Stretchable Electronics Based on PDMS Substrates

Shape-stabilized flexible thermochromic films with one-sided adhesion via gradient crosslinking strategy for temperature indicating

Thermochromic dyes (TCDs) based on a three-component color change system suffer from solid rigidity and liquid leakage issues because of the intrinsic solid-liquid phase change performance, resulting in difficulty in temperature visualization applications for smart wearable fields. Despite considerable efforts in microencapsulation of thermochromic dyes, designing and fabricating essentially flexible thermochromic phase change films still need to be explored. Herein, a one-sided adhesive gradient-crosslinked thermochromic film is reported to address these issues to make a trade-off between stability and flexibility, excellent thermochromic performance, and temperature visualization. The thermochromic wearable films have been fabricated exploiting tea polyphenol thermochromic dyes, vinyl dimethylsiloxane, and hydrosilicone oil via the salt-template-assisted method and gradient crosslinking strategy, which have porous structures with an average pore size of 12.8 μm and a porosity of 28 %. Due to the spatial limiting threshold effect of the porosity structure, interconnected 3D polysiloxane porous networks can provide ample support for tea polyphenol thermochromic dyes and effectively prevent liquid leakage. Upon heating, the thermochromic film changes from blue to white with the K/S value decreasing from 7.69 to 0.78 and the ΔE* increasing from 2.7 to 16.1 at 610 nm, and the color-changing temperature is 42 °C. Gradient crosslinked thermochromic films exhibit excellent temperature-responsive color change properties, desirable one-side adhesion, and thermal energy storage, enabling multicolor temperature displays and temperature-controlled multilevel information transfer.

Breathable and Stretchable Epidermal Electronics for Health Management: Recent Advances and Challenges

Advanced epidermal electronic devices, capable of real-time monitoring of physical, physiological, and biochemical signals and administering appropriate therapeutics, are revolutionizing personalized healthcare technology. However, conventional portable electronic devices are predominantly constructed from impermeable and rigid materials, which thus leads to the mechanical and biochemical disparities between the devices and human tissues, resulting in skin irritation, tissue damage, compromised signal-to-noise ratio (SNR), and limited operational lifespans. To address these limitations, a new generation of wearable on-skin electronics built on stretchable and porous substrates has emerged. These substrates offer significant advantages including breathability, conformability, biocompatibility, and mechanical robustness, thus providing solutions for the aforementioned challenges. However, given their diverse nature and varying application scenarios, the careful selection and engineering of suitable substrates is paramount when developing high-performance on-skin electronics tailored to specific applications. This comprehensive review begins with an overview of various stretchable porous substrates, specifically focusing on their fundamental design principles, fabrication processes, and practical applications. Subsequently, a concise comparison of various methods is offered to fabricate epidermal electronics by applying these porous substrates. Following these, the latest advancements and applications of these electronics are highlighted. Finally, the current challenges are summarized and potential future directions in this dynamic field are explored.

Polyurethane Vitrimers Engineered with Nitrogen-Coordinating Cyclic Boronic Diester Bonds for Sustainable Bioelectronics

Flexible bioelectronic devices seamlessly interface with organs and tissues, offering unprecedented opportunity for timely prevention, early diagnosis, and medical therapies. However, the majority of flexible substrates utilized in bioelectronics still encounter significant challenges in terms of recyclability and reprocessing, leading to the accumulation of environmentally and biologically hazardous toxic waste. Here, the study reports the design of recyclable polyurethane (PU) vitrimers engineered with internal boron-nitrogen coordination bonds that can reversibly dissociate to boronic acids and hydroxyl, or undergo metathesis reaction following an associative pathway. The study demonstrates the capacity of these recyclable PU vitrimers as flexible substrates in various wearable and implantable bioelectronic applications, achieving high-quality electrophysiological recordings and stimulation. Furthermore, the study establishes a sustainable recycling process by reconstructing a range of bioelectronic devices from the recycled PU vitrimers without compromising the mechanical performance. This closed-loop approach not only addresses the critical challenge of the reclaiming medical electronic waste but also paves the way for the development of sustainable flexible bioelectronics for healthcare applications.

High toughness, healable, self-cleaning polydimethylsiloxane elastomers with "rigid-while-flexible" mutual network structure

Polydimethylsiloxane (PDMS) elastomers with high mechanical and healing properties are developed as smart materials for electrical power systems and electronic devices to address electrical or mechanical damage. However, the challenge is to reconcile the conflicting molecular mechanisms of mechanical and healing properties in the development of PDMS elastomers. This study adopts the "rigid-while-flexible" mutual network structure by copolymerizing the rigid polyimide (PI) with flexible segments with dynamic reversible crosslinking designed on the PDMS backbones. This elastomer (designated PSiPI) exhibits high toughness, tensile strength and elongation at break, as well as excellent healing efficiency and recyclability. Moreover, the PSiPI elastomer also exhibits good insulation and corona damage healing properties. Taking advantage of the recyclability and healing properties of PSiPI elastomers, healable superhydrophobic coatings with contact angles greater than 150° have been prepared by compositing PSiPI elastomers with SiO2. Likewise, combining the elastomer with conductive materials can create a healing flexible conductor. This "rigid-while-flexible" design approach provides important inspiration for the development of high-performance, sustainable and environmentally friendly PDMS elastomers for electrical and electronic applications.

Raman spectroscopic quantification of polyethylene particles in water using polydimethylsiloxane-coated nickel foam as a particle-capturing platform

Nickel foam (NF) was evaluated as a medium for the capture of polyethylene (PE) particles in water. NF is a hydrophobic and porous material with a large surface area, making it a promising candidate for attracting PE particles. However, the particle-capturing efficiency using bare NF was only 69.5%. To increase capturing efficiency, a circular polydimethylsiloxane (PDMS)-coated NF (PDMS@NF, diameter: 6 mm) was employed to enhance the hydrophobicity. The capturing efficiency using the PDMS@NF was substantially increased to 97.6 % owing to the increase in hydrophobicity. To quantify the captured PE particles on/in the PDMS@NF using Raman spectroscopy, a wide area illumination (WAI) scheme providing 6 mm-diameter laser illumination was adopted to fully cover the PDMS@NF for representative spectroscopic sampling and accurate quantification. The intensity ratios of PE to PDMS peaks in the collected spectra clearly increased with the quantity of dispersed PE particles (0.1 ∼ 4.0 mg range, R2: 0.992) in the water samples, and the limit of detection was 0.08 mg. Moreover, the capturing efficiencies for polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) particles (1 mg of each) using the PDMS@NF were also superior, ranging from 96.4 to 98.2 %. Therefore, the proposed scheme incorporating the PDMS@NF as a particle-capturing and Raman measurement platform has potential as a method for on-line detection of microplastics in water.

