs) are “smart” materials that deform in response to electrical simulation and are often addressed as artificial muscles due to their functional similarity with natural muscles. They offer unique possibilities and are perfect candidates for such actuators since they are lightweight, silent, and driven at low voltages.
Our goal is to develop soft and silent actuators to provide natural motion to soft robotics, prosthetics and exoskeletons. This ambitious goal is accomplished by merging one of humankind oldest technology with one of the latest, that is to combine the textile techniques of weaving and knitting with conducting polymers. We have developed new CP based fibres and novel architectures employing parallel assembly of the CP fibres using advanced textile technology resulting in electroactive textile actuators. These will provide enhanced actuation strain, speed and stress, similar to natural muscles. Textile manufacturing allows efficient large scale manufacturing.
We will present the fabrication and characterisation of these CP based textiles as well as their performance as linear actuators.

Sensoria focuses on the development of smart garments as wearable technology. With the vision that The Garment Is the Computer®, our goal is to provide meaningful impact to everyday activities by introducing technology through natural and intuitive ways. We have developed a flexible platform with common components that enable rapid creation of different systems to address a variety of scenarios.


This presentation will include a discussion of the technology platform and examples of smart garment systems that have been developed. This includes a running system for consumers consisting of smart sports bra and t-shirt with integrated heart rate monitoring, along with smart socks infused with our proprietary textile pressure sensors that are soft, comfortable and washable. The socks and associated electronics help track running parameters such as foot landing, cadence and time on the ground. The same technology components are also utilized in the development of the first IoT-enabled orthotic to help improve balance and reduce the risk of falls. In addition, the smart sock has also been integrated with a next generation rehabilitation system to help monitor gait and balance during rehab exercises.

The skin repairing and scaring processes are related to the temperature and humidity retention capabilities of the wound site. The traditional bandages routinely used for wound protection. Their daily checkup and recurrent replacement are not just increasing the chance of bacterial contamination but also disturb the skin repairing processes. It slows down the rate of chemical and enzymatic healing processes as well as the metabolism of tissue cells. The monitoring of the wound site temperature and the local moisture level is essential to detect the beginning of an infection. Medical professionals are using infrared detectors that allow only for non-contact temperature monitoring. We build the thin-film biosensor that can integrate in medical textile bandages with capability to monitor both temperature and moisture. The sensors are made of organic materials that can quickly detect temperature variation within few seconds. These materials are also sensitive to the humidity deviation. Such sensors can be placed in the close proximity of the damaged skin surface non-invasively and provide real-time diagnosis of the wound healing.