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Epidermal electronics has garnered significant research attention due to its promising applications in wearable human‐machine interfaces and intelligent healthcare sensing. However, their widespread use faces challenges due to complex manufacturing processes, high material costs, inadaptability to different skin surfaces, and inadequate reusability. Herein, inspired by the biological reshapability and environmental adaptability of amoeba, an ultra‐deformable (≈2600% strain), bioadhesive (adhesive strength ≈3 kPa), strong self‐healing (fastest recovery time ≈1s, maximum wound distance ≈5 mm), and electromechanical‐durable wearable electronic slime (E‐slime) is proposed, which can instantaneously form on‐skin electronics in situ to detect body motion and physiological signals. E‐slime demonstrates desired sensing performance with high sensitivity (gauge factor 2.95), wide sensing range (up to 400% strain), and low detection limit (≈1% strain), which can seamlessly adhere to the skin and can be easily reused multiple times (≈100 cycles usage). E‐slime also enables on‐the‐fly deployment of motion monitoring tasks at various body locations, showcasing its versatility and reliability for body motion recognition and personal health monitoring. This study holds potential for next‐generation green electronics, motion sensing devices, and wearable human‐machine interfaces, ultimately helping to ensure healthy lives and promote well‐being. [ABSTRACT FROM AUTHOR]

Monitoring tactile pressure and recognizing action are important functionalities for artificial electronic skin (e‐skin). Furthermore, in order to create conformable coverings for 3D objects, an e‐skin needs to be stretchable, without sacrificing sensitivity to tactile pressure. However, stretching of sensors normally affects their output stability. In this study, a stretchable e‐skin is developed using laser‐induced graphene and a liquid metal alloy, GaInSn, in an elastic ecoflex polymer to create a stretchable, resistive‐type tactile pressure sensor. Furthermore, a pressure sensor array is fabricated as an e‐skin, and output is signal‐processed using machine learning. With this system, the e‐skin also monitors its stretching state, with the result that tactile pressure can be calculated regardless of the degree of stretching. With machine learning‐assisted e‐skin, actions such as patting, sliding, and grabbing are successfully recognized in the manner of human skin. [ABSTRACT FROM AUTHOR]

Field concentration is often regarded as a problematic issue in soft electronics applications, especially when using curved electrodes, and in particular, those with sharp edges. However, field concentration can be turned into an advantage with appropriate device design. Herein, the applications of field concentration in hydrogel‐elastomer devices are explored. Three different types of electroluminescent hydrogel‐elastomer devices are fabricated using different types of electrodes and different light patterns. In addition, the effect of the field concentration can be extended into the bulk of the elastomer by preparing porous silicone elastomers and filling them with silicone oil. These devices are shown to be flexible and possess both good luminance and a long lifetime. [ABSTRACT FROM AUTHOR]

Stretchable devices and magneto-rheological elastomers (MREs) are together studied in the present work. The device based on composites generates an impressive ~ 8.5 V, and the composites based on iron oxide (Fe2O3) act as a catalyst for magneto-sensitive behavior. The composites were prepared by solution mixing of room-temperature vulcanized silicone rubber (RTV-SR), multi-wall carbon nanotube (MWCNTs), Fe2O3, molybdenum disulfide (MoS2), and their hybrid. From the experimental results, the hybrids were exhibiting a synergistic effect in properties and MWCNT at as low as 2 per hundred parts of rubber (phr) shows the robust increase in properties of the composites. The higher properties of MWCNT were proposed due to its high aspect ratio of 65, tube shape morphology which is easy to disperse, and higher cross-link density in the composites. This work provides insight to readers on a way to obtain robust properties of composite that are good for high-performance applications in MREs and remarkable piezo-electric energy harvesting. [ABSTRACT FROM AUTHOR]

Herein, PEO/Al@SiO2 core–shell polymer nanocomposite (CSPNC) was synthesized through the casting route. The product obtained was evidenced using XRD, FTIR, FESEM, and SEM/EDS techniques. XRD patterns confirmed the semicrystalline nature of the as-synthesized film. FTIR absorption spectra confirmed the functional groups of the CSPNC film. FESEM revealed uniform polymer networks and a spherical-like shape of the bimetallic core–shell nanoparticles (BCSNPs), with average diameters ranging from 30.47 to 36.38 nm in size for the Al core and 278.55 to 428.73 nm in size for the SiO2 shell. EDS analysis revealed the presence of C, O, Al, and Si elements. All the optical coefficients were enhanced upon CSPNC loading. The reduced bandgap (direct and indirect) values of the CSPNC's film as compared to that of PEO polymer demonstrated a significant structural disorder of the PEO functional groups, which explains the localized state creation that helped the transition of electrons. The product's dielectric properties were significantly improved, and the resistance values were changed from 180 MΩ to 35 MΩ in the 100 Hz–5 MHz frequency range. Ultimately, the synthesized CSPNC is recommended for use in the fabrication of stretchable optoelectronic devices. [ABSTRACT FROM AUTHOR]