Ultra-Thin GaAs Single-Junction Solar Cells for Self-Powered Skin-Compatible Electrocardiogram Sensors

GaAs thin-film solar cells have high efficiency, reliability, and operational stability, making them a promising solution for self-powered skin-conformal biosensors. However, inherent device thickness limits suitability for such applications, making them uncomfortable and unreliable in flexural environments. Therefore, reducing the flexural rigidity becomes crucial for integration with skin-compatible electronic devices. Herein, this study demonstrated a novel one-step surface modification bonding methodology, allowing a streamlined transfer process of ultra-thin (2.3 µm thick) GaAs solar cells on flexible polymer substrates. This reproducible technique enables strong bonding between dissimilar materials (GaAs-polydimethylsiloxane, PDMS) without high external pressures and temperatures. The fabricated solar cell showed exceptional performance with an open-circuit voltage of 1.018 V, short-circuit current density of 20.641 mA cm-2, fill factor of 79.83%, and power conversion efficiency of 16.77%. To prove the concept, the solar cell is integrated with a skin-compatible organic electrochemical transistor (OECT). Competitive electrical outputs of GaAs solar cells enabled high current levels of OECT under subtle light intensities lower than 50 mW cm-2, which demonstrates a self-powered electrocardiogram sensor with low noise (signal-to-noise ratio of 32.68 dB). Overall, this study presents a promising solution for the development of free-form and comfortable device structures that can continuously power wearable devices and biosensors.

Versatile Patterning of Liquid Metal via Multiphase 3D Printing

This paper presents a scalable and straightforward technique for the immediate patterning of liquid metal/polymer composites via multiphase 3D printing. Capitalizing on the polymer's capacity to confine liquid metal (LM) into diverse patterns. The interplay between distinctive fluidic properties of liquid metal and its self-passivating oxide layer within an oxidative environment ensures a resilient interface with the polymer matrix. This study introduces an inventive approach for achieving versatile patterns in eutectic gallium indium (EGaIn), a gallium alloy. The efficacy of pattern formation hinges on nozzle's design and internal geometry, which govern multiphase interaction. The interplay between EGaIn and polymer within the nozzle channels, regulated by variables such as traverse speed and material flow pressure, leads to periodic patterns. These patterns, when encapsulated within a dielectric polymer polyvinyl alcohol (PVA), exhibit an augmented inherent capacitance in capacitor assemblies. This discovery not only unveils the potential for cost-effective and highly sensitive capacitive pressure sensors but also underscores prospective applications of these novel patterns in precise motion detection, including heart rate monitoring, and comprehensive analysis of gait profiles. The amalgamation of advanced materials and intricate patterning techniques presents a transformative prospect in the domains of wearable sensing and comprehensive human motion analysis.

Inside out: Exploring edible biocatalytic biosensors for health monitoring

Edible biosensors can measure a wide range of physiological and biochemical parameters, including temperature, pH, gases, gastrointestinal biomarkers, enzymes, hormones, glucose, and drug levels, providing real-time data. Edible biocatalytic biosensors represent a new frontier within healthcare technology available for remote medical diagnosis. The main challenges to develop edible biosensors are: i) finding edible materials (i.e. redox mediators, conductive materials, binders and biorecognition elements such as enzymes) complying with Food and Drug Administration (FDA), European Food Safety Authority (EFSA) and European Medicines Agency (EMEA) regulations; ii) developing bioelectronics able to operate in extreme working conditions such as low pH (∼pH 1.5 gastric fluids etc.), body temperature (between 37 °C and 40 °C) and highly viscous bodily fluids that may cause surface biofouling issues. Nowadays, advanced printing techniques can revolutionize the design and manufacturing of edible biocatalytic biosensors. This review outlines recent research on biomaterials suitable for creating edible biocatalytic biosensors, focusing on their electrochemical properties such as electrical conductivity and redox potential. It also examines biomaterials as substrates for printing and discusses various printing methods, highlighting challenges and perspectives for edible biocatalytic biosensors.

Investigation of Interferences of Wearable Sensors with Plant Growth

Plant wearable sensors have shown exceptional promise in continuously monitoring plant health. However, the potential adverse effects of these sensors on plant growth remain unclear. This study systematically quantifies wearable sensors' interference with plant growth using two ornamental species, Peperomia tetraphylla and Epipremnum aureum. We evaluated the impacts of four common disturbances-mechanical pressure, hindrance of gas exchange, hindrance of light acquisition, and mechanical constraint-on leaf growth. Our results indicated that the combination of light hindrance and mechanical constraint demonstrated the most significant interference. When the sensor weight was no greater than 0.6 g and the coverage was no greater than 5% of the leaf area, these four disturbances resulted in slight impacts on leaf growth. Additionally, we fabricated a minimally interfering wearable sensor capable of measuring the air temperature of the microclimate of the plant while maintaining plant growth. This research provides valuable insights into optimizing plant wearable sensors, balancing functionality with minimal plant interference.

Diving into Sweat: Advances, Challenges, and Future Directions in Wearable Sweat Sensing

Sweat analysis has advanced from diagnosing cystic fibrosis and testing for illicit drugs to noninvasive monitoring of health biomarkers. This article introduces the rapid development of wearable and flexible sweat sensors, highlighting key milestones and various sensing strategies for real-time monitoring of analytes. We discuss challenges such as developing high-performance nanomaterial-based biosensors, ensuring continuous sweat production and sampling, achieving high sweat/blood correlation, and biocompatibility. The potential of machine learning to enhance these sensors for personalized healthcare is presented, enabling real-time tracking and prediction of physiological changes and disease onset. Leveraging advancements in flexible electronics, nanomaterials, biosensing, and data analytics, wearable sweat biosensors promise to revolutionize disease management, prevention, and prediction, promoting healthier lifestyles and transforming medical practices globally.

Micropatterned Polymer Nanoarrays with Distinct Superwettability for a Highly Efficient Sweat Collection and Sensing Patch

Wearable sweat sensor offers a promising means for noninvasive real-time health monitoring, but the efficient collection and accurate analysis of sweat remains challenging. One of the obstacles is to precisely modulate the surface wettability of the microfluidics to achieve efficient sweat collection. Here a facile initiated chemical vapor deposition (iCVD) method is presented to grow and pattern polymer nanocone arrays with distinct superwettability on polydimethylsiloxane microfluidics, which facilitate highly efficient sweat transportation and collection. The nanoarray is synthesized by manipulating monomer supersaturation during iCVD to induce controlled nucleation and preferential vertical growth of fluorinated polymer. Subsequent selective vapor deposition of a conformal hydrogel nanolayer results in superhydrophilic nanoarray floor and walls within the microchannel that provide a large capillary force and a superhydrophobic ceiling that drastically reduces flow friction, enabling rapid sweat transport along varied flow directions. A carbon/hydrogel/enzyme nanocomposite electrode is then fabricated by sequential deposition of highly porous carbon nanoparticles and hydrogel nanocoating to achieve sensitive and stable sweat detection. Further encapsulation of the assembled sweatsensing patch with superhydrophobic nanoarray imparts self-cleaning and water-proof capability. Finally, the sweat sensing patch demonstrates selective and sensitive glucose and lactate detection during the on-body test.

