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Biocompatible, sustainable, and conductive inks are of special interest and are highly valued in the printable bioelectronics. However, the conventional inks, which increase electrical conductivity by mixing metal particles or graphene, can cause long‐term damage when applied to the body and environment. Herein, a method for creating a stable matrix based on a UV‐cross‐linkable polymer to which a conductive polymer can be grafted is investigated to solve the above problems by recycling biomass. Through this, it is possible to achieve high conductivity using only biocompatible and sustainable polymers. Here, conductive inks for printable bioelectronics are developed by grafting polypyrrole on methacrylate‐modified sericin and poly(ethylene glycol) diacrylate (PEGDA). The highest electrical conductivity is achieved by adjusting the ratio of the pyrrole monomers polymerized on each polymer until the conductivity is optimized. Owing to the photoreactive nature of PEGDA, the prepared conductive inks are cross‐linked by UV light, thus giving them easy‐printing properties. The biodegradability, biocompatibility, and electrical properties of the printed patterns are systematically analyzed. This study has significant implications in the field of sustainable and printable bioelectronics as it has developed of a conductive ink with the biocompatibility, biodegradability, and high conductivity that is safer and simpler than conventional methods. [ABSTRACT FROM AUTHOR]

Anisotropic conductive adhesives (ACAs) are the preferred interconnection technology for applications that employ large dies, flexible substrates, and ultra fine‐pitch interconnects. Conventional ACAs require relatively high bonding pressures and temperatures, and ultra fine‐pitch applications challenge the trade‐off between low interconnect resistance and risk of short circuits. This study introduces an ACA‐like interconnection technology that addresses these limitations, allowing for low‐pressure, low‐temperature assembly processes with enhanced particle control at the interconnects. Conductive particles are deposited onto a patterned carrier and subsequently transferred to electrical pads using either non‐conductive film or Ag sintering. The Ag sintering process is performed at a low temperature (140 °C) and low bonding pressure (1 N for a 10 × 10 mm2 chip). The capability of controlling the position and number of conductive particles within individual interconnects is demonstrated. This presents possibilities for achieving ultra‐fine pitch interconnects with negligible risk of short circuits, without compromising electrical resistance. It is demonstrated that interconnect resistance can be tuned by varying the number of conductive particles (achieving a resistance as low as 33 mΩ with 25 particles per interconnect). This approach is applicable to scenarios where the bonding force and temperature must remain low due to the nature of substrate materials. [ABSTRACT FROM AUTHOR]

The printed electronics (PEs) market has witnessed substantial growth, reaching a valuation of USD 10.47 billion in the previous year. Driven by its extensive use in a multitude of applications, this growth trend is expected to continue with a projected compound annual growth rate of 22.3% from 2022 to 2032. Compared to screen printing, the adoption of inkjet printing (IJP) technology to manufacture PEs has been limited to laboratory‐scale research only. The fact that IJP's inability to maintain consistent high‐resolution quality over large printing areas has made transitioning IJP for commercial production arduous. Most of the previous literatures have focused on holistic discussion on material design for IJP, but this review provides insight into key aspects in material processing up to printing optimization to realize high‐resolution PEs. This review also highlights the challenges in controlling the functional ink properties and their interaction with the substrate as well as printing parameters to deliver the desired quality of the droplets and final prints. Imminent application of IJP in PEs and future perspectives are also included in this review. [ABSTRACT FROM AUTHOR]

Energy‐harvesting technologies offer a sustainable, maintenance‐free alternative to conventional energy‐storage solutions in distributed low‐power applications. Flexible thermoelectric generators (TEGs) can generate electric power from a temperature gradient, even on complex surfaces. Organic materials are ideal candidates for flexible TEGs due to their good solution‐processability, natural abundance, low weight, and flexibility. Electronic and thermoelectric properties of organic materials have steadily progressed, while device architectures leveraging their advantages are largely missing. Here, a design and fabrication method are proposed for producing fully screen‐printed, flexible monolithic organic TEGs scalable up to m2, compatible with any screen‐printable ink. This approach is validated, along with its scalability, by printing TEGs composed of two different active inks, in three configurations, with up to 800 thermoelements, with performances well matching simulations based on materials parameters. It is demonstrated that by using an additive‐free graphene ink, a remarkable power density of 15 nW cm−2 at ΔT = 29.5 K can be achieved, with an estimated weight‐normalized power output of 1 µW g−1, highlighting a strong potential in portability. Owing to such power density, only limited areas are required to generate microwatts, sufficient for operating low‐power electronic devices such as sensors, and wearables. [ABSTRACT FROM AUTHOR]