Recently, the advances in stretchable electronic devices have attracted great attention around the world. New technologies are constantly updated to obtain a stretchable device with high performance and robust durability. The stretchable device‐based rubber composites were prepared with the addition of room‐temperature‐vulcanized silicone rubber (RTV‐SR) and different types of nanofillers such as graphite nanoplatelets (GNP), molybdenum disulfide (MoS2), and their hybrid. The hybrid composites contain both nanofillers in 50:50 ratios. The mechanical performance of the stretchable device was studied and presented. For example, the compressive modulus was 1.86 MPa (virgin), and at 20 per hundred parts of rubber (phr) was 3.9 MPa (GNP), 2.3 MPa (MoS2), and 2.72 MPa (Hybrid). The mechanical stretching ability of the composites was 120% (virgin), and at 20 phr was 170% (GNP), 182% (MoS2), and 171% for (Hybrid). At end of the work, a novel stretchable device based on a piezo‐electric effect is presented which provides an output voltage of ~1.2 V and high durability of >0.1 million cycles without significant degradation. This device is based on a rubber composite with the inclusion of electro‐active and dielectric materials as described in the subsequent section of the paper. [ABSTRACT FROM AUTHOR]

Past decades have witnessed the generation of new stretchable photodetectors in electronic eyes, health sensing, wearable devices, intelligent monitoring and other fields. Stretchable devices require not only outstanding performance but also excellent flexibility, adaptability and stability. Innovative strategies have been proposed to realize the stretchability of devices. In addition, novel functional materials including zero‐dimensional nanomaterials, one‐dimensional inorganic nanomaterials, two‐dimensional layered materials, organic materials, and organic‐inorganic composite materials with excellent properties are emerging to continuously improve the performance of devices. Here, the recent research progress of stretchable photodetectors in terms of both various design methods and functional materials is outlined. The optical performance and stretchable properties are also comprehensively reviewed. Finally, a summary and the challenges associated with the application of stretchable photodetectors are presented. [ABSTRACT FROM AUTHOR]

Recently, organic electrochemical crystals (OECT) using conjugated polymers as channel materials have become a hot research topic due to their ease of preparation, ionelectron conversion capability and biointerface compatibility. However, most of the reported OECT channel materials for OECT are p-type conjugated polymers (hole transport), while few OECTs have been developed based on n-type conjugated polymers (electron transport), and the unbalanced development hinders the realization of complex complementary circuits. The recently reported n-type Poly (benzimidazobenzophenanthroline) (BBL) OECT of polyconjugated polymers provides an effective solution to the above problem. However, BBL films are inherently brittle and cannot be stretched to meet the use of flexible devices, which greatly hinders their application and development. In this work, we propose the preparation of a device stretchable n-type BBL OECT device and verify its feasibility for sweat sensing. [ABSTRACT FROM AUTHOR]

Stretchable devices, garnering increasing attention as next-generation form factors, have a crucial problem in that vertical contraction occurs during stretching, causing image distortion of stretchable displays and discomfort in skin-attached devices. Previous structural strategies to mitigate vertical contraction, such as auxetic reentrants and wrinkles, suffer from the drawback that their structure becomes visible during stretching. In this study, this issue is addressed by unidirectionally aligning nanoscopic cylinders within block copolymer elastomer films. Employing a shear-rolling process at high temperatures on thick films of polystyrene-block-polyisobutylene-block-polystyrene thermoplastic elastomers, macroscopic mechanical anisotropy is achieved, resulting in completely transparent and monotonically stretchable substrates devoid of vertical or depth distortion during deformation. Significantly, the unidirectional orientation of high-modulus cylindrical nanostructures induces macroscopic mechanical anisotropy with a modulus ratio exceeding five times. While the Poisson's ratio of conventional elastic materials hovers around ≈0.5, this mechanical anisotropy minimizes vertical contraction, yielding a Poisson's ratio below 0.07. Moreover, owing to the negligible size of the nanocylinders compared to visible-light wavelengths, the substrate can be monotonically uniaxially stretched while maintaining high transmittance without introducing distortions, surface undulations, or haziness, resulting in distortion-free stretchable substrates., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

New technologies are constantly addressed in the scientific community for updating novel stretchable devices, such as flexible electronics, electronic packaging, and piezo-electric energy-harvesting devices. The device promoted in the present work was found to generate promising ~6V and durability of >0.4 million cycles. This stretchable device was based on rubber composites. These rubber composites were developed by solution mixing of room temperature silicone rubber (RTV-SR) and nanofiller, such as multi-wall carbon nanotube (MWCNT) and micron-sized copper particles and their hybrid. The hybrid composite consists of 50:50 of both fillers. The mechanical stretchability and compressive modulus of the composites were studied in detail. For example, the compressive modulus was 1.82 MPa (virgin) and increased at 3 per hundred parts of rubber (phr) to 3.75 MPa (MWCNT), 2.2 MPa (copper particles) and 2.75 MPa (hybrid). Similarly, the stretching ability for the composites used in fabricating devices was 148% (virgin) and changes at 3 phr to 144% (MWCNT), 230% (copper particles) and 199% (hybrid). Hence, the hybrid composite was found suitable with optimum stiffness and robust stretching ability to be useful for stretching electronic devices explored in this work. These improved properties were tested for a real-time stretchable device, such as a piezoelectric energy-harvesting device and their improved voltage output and durability were reported. In the end, a series of experiments conducted were summarized and a discussion on the best candidate with higher properties useful for prospective applications was reported. [ABSTRACT FROM AUTHOR]