3D Printed MXene-Based Wire Strain Sensors with Enhanced Sensitivity and Anisotropy

Stretchable strain sensors play a crucial role in intelligent wearable systems, serving as the interface between humans and environment by translating mechanical strains into electrical signals. Traditional fiber strain sensors with intrinsic uniform axial strain distribution face challenges in achieving high sensitivity and anisotropy. Moreover, existing micro/nano-structure designs often compromise stretchability and durability. To address these challenges, a novel approach of using 3D printing to fabricate MXene-based flexible sensors with tunable micro and macrostructures.  Poly(tetrafluoroethylene) (PTFE) as a pore-inducing agent is added into 3D printable inks to achieve controllable microstructural modifications. In addition to microstructure tuning, 3D printing is employed for macrostructural design modifications, guided by finite element modeling (FEM) simulations. As a result, the 3D printed sensors exhibit heightened sensitivity and anisotropy, making them suitable for tracking static and dynamic displacement changes. The proposed approach presents an efficient and economically viable solution for standardized large-scale production of advanced wire strain sensors.

Recent Advances in Flexible Temperature Sensors: Materials, Mechanism, Fabrication, and Applications

Flexible electronics is an emerging and cutting-edge technology which is considered as the building blocks of the next generation micro-nano electronics. Flexible electronics integrate both active and passive functions in devices, driving rapid developments in healthcare, the Internet of Things (IoT), and industrial fields. Among them, flexible temperature sensors, which can be directly attached to human skin or curved surfaces of objects for continuous and stable temperature measurement, have attracted much attention for applications in disease prediction, health monitoring, robotic signal sensing, and curved surface temperature measurement. Preparing flexible temperature sensors with high sensitivity, fast response, wide temperature measurement interval, high flexibility, stretchability, low cost, high reliability, and stability has become a research target. This article reviewed the latest development of flexible temperature sensors and mainly discusses the sensitive materials, working mechanism, preparation process, and the applications of flexible temperature sensors. Finally, conclusions based on the latest developments, and the challenges and prospects for research in this field are presented.

Recent advances in flexible memristors for advanced computing and sensing

Conventional computing systems based on von Neumann architecture face challenges such as high power consumption and limited data processing capability. Improving device performance via scaling guided by Moore's Law becomes increasingly difficult. Emerging memristors can provide a promising solution for achieving high-performance computing systems with low power consumption. In particular, the development of flexible memristors is an important topic for wearable electronics, which can lead to intelligent systems in daily life with high computing capacity and efficiency. Here, recent advances in flexible memristors are reviewed, from operating mechanisms and typical materials to representative applications. Potential directions and challenges for future study in this area are also discussed.

Research Progress of Flexible Piezoresistive Sensors Based on Polymer Porous Materials

Flexible piezoresistive sensors are in high demand in areas such as wearable devices, electronic skin, and human-machine interfaces due to their advantageous features, including low power consumption, excellent bending stability, broad testing pressure range, and simple manufacturing technology. With the advancement of intelligent technology, higher requirements for the sensitivity, accuracy, response time, measurement range, and weather resistance of piezoresistive sensors are emerging. Due to the designability of polymer porous materials and conductive phases, and with more multivariate combinations, it is possible to achieve higher sensitivity and lower detection limits, which are more promising than traditional flexible sensor materials. Based on this, this work reviews recent advancements in research on flexible pressure sensors utilizing polymer porous materials. Furthermore, this review examines sensor performance optimization and development from the perspectives of three-dimensional porous flexible substrate regulation, sensing material selection and composite technology, and substrate and sensing material structure design.

A seamless auxetic substrate with a negative Poisson's ratio of -1

Auxetic metamaterials are a unique class of materials or structures with a negative Poisson's ratio and a wide array of functionalities. However, their inherent porosity presents challenges in practical applications. Filling the inherent perforations while preserving their unique auxeticity is difficult because it demands the seamless integration of components that have highly distinct mechanical characteristics. Here we introduce a seamless auxetic substrate film capable of achieving a negative Poisson's ratio of -1, the theoretical limit of isotropic materials. This breakthrough is realized by incorporating a highly rigid auxetic structure reinforced by glass-fabric, with surface-flattening soft elastomers. We effectively optimize the mechanical properties of these components by systematic experimental and theoretical investigations into the effects of relative differences in the moduli of the constituents. Using the developed auxetic film we demonstrate an image distortion-free display having 25 PPI resolution of micro-LEDs that is capable of 25% stretching without performance degradation.

Indoor Light Harvesting Perovskite Solar Cells on Conducting Oxide-Free Ultrathin Deformable Substrates

Perovskite solar cells (PSCs) are receiving renewed interest since they have reached high power conversion efficiency (PCE) and show potential for application not only on rigid and flexible substrates but also on mechanically deformable substrates for integration on nonplanar curvilinear surfaces. Here we demonstrate PSCs fabricated on transparent conducting oxide-free ultrathin polyethylene terephthalate substrates capable of efficiently harvesting indoor light even under compressive strain. Interface engineering with poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) improved the shunt resistance and band alignment at the perovskite-hole transport layer interface, which resulted in enhanced charge extraction, leading to 114% improvement in PCE from 5.57 to 11.91% under 500 lx indoor white LED (4000 K) illumination. The champion device exhibited a PCE of 18.37% under 250 lx cool white LED (4000 K) light. The maximum power output (P max) of the devices varied from 13.78 to 25.38 μW/cm2 by changing the indoor light illumination from 250 to 1000 lx, respectively. Moreover, the devices showed impressive performance even after mechanical deformation and retained 83 and 76% for 1 sun and indoor light, respectively, under 30% compressive strain. Our approach paves the way for fabrication of efficient indoor light harvesting PSCs on mechanically deformable substrates for integration on nonplanar surfaces prone to compressive strain.

An ultrathin, rapidly fabricated, flexible giant magnetoresistive electronic skin

In recent years, there has been a significant increase in the prevalence of electronic wearables, among which flexible magnetoelectronic skin has emerged as a key component. This technology is part of the rapidly progressing field of flexible wearable electronics, which has facilitated a new human perceptual development known as the magnetic sense. However, the magnetoelectronic skin is limited due to its low sensitivity and substantial field limitations as a wearable electronic device for sensing minor magnetic fields. Additionally, achieving efficient and non-destructive delamination in flexible magnetic sensors remains a significant challenge, hindering their development. In this study, we demonstrate a novel magnetoelectronic touchless interactive device that utilizes a flexible giant magnetoresistive sensor array. The flexible magnetic sensor array was developed through an electrochemical delamination process, and the resultant ultra-thin flexible electronic system possessed both ultra-thin and non-destructive characteristics. The flexible magnetic sensor is capable of achieving a bending angle of up to 90 degrees, maintaining its performance integrity even after multiple repetitive bending cycles. Our study also provides demonstrations of non-contact interaction and pressure sensing. This research is anticipated to significantly contribute to the advancement of high-performance flexible magnetic sensors and catalyze the development of more sophisticated magnetic electronic skins.