In recent years, additive manufacturing tools, such as 3D printing, has gained enormous attention in biomedical engineering for developing ionotropic devices, flexible electronics, skin‐electronic interfaces, and wearable sensors with extremely high precision and sensing accuracy. Such printed bioelectronics are innovative and can be used as multi‐stimuli response platforms for human health monitoring and disease diagnosis. This review systematically discusses the past, present, and future of the various printable and stretchable soft bioelectronics for precision medicine. The potential of various naturally and chemically derived conductive biopolymer inks and their nanocomposites with tunable physico‐chemical properties is also highlighted, which is crucial for bioelectronics fabrication. Then, the design strategies of various printable sensors for human body sensing are summarized. In conclusion, the perspectives on the future advanced bioelectronics are described, which will be helpful, particularly in the field of nano/biomedicine. An in‐depth knowledge of materials design to functional aspects of printable bioelectronics is demonstrated, with an aim to accelerate the development of next‐generation wearables. [ABSTRACT FROM AUTHOR]

Flexible textile antennas are important for wireless communication within the expansion of 5G and the Internet of Things (IoT), as it allows for their integration in daily life objects. However, achieving these functionalities in textiles is challenging because of limitations in the electronic performance, flexibility with scalable fabrication process. This paper presents two flexible textile antennas for wearable and non‐ wearable devices compatible with 5G technology created by printing highly conductive silver nanoparticle inks. Two textile substrates are explored, as the dielectric component, a 3D polyester, and a natural origin fabric, burel. The processes used are cost‐effective and scalable, with the antennas designed to operate at 3–3.5 GHz, maintaining their return loss performance even under bending deformation and washing cycles. By transferring the optimized devices into clothes and wall covering, a detailed analysis with experimental measurements of the textile‐based antenna for different operation scenarios is introduced. The work highlights the suitability of these antennas for wearable applications and their alignment with green wireless technologies, contributing to the advancement of sustainable wireless communication systems. [ABSTRACT FROM AUTHOR]

Electronics and mechatronics waste is an exponentially increasing environmental issue, especially for wearable devices, due to their widespread diffusion into society and short life cycle. To promote their enormous benefits (e.g., in assisting visually impaired individuals) in a sustainable way, biobased and/or biodegradable organic materials should be used instead of traditional components. This manuscript presents a multidisciplinary approach, which bridges materials science and mechatronics, to propose the first ECO‐friendly wearable vibroTACtile device (Eco‐Tac). The design of Eco‐Tac includes integration on a cotton t‐shirt through a novel biodegradable conductive ink forming electrical tracks, a flexible commercially available solar panel, and the vibrotactile haptic device itself. The ink comprises a green solvent, anisole, a soft polybutylene adipate terephthalate biodegradable binder, and conductive nanocarbon materials. The device case is a biodegradable biocomposite. As such, the feasibility of using a sustainable energy source to supply power to the device and the possibility of using biodegradable materials in its manufacturing are demonstrated. An experiment with 20 blindfolded subjects is conducted, reporting the device's potential for assistance in manipulation tasks. Overall, the results of this work represent the first significant step toward the creation of wearable and sustainable haptic devices with green electronics and mechatronics approaches. [ABSTRACT FROM AUTHOR]

Stretchable strain sensors are widely used in the fields of wearable devices, soft robotics, healthcare monitoring, and more. Despite tremendous efforts, strain sensors capable of detecting large‐scale soil deformation for urban geological hazard prevention have not yet been demonstrated. In this paper, a soft strain sensor of a highly stretchable Ecoflex‐0030 elastomeric matrix with microchannel‐confined environmentally benign conductive Chinese ink as the liquid‐state strain‐sensitive material that can reliably detect a wide range of working strain up to 300% is demonstrated. The sensor exhibits a negligible hysteresis error of 2.1%, with a considerably good gauge factor of 1.95. The sensor performance is evaluated under both creep and cyclic loading tests, indicating superior stability (0.65% fluctuation), and repeatability (0.28% variation in 1000 cycles), even under a lower underground environment temperature of 18°C. As a proof‐of‐concept demonstration, a liquid‐state strain sensor array with a strain amplification mechanism capable of accurately monitoring the formation of various underground cavities and providing timely demanded information for early warning of catastrophic road collapse is demonstrated and verified by the computer vision‐based particle image velocimetry (PIV) method. [ABSTRACT FROM AUTHOR]

