Percolating Network of Ultrathin Gold Nanowires and Silver Nanowires toward “Invisible” Wearable Sensors for Detecting Emotional Expression and Apexcardiogram
TL;DR: In this paper, highly sensitive, stretchable, patchable, and transparent strain sensors are fabricated based on the hybrid films of soft/hard networks, which are mechanically stretchable and optically transparent, and electrically conductive.
Abstract: 2 nm thin gold nanowires (AuNWs) have extremely high aspect ratio (≈10 000) and are nanoscale soft building blocks; this is different from conventional silver nanowires (AgNWs), which are more rigid. Here, highly sensitive, stretchable, patchable, and transparent strain sensors are fabricated based on the hybrid films of soft/hard networks. They are mechanically stretchable, optically transparent, and electrically conductive and are fabricated using a simple and cost-effective solution process. The combination of soft and more rigid nanowires enables their use as high-performance strain sensors with the maximum gauge factor (GF) of ≈236 at low strain (<5%), the highest stretchability of up to 70% strain, and the optical transparency is from 58.7% to 66.7% depending on the amount of the AuNW component. The sensors can detect strain as low as 0.05% and are energy efficient to operate at a voltage as low as 0.1 V. These attributes are difficult to achieve with a single component of either AuNWs or AgNWs. The outstanding sensing performance indicates their potential applications as “invisible” wearable sensors for biometric information collection, as demonstrated in applications for detecting facial expressions, respiration, and apexcardiogram.
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TL;DR: This review summarizes the latest advances in this emerging field of "bio-integrated" technologies in a comprehensive manner that connects fundamental developments in chemistry, material science, and engineering with sensing technologies that have the potential for widespread deployment and societal benefit in human health care.
Abstract: Bio-integrated wearable systems can measure a broad range of biophysical, biochemical, and environmental signals to provide critical insights into overall health status and to quantify human performance. Recent advances in material science, chemical analysis techniques, device designs, and assembly methods form the foundations for a uniquely differentiated type of wearable technology, characterized by noninvasive, intimate integration with the soft, curved, time-dynamic surfaces of the body. This review summarizes the latest advances in this emerging field of “bio-integrated” technologies in a comprehensive manner that connects fundamental developments in chemistry, material science, and engineering with sensing technologies that have the potential for widespread deployment and societal benefit in human health care. An introduction to the chemistries and materials for the active components of these systems contextualizes essential design considerations for sensors and associated platforms that appear in f...
727 citations
TL;DR: The recent advances in stretchable conductors based on the percolation networks of nanoscale conductive fillers in elastomeric media are summarized and various techniques that are used to reduce the contact resistance between the conductive filler materials are highlighted.
Abstract: Highly conductive and intrinsically stretchable electrodes are vital components of soft electronics such as stretchable transistors and circuits, sensors and actuators, light-emitting diode arrays, and energy harvesting devices. Many kinds of conducting nanomaterials with outstanding electrical and mechanical properties have been integrated with elastomers to produce stretchable conductive nanocomposites. Understanding the characteristics of these nanocomposites and assessing the feasibility of their fabrication are therefore critical for the development of high-performance stretchable conductors and electronic devices. We herein summarise the recent advances in stretchable conductors based on the percolation networks of nanoscale conductive fillers in elastomeric media. After discussing the material-, dimension-, and size-dependent properties of conductive fillers and their implications, we highlight various techniques that are used to reduce the contact resistance between the conductive filler materials. Furthermore, we categorize elastomer matrices with different stretchabilities and mechanical properties based on their polymeric chain structures. Then, we discuss the fabrication techniques of stretchable conductive nanocomposites toward their use in soft electronics. Finally, we provide representative examples of stretchable device applications and conclude the review with a brief outlook for future research.
347 citations
TL;DR: The developed wearable device is demonstrated by measuring sweat‐alcohol and ISF‐glucose in human subjects consuming food and alcoholic drinks and makes the developed platform extremely attractive for enhancing the power and scope of next‐generation noninvasive epidermal biosensing systems.
Abstract: The development of wearable biosensors for continuous noninvasive monitoring of target biomarkers is limited to assays of a single sampled biofluid. An example of simultaneous noninvasive sampling and analysis of two different biofluids using a single wearable epidermal platform is demonstrated here. The concept is successfully realized through sweat stimulation (via transdermal pilocarpine delivery) at an anode, alongside extraction of interstitial fluid (ISF) at a cathode. The system thus allows on-demand, controlled sampling of the two epidermal biofluids at the same time, at two physically separate locations (on the same flexible platform) containing different electrochemical biosensors for monitoring the corresponding biomarkers. Such a dual biofluid sampling and analysis concept is implemented using a cost-effective screen-printing technique with body-compliant temporary tattoo materials and conformal wireless readout circuits to enable real-time measurement of biomarkers in the sampled epidermal biofluids. The performance of the developed wearable device is demonstrated by measuring sweat-alcohol and ISF-glucose in human subjects consuming food and alcoholic drinks. The different compositions of sweat and ISF with good correlations of their chemical constituents to their blood levels make the developed platform extremely attractive for enhancing the power and scope of next-generation noninvasive epidermal biosensing systems.
312 citations
TL;DR: In this article, a new class of nature-inspired ionic conductors based on supramolecular sodium alginate (SA) nanofibrillar double network (DN) hydrogels with complex shapes by injection is demonstrated.