Exploring the Elastomer Influence on the Electromechanical Performance of Stretchable Conductors

Stretchable electronics has received major attention in recent years due to the prospects of integrating electronics onto and into the human body. While many studies investigate how different conductive fillers perform in stretchable composites, the effect of different elastomers on composite performance, and the related fundamental understanding of what is causing the performance differences, is poorly understood. Here, we perform a systematic investigation of the elastomer influence on the electromechanical performance of gold nanowire-based stretchable conductors based on five chemically different elastomers of similar Young's modulus. The choice of elastomer has a huge impact on the electromechanical performance of the conductors under cyclic strain, as some composites perform well, while others fail rapidly at 100% strain cycling. The lack of macroscopic crack formation in the failing composites indicates that the key aspect for good electromechanical performance is not homogeneous films on the macroscale but rather beneficial interactions on the nanoscale. Based on the comprehensive characterization, we propose a failure mechanism related to the mechanical properties of the elastomers. By improving our understanding of elastomer influence on the mechanisms of electrical failure, we can move toward rational material design, which could greatly benefit the field of stretchable electronics.

Strain-Sensor-In-Pixel Technology for Resolution-Sustainable Stretchable Displays

One of the limitations of stretchable displays is the severe degradation of resolution or the decrease in the number of pixels per unit area when stretched. Hence, we suggest a strain-sensor-in-pixel (S-SIP) system through the adoption of hidden pixels that are activated only during the stretch mode for maintaining the density of on-state pixels. For the S-SIP system, the gate and source electrodes of InGaZnO thin-film transistors (TFTs) in an existing pixel are connected to a resistive strain sensor through the facile and selective deposition of silver nanowires (AgNWs) via electrohydrodynamic-jet-printing. With this approach, the strain sensor integrated TFT functions as a strain-triggered switch, which responds only to stretching along the designated axes by finely tuning the orientation and cycles of AgNW printing. The strain sensor-integrated TFT remains in an off-state when unstretched and switches to an on-state when stretched, exhibiting a large negative gauge factor of -1.1 × 1010 and a superior mechanical stability enduring 6000 cycles, which enables the efficient structure to operate hidden pixels without requiring additional signal processing. Furthermore, the stable operation of the S-SIP in a 5 × 5-pixel array is demonstrated via circuit simulation, implying the outstanding applicability and process compatibility to the conventional active-matrix display backplanes.

Bio-Skin-Inspired Flexible Pressure Sensor Based on Carbonized Cotton Fabric for Human Activity Monitoring

With the development of technology, people's demand for pressure sensors with high sensitivity and a wide working range is increasing. An effective way to achieve this goal is simulating human skin. Herein, we propose a facile, low-cost, and reproducible method for preparing a skin-like multi-layer flexible pressure sensor (MFPS) device with high sensitivity (5.51 kPa-1 from 0 to 30 kPa) and wide working pressure range (0-200 kPa) by assembling carbonized fabrics and micro-wrinkle-structured Ag@rGO electrodes layer by layer. In addition, the highly imitated skin structure also provides the device with an extremely short response time (60/90 ms) and stable durability (over 3000 cycles). Importantly, we integrated multiple sensor devices into gloves to monitor finger movements and behaviors. In summary, the skin-like MFPS device has significant potential for real-time monitoring of human activities in the field of flexible wearable electronics and human-machine interaction.

Modulus-tunable multifunctional hydrogel ink with nanofillers for 3D-Printed soft electronics

Seamless integration and conformal contact of soft electronics with tissue surfaces have emerged as major challenges in realizing accurate monitoring of biological signals. However, the mechanical mismatch between the electronics and biological tissues impedes the conformal interfacing between them. Attempts have been made to utilize soft hydrogels as the bioelectronic materials to realize tissue-comfortable bioelectronics. However, hydrogels have several limitations in terms of their electrical and mechanical properties. In this study, we present the development of a 3D-printable modulus-tunable hydrogel with multiple functionalities. The hydrogel has a cross-linked double network, which greatly improves its mechanical properties. Functional fillers such as XLG or functionalized carbon nanotubes (fCNT) can be incorporated into the hydrogel to provide tunable mechanics (Young's modulus of 10-300 kPa) and electrical conductivity (electrical conductivity of ∼20 S/m). The developed hydrogel exhibits stretchability (∼1000% strain), self-healing ability (within 5 min), toughness (400-731 kJ/m3) viscoelasticity, tissue conformability, and biocompatibility. Upon examining the rheological properties in the modulated region, hydrogels can be 3D printed to customize the shape and design of the bioelectronics. These hydrogels can be fabricated into ring-shaped strain sensors for wearable sensor applications.

Cyclodextrins-Based Polyrotaxanes: From Functional Polymers to Applications in Electronics and Energy Storage Materials

The concept of polyrotaxane comes from the rotaxane structure in the supramolecular field. It is a mechanically interlocked supramolecular assembly composed of linear polymer chains and cyclic molecules. Over recent decades, the synthesis and application of polyrotaxanes have seen remarkable growth. Particularly, cyclodextrin-based polyrotaxanes have been extensively reported due to the low-price raw materials, good biocompatibility, and ease of modification. Hence, it is also one of the most promising mechanically interlocking supramolecules for wide industrialization in the future. Polyrotaxanes are widely introduced into materials such as elastomers, hydrogels, and engineering polymers to improve their mechanical properties or impart functionality to the materials. In these materials, polyrotaxane acts as a slidable cross-linker to dissipate energy through sliding or assist in dispersing stress concentration in the cross-linked network, thereby enhancing the toughness of the materials. Further, the unique sliding-ring effect of cyclodextrin-based polyrotaxanes has pioneered advancements in stretchable electronics and energy storage materials. This includes their innovative use in stretchable conductive composite and binders for anodes, addressing critical challenges in these fields. In this mini-review, our focus is to highlight the current progress and potential wider applications in the future, underlining their transformative impact across various domains of material science.

Patterning Techniques Based on Metallized Electrospun Nanofibers for Advanced Stretchable Electronics

Stretchable electronics have experienced remarkable progress, especially in sensors and wireless communication systems, attributed to their ability to conformably contact with rough or uneven surfaces. However, the development of complex, multifunctional, and high-precision stretchable electronics faces substantial challenges, including instability at rigid-soft interfaces and incompatibility with traditional high-precision patterning technologies. Metallized electrospun nanofibers emerge as a promising conductive filler, offering exceptional stretchability, electrical conductivity, transparency, and compatibility with existing patterning technologies. Here, this review focuses on the fundamental properties, preparation processes, patterning technologies, and application scenarios of conductive stretchable composites based on metallized nanofibers. Initially, it introduces the fabrication processes of metallized electrospun nanofibers and their advantages over alternative materials. It then highlights recent progress in patterning technologies, including collector collection, vapor deposition with masks, and lithography, emphasizing their role in enhancing precision and integration. Furthermore, the review shows the broad applicability and potential influence of metallized electrospun nanofibers in various fields through their use in sensors, wireless systems, semiconductor devices, and intelligent healthcare solutions. Ultimately, this review seeks to spark further innovation and address the prevailing challenges in stretchable electronics, paving the way for future breakthroughs in this dynamic field.