The generation of electronic waste (e‐waste) poses a significant environmental challenge, necessitating strategies to extend electronics' lifespan and incorporate eco‐friendly materials to enable their rapid degradation after disposal. Foldable electronics utilizing eco‐friendly materials offer enhanced durability during operation and degradability at the end of their life cycle. However, ensuring robust physical adhesion between electrodes/circuits and substrates during the folding process remains a challenge, leading to interface delamination and electronic failure. In this study, electrohydrodynamic (EHD) printing is employed as a cost‐effective method to fabricate the eco‐friendly foldable electronics by printing PEDOT:PSS/graphene composite circuits onto polyvinyl alcohol (PVA) films. The morphology and electrical properties of the printed patterns using inks with varying graphene and PEDOT:PSS weight ratios under different printing conditions are investigated. The foldability of the printed electronics is demonstrated, showing minimal resistance variation and stable electronic response even after four folds (16 layers) and hundreds of folding and unfolding cycles. Additionally, the application of printed PEDOT:PSS/graphene circuit is presented as a resistive temperature sensor for monitoring body temperature and respiration behavior. Furthermore, the transient features and degradation of the PEDOT:PSS/graphene/PVA based foldable electronics are explored, highlighting the potential promise as transient electronics in reducing electronic waste. [ABSTRACT FROM AUTHOR]

The increasing interest in disposable electronics such as wearable patches, e‐textiles, and smart packaging, warns emergence of another man‐made disaster. A paradigm shift toward a more sustainable future through the development of soft material architectures that are robust and durable, but also degradable by external stimuli is proposed. Hydrogels, a class of soft polymers with exceptional properties, and high water content are rarely used as substrates, mainly due to lack of ink‐adhesion and rapid dehydration. Herein, photodegradable hydrogels are tailor‐made that are nondrying, robust, adhesive to ink, and permit triggerable degradation, making them suitable substrates for sustainable electronics. These hydrogels are prepared by reversible ionic crosslinking between sodium alginate and divalent cations (Ca2+) and light‐responsive crosslinking of poly(acrylamide) (PAAm) chains through synthesized ortho‐nitrobenzyl (ONB)‐based crosslinkers. By displacing the water molecules in the hydrogels by immersion in glycerol, the drying problem and printability of conductive ink are addressed. It is demonstrated that digital printing of a liquid metal (LM)‐based stretchable ink over the developed substrate, shows several body‐worn printed wearable sensors, and demonstrates their degradation and recycling of the expensive metals. This work lays the foundation for the use of hydrogels as promising substrates for the next generation of environmentally friendly electronics. [ABSTRACT FROM AUTHOR]

The ongoing research on printed and flexible electronics is primarily focused on conductive three‐dimensional (3D) print patterning. However, due to the nonhomogeneous distribution of conductive elements in a polymer matrix and their tendency to shrink, 3D‐printed patterns often suffer from low‐printing accuracies and poor mechanical and electrical properties. Herein, poly(vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate) (PVBVA) is reinforced with microwave‐exfoliated graphene to develop a conductive ink for 3D printing. Compared with the pure PVBVA patterns, the PVBVA/graphene patterns exhibit a high‐electrical conductivity, a twofold enhancement in tensile strength, an improved printing accuracy, and a high stability because of the graphene addition. The PVBVA/graphene inks flow well during the printing; loading of up to 0.1 wt% graphene in the PVBVA gel results in notable changes in the rheological properties of the ink. The printed conductive patterns show a high flexibility suitable for wearable electronics. Additionally, multifunctional electronic operations such as photoinduced heating, temperature sensing, and motion sensing are possible. This study may pave the way for the development of a new class of smart wearable electronics for healthcare and soft robotics. [ABSTRACT FROM AUTHOR]