Abstract: There is a growing demand for flexible and stretchable strain/pressure sensors for different applications. However, existing conductors usually cannot meet all the requirements for use in next-generation wearable sensors. In this work, we demonstrate a new class of nature-inspired ionic conductors based on supramolecular sodium alginate (SA) nanofibrillar double network (DN) hydrogels with complex shapes by injection. Owing to their dermis-mimicking structures, these hydrogels exhibit unique features, such as high transparency (99.6%), high tension/compression strength (0.750 MPa/4 MPa), high stretchability (3120%), high toughness (4.77 MJ m−3) and superior elasticity (100%) at high strain (1000%). In particular, the use of salts (e.g., NaCl) as triggers in supramolecular assembly combining SA makes the hydrogels ideal ionic conductors. The ionic conductors were demonstrated as strain sensors with high sensitivity to an extremely broad strain window (0.3–1800%) and a low applied voltage (down to 0.04 V), as well as with high pressure sensitivity (1.45 kPa−1). These hydrogel-based ionic sensors may find applications in sports monitoring, human/machine interfaces and soft robotics.
299 citations
TL;DR: The basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them, among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included.
Abstract: Considerable progress in materials development and device integration for mechanically bendable and stretchable optoelectronics will broaden the application of "Internet-of-Things" concepts to a myriad of new applications. When addressing the needs associated with the human body, such as the detection of mechanical functions, monitoring of health parameters, and integration with human tissues, optoelectronic devices, interconnects/circuits enabling their functions, and the core passive components from which the whole system is built must sustain different degrees of mechanical stresses. Herein, the basic characteristics and performance of several of these devices are reported, particularly focusing on the conducting element constituting them. Among these devices, strain sensors of different types, energy storage elements, and power/energy storage and generators are included. Specifically, the advances during the past 3 years are reported, wherein mechanically flexible conducting elements are fabricated from (0D, 1D, and 2D) conducting nanomaterials from metals (e.g., Au nanoparticles, Ag flakes, Cu nanowires), carbon nanotubes/nanofibers, 2D conductors (e.g., graphene, MoS2 ), metal oxides (e.g., Zn nanorods), and conducting polymers (e.g., poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate), polyaniline) in combination with passive fibrotic and elastomeric materials enabling, after integration, the so-called electronic skins and electronic textiles.
284 citations
References
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TL;DR: Inorganic and organic electronic materials in microstructured and nanostructured forms, intimately integrated with elastomeric substrates, offer particularly attractive characteristics, with realistic pathways to sophisticated embodiments, and applications in systems ranging from electronic eyeball cameras to deformable light-emitting displays are described.
Abstract: Recent advances in mechanics and materials provide routes to integrated circuits that can offer the electrical properties of conventional, rigid wafer-based technologies but with the ability to be stretched, compressed, twisted, bent, and deformed into arbitrary shapes. Inorganic and organic electronic materials in microstructured and nanostructured forms, intimately integrated with elastomeric substrates, offer particularly attractive characteristics, with realistic pathways to sophisticated embodiments. Here, we review these strategies and describe applications of them in systems ranging from electronic eyeball cameras to deformable light-emitting displays. We conclude with some perspectives on routes to commercialization, new device opportunities, and remaining challenges for research.
4,127 citations
TL;DR: A class of wearable and stretchable devices fabricated from thin films of aligned single-walled carbon nanotubes capable of measuring strains up to 280% with high durability, fast response and low creep is reported.
Abstract: Thin films of single-wall carbon nanotube have been used to create stretchable devices that can be incorporated into clothes and used to detect human motions.
2,790 citations
TL;DR: In this article, the authors present recent advancements in the development of flexible and stretchable strain sensors, including skin-mountable and wearable strain sensors for personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth.
Abstract: There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin-mountable, and wearable strain sensors are needed for several potential applications including personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin-mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.
2,154 citations
TL;DR: The applicability of the high performance strain sensors based on the nanocomposite of silver nanowire network and PDMS elastomer in the form of the sandwich structure is demonstrated by fabricating a glove integrated with five strain sensors for the motion detection of fingers and control of an avatar in the virtual environment.
Abstract: The demand for flexible and wearable electronic devices is increasing due to their facile interaction with human body. Flexible, stretchable and wearable sensors can be easily mounted on clothing or directly attached onto the body. Especially, highly stretchable and sensitive strain sensors are needed for the human motion detection. Here, we report highly flexible, stretchable and sensitive strain sensors based on the nanocomposite of silver nanowire (AgNW) network and PDMS elastomer in the form of the sandwich structure (i.e., AgNW thin film embedded between two layers of PDMS). The AgNW network-elastomer nanocomposite based strain sensors show strong piezoresistivity with tunable gauge factors in the ranges of 2 to 14 and a high stretchability up to 70%. We demonstrate the applicability of our high performance strain sensors by fabricating a glove integrated with five strain sensors for the motion detection of fingers and control of an avatar in the virtual environment.
1,837 citations
TL;DR: An efficient, low-cost fabrication strategy to construct a highly sensitive, flexible pressure sensor by sandwiching ultrathin gold nanowire-impregnated tissue paper between two thin polydimethylsiloxane sheets is reported, enabling facile large-area integration and patterning for mapping spatial pressure distribution.
Abstract: Flexible electronics hold great promise for wearable biomedical sensors. Here, the authors report a pressure sensor composed of gold nanowire-impregnated tissue paper, sandwiched between polydimethylsiloxane sheets, and demonstrate that the design is appropriate for large-area flexible electronics.
1,678 citations