Mobile Diagnostic Clinics

This article reviews the revolutionary impact of emerging technologies and artificial intelligence (AI) in reshaping modern healthcare systems, with a particular focus on the implementation of mobile diagnostic clinics. It presents an insightful analysis of the current healthcare challenges, including the shortage of healthcare workers, financial constraints, and the limitations of traditional clinics in continual patient monitoring. The concept of "Mobile Diagnostic Clinics" is introduced as a transformative approach where healthcare delivery is made accessible through the incorporation of advanced technologies. This approach is a response to the impending shortfall of medical professionals and the financial and operational burdens conventional clinics face. The proposed mobile diagnostic clinics utilize digital health tools and AI to provide a wide range of services, from everyday screenings to diagnosis and continual monitoring, facilitating remote and personalized care. The article delves into the potential of nanotechnology in diagnostics, AI's role in enhancing predictive analytics, diagnostic accuracy, and the customization of care. Furthermore, the article discusses the importance of continual, noninvasive monitoring technologies for early disease detection and the role of clinical decision support systems (CDSSs) in personalizing treatment guidance. It also addresses the challenges and ethical concerns of implementing these advanced technologies, including data privacy, integration with existing healthcare infrastructure, and the need for transparent and bias-free AI systems.

MnO2 Nanoparticles Decorated PEDOT:PSS for High Performance Stretchable and Transparent Supercapacitors

With the swift advancement of wearable electronics and artificial intelligence, the integration of electronic devices with the human body has advanced significantly, leading to enhanced real-time health monitoring and remote disease diagnosis. Despite progress in developing stretchable materials with skin-like mechanical properties, there remains a need for materials that also exhibit high optical transparency. Supercapacitors, as promising energy storage devices, offer advantages such as portability, long cycle life, and rapid charge/discharge rates, but achieving high capacity, stretchability, and transparency simultaneously remains challenging. This study combines the stretchable, transparent polymer PEDOT:PSS with MnO2 nanoparticles to develop high-performance, stretchable, and transparent supercapacitors. PEDOT:PSS films were deposited on a PDMS substrate using a spin-coating method, followed by electrochemical deposition of MnO2 nanoparticles. This method ensured that the nanosized MnO2 particles were uniformly distributed, maintaining the transparency and stretchability of PEDOT:PSS. The resulting PEDOT:PSS/MnO2 nanoparticle electrodes were gathered into a symmetric device using a LiCl/PVA gel electrolyte, achieving an areal capacitance of 1.14 mF cm-2 at 71.2% transparency and maintaining 89.92% capacitance after 5000 cycles of 20% strain. This work presents a scalable and economical technique to manufacturing supercapacitors that combine high capacity, transparency, and mechanical stretchability, suggesting potential applications in wearable electronics.

Robust and Lubricating Interface Semi-Interpenetrating Network on Inert Polymer Substrates Enabled by Subsurface-Initiated Polymerization

Lubricating hydrogel coatings on inert rubber and plastic surfaces significantly reduce friction and wear, thus enhancing material durability and lifespan. However, achieving optimal hydration lubrication typically requires a porous polymer network, which unfortunately reduces their mechanical strength and limits their applicability where robust durability and wear-resistance are essential. In the research, a hydrogel coating with remarkable wear resistance and surface stability is developed by forming a semi-interpenetrating polymer network with polymer substrate at the interface. By employing a good solvent swelling method, monomers, and photoinitiators are embedded within the substrates' subsurface, followed by in situ polymerization under ultraviolet light, creating a robust semi-interpenetrating and entangled network structure. This approach, offering a thicker energy-dissipating layer, outperforms traditional surface modifications in wear resistance while preserving anti-fatigue, hydrophilicity, oleophobicity, and other properties. Adaptable to various rubber and plastic substrates by using suitable solvents, this method provides an efficient solution for creating durable, lubricating surfaces, broadening the potential applications in multiple industries.

Biocompatible Electronic Skins for Cardiovascular Health Monitoring

Cardiovascular diseases represent a significant threat to the overall well-being of the global population. Continuous monitoring of vital signs related to cardiovascular health is essential for improving daily health management. Currently, there has been remarkable proliferation of technology focused on collecting data related to cardiovascular diseases through daily electronic skin monitoring. However, concerns have arisen regarding potential skin irritation and inflammation due to the necessity for prolonged wear of wearable devices. To ensure comfortable and uninterrupted cardiovascular health monitoring, the concept of biocompatible electronic skin has gained substantial attention. In this review, biocompatible electronic skins for cardiovascular health monitoring are comprehensively summarized and discussed. The recent achievements of biocompatible electronic skin in cardiovascular health monitoring are introduced. Their working principles, fabrication processes, and performances in sensing technologies, materials, and integration systems are highlighted, and comparisons are made with other electronic skins used for cardiovascular monitoring. In addition, the significance of integrating sensing systems and the updating wireless communication for the development of the smart medical field is explored. Finally, the opportunities and challenges for wearable electronic skin are also examined.

Tunable photo/thermochromic properties of Cd(II)-viologen coordination polymers modulated by coordination modes for flexible imaging films and anti-counterfeiting

Two photochromic Cd(II)-CPs were obtained based on the viologen ligand using different synthetic routes, named {[Cd4(p-BDC)4(CPB)2(H2O)2]·2H2O·EtOH}n (1) and {[Cd(p-BDC)(CPB)(H2O)]·(L)·DMF}n (2) (p-H2BDC = 1,4-benzene-dicarboxylate, HCPB·Cl = 1-(4-carboxyphenyl)-4,4'-bipyridinium·Cl, L = 2,4-dinitrochlorobenzene, and DMF = N,N-dimethylformamide), respectively. Due to different coordination modes, the two Cd(II)-CPs show different structures. Compound 1 exhibits a three-dimensional (3D) framework with bimetallic nodes, while compound 2 displays a 2-fold interpenetrated (4,4) net topology. Notably, the two Cd(II)-CPs exhibit substantial disparities in photo/thermochromism, which can be attributed to variations in donor-acceptor (D-A) distances arising from structural differences. Compound 1 showed visually sensitive photo- and thermochromic behavior due to multi-pathway electron transfer and short D-A distances, which is relatively rare in electron-transfer type photochromic systems. In contrast, 2 only demonstrates insensitive photochromic behavior, with a slight deepening of the color observed after 2 hours of UV light, which is due to the mono-pathway electron transfer and long D-A distance. Moreover, we first combined Cd(II)-viologen CPs with polydimethylsiloxane (PDMS) to prepare a 1@PDMS flexible UV imaging film. 1@PDMS exhibits excellent bendability and stretchability and maintains good photochromic properties after 100 bending cycles. To demonstrate the rapid color response and distinct color contrast of 1, its application in anti-counterfeiting is also demonstrated.

Design and Optimization of NR-Based Stretchable Conductive Composites Filled with MoSi2 Nanoparticles and MWCNTs: Perspectives from Experimental Characterization and Molecular Dynamics Simulations

Stretchable conductive composites play a pivotal role in the development of personalized electronic devices, electronic skins, and artificial implant devices. This article explores the fabrication and characterization of stretchable composites based on natural rubber (NR) filled with molybdenum disilicide (MoSi2) nanoparticles and multi-walled carbon nanotubes (MWCNTs). Experimental characterization and molecular dynamics (MD) simulations are employed to investigate the static and dynamic properties of the composites, including morphology, glass transition temperature (Tg), electrical conductivity, and mechanical behavior. Results show that the addition of MoSi2 nanoparticles enhances the dispersion of MWCNTs within the NR matrix, optimizing the formation of a conductive network. Dynamic mechanical analysis (DMA) confirms the Tg reduction with the addition of MWCNTs and the influence of MoSi2 content on Tg. Mechanical testing reveals that the tensile strength increases with MoSi2 content, with an optimal ratio of 4:1 MoSi2:MWCNTs. Electrical conductivity measurements demonstrate that the MoSi2/MWCNTs/NR composites exhibit enhanced conductivity, reaching optimal values at specific filler ratios. MD simulations further support experimental findings, highlighting the role of MoSi2 in improving dispersion and mechanical properties. Overall, the study elucidates the synergistic effects of nanoparticles and nanotubes in enhancing the properties of stretchable conductive composites.

Preparation of Polyaniline-Modified Cellulose/PDMS Composite Triboelectric Material and Application of Its Pretreatment in MOW Pulp

Self-powered electronic equipment has rapidly developed in the fields of sensing, motion monitoring, and energy collection, posing a greater challenge to triboelectric materials. Triboelectric materials need to enhance their electrical conductivity and mechanical strength to address the increasing demand for stability and to mitigate unpredictable physical damage. In this study, polyaniline-modified cellulose was prepared by means of in situ polymerization and compounded with polydimethylsiloxane, resulting in a triboelectric material with enhanced strength and conductivity. The material was fabricated into a tubular triboelectric nanogenerator (TENG) (G-TENG), and an electrocatalytic pretreatment of mixed office waste paper (MOW) pulp was performed using papermaking white water as the flowing liquid to improve the deinking performance. The electrical output performance of G-TENG is highest at a flow rate of 400 mL/min, producing a voltage of 22.76 V and a current of 1.024 μA. Moreover, the deinking effect of MOW was enhanced after the electrical pretreatment. This study explores the potential application of G-TENG as a self-powered sensor power supply and emphasizes its prospect as an energy collection device.

Wireless sequential dual light delivery for programmed PDT in vivo

Using photodynamic therapy (PDT) to treat deep-seated cancers is limited due to inefficient delivery of photosensitizers and low tissue penetration of light. Polymeric nanocarriers are widely used for photosensitizer delivery, while the self-quenching of the encapsulated photosensitizers would impair the PDT efficacy. Furthermore, the generated short-lived reactive oxygen spieces (ROS) can hardly diffuse out of nanocarriers, resulting in low PDT efficacy. Therefore, a smart nanocarrier system which can be degraded by light, followed by photosensitizer activation can potentially overcome these limitations and enhance the PDT efficacy. A light-sensitive polymer nanocarrier encapsulating photosensitizer (RB-M) was synthesized. An implantable wireless dual wavelength microLED device which delivers the two light wavelengths sequentially was developed to programmatically control the release and activation of the loaded photosensitizer. Two transmitter coils with matching resonant frequencies allow activation of the connected LEDs to emit different wavelengths independently. Optimal irradiation time, dose, and RB-M concentration were determined using an agent-based digital simulation method. In vitro and in vivo validation experiments in an orthotopic rat liver hepatocellular carcinoma disease model confirmed that the nanocarrier rupture and sequential low dose light irradiation strategy resulted in successful PDT at reduced photosensitizer and irradiation dose, which is a clinically significant event that enhances treatment safety.

Tunable Radiative Cooling by Mechanochromic Electrospun Micro-Nanofiber Matrix

Radiative thermoregulation has been regarded as an energy-efficient method for thermal management. In this study, the development of a mechanoresponsive polydimethylsiloxane (PDMS) micro-nanofiber matrix capable of both sub-ambient radiative cooling and solar heating is presented, achieved through a core-shell electrospinning technique. The electrospun PDMS micro-nanofibers, with diameters comparable to the solar wavelengths, exhibit excellent solar reflectivity (≈93%) while preserving its pristine high infrared (IR) emissivity. As a result, the electrospun PDMS radiative cooler (EPRC) successfully demonstrated sub-ambient radiative cooling performance (≈3.8°C) during the daytime. Furthermore, the exceptional resilient property of PDMS facilitated the reversible alteration of the structural morphology created by the fiber-based matrix under mechanical force, resulting in the modulation of solar reflectivity (≈80%). The precise modulation of solar reflectivity enabled reversibly switchable multi-step radiative thermoregulation, offering enhanced flexibility in addressing varying thermal environments even in maintaining the desired temperature. The findings of this work offer a promising approach toward dynamic radiative thermoregulation, which holds significant potential for addressing global climate change concerns and energy shortage.

Recent progress in multifunctional, reconfigurable, integrated liquid metal-based stretchable sensors and standalone systems

Possessing a unique combination of properties that are traditionally contradictory in other natural or synthetical materials, Ga-based liquid metals (LMs) exhibit low mechanical stiffness and flowability like a liquid, with good electrical and thermal conductivity like metal, as well as good biocompatibility and room-temperature phase transformation. These remarkable properties have paved the way for the development of novel reconfigurable or stretchable electronics and devices. Despite these outstanding properties, the easy oxidation, high surface tension, and low rheological viscosity of LMs have presented formidable challenges in high-resolution patterning. To address this challenge, various surface modifications or additives have been employed to tailor the oxidation state, viscosity, and patterning capability of LMs. One effective approach for LM patterning is breaking down LMs into microparticles known as liquid metal particles (LMPs). This facilitates LM patterning using conventional techniques such as stencil, screening, or inkjet printing. Judiciously formulated photo-curable LMP inks or the introduction of an adhesive seed layer combined with a modified lift-off process further provide the micrometer-level LM patterns. Incorporating porous and adhesive substrates in LM-based electronics allows direct interfacing with the skin for robust and long-term monitoring of physiological signals. Combined with self-healing polymers in the form of substrates or composites, LM-based electronics can provide mechanical-robust devices to heal after damage for working in harsh environments. This review provides the latest advances in LM-based composites, fabrication methods, and their novel and unique applications in stretchable or reconfigurable sensors and resulting integrated systems. It is believed that the advancements in LM-based material preparation and high-resolution techniques have opened up opportunities for customized designs of LM-based stretchable sensors, as well as multifunctional, reconfigurable, highly integrated, and even standalone systems.

Mechanically and Thermally Guided, Honeycomb-like Nanocomposites with Strain-Insensitive High Thermal Conductivity for Stretchable Electronics

Thermal management materials have become increasingly crucial for stretchable electronic devices and systems. Drastically different from conventional thermally conductive materials, which are applied at static conditions, thermal management materials for stretchable electronics additionally require strain-insensitive thermal conductivity, as they generally undergo cyclic deformation. However, realizing such a property remains challenging mainly because conventional thermally conductive polymer composites generally lack a mechanically guided design. Here, we report a honeycomb-like nanocomposite with a three-dimensional (3D) thermally conductive network fabricated by an arrayed ice-templating technique followed by elastomer infiltration. The hexagonal honeycomb-like structure with thin, compact walls (≈ 40 μm) endows our composite with a high through-plane thermal conductivity (≈ 1.54 W m-1 K-1) at an ultralow boron nitride nanosheet (BNNS) loading (≈ 0.85 vol %), with an enhancement factor of thermal conductivity up to 820% and thermal-insensitive strain up to 200%, which are 2.7 and 2 times higher than those reported in the literature. We report an intelligent strategy for the development of advanced thermal management materials for high-performance stretchable electronics.