Liquid metals (LMs) and conjugated polymers are both critically important materials in modern technologies including soft robotics, printable circuits, and stretchable electronics. Although broadly applied, the joint use of LMs and conjugated polymers are rarely explored due to the notoriously interfacial challenges of the high surface tension of LMs and the unfavorable rigid backbones of conjugated polymer chains. This work successfully introduced conjugated polymers (poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate, (PEDOT:PSS)) into the system of liquid metals to provide a highly stable, aqueous, and electrically conductive ink (LM‐PEDOT:PSS inks, LMPInks) for flexible electronics. The PSS segments act as a strong ionic bridge to effectively stabilize core‐shell structure of the PEDOT and LMs in the homogenous ink. Different from previous insulated LM‐inks, LMPInk is aqueous and more importantly, electrically conductive without posttreatments due to the intrinsically conductive PEDOT:PSS. Interestingly, with low content of LM particles (<2 wt%), the printed circuits inherit the valuable transparency of PEDOT:PSS (transmission >92% in visible region), which has never been observed in LM‐based organic systems. Furthermore, such LMPInks show distinguished electrical robustness, which can automatically recover their initial electrical conductivity even after severe physical damage. With the above phenomenal advantages, various flexible circuits on different substrates are successfully provided. [ABSTRACT FROM AUTHOR]

Kirigami, with a simple mechanical transformation fashion, offers versatile ways and unconventional approaches for realizing cutting‐edge tunable devices. Here, a rotational kirigami tessellation metasurface with tunable chirality using 2D‐to‐2D in‐plane transformation is designed and experimentally demonstrated. The rotational metasurface is built using flexible filament as a supporting dielectric and silver ink as conductive patterns on the top and bottom layers and operated via mechanical transformation. Unlike conventional works where the symmetric‐breaking feature is obtained from 2D to 3D transformation, the proposed structure is designed in such a way that it can break mirror‐symmetric by misaligning the conductive pattern via rotating sub‐elements of the structure led to achieving dual‐band bifunctional tunable chiral transmission responses. Finally, achiral and chiral transmission responses at different rotation angle states are experimentally confirmed. The proposed approach can be applied to various applications, opening new avenues to design 2D‐to‐2D in‐plane transformation mechanical‐based electromagnetic devices. [ABSTRACT FROM AUTHOR]

Multilayer circuits, especially in stretchable electronic devices, are considered to be an effective way to integrate various components and modules for complex functions. However, the existing manufacturing methods for multilayer flexible and stretchable electronics have problems such as complex technology, expensive equipment, and low production efficiency. Here, a direct ink writing 3D printing method is proposed to fabricate multilayer stretchable electronic devices by using high‐viscosity stretchable silver paste as the material for interconnecting wires, and stretchable polydimethylsiloxane as the dielectric layer. The optimal range of printing parameters is explored to realize the stable and repeatable manufacturing of wires. A protective layer is printed on the interconnection wires and rigid components to connect the soft substrate and the rigid electronic components. The results show that stress concentration is reduced and stable electrical response of the device is achieved under more than 49% tensile deformation. Vertical interconnect accesses and arc‐shaped wires are applied to a multilayer flexible thermal imaging display device and a NE555 timer device, and the outcomes prove that the direct ink writing 3D printing method provides an efficient, simple, and low‐cost manufacturing method for fabricating multilayer stretchable electronics. [ABSTRACT FROM AUTHOR]

With the rapid advances in wearable technology, several excellent strain sensors have been developed. Recent strain sensors have met various requirements, such as mechanical applicability, rapid responsiveness, and high sensitivity. Nevertheless, the processing technology, wearing comfort, and safety of strain sensors, which have received inadequate attention, have greatly hindered their commercial development and large‐scale use. Through mature electrospinning and screen‐printing, a high‐performance, safe, comfortable, waterproof, breathable, economical, and reliable wearable strain sensor is simply and quickly prepared. This strain sensor has excellent repeatability and stability with remarkable sensitivity (maximum gauge factor = 520), a broad working strain range (500%), and an ultrafast response time (100 ms). Notably, the mechanical properties of the proposed strain sensor are similar to those of natural skin, making the sensor a good match to the skin. Additionally, the strain sensor has incomparable biofriendly, enabling long‐term harmless contact with the skin. To the best of the authors' knowledge, this is the first report on the optimization of flexible electronic equipment in terms of the manufacturing process, sensing performance, and wearing experience. The results of this study have important implications for the development and practical application of flexible electronics. [ABSTRACT FROM AUTHOR]

The high sensitivity and portability of flexible pressure sensors have attracted widespread attention from researchers owing to their potential use in health monitoring and exercise detection applications. However, to improve the performance of pressure sensors, a special microstructure‐shaped design is necessary, which usually requires a complicated manufacturing process. In this study, the use of 3D printing technology is proposed to develop a polydimethylsiloxane‐based material along with several conductive materials—carbon black, multiwalled carbon nanotubes, and copper mixed conductive ink—to develop a multilevel inclined‐tip cone array structure to obtain a flexible pressure sensor with a wide detection range and high sensitivity. The final pressure sensor demonstrates a wide range of 0–396 kPa, achieving a high sensitivity of 212 kPa−1, a response time of 32 ms, a low detection limit of 7.69 Pa, along with high stability and consistency under a 5000 cycles compression test. 3D printing technology is used directly in the manufacturing process to achieve low‐cost production. The pressure sensor can accurately identify finger, arm (bending), and leg (jumping) movements, along with the detection of pulse waves. It has opened up new test methods for pulse diagnosis in traditional Chinese medicine and has far‐reaching research significance. [ABSTRACT FROM AUTHOR]

This study reports a new strategy—3D co‐printing technology by collaboratively employing a dual‐light curing process—to fabricate 3D electronics selectively either deposited on a free‐form surface or embedded within a bulk structure. The 3D co‐printing technology only involves one printing material, which works for both the construction of polymeric structures and the metallization process of conductive circuits resulted from the metal precursor loaded in photosensitive resin. The photoreduction of metal nanoparticles (NPs) can be efficiently activated with a second laser scanning. 3D co‐printing technology addresses the challenge of conventional methods requiring multiple materials deposition processes. The resultant conductive trace composed of NPs exhibits a superior resistivity as low as ≈6.12 µΩ m. The resistivity is further controllable ranging from 10−6 to 10 Ω m through adjusting the material formulation and processing parameters. This study has demonstrated that the proposed 3D co‐printing is a high‐efficiency and low‐cost co‐printing approach which opens a new avenue of making 3D electronics. [ABSTRACT FROM AUTHOR]

Stretchable devices significantly expand the scope of applications such as flexible displays and wearable devices/sensors. To enable stretchable wearable electronics, methods for connecting unit devices and developing circuits are required. Previously, research was performed to manufacture circuits with 3D structures or patterns that remain intact when the flexible and stretchable substrates are deformed. A method for drawing a circuit directly on a substrate with a conductive ink pen is proposed, although it is limited by the surface properties of the substrate. Most existing transparent papers are not sufficiently stretchable for flexible and wearable electronics applications. Therefore, a polydimethylsiloxane–cellulose nanocrystals (PDMS–CNC) composite paper is developed that is both highly flexible and stretchable, while maintaining a high transmittance. The versatility of the composite paper is demonstrated as a suitable substrate for flexible devices by patterning with a conductive ink pen. The PDMS–CNC composite paper has an excellent transmittance of ≈70%, and can withstand over 800% tensile strain. The patterned circuits have only minor increase in resistance after a 50% deformation and recovery. The composite paper is a suitable technology for fabricating electrical components and devices for the Internet of Things and wearable and flexible electronics applications. [ABSTRACT FROM AUTHOR]

While the efficiency of synthetic surfactants in controlling the dispersion behaviour of nanomaterials in aqueous solution has been well documented, issues on environmental impact remain unsolved. The aim of this study is to synthesize multi‐walled carbon nanotubes (MWCNTs) inks using green surfactants and their chemical, physical, and electrical performances are compared to those of synthetic surfactant inks. The conductive ink is synthesized by dispersing MWCNTs in surfactant solution (gum Arabic [GA], alkali lignin [AL], polyvinylpyrrolidone [PVP] or pluronic F‐127 [PL]) with various concentrations. Among four investigated surfactants, GA/MWCNTs and PVP/MWCNTs inks are selected for further investigation due to their excellent dispersion stability. The printability of both inks is assessed by analyzing the quality of the conductive patterns printed with different inkjet printers theoretically and experimentally. It is found that multi‐nozzle printer is capable of developing printed patterns with lower sheet resistance compared to single‐nozzle printer. Overall, 5 GA/MWCNTs ink recorded as the most stable ink with only 14.4% reduction of absorbance after 30 days and with zeta potential value of −40.3 ± 5.36 mV. Ten layers of 5 GA/MWCNTs ink printed on PVA demonstrate a dense MWCNTs networks, which contribute to the lowest surface resistance of 3.0 kΩ sq−1. [ABSTRACT FROM AUTHOR]

The printed electronic technology, a simple, low‐cost, and high‐throughput method, exhibits great potential applications in various fields, particularly in intelligent and tamper‐evident packaging. In this study, an all‐printed flexible sensor is prepared for sensing tamper‐evident packaging by screen printing the water‐based silver nanowires (Ag NWs) conductive ink onto a polyethylene terephthalate substrate. This bendable sensor shows a corresponding variation relationship between the resistance of the Ag NWs layer and bending angles. In addition, it presents a stable resistance sensitivity at the bending angles of 45°, 90°, and 135°. The mechanisms of different printed structures on the sensitivity of the sensor have been discussed. The results show that the straight‐line sensor with a linewidth of 2.0 mm has the best sensitive performance (the gauge factors at bending angles of 45°, 90°, and 135° are 37.1, 39.3, and 39, respectively). Moreover, the sensor exhibits a long‐term mechanical cyclic stability (no apparent decay after 1000 bending cycles) and excellent adhesion performance (no distinct increase in resistance after 20 times). Because of the excellent sensing performance, the Ag NWs‐based flexible sensor can accurately detect the opening status of the packaging, showing promising potential for practical tamper‐evident applications. [ABSTRACT FROM AUTHOR]

Abstract: Narrow metal lines with low electrical resistance are essential for many printable electronic devices. Printing metal lines of narrower than 10 µm and with a high thickness‐to‐width aspect ratio is very difficult and remains a technical challenge in printable electronics. In this work, by controlling the ink–substrate interaction and ink drying dynamics, 4.6 µm wide inkjet‐printed silver lines are demonstrated with an aspect ratio of 0.7 and an elliptical cross‐section. The silver lines are obtained by jetting a silver nanoparticle‐based ink onto an SU‐8‐coated polyethylene terephthalate substrate to form well‐defined silver lines, and then heating the lines to transform them into high aspect ratio narrow lines through ink dewetting and receding. The simultaneous dissolution and redistribution of SU‐8 by the ink result in a concave structure, which prevents the lines from bulging and allows the lines to become embedded into the SU‐8 film. [ABSTRACT FROM AUTHOR]

Keywords: flexible electronics; foldable 5G antenna; low dielectric loss; screen printing; silver nanowires EN flexible electronics foldable 5G antenna low dielectric loss screen printing silver nanowires 1 1 1 11/09/21 20211101 NES 211101 B Dielectric & Metallic Inks b In article number 2100525, Weiwei Li and co-workers develop acrylonitrile butadiene styrene-based dielectric ink and silver nanowires-based metallic ink to realize flexible and foldable electronic devices. All Screen-Printed, Polymer-Nanowire Based Foldable Electronics for mm-Wave Applications (Adv. Flexible electronics, foldable 5G antenna, low dielectric loss, screen printing, silver nanowires. [Extracted from the article]

As the need for assistive robots increases in aging societies, various assistive robot systems including humanoid robots have been developed. Humanoid robotic hands are one of the most useful parts to assist humans efficiently. While sensing pressure or temperature from the robotic hands is extensively studied, sensing chemicals is less widely studied despite the significant importance. Here, a unique platform of smartly moving humanoid fingers actuated by chemical sensing is reported. The sensor is printed with disposable and biocompatible cellulose conductive ink materials. Rf intensity change of the sensor with NH4+ membrane depends on NH4+ ion concentration where R² is 0.9576. The smart bending motion of a finger is accomplished by logically programed actuation through detecting the change of interested ion concentration from 0.01 to 1 m at the ion‐selective membrane electrode (ISME) sensor with resulted bending angles from 10° to 67° accordingly. The overall signal‐to‐noise ratio is over 10. This sensing robot concept may be expanded to applications of microrobots which receive external stimulus, judge, and execute the actuation to carry out programed tasks. [ABSTRACT FROM AUTHOR]

The progress in 3D printing research has led to significant developments ranging from customized printing to rapid prototyping. However, the 3D printing of electrodes, especially stretchable electrodes for the fabrication of 3D printable electronic devices, is challenging due to the inherent weakness with respect to the printing material. A novel preparation method is reported for a 3D printable conductive ink with a self‐wiring effect during heat treatment, which pushes the silicone rubber outward and results in the accumulation of the conductors within the wire. This effect results in the formation of a polymer shell around the conductor, thus yielding conductors with larger stretchability and soft passivation characteristics. The conductive ink is prepared via the following steps: i) mixing of conductive filler, silicone rubbers, and solvent; followed by ii) soft heat treatment for soft curing and solvent evaporation. Furthermore, a capacitive sensor is fabricated using this dielectric polymer layer. As a demonstration, a mouse controller is fabricated using a capacitive sensor array prepared using the conductors developed in this study. [ABSTRACT FROM AUTHOR]

Printable silver‐nanowire (Ag NW) inks with simple formulation, low cost, and high conductivity are developed and screen printed on flexible poly(ethylene terephthalate) substrates. By using ultralong Ag NWs (≈75 µm in length) as the conductor, the screen‐printed Ag NW patterns exhibit exceptional conductivity (up to 8.32 × 103 S cm−1) and excellent mechanical robustness. Rheological behavior suitable for screen printing is achieved by adjusting the formulation of the inks, which assures neat and smooth screen‐printed lines with resolution as high as 100 µm. Uniform and honeycomb‐structured Ag NW transparent conductive films with superior flexibility and optical transmittance ≈80% are obtained by screen printing the Ag NW inks. Flexible all‐solid‐state supercapacitors based on Ag NW/PEDOT:PSS electrodes reach areal specific capacitance as high as 8.58 mF cm−2, a value threefold higher than that of pristine PEDOT:PSS electrodes. Moreover, a high flexibility with a bending angle of 180° and long‐term stability with ≈90% capacitance retention over 2500 cycles, is also obtained, manifesting this material's great potential applications for flexible and wearable energy‐storage devices. [ABSTRACT FROM AUTHOR]

Printed electronics is attracting a great deal of attention in both research and commercialization as it enables fabrication of large‐scale, low‐cost electronic devices on a variety of substrates. Printed electronics plays a critical role in facilitating widespread flexible electronics and more recently stretchable electronics. Conductive nanomaterials, such as metal nanoparticles and nanowires, carbon nanotubes, and graphene, are promising building blocks for printed electronics. Nanomaterial‐based printing technologies, formulation of printable inks, post‐printing treatment, and integration of functional devices have progressed substantially in the recent years. This review summarizes basic principles and recent development of common printing technologies, formulations of printable inks based on conductive nanomaterials, deposition of conductive inks via different printing techniques, and performance enhancement by using various sintering methods. While this review places emphasis on conductive nanomaterials, the printing techniques and ink formulations can be applied to other materials such as semiconducting and insulating nanomaterials. Moreover, some applications of printed flexible and stretchable electronic devices are reviewed to illustrate their potential. Finally, the future challenges and prospects for printing conductive nanomaterials are discussed. [ABSTRACT FROM AUTHOR]

As a type of flexible electronics, wearable heaters have attracted broad attention because of their giant potential market value, such as for use in wearable thermotherapy. Wearable heaters are required to simultaneously possess high stretchability and dynamic stability, in order to realize joints or muscles thermotherapy during exercising. Here, a high‐performance electrically driven heater using the conductive composite of liquid‐metal (LM) and polydimethylsiloxane (PDMS) is reported, which is patterned as sinusoidal structure by the printing technology of direct ink writing. Because high conductive LM is chosen as the active material, the LM@PDMS stretchable heater possesses high stretchability (>100% strain) and good conductivity (1.81 × 103 S cm−1). It also exhibits superb dynamic stability, due to the 3D conductive network of LM in matrix and the sinusoidal structure of the composite. While being stretched to the strain level of 100%, the heating temperature variation of LM@PDMS stretchable heater is less than 8%. This relatively low temperature variation is several times smaller than that of existing heaters at the same large strain levels. It is demonstrated that the LM@PDMS stretchable heater worn on the knee joint works well during strenuous exercise, thus proving great potential in wearable thermotherapy. The stretchable heater with sinusoidal structure pattern is prepared by printing the conductive ink of polydimethylsiloxane filled with liquid‐metal (LM@PDMS). This stretchable heater simultaneously possesses high stretchability and superb dynamic stability. Even if stretching to 100%, its heating temperature decays by only 7.56%. High‐performance LM@PDMS stretchable heater is promising to do thermotherapy for joints or muscles while exercising strenuously. [ABSTRACT FROM AUTHOR]