Alternating current‐driven electroluminescent (ACEL) devices have recently emerged as a potential candidate for next‐generation smart lighting, stretchable displays, and wearable electronics. Herein, a simple and efficient method is developed to fabricate high brightness, chromatic‐stable, and stretchable white ACEL devices through doping wide‐spectrum yellow photoluminescent phosphor into blue electroluminescent emissive layer. By tuning the ratio of electroluminescent to photoluminescent phosphors in the emissive layer, the optimized device achieved a maximum brightness of 3150 cd m−2 for white emission with Commison Internationale de L'Eclairage coordinates of (0.28, 0.34), and manifested a more stable chromaticity than traditional ACEL devices. Moreover, a digital display and stretchable white ACEL device (with a tensile strain of 150%) are demonstrated to show the generality of this approach. The high brightness white ACEL devices proposed in this work offer a simplified architecture with facile fabrication process and large‐area compatibility, which may find broad range of applications in wearable optoelectronics. [ABSTRACT FROM AUTHOR]

Increasing surface area between electrodes and electrolytes drastically has proven to improve electrochemical performances of microbatteries. 3D surface enhancement owing to the design of micropillar electrodes has permitted to fulfill this need while maintaining the same footprint area. Lithium nickel manganese oxide (cathode) and Lithium titanate (anode) micropillars with different sizes are successfully fabricated on aluminum foils by laser ablation technique and are then separated by a polymer electrolyte to form stretchable lithium-ion microbatteries. The electrochemical performance of full batteries composed of different micropillar sizes is studied in detail. The importance of controlling the width of micropillars is demonstrated and correlated with a simple theoretical model to optimize the battery properties. It is also shown that areal capacity values can be enhanced by improving the electrode/electrolyte interfaces using a simple treatment under vacuum. [ABSTRACT FROM AUTHOR]

Stretchable electronics have demonstrated excellent potential in wearable healthcare and conformal integration. Achieving the scalable fabrication of stretchable devices with high functional density is the cornerstone to enable the practical applications of stretchable electronics. Here, a comprehensive methodology for realizing large-scale, 3D, and stretchable circuits (3D-LSC) is reported. The soft copper-clad laminate (S-CCL) based on the "cast and cure" process facilitates patterning the planar interconnects with the scale beyond 1 m. With the ability to form through, buried and blind VIAs in the multilayer stack of S-CCLs, high functional density can be achieved by further creating vertical interconnects in stacked S-CCLs. The application of temporary bonding substrate effectively minimizes the misalignments caused by residual strain and thermal strain. 3D-LSC enables the batch production of stretchable skin patches based on five-layer stretchable circuits, which can serve as a miniaturized system for physiological signals monitoring with wireless power delivery. The fabrications of conformal antenna and stretchable light-emitting diode display further illustrate the potential of 3D-LSC in realizing large-scale stretchable devices., (© 2024 Wiley‐VCH GmbH.)

Plasmonic nanostructures are important building blocks in modern nanoscience and nanotechnology. Significant research efforts have been directed toward developing solution‐based or rigid‐substrate‐supported metallic nanostructures for novel applications in biophotonics, sensing, energy, and medicine. In parallel, there has been an increasing interest in the fabrication of plasmonic nanostructures on elastomeric substrates and exploring the impact of mechanical deformation including bending, torsion, and stretching on the collective plasmonic resonance properties. This burgeoning field may be defined as soft plasmonics (or soft mechanoplasmonics), analogous to soft electronics. This review describes the recent progress in the design, fabrication, characterization, properties, and applications of soft plasmonics. Soft plasmonics are expected to afford complementary features and functions to the field of soft electronics, enabling applications that are difficult or impossible to achieve with traditional rigid plasmonic structures, such as conformal attachment or integration with soft biological systems for real‐time sensing, actuation, and close‐loop feedback. [ABSTRACT FROM AUTHOR]

Refractive freeform components are becoming increasingly relevant for generating controlled patterns of light, because of their capability to spatially modulate optical signals with high efficiency and low background. However, the use of these devices is still limited by difficulties in manufacturing macroscopic elements with complex, 3D surface reliefs. Here, 3D‐printed and stretchable magic windows generating light patterns by refraction are introduced. The shape and, consequently, the light texture achieved can be changed through controlled device strain. Cryptographic magic windows are demonstrated through exemplary light patterns, including micro‐QR‐codes, that are correctly projected and recognized upon strain gating while remaining cryptic for as‐produced devices. The light pattern of micro‐QR‐codes can also be projected by two coupled magic windows, with one of them acting as the decryption key. Such novel, freeform elements with 3D shape and tailored functionalities is relevant for applications in illumination design, smart labels, anti‐counterfeiting systems, and cryptographic communication. [ABSTRACT FROM AUTHOR]