Ultrafast universal fabrication of configurable porous silicone-based elastomers by Joule heating chemistry

Silicone-based elastomers (SEs) have been extensively applied in numerous cutting-edge areas, including flexible electronics, biomedicine, 5G smart devices, mechanics, optics, soft robotics, etc. However, traditional strategies for the synthesis of polymer elastomers, such as bulk polymerization, suspension polymerization, solution polymerization, and emulsion polymerization, are inevitably restricted by long-time usage, organic solvent additives, high energy consumption, and environmental pollution. Here, we propose a Joule heating chemistry method for ultrafast universal fabrication of SEs with configurable porous structures and tunable components (e.g., graphene, Ag, graphene oxide, TiO2, ZnO, Fe3O4, V2O5, MoS2, BN, g-C3N4, BaCO3, CuI, BaTiO3, polyvinylidene fluoride, cellulose, styrene-butadiene rubber, montmorillonite, and EuDySrAlSiOx) within seconds by only employing H2O as the solvent. The intrinsic dynamics of the in situ polymerization and porosity creation of these SEs have been widely investigated. Notably, a flexible capacitive sensor made from as-fabricated silicone-based elastomers exhibits a wide pressure range, fast responses, long-term durability, extreme operating temperatures, and outstanding applicability in various media, and a wireless human-machine interaction system used for rescue activities in extreme conditions is established, which paves the way for more polymer-based material synthesis and wider applications.

Deformation-Induced Photoprogrammable Pattern of Polyurethane Elastomers Based on Poisson Effect

Elastomers with high aspect ratio surface patterns are a promising class of materials for designing soft machines in the future. Here, a facile method for fabricating surface patterns on polyurethane elastomer by subtly utilizing the Poisson effect and gradient photocrosslinking is demonstrated. By applying uniaxial tensile strains, the aspect ratio of the surface patterns can be optionally manipulated. At prestretched state, the pattern on the polyurethane elastomer can be readily constructed through compressive stress, resulting from the gradient photocrosslinking via selective photodimerization of an anthracene-functionalized polyurethane elastomer (referred to as ANPU). The macromolecular aggregation structures during stretching deformation significantly contribute to the fabrication of high aspect ratio surface patterns. The insightful finite element analysis well demonstrates that the magnitude and distribution of internal stress in the ANPU elastomer can be regulated by selectively gradient crosslinking, leading to polymer chains migrate from the exposed region to the unexposed region, thereby generating a diverse array of surface patterns. Additionally, the periodic surface patterns exhibit tunable structural color according to the different stretching states and are fully reversible over multiple cycles, opening up avenues for diverse applications such as smart displays, stretchable strain sensors, and anticounterfeiting devices.

Soft Sensors and Actuators for Wearable Human-Machine Interfaces

Haptic human-machine interfaces (HHMIs) combine tactile sensation and haptic feedback to allow humans to interact closely with machines and robots, providing immersive experiences and convenient lifestyles. Significant progress has been made in developing wearable sensors that accurately detect physical and electrophysiological stimuli with improved softness, functionality, reliability, and selectivity. In addition, soft actuating systems have been developed to provide high-quality haptic feedback by precisely controlling force, displacement, frequency, and spatial resolution. In this Review, we discuss the latest technological advances of soft sensors and actuators for the demonstration of wearable HHMIs. We particularly focus on highlighting material and structural approaches that enable desired sensing and feedback properties necessary for effective wearable HHMIs. Furthermore, promising practical applications of current HHMI technology in various areas such as the metaverse, robotics, and user-interactive devices are discussed in detail. Finally, this Review further concludes by discussing the outlook for next-generation HHMI technology.

In Situ Polymer-Solution-Processed Graphene-PDMS Nanocomposites for Application in Intracranial Pressure Sensors

Polydimethylsiloxane (PDMS) has emerged as a promising candidate for the dielectric layer in implantable sensors due to its exceptional biocompatibility, stability, and flexibility. This study introduces an innovative approach to produce graphene-reinforced PDMS (Gr-PDMS), where graphite powders are exfoliated into mono- and few-layer graphene sheets within the polymer solution, concurrently forming cross-linkages with PDMS. This method yields a uniformly distributed graphene within the polymer matrix with improved interfaces between graphene and PDMS, significantly reducing the percolation threshold of graphene dispersed in PDMS from 10% to 5%. As-synthesized Gr-PDMS exhibits improved mechanical and electrical properties, tested for potential use in capacitive pressure sensors. The results demonstrate an impressive pressure sensitivity up to 0.0273 kpa-1, 45 times higher than that of pristine PDMS and 2.5 times higher than the reported literature value. The Gr-PDMS showcases excellent pressure sensing ability and stability, fulfilling the requirements for implantable intracranial pressure (ICP) sensors.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

Topologically Engineered Strain Redistribution in Elastomeric Substrates for Dually Tunable Anisotropic Plasmomechanical Responses

The prompt visual response is considered to be a highly intuitive tenet among sensors. Therefore, plasmomechanical strain sensors, which exhibit dynamic structural color changes, have recently been developed by using mechanical stimulus-based elastomeric substrates for wearable sensors. However, the reported plasmomechanical strain sensors either lack directional sensitivity or require complex signal processing and device design strategies to ensure anisotropic optical responses. To the best of our knowledge, there have been no reports on utilizing anisotropic mechanical substrates to obtain directional optical responses. Herein, we propose an anisotropic plasmomechanical sensor to distinguish between the applied force direction and the force magnitude. We employ a simple strain-engineered topological elastomer to mechanically transform closely packed metallic nanoparticles (NPs) into anisotropic directional rearrangements depending on the applied force direction. The proposed structure consists of a heterogeneous-modulus elastomer that exhibits a highly direction-dependent Poisson effect owing to the periodically line-patterned local strain redistribution occurring due to the same magnitude of applied external force. Consequently, the reorientation of the self-assembled gold (Au)-NP array manifests dual anisotropy, i.e., force- and polarization-direction-dependent plasmonic coupling. The cost-effectiveness and simple design of our proposed heterogeneous-modulus platform pave the way for numerous optical applications based on dynamic transformation and topological inhomogeneities.

