Highly conductive and elastic nanomembrane for skin electronics

Miniaturized Soft and Stretchable Multilayer Circuits through Laser-Defined High Aspect-Ratio Printing

Stretchable electronics enable seamless integration of wearables with the human body, thereby creating new opportunities in biomedical applications. Miniaturized multilayer stretchable printed circuit boards are key for achieving high functional density circuits with minimal footprint. However, current microfabrication technologies struggle with simultaneously achieving tissue-like softness (<<1 MPa), high resolution and low sheet resistance. This study demonstrates a scalable printing method that enables ultra-soft (<0.4 MPa) stretchable conductors (>300% strain) with high-resolution (<2.5 µm width) and high aspect-ratio tracks (>1) connected by ultra-fine (20 µm) vertical-interconnect-access (VIA) for multi-layered configurations. The method is based on stencil printing into laser-defined bio-masks comprising the abundant biopolymer lignin, thereby achieving printing capabilities beyond conventional methods in a sustainable manner. Based on the unique capabilities, a miniaturized multilayer ultra-soft wireless near-field-communication temperature logger is developed. Laser-defined printing can pave the way for the next generation of ultra-soft miniaturized wearables.

Recent Progress on Liquid Superspreading and Its Applications

The dynamic spreading of liquids on solid surfaces is essential across numerous daily and industrial processes. Surfaces that enable liquid superspreading, characterized by rapid or extensive spreading, are particularly valuable due to their implications in functional film fabrication, heat management, liquid/liquid separation, and more. Recently, significant research is conducted on liquid superspreading surfaces, with microstructure-regulated surfaces gaining increasing attention. However, the deeper correlations between microstructural physical factors and the superspreading behaviors, along with the relevant applications, remain inadequately understood. This review aims to consolidate the existing knowledge from published results and stimulate further investigation by detailing structures, functionalities, and principles for constructing liquid superspreading surfaces. Examining is began by the energy balance between input and dissipation that underpins droplet spreading dynamics. Then current designs are reviewed for superspreading surfaces, with a focus on chemical and physical aspects, giving greater emphasis to the physical perspective. Additionally, several typical applications are categorized based on liquid superspreading behaviors across various fields. Finally, the prevailing challenges are highlighted and provide insights into future research directions.

Fluid drawing printing 3D conductive structures for flexible circuit manufacturing

Three-dimensional (3D) conductive structures significantly reduce flexible circuit complexity and enhance circuit integration. Direct extrusion printing technology offers the advantages of various material applicability and high flexibility for fabricating filamentary interconnects. The printing resolution is, however, highly dependent on the needle size. A micro-printing method was proposed based on fluid drawing to fabricate freestanding 3D conductive structures. The delicate structure is drawn out under the tension when printing. The printing material is a high-viscosity ink composed of silver nanoparticles (AgNPs) and polyvinylpyrrolidone (PVP). The viscosity is controlled by evaporating the ink's solvent for drawing prints. This unique printing method utilizes a single needle, controlled by precise air pressure and speed, to construct 3D filamentary structures with varied wire widths. The 3D conductive structures exhibit superior structural retention and enhanced conductivity by thermal treatment. The drawing printing method has been successfully implemented on flexible circuits, including light-emitting diode (LED) arrays, thermal imaging displays, and multivibrator circuits. This work establishes a novel paradigm for flexible electronics manufacturing through fluid-drawing printing, achieving unprecedented customization and compatibility in fabricating 3D interconnects.

A Durable Metalgel Maintaining 3×106 S∙M‒1 Conductivity under 1 000 000 Stretching Cycles

Conductive elastomers are in high demand for emerging fields such as wearable electronics and soft robotics. However, it remains unavailable to realize the desired metal-level conductivity after extensive stretching cycles, which is a necessity for the above promising application. Here, a new material is presented that employs an elastic, homogeneous, and dense waterborne polyurethane network to immobilize the liquid metal continuum via electrostatic interactions. This new design enables the liquid metal continuum to deform synchronously and reversibly with the polymer network, preserving its conductive structure and significantly enhancing durability. The resulting durable metalgel exhibits conductivity of 3 × 106 S∙m-1, which remains stable after 1 000 000 stretching cycles. This work overcomes the performance limitations of current conductive elastomers and unlocks new opportunities for cutting-edge applications in wearable technology and robotics.

Stretchable composites with high oxide loading

Oxide/elastomer composites combine the functional attributes of metal oxides with the mechanical deformability of elastomers, but face the challenge of balancing oxide loading and stretchability as ceramic fillers decrease the entropic elasticity of polymer networks. Here, we report an interfacial composite design that enables high oxide fraction and large stretchability by minimizing the contact area yet maximizing the binding strength between the oxide and elastomer. The elongation at break for an interfacial composite with 80 vol% of oxides reaches 500%, whereas that of a regular bulk composite with the same oxide fraction is 20%. These composites are synthesized based on a Marangoni co-assembly process with tuned interfacial tension and reaction at the water-oil interface. The assembly chemistry is nearly independent of oxides' sizes, compositions, geometries, and functions, making this interfacial structure broadly applicable to optical, electric, magnetic, and thermal-conducting oxides. Compared to bulk composites, the interfacial composites deliver larger magnetic actuation, lower thermal resistance, and higher conformability with nonplanar surfaces, providing rich implications for designing intelligent and electronic systems.

Photo-crosslinkable organic materials for flexible and stretchable electronics

As technology advances to enhance human perceptual experiences of the surrounding environment, significant research on stretchable electronics is actively progressing, spanning from the synthesis of materials to their applications in fully integrated devices. A critical challenge lies in developing materials that can maintain their electrical properties under substantial stretching. Photo-crosslinkable organic materials have emerged as a promising solution due to their ability to be precisely modified with light to achieve desired properties, such as enhanced durability, stable conductivity, and micropatterning. This review examines recent research on photo-crosslinkable organic materials, focusing on their components and integration within stretchable electronic devices. We explore the essential characteristics required for each device component (insulators, semiconductors, and conductors) and explain how photo-crosslinking technology addresses these needs through its principles and implementation. Additionally, we discuss the integration and utilization of these components in real-world applications, including physical sensors, organic field-effect transistors (OFETs), and organic solar cells (OSCs). Finally, we offer a concise perspective on the future directions and potential challenges in ongoing research on photo-crosslinkable organic materials.

Motion-unrestricted dynamic electrocardiogram system