Search Results (43)

As conductive materials, ionogels have attracted significant attention for their potential applications in flexible wearable electronics. However, preparing an ionogel with mechanical properties akin to human skin while also achieving transparency, adhesion, and low hysteresis through simple processes remains challenging. Here, we introduce a multifunctional ionogel synthesized via a one-step photopolymerization method. By leveraging the good compatibility between the ionic liquid and the polymer network, as well as the hydrogen bonding and chemical crosslinking within the gel network, we achieved an ionogel with high transparency (>98%), stretchability (fracture strain of 19), low hysteresis (<5.83%), strong adhesion, robust mechanical stability, excellent electrical properties, a wide operating temperature range, and a tunable modulus (1–103 kPa) that matches human skin. When used as a conductor in soft actuators, the ionogel enabled a large area strain of 36% and a fast electromechanical conversion time of less than 1 s. The actuator demonstrated good actuation performance with voltage and frequency dependence, electrochemical stability, and outstanding durability over millions of cycles. This study provides a simple and effective method to produce multifunctional ionogels with tailored mechanical properties that match those of human skin, paving the way for their application in flexible wearable electronics. Full article

Ionogels, as emerging stretchable conductor materials, have garnered significant attention for their potential applications in flexible electronics, particularly in wearable strain sensors. However, a persistent challenge in optimizing ionogels lies in achieving a balance between enhanced mechanical properties and electrical conductivity. In this study, we successfully addressed this challenge by incorporating carbon nanotubes (CNTs) into ionogels, achieving a simultaneous improvement in the electrical conductivity (2.67 mS/cm) and mechanical properties (400.83 kPa). The CNTs served dual purposes, acting as a continuous conductive pathway to facilitate electrical signal transmission and as reinforcing nanotubes to bolster the mechanical robustness of the ionogels. Additionally, the polymer network, composed of acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA), established a purely physical cross-linking network characterized by dense hydrogen bonding, which ensured sufficient toughness within the ionogels. Notably, the assembled ionogels, when utilized as wireless strain sensors, demonstrated exceptional sensitivity in detecting subtle finger movements, with the CNTs significantly amplifying the electrical response. This work provides new insights into the integration of carbon nanotubes in ionogels, expanding their applications and pioneering a fresh approach to functionalized ionogel design. Full article

Stretchable composite conductive fibers (SCCFs) exhibit remarkable conductivity, stretchability, breathability, and biocompatibility, making them ideal candidates for wearable electronics and bioelectronics. The exploitation of SCCFs in electronic devices requires a careful balance of many aspects, including material selection and process methodologies, to address the complex challenges associated with their electrical and mechanical properties. In this review, we elucidate the conductive mechanism of SCCFs and summarize strategies for integrating various conductors with stretchable fibers, emphasizing the primary challenges in fabricating highly conductive fibers. Furthermore, we explore the multifaceted applications of SCCFs-based frameworks in wearable electronic devices. This review aims to emphasize the significance of SCCFs and offers insights into their conductive mechanisms, material selection, manufacturing technologies, and performance improvement. Hopefully, it can guide the innovative development of SCCFs and broaden their application potential. Full article

Wearable electronic sensors have recently attracted tremendous attention in applications such as personal health monitoring, human movement detection, and sensory skins as they offer a promising alternative to counterparts made from traditional metallic conductors and bulky metallic conductors. However, the real-world use of most wearable sensors is often hindered by their limited stretchability and sensitivity, and ultimately, their difficulty to integrate into textiles. To overcome these limitations, wearable sensors can incorporate flexible conductive fibers as electrically active components. In this study, we adopt a scalable wet-spinning approach to directly produce flexible and conductive fibers from aqueous mixtures of Ti₃C₂T_x MXene and natural rubber (NR). The electrical conductivity and stretchability of these fibers were tuned by varying their MXene loading, enabling knittability into textiles for wearable sensors. As individual filaments, these MXene/NR fibers exhibit suitable conductivity dependence on strain variations, making them ideal for motivating sensors. Meanwhile, textiles from knitted MXene/NR fibers demonstrate great stability as capacitive touch sensors. Collectively, we believe that these elastic and conductive MXene/NR-based fibers and textiles are promising candidates for wearable sensors and smart textiles. Full article