Anti-friction gold-based stretchable electronics enabled by interfacial diffusion-induced cohesion

Stretchable electronics that prevalently adopt chemically inert metals as sensing layers and interconnect wires have enabled high-fidelity signal acquisition for on-skin applications. However, the weak interfacial interaction between inert metals and elastomers limit the tolerance of the device to external friction interferences. Here, we report an interfacial diffusion-induced cohesion strategy that utilizes hydrophilic polyurethane to wet gold (Au) grains and render them wrapped by strong hydrogen bonding, resulting in a high interfacial binding strength of 1017.6 N/m. By further constructing a nanoscale rough configuration of the polyurethane (RPU), the binding strength of Au-RPU device increases to 1243.4 N/m, which is 100 and 4 times higher than that of conventional polydimethylsiloxane and styrene-ethylene-butylene-styrene-based devices, respectively. The stretchable Au-RPU device can remain good electrical conductivity after 1022 frictions at 130 kPa pressure, and reliably record high-fidelity electrophysiological signals. Furthermore, an anti-friction pressure sensor array is constructed based on Au-RPU interconnect wires, demonstrating a superior mechanical durability for concentrated large pressure acquisition. This chemical modification-free approach of interfacial strengthening for chemically inert metal-based stretchable electronics is promising for three-dimensional integration and on-chip interconnection.

Simultaneous Visualization of Microscopic Conductivity and Deformation in Conductive Elastomers

Conductive elastomers are promising for a wide range of applications in many fields due to their unique mechanical and electrical properties, and an understanding of the conductive mechanisms of such materials under deformation is crucial. However, revealing the microscopic conduction mechanism of conductive elastomers is a challenge. In this study, we developed a method that combines in situ deformation nanomechanical atomic force microscopy (AFM) and conductive AFM to successfully and simultaneously characterize the microscopic deformation and microscopic electrical conductivity of nanofiller composite conductive elastomers. With this approach, we visualized the conductive network structure of carbon black and carbon nanotube composite conductive elastomers at the nanoscale, tracked their microscopic response under different compressive strains, and revealed the correlation between microscopic and macroscopic electrical properties. This technique is important for understanding the conductive mechanism of conductive elastomers and improving the design of conductive elastomers.

Flexible, Transparent and Conductive Metal Mesh Films with Ultra-High FoM for Stretchable Heating and Electromagnetic Interference Shielding

Despite the growing demand for transparent conductive films in smart and wearable electronics for electromagnetic interference (EMI) shielding, achieving a flexible EMI shielding film, while maintaining a high transmittance remains a significant challenge. Herein, a flexible, transparent, and conductive copper (Cu) metal mesh film for EMI shielding is fabricated by self-forming crackle template method and electroplating technique. The Cu mesh film shows an ultra-low sheet resistance (0.18 Ω □-1), high transmittance (85.8%@550 nm), and ultra-high figure of merit (> 13,000). It also has satisfactory stretchability and mechanical stability, with a resistance increases of only 1.3% after 1,000 bending cycles. As a stretchable heater (ε > 30%), the saturation temperature of the film can reach over 110 °C within 60 s at 1.00 V applied voltage. Moreover, the metal mesh film exhibits outstanding average EMI shielding effectiveness of 40.4 dB in the X-band at the thickness of 2.5 μm. As a demonstration, it is used as a transparent window for shielding the wireless communication electromagnetic waves. Therefore, the flexible and transparent conductive Cu mesh film proposed in this work provides a promising candidate for the next-generation EMI shielding applications.

Integrating Benzoxazine-PDMS 3D Networks with Carbon Nanotubes for flexible Pressure Sensors

Shapeable and flexible pressure sensors with superior mechanical and electrical properties are of major interest as they can be employed in a wide range of applications. In this regard, elastomer-based composites incorporating carbon nanomaterials in the insulating matrix embody an appealing solution for designing flexible pressure sensors with specific properties. In this study, PDMS chains of different molecular weight were successfully functionalized with benzoxazine moieties in order to thermally cure them without adding a second component, nor a catalyst or an initiator. These precursors were then blended with 1 weight percent of multi-walled carbon nanotubes (CNTs) using an ultrasound probe, which induced a transition from a liquid-like to a gel-like behavior as CNTs generate an interconnected network within the matrix. After curing, the resulting nanocomposites exhibit mechanical and electrical properties making them highly promising materials for pressure-sensing applications.

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Materials, Designs, and Implementations of Wearable Antennas and Circuits for Biomedical Applications: A Review

The intersection of biomedicine and radio frequency (RF) engineering has fundamentally transformed self-health monitoring by leveraging soft and wearable electronic devices. This paradigm shift presents a critical challenge, requiring these devices and systems to possess exceptional flexibility, biocompatibility, and functionality. To meet these requirements, traditional electronic systems, such as sensors and antennas made from rigid and bulky materials, must be adapted through material science and schematic design. Notably, in recent years, extensive research efforts have focused on this field, and this review article will concentrate on recent advancements. We will explore the traditional/emerging materials for highly flexible and electrically efficient wearable electronics, followed by systematic designs for improved functionality and performance. Additionally, we will briefly overview several remarkable applications of wearable electronics in biomedical sensing. Finally, we provide an outlook on potential future directions in this developing area.

Liquid metal-hydrogel composites for flexible electronics

As an emerging functional material, liquid metal-hydrogel composites exhibit excellent biosafety, high electrical conductivity, tunable mechanical properties and good adhesion, thus providing a unique platform for a wide range of flexible electronics applications such as wearable devices, medical devices, actuators, and energy conversion devices. Through different composite methods, liquid metals can be integrated into hydrogel matrices to form multifunctional composite material systems, which further expands the application range of hydrogels. In this paper, we provide a brief overview of the two materials: hydrogels and liquid metals, and discuss the synthesis method of liquid metal-hydrogel composites, focusing on the improvement of the performance of hydrogel materials by liquid metals. In addition, we summarize the research progress of liquid metal-hydrogel composites in the field of flexible electronics, pointing out the current challenges and future prospects of this material.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Interactive deformable electroluminescent devices enabled by an adaptable hydrogel system with optical/photothermal/mechanical tunability

Deformable electroluminescent devices (DELDs) with mechanical adaptability are promising for new applications in smart soft electronics. However, current DELDs still present some limitations, including having stimuli-insensitive electroluminescence (EL), untunable mechanical properties, and a lack of versatile stimuli response properties. Herein, a facile approach for fabricating in situ interactive and multi-stimuli responsive DELDs with optical/photothermal/mechanical tunability was proposed. A polyvinyl alcohol (PVA)/polydopamine (PDA)/graphene oxide (GO) adaptable hydrogel exhibiting optical/photothermal/mechanical tunability was used as the top ionic conductor (TIC). The TIC can transform from a viscoelastic state to an elastic state via a special freezing-salting out-rehydration (FSR) process. Meanwhile, it endows the DELDs with a photothermal response and thickness-dependent light shielding properties, allowing them to dynamically demonstrate "on" or "off" or "gradually change" EL response to various mechanical/photothermal stimuli. Thereafter, the DELDs with a viscoelastic TIC can be utilized as pressure-responsive EL devices and laser-engravable EL devices. The DELDs with an elastic TIC can withstand both linear and out-of-plane deformation, enabling the designs of various interactive EL devices/sensors to monitor linear sliders, human finger bending, and pneumatically controllable bulging. This work offers new opportunities for developing next-generation EL-responsive devices with widespread application based on adaptable hydrogel systems.