The development of stretchable broadband photodetectors for applications in wearable optoelectronics and personal healthcare still has some limitations in obtaining materials, designing device structures, and developing reliable fabrication processes. Here, stretchable broadband plasmonic photodetectors (SBPPDs) by fabricating plasmonic photodetectors on a stress‐adaptable modulated polydimethylsiloxane (PDMS) substrate are proposed. The plasmonic photodetectors are developed via two approaches for the sensing layers: (i) hybrid of silver nanoparticles (AgNPs) with poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and (ii) nanocomposite of AgNPs embedded into PEDOT:PSS. These sensing layers are directly formed on the substrate to be capable of sustaining tensile strain. The working principle of SBPPDs is based on the injection of hot‐carriers generated from surface plasmon decay on AgNPs to PEDOT:PSS under visible (Vis) and near‐infrared (NIR) illumination. Both SBPPDs show high responsivity to wavelengths of Vis (565 nm), Vis (660 nm), NIR (880 nm), and NIR (970 nm) as well as reliable electrical performance under applied stretching up to 30%. The proposed SBPPDs are promising for future stretchable wearable optoelectronics. [ABSTRACT FROM AUTHOR]

As stretchable devices become well established for applications in soft robotics and wearable devices, the compliant conductors that make these applications possible must also be reliable and survive for the entire device lifetime. Liquid metals such as Galinstan are a potential solution as non‐toxic, stretchable, and low‐resistance conductors. Rigorous investigations of liquid metal lifetimes, however, are limited. This work presents the median lifetime of liquid metal‐filled silicone tubes under current density on the order of 1 kAcm−2, which is necessary for applications such as electromagnetic actuators. In these conductors, the median lifetime increases by a factor of over 4700 as current decreases from 2 to 1 kAcm−2. By cooling the sample, median failure time increases from 112 s to 9.4 h, which suggests straightforward solutions to maximize liquid metal wire lifetime by increasing thermal conductivity or by duty cycling the applied current. [ABSTRACT FROM AUTHOR]

The development of wearable sensors is aimed at enabling continuous real-time health monitoring, which leads to timely and precise diagnosis anytime and anywhere. Unlike conventional wearable sensors that are somewhat bulky, rigid, and planar, research for next-generation wearable sensors has been focused on establishing fully-wearable systems. To attain such excellent wearability while providing accurate and reliable measurements, fabrication strategies should include (1) proper choices of materials and structural designs, (2) constructing efficient wireless power and data transmission systems, and (3) developing highly-integrated sensing systems. Herein, we discuss recent advances in wearable devices for non-invasive sensing, with focuses on materials design, nano/microfabrication, sensors, wireless technologies, and the integration of those. [ABSTRACT FROM AUTHOR]

The integration of flexible electronics with optics can help realize a powerful tool that facilitates the creation of a smart society wherein internal evaluations can be easily performed nondestructively from the surface of various objects that is used or encountered in daily lives. Here, organic-material-based stretchable optical sensors and imagers that possess both bending capability and rubber-like elasticity are reviewed. The latest trends in nondestructive evaluation equipment that enable simple on-site evaluations of health conditions and abnormalities are discussed without subjecting the targeted living bodies and various objects to mechanical stress. Real-time performance under real-life conditions is becoming increasingly important for creating smart societies interwoven with optical technologies. In particular, the terahertz (THz)-wave region offers a substance- and state-specific fingerprint spectrum that enables instantaneous analyses. However, to make THz sensors accessible, the following issues must be addressed: broadband and high-sensitivity at room temperature, stretchability to follow the surface movements of targets, and digital transformation compatibility. The materials, electronics packaging, and remote imaging systems used to overcome these issues are discussed in detail. Ultimately, stretchable optical sensors and imagers with highly sensitive and broadband THz sensors can facilitate the multifaceted on-site evaluation of solids, liquids, and gases., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

The growing prominence of wearable electronics has paved the way toward stretchable and flexible strain sensors. Stress signals extracted from the human body are crucial parameters to monitor health conditions. High‐sensitivity shape‐adaptive strain sensors have become the main challenge considering the curvilinear surfaces of the practical applications. Herein, a highly sensitive performance‐enhanced stretchable strain sensor based on the combination of a wrinkled structure and microcracks is reported on. The strain sensor is fabricated by transfer printing gold thin films with controllable microcracks onto prestretched soft substrates. Maximum strain of 40% and a maximum gauge factor of 11.54 are demonstrated using the prototype device. More importantly, the device shows excellent time response characteristics and stable performance in the subsequent stability test. It is proved that the fabrication method to generate the mixed microcracks and wrinkled structure is efficient and the corresponding device is an excellent stretchable strain sensor. The device is an attractive candidate that meets the needs of human health monitoring. [ABSTRACT FROM AUTHOR]

Research in stretchable, printed electronics combines multidisciplinary, state‐of‐the‐art developments in material science and structural engineering. In addition to major advances based on developing novel materials and fabrication processes, synergistic structural innovations are of equal importance for enabling stretchability in printed devices and should not be overlooked. Planar printing techniques are preferred, compared to microfabrication or 3D printing processes, owing to their low cost, high throughput, and compatibility with a wide range of materials. Various printing strategies for controlling the substrate, bonding, distribution of strain, and buckling can be used to fabricate a variety of devices featuring wrinkled, textile‐embedded, serpentine, island‐bridge, or 2D‐transformed 3D and 4D structures. Such structural innovations allow the use of ordinary printable materials for creating highly stretchable devices with minimal compromise in device performance and mechanical resiliency. This article provides an overview of the structures used in printed devices and summarizes their corresponding fabrication strategies and distinct features. The challenges of advancing the structural designs in printed devices and the prospects of transforming stretchable structures toward smart, responsive devices are also discussed. Future efforts will greatly expand the possibilities of using planar printing processes for fabricating complex structures with new functionalities. [ABSTRACT FROM AUTHOR]

Flexible and stretchable organic solar cells (OSCs) have attracted enormous attention due to their potential applications in wearable and portable devices. To achieve flexibility and stretchability, many efforts have been made with regard to mechanically robust electrodes, interface layers, and photoactive semiconductors. This has greatly improved the performance of the devices. State‐of‐the‐art flexible and stretchable OSCs have achieved a power conversion efficiency of 15.21% (16.55% for tandem flexible devices) and 13%, respectively. Here, the recent progress of flexible and stretchable OSCs in terms of their components and processing methods are summarized and discussed. The future challenges and perspectives for flexible and stretchable OSCs are also presented. [ABSTRACT FROM AUTHOR]

Recent studies are actively contributing to the implementation of the use of five human senses in electronic skins. In order to achieve this, it is critical to develop sensors with the ability to heal after being subjected to stretching or damage; this should be achieved without any significant deterioration in performance, as is possible for human skin. This study investigates the potential for producing stretchable, cuttable, and healable photodetectors. To this end, a reversibly cross‐linkable silicone polymer, polydimethylsiloxane (rcPDMS), is synthesized via a Diels–Alder reaction; subsequently, ZnS:Cu particles are dispersed therein to form a composite film. Ag nanowires (AgNWs) are formed on both the surfaces of the film to realize a three‐layer sandwich structured capacitor, namely: AgNWs/ZnS:Cu‐rcPDMS/AgNWs. Light irradiation of the film induces the photodielectric effect in ZnS:Cu particles and the dielectric response of photoinduced dipole moments composed of localized photoactive carriers results in a change in the capacitance of the film. Based on this, a photodetector is developed that is stretchable, healable, and demonstrates no reduction in the device performance even before and after cutting as well as healing. [ABSTRACT FROM AUTHOR]

The development of two‐dimensional (2D) materials has brought the breakthrough for scientific discoveries and widespread applications in many emerging devices. However, the related study on lasers is rather limited. In this study, a stretchable and broadband cavity‐free laser device based on all 2D metamaterials consisting of molybdenum disulfide (MoS2)/graphene nanocomposites is designed and demonstrated. When the pumping power density of the device is more than 200 W cm−2, multiple pronounced narrow peaks with linewidth <0.5 nm superimpose on the spectra, providing the signature for laser actions. The optical properties of MoS2/graphene meta‐nanocomposites for MoS2 quantum dots (QDs) with different concentration of l‐histidine doping are also examined. It is emphasized that under optimized doping concentration of MoS2 QDs, the laser action of the device can be effectively enhanced. Furthermore, it is shown that the laser action of the devices is controllable by applying an external strain. It is demonstrated that after stretching for more than 200 times, the performance still remains the same with negligible change, indicating the robustness of the device. The presented stretchable laser devices based on all 2D meta‐nanocomposites therefore can open new possibilities for future developments of not‐yet realized optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin‐film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion‐sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge‐progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as‐fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next‐generation devices featuring wearable, deformable, printable, ultrathin, and see‐through characteristics.

The development of wearable sensors is aimed at enabling continuous real-time health monitoring, which leads to timely and precise diagnosis anytime and anywhere. Unlike conventional wearable sensors that are somewhat bulky, rigid, and planar, research for next-generation wearable sensors has been focused on establishing fully-wearable systems. To attain such excellent wearability while providing accurate and reliable measurements, fabrication strategies should include (1) proper choices of materials and structural designs, (2) constructing efficient wireless power and data transmission systems, and (3) developing highly-integrated sensing systems. Herein, we discuss recent advances in wearable devices for non-invasive sensing, with focuses on materials design, nano/microfabrication, sensors, wireless technologies, and the integration of those.

Considerable attention has been devoted to the development of nanomaterial-based photoacoustic transmitters for ultrasound therapy and diagnosis applications. Here, we fabricate and characterize candle-soot nanoparticles (CSNPs) and polydimethylsiloxane (PDMS) composite-based photoacoustic transmitters, based on a solution process, not just to achieve high-frequency and high-amplitude pressure outputs, but also to develop physically stretchable ultrasound transmitters. Owing to its non-porous and non-agglomerative characteristics, the composite exhibits unique photo-thermal and mechanical properties. The output pressure amplitudes from CSNPs–PDMS composites were 20–26 dB stronger than those of Cr film, used as a reference. The proposed transmitters also offered a center frequency of 2.44–13.34 MHz and 6-dB bandwidths of 5.80–13.62 MHz. Importantly, we characterize the mechanical robustness of CSNPs–PDMS quantitatively, by measuring laser-damage thresholds, to evaluate the upper limit of laser energy that can be ultimately used as an input, i.e., proportional to the maximum-available pressure output. The transmitters could endure an input laser fluence of 54.3–108.6 mJ·cm−2. This is 1.65–3.30 times higher than the Cr film, and is significantly higher than the values of other CSNPs–PDMS transmitters reported elsewhere (22–81 mJ·cm−2). Moreover, we characterized the strain-dependent photoacoustic output of a stretchable nanocomposite film, obtained by delaminating it from the glass substrate. The transmitter could be elongated elastically up to a longitudinal strain of 0.59. Under this condition, it maintained a center frequency of 6.72–9.44 MHz, and 6-dB bandwidth ranges from 12.05 to 14.02 MHz. We believe that the stretchable CSNPs–PDMS composites would be useful in developing patch-type ultrasound devices conformally adhered on skin for diagnostic and therapeutic applications.

Various carbon allotropes are fundamental components in electrochemical energy-conversion and energy-storage devices, e.g., biofuel cells (BFCs) and supercapacitors. Recently, biodevices, particularly wearable and implantable devices, are of distinct interest in biomedical, fitness, academic, and industrial fields due to their new fascinating capabilities for personalized applications. However, all biodevices require a sustainable source of energy, bringing widespread attention to energy research. In this review, we detail the progress in BFCs and supercapacitors attributed to carbon materials. Self-powered biosensors for futuristic biomedical applications are also featured. To develop these energy devices, many challenges needed to be addressed. For this reason, there is a need to: optimize the electron transfer between the enzymatic site and electrode; enhance the power efficiency of the device in fluctuating oxygen conditions; strengthen the efficacy of enzymatic reactions at the carbon-based electrodes; increase the electrochemically accessible surface area of the porous electrode materials; and refine the flexibility of traditional devices by introducing a mechanical resiliency of electrochemical devices to withstand daily multiplexed movements. This article will also feature carbon nanomaterial research alongside opportunities to enhance energy technology and address the challenges facing the field of personalized applications. Carbon-based energy devices have proved to be sustainable and compatible energy alternatives for biodevices within the human body, serving as attractive options for further developing diverse domains, including individual biomedical applications.

Conjugated polymers have been well-known as a critical candidate for stretchable electronics applications. However, further research is still needed to fully understand what kind of film morphology is beneficial to keep the charge mobility under cycling deformation. Herein, we proposed that the co-deformation of crystalline domains and amorphous regions can effectively dissipate strain energy. To verify our idea, we developed three kinds of the morphology of a diketopyrrolopyrrole-based polymer (DPP-TVT) with different crystallinity by changing the interaction parameter between solvent and sidechain (R a solvent-sidechain). The films cast from TCB with medium crystallinity exhibited 100% mobility retention (0.42 cm2V−1s−1) under 100% strain and after 100 stretch-release cycles at 50% strain. However, the mobility of CN films with high crystallinity decreased from 0.45 to 0.23 cm2V−1s−1 under a single stretch at 100% strain, while the performance of CF films with low crystallinity decreased from 0.34 to 0.052 cm2V−1s−1 after 100 stretch-release cycles at 50% strain. The optimized performance of TCB films stems from the fact that the dispersed crystallites embedded in the amorphous matrix provide an efficient and robust charge transport network under single and repeating deformation. This research would aid in manipulating the mechanical and electrical properties of conjugated polymers. [Display omitted] • Simply solvent processing. • High fatigue resistance. • Crystallinity-stretchability relation. [ABSTRACT FROM AUTHOR]

Nanostructures, novel materials, optoelectronic performance, photodetectors, stretchable devices The preparation methods, optoelectronic materials and performance parameters of these photodetectors are discussed. Keywords: nanostructures; novel materials; optoelectronic performance; photodetectors; stretchable devices EN nanostructures novel materials optoelectronic performance photodetectors stretchable devices 1 1 1 03/03/23 20230301 NES 230301 B The development of novel optoelectrical materials b is an effective way to achieve high-performance stretchable photodetectors. [Extracted from the article]

Stretchable electrochromic (EC) devices that can adapt the irregular and dynamic human surfaces show promising applications in wearable display, adaptive camouflage, and visual sensation. However, challenges exist in lacking transparent conductive electrodes with both tensile and electrochemical stability to assemble the complex device structure and endure harsh electrochemical redox reactions. Herein, a wrinkled, semi-embedded Ag@Au nanowire (NW) networks are constructed on elastomer substrates to fabricate stretchable, electrochemically-stable conductive electrodes. The stretchable EC devices are then fabricated by sandwiching a viologen-based gel electrolyte between two conductive electrodes with the semi-embedded Ag@Au NW network. Because the inert Au layer inhibits the oxidation of Ag NWs, the EC device exhibits much more stable color changes between yellow and green than those with pure Ag NW networks. In addition, since the wrinkled semi-embedded structure is deformable and reversibly stretched without serious fractures, the EC devices still maintain excellent color-changing stability under 40% stretching/releasing cycles., (© 2023 Wiley-VCH GmbH.)

Recently, stretchable micro-supercapacitors (MSCs) that can be easily integrated into electronic devices have attracted research and industrial attentions. In this work, three-dimensional (3D) stretchable MSCs with an octet-truss electrode (OTE) design have been demonstrated by a rapid digital light processing (DLP) process. The 3D-printed electrode structure is beneficial for electrode-electrolyte interface formation and consequently increases the number of ions adsorbed on the electrode surface. The designed MSCs can achieve a high capacitance as ≈74.76 mF cm -3 under 1 mA cm -3 at room temperature even under a high mechanical deformation, and can achieve 19.53 mF cm -3 under 0.1 mA cm -3 at a low temperature (-30 °C). Moreover, finite element analysis (FEA) reveals the OTE structure provides 8 times more contact area per unit volume at the electrode-electrolyte interface compared to the traditional interdigital electrode (IDE). This work combines structural design and 3D printing techniques, which provides new insights into highly stretchable MSCs for next-generation electronic devices., (© 2023 Wiley-VCH GmbH.)

We present the first example of an all-printed, inexpensive, highly stretchable CNT-based electrochemical sensor and biofuel cell array. The synergistic effect of utilizing specially tailored screen printable stretchable inks that combine the attractive electrical and mechanical properties of CNTs with the elastomeric properties of polyurethane as a binder along with a judiciously designed free-standing serpentine pattern enables the printed device to possess two degrees of stretchability. Owing to these synergistic design and nanomaterial-based ink effects, the device withstands extremely large levels of strains (up to 500% strain) with negligible effect on its structural integrity and performance. This represents the highest stretchability offered by a printed device reported to date. Extensive electrochemical characterization of the printed device reveal that repeated stretching, torsional twisting, and indenting stress has negligible impact on its electrochemical properties. The wide-range applicability of this platform to realize highly stretchable CNT-based electrochemical sensors and biofuel cells has been demonstrated by fabricating and characterizing potentiometric ammonium sensor, amperometric enzyme-based glucose sensor, enzymatic glucose biofuel cell, and self-powered biosensor. Highly stretchable printable multianalyte sensor, multifuel biofuel cell, or any combination thereof can thus be realized using the printed CNT array. Such combination of intrinsically stretchable printed nanomaterial-based electrodes and strain-enduring design patterns holds considerable promise for creating an attractive class of inexpensive multifunctional, highly stretchable printed devices that satisfy the requirements of diverse healthcare and energy fields wherein resilience toward extreme mechanical deformations is mandatory. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO)-based materials have shown good performance as electrodes in flexible energy storage devices owing to their physical properties, high specific surface area, and excellent electrical conductivity. Here, a novel road is reported for fabricating high-performance supercapacitors based on 3D rGO electrodes and solid electrolyte multilayers via pressure spray printing and machine coating. These supercapacitors demonstrate high and adjustable volumetric capacitance, excellent flexibility, and stretchability. The results show that this commercial strategy has its essential merits such as low-cost, inexpensive, and simple fabrication for large area production. These properties are in the favor of fabricating high-performance supercapacitor to meet the practical energy demands in devices, especially flexible electronic devices. Furthermore, this novel 3D interdigital electrode concept can be widely applied to other energy devices for enhancing performances and to other micro devices for reducing cost. [ABSTRACT FROM AUTHOR]

Recently, Ag nanowires (AgNWs) has had a great interest as a conducting material for flexible and transparent devices, but it still shows several problems such as the ultimate detachment of AgNWs from substrate and a high contact resistance on AgNW junctions. Therefore, the novel concept to enhance permanent and closed attachment of AgNWs by silane modification to polydimethylsilaoxane (PDMS) substrate well known as high stretchable film with extremly low adhesive is suggested. According to this experiment, higher sigma (σ)-donating ability and hydrophilicity indicate better electrical and mechanical properties in real device. Especially, densely amine self-assembled PDMS surface exhibits the strongest contact force to the AgNWs, especially for junction side, and the longest maintenance of hydrophilicity by coordination-type bonding. In addition, AgNWs adhere permanently to stretchable substrates while simultaneously maintaining high transparency (87%) and high conductivity (27 Ω sq-1). Consequently, the resulting AgNW film shows excellent mechanical durability which includes enhanced performance of both flexibility and stretchability. [ABSTRACT FROM AUTHOR]

This paper describes the realization of a soft, flexible, coil fabricated by means of a liquid metal alloy encased in a biocompatible elastomeric substrate for operation in a telemetry system, primarily for application to biomedical implantable devices. Fluidic conductors are in fact well suited for applications that require significant flexibility as well as conformable and stretchable devices, such as implantable coils for wireless telemetry. A coil with high conductivity, and therefore low losses and high unloaded Q factor, is required to realize an efficient wireless telemetry system. Unfortunately, the conductivity of the liquid metal alloy considered-eutectic gallium indium (EGaIn)-is approximately one order of magnitude lower than gold or copper. The goal of this paper is to demonstrate that despite the lower conductivity of liquid metal alloys, such as EGaIn, compared with materials, such as copper or gold, it is still possible to realize an efficient biomedical telemetry system employing liquid metal coils on the implant side. A wireless telemetry system for an artificial retina to restore partial vision to the blind is used as a testbed for the proposed liquid metal coils. Simulated and measured results show that power transfer efficiency of 43% and 21% are obtained at operating distances between coils of 5 and 12 mm, respectively. Further, liquid metal based coil retains more than 72% of its performance (voltage gain, resonance bandwidth, and power transfer efficiency) when physically deformed over a curved surface, such as the surface of the human eye. This paper demonstrates that liquid metal-based coils for biomedical implant provide an alternative to stiff and uncomfortable traditional coils used in biomedical implants. [ABSTRACT FROM PUBLISHER]

Colors enable interaction and communication between living species in a myriad of biological and artificial environments. While living organisms feature low-power mechanisms to dynamically control color in soft tissues, man-made color-changing devices remain predominantly rigid and energy intensive. Here, architectured composites that display striking color changes when stretched in selective directions under ambient light with minimum power input are reported. The orientation-dependent color change results from the rotation of reflective coated platelets that are embedded in a soft polymer matrix and pre-aligned in a well-defined architecture. The light reflected by the platelets generates structural color defined by the oxide coating on the platelet surface. By magnetically programming the initial orientation and spatial distribution of selected platelets within the soft matrix, composites with strain-modulated color-changing effects that cannot be achieved using state-of-the-art technologies are created. The proposed concept of strain-induced architectured color can be harnessed to develop low-power smart stretchable displays, tactile synthetic skins, and autonomous soft robotic devices that undergo fast and reversible color changes through the mechano-optic coupling programmed within their soft composite architecture., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The growing demand for wearable devices, soft robotics, and tissue engineering in recent years has led to an increased effort in the field of soft materials. With the advent of personalized devices, the one-shape-fits-all manufacturing methods may soon no longer be the standard for the rapidly increasing market of soft devices. Recent findings have pushed technology and materials in the area of additive manufacturing (AM) as an alternative fabrication method for soft functional devices, taking geometrical designs and functionality to greater heights. For this reason, this review aims to highlights recent development and advances in AM processable soft materials with self-healing, shape memory, electronic, chromic or any combination of these functional properties. Furthermore, the influence of AM on the mechanical and physical properties on the functionality of these materials is expanded upon. Additionally, advances in soft devices in the fields of soft robotics, biomaterials, sensors, energy harvesters, and optoelectronics are discussed. Lastly, current challenges in AM for soft functional materials and future trends are discussed. [ABSTRACT FROM AUTHOR]

Memristors constitute a promising functional component for information storage and in-memory computing in flexible and stretchable electronics including wearable devices, prosthetics, and soft robotics. Despite tremendous efforts made to adapt conventional rigid memristors to flexible and stretchable scenarios, stretchable and mechanical-damage-endurable memristors, which are critical for maintaining reliable functions under unexpected mechanical attack, have never been achieved. Here, the development of stretchable memristors with mechanical damage endurance based on a discrete structure design is reported. The memristors possess large stretchability (40%) and excellent deformability (half-fold), and retain stable performances under dynamic stretching and releasing. It is shown that the memristors maintain reliable functions and preserve information after extreme mechanical damage, including puncture (up to 100 times) and serious tearing situations (fully diagonally cut). The structural strategy offers new opportunities for next-generation stretchable memristors with mechanical damage endurance, which is vital to achieve reliable functions for flexible and stretchable electronics even in extreme and highly dynamic environments., (© 2021 Wiley-VCH GmbH.)

The development of self-healing elastomers with superior physical properties is a challenging task. Herein, we present a design concept for a self-healing, highly stretchable, and robust poly(urethane–urea) elastomer prepared via a thiol-ene click reaction by a facile one-pot in situ photopolymerization method. The objective of the utilized approach is to incorporate weak noncovalent H-bonds, dynamic covalent urea bonds, and products of a thiol-ene click reaction into a polymeric backbone. This study also applies polytetramethylene ether glycol domains as soft segments to facilitate the polymeric chain diffusion and dynamic exchange reaction. Owing to these unique molecular characteristics, the resultant elastomer possesses a uniform structure and versatile properties, such as high stretchability corresponding to a maximum strain of 464%, ultimate tensile strength of 10.9 MPa, self-recoverability, high self-healing efficiency of 99%, high recyclability, and good weldability. Upon rupture, the as-prepared elastomer completely restores its original mechanical properties after heating to 80 °C for 5 h. The dynamic reversibility of the elastomer is evidenced by stress relaxation analysis and rheological testing. In addition, it can be effectively encapsulated and potentially used for fabricating self-healing stretchable conductive devices. • Self-healing poly(urethane–urea) elastomer is prepared by photopolymerization. • The obtained elastomer possesses a uniform structure and versatile characteristics. • Ruptured poly(urethane–urea) elastomer easily restores its mechanical properties. • The poly(urethane-urea) elastomer shows potential in self-healing stretchable conductive devices. [ABSTRACT FROM AUTHOR]