Wearable sensors are rapidly gaining influence in the diagnostics, monitoring, and treatment of disease, thereby improving patient outcomes. In this review, we aim to explore how these advances can be applied to magnetic resonance imaging (MRI). We begin by (i) introducing limitations in current flexible/stretchable RF coils and then move to the broader field of flexible sensor technology to identify translatable technologies. To this goal, we discuss (ii) emerging materials currently used for sensor substrates, (iii) stretchable conductive materials, (iv) pairing and matching of conductors with substrates, and (v) implementation of lumped elements such as capacitors. Applicable (vi) fabrication methods are presented, and the review concludes with a brief commentary on (vii) the implementation of the discussed sensor technologies in MRI coil applications. The main takeaway of our research is that a large body of work has led to exciting new sensor innovations allowing for stretchable wearables, but further exploration of materials and manufacturing techniques remains necessary, especially when applied to MRI diagnostics. Full article

Stretchable ionogels, as soft ion-conducting materials, have generated significant interest. However, the integration of multiple functions into a single ionogel, including temperature tolerance, self-adhesiveness, and stability in diverse environments, remains a challenge. In this study, a new class of fluorine-containing ionogels was synthesized through photo-initiated copolymerization of fluorinated hexafluorobutyl methacrylate and butyl acrylate in a fluorinated ionic liquid 1-butyl-3-methyl imidazolium bis (trifluoromethylsulfonyl) imide. The resulting ionogels demonstrate good stretchability with a fracture strain of ~1300%. Owing to the advantages of the fluorinated network and the ionic liquid, the ionogels show excellent stability in air and vacuum, as well as in various solvent media such as water, sodium chloride solution, and hexane. Additionally, the ionogels display impressive wide temperature tolerance, functioning effectively within a wide temperature range from −60 to 350 °C. Moreover, due to their adhesive properties, the ionogels can be easily attached to various substrates, including plastic, rubber, steel, and glass. Sensors made of these ionogels reliably respond to repetitive tensile-release motion and finger bending in both air and underwater. These findings suggest that the developed ionogels hold great promise for application in wearable devices. Full article

Three-dimensional (3D) printing, alternatively known as additive manufacturing, is a transformative technology enabling precise, customized, and efficient manufacturing of components with complex structures. It revolutionizes traditional processes, allowing rapid prototyping, cost-effective production, and intricate designs. The 3D printed graphene-based materials combine graphene’s exceptional properties with additive manufacturing’s versatility, offering precise control over intricate structures with enhanced functionalities. To gain comprehensive insights into the development of 3D printed graphene and graphene/polymer composites, this review delves into their intricate fabrication methods, unique structural attributes, and multifaceted applications across various domains. Recent advances in printable materials, apparatus characteristics, and printed structures of typical 3D printing techniques for graphene and graphene/polymer composites are addressed, including extrusion methods (direct ink writing and fused deposition modeling), photopolymerization strategies (stereolithography and digital light processing) and powder-based techniques. Multifunctional applications in energy storage, physical sensor, stretchable conductor, electromagnetic interference shielding and wave absorption, as well as bio-applications are highlighted. Despite significant advancements in 3D printed graphene and its polymer composites, innovative studies are still necessary to fully unlock their inherent capabilities. Full article

Stretchable electronics rely on sophisticated structural designs to allow brittle metallic conductors to adapt to curved or moving substrates. Patterns of soft islands and stable cracks in layered silver-PDMS composites provide exceptional stretchability by means of strain localization as the cracks open and the islands strain. To investigate the reliability and potential failure modes, we study the initiation and propagation of delamination in dependence of structure geometry and quality of the metal-polymer bonding. Our numerical experiments show a well-bonded metal film to be under no risk of delamination. Even weakly bonded metal films sustain moderate strains well above the limits of classical electronic materials before the onset of delamination in the soft islands structures. If delamination occurs, it does so in predictable patterns that retain functionality over a remarkable strain range in the double-digit percent range before failure, thus, providing safety margins in applications. Full article

Three-dimensional (3D) printing has various applications in many fields, such as soft electronics, robotic systems, biomedical implants, and the recycling of thermoplastic composite materials. Three-dimensional printing, which was only previously available for prototyping, is currently evolving into a technology that can be utilized by integrating various materials into customized structures in a single step. Owing to the aforementioned advantages, multi-functional 3D objects or multi-material-designed 3D patterns can be fabricated. In this study, we designed and fabricated 3D-printed expandable structural electronics in a substrateless auxetic pattern that can be adapted to multi-dimensional deformation. The printability and electrical conductivity of a stretchable conductor (Ag-RTV composite) were optimized by incorporating a lubricant. The Ag-RTV and RTV were printed in the form of conducting voxels and frame voxels through multi-nozzle printing and were arranged in a negative Poisson’s ratio pattern with a missing rib structure, to realize an expandable passive component. In addition, the expandable structural electronics were embedded in a soft actuator via one-step printing, confirming the possibility of fabricating stable interconnections in expanding deformation via a missing rib pattern. Full article

As an indispensable part of wearable devices and mechanical arms, stretchable conductors have received extensive attention in recent years. The design of a high-dynamic-stability, stretchable conductor is the key technology to ensure the normal transmission of electrical signals and electrical energy of wearable devices under large mechanical deformation, which has always been an important research topic domestically and abroad. In this paper, a stretchable conductor with a linear bunch structure is designed and prepared by combining numerical modeling and simulation with 3D printing technology. The stretchable conductor consists of a 3D-printed bunch-structured equiwall elastic insulating resin tube and internally filled free-deformable liquid metal. This conductor has a very high conductivity exceeding 10⁴ S cm⁻¹, good stretchability with an elongation at break exceeding 50%, and great tensile stability, with a relative change in resistance of only about 1% at 50% tensile strain. Finally, this paper demonstrates it as a headphone cable (transmitting electrical signals) and a mobile phone charging wire (transmitting electrical energy), which proves its good mechanical and electrical properties and shows good application potential. Full article

The production of flexible electronic systems includes stretchable electrical interconnections and flexible electronic components, promoting the research and development of flexible conductors and stretchable conductive materials with large bending deformation or torsion resistance. Silver nanowires have the advantages of high conductivity, good transparency and flexibility in the development of flexible electronic products. In order to further prepare system-level flexible systems (such as autonomous full-software robots, etc.), it is necessary to focus on the conductivity of the system’s composite conductor and the robustness of the system at the physical level. In terms of conductor preparation processes and substrate adhesion strategies, the more commonly used solutions are selected. Four kinds of elastic preparation processes (pretensioned/geometrically topological matrix, conductive fiber, aerogel composite, mixed percolation dopant) and five kinds of processes (coating, embedding, changing surface energy, chemical bond and force, adjusting tension and diffusion) to enhance the adhesion of composite conductors using silver nanowires as current-carrying channel substrates were reviewed. It is recommended to use the preparation process of mixed percolation doping and the adhesion mode of embedding/chemical bonding under non-special conditions. Developments in 3D printing and soft robots are also discussed. Full article

In recent decades, thriving Internet of Things (IoT) technology has had a profound impact on people’s lifestyles through extensive information interaction between humans and intelligent devices. One promising application of IoT is the continuous, real-time monitoring and analysis of body or environmental information by devices worn on or implanted inside the body. This research area, commonly referred to as wearable electronics or wearables, represents a new and rapidly expanding interdisciplinary field. Wearable electronics are devices with specific electronic functions that must be flexible and stretchable. Various novel materials have been proposed in recent years to meet the technical challenges posed by this field, which exhibit significant potential for use in different wearable applications. This article reviews recent progress in the development of emerging nanomaterial-based wearable electronics, with a specific focus on their flexible substrates, conductors, and transducers. Additionally, we discuss the current state-of-the-art applications of nanomaterial-based wearable electronics and provide an outlook on future research directions in this field. Full article

The increasing interest in stretchable conductive composite materials, that can be versatile and suitable for wide-ranging application, has sparked a growing demand for studies of scalable fabrication techniques and specifically tailored geometries. Thanks to the combination of the conductivity and robustness of carbon nanotube (CNT) materials with the viscoelastic properties of polymer films, in particular their stretchability, “surface composites” made of a CNT on polymeric films are a promising way to obtain a low-cost, conductive, elastic, moldable, and patternable material. The use of polymers selected for specific applications, however, requires targeted studies to deeply understand the interface interactions between a CNT and the surface of such polymer films, and in particular the stability and durability of a CNT grafting onto the polymer itself. Here, we present an investigation of the interface properties for a selected group of polymer film substrates with different viscoelastic properties by means of a series of different and complementary experimental techniques. Specifically, we studied the interaction of a single-wall carbon nanotube (SWCNT) deposited on two couples of different polymeric substrates, each one chosen as representative of thermoplastic polymers (i.e., low-density polyethylene (LDPE) and polypropylene (PP)) and thermosetting elastomers (i.e., polyisoprene (PI) and polydimethylsiloxane (PDMS)), respectively. Our results demonstrate that the characteristics of the interface significantly differ for the two classes of polymers with a deeper penetration (up to about 100 μm) into the polymer bulk for the thermosetting substrates. Consequently, the resistance per unit length varies in different ranges, from 1–10 kΩ/cm for typical thermoplastic composite devices (30 μm thick and 2 mm wide) to 0.5–3 MΩ/cm for typical thermosetting elastomer devices (150 μm thick and 2 mm wide). For these reasons, the composites show the different mechanical and electrical responses, therefore suggesting different areas of application of the devices based on such materials. Full article

Nanocellulose-reinforced ionic conductive hydrogels were prepared using cellulose nanofiber (CNF) and polyvinyl alcohol (PVA) as raw materials, and the hydrogels were prepared in a dimethyl sulfoxide (DMSO)/water binary solvent by a one-pot method. The prepared hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The mechanical properties, electrical conductivity, and sensing properties of the hydrogels were studied by means of a universal material testing machine and LCR digital bridge. The results show that the ionic conductive hydrogel exhibits high stretchability (elongation at break, 206%) and firmness (up to 335 KPa). The tensile fracture test shows that the hydrogel has good properties in terms of tensile strength, toughness, and elasticity. The hydrogel as a conductor medium is assembled into a self-powered strain sensor and the open-circuit voltage can reach 0.830 V. It shows good sensitivity in the bend sensing testing, indicating that the hydrogel has good sensing performance. The water retention and anti-freezing performance experiments show that the addition of dimethyl sulfoxide solvents can effectively improve the anti-freezing and water retention properties of hydrogels. Full article

Conductive and stretchable fibers are the cornerstone of intelligent textiles and imperceptible electronics. Among existing fiber conductors, gallium-based liquid metals (LMs) featuring high conductivity, fluidity, and self-healing are excellent candidates for highly stretchable fibers with sensing, actuation, power generation, and interconnection functionalities. However, current LM fibers fabricated by direct injection or surface coating have a limitation in shape programmability. This hinders their applications in functional fibers with tunable electromechanical response and miniaturization. Here, we reported a simple and efficient method to create shape-programmable LM fibers using the phase transition of gallium. Gallium metal wires in the solid state can be easily shaped into a 3D helical structure, and the structure can be preserved after coating the wire with polyurethane and liquifying the metal. The 3D helical LM fiber offered enhanced stretchability with a high breaking strain of 1273% and showed invariable conductance over 283% strain. Moreover, we can reduce the fiber diameter by stretching the fiber during the solidification of polyurethane. We also demonstrated applications of the programmed fibers in self-powered strain sensing, heart rate monitoring, airflow, and humidity sensing. This work provided simple and facile ways toward functional LM fibers, which may facilitate the broad applications of LM fibers in e-skins, wearable computation, soft robots, and smart fabrics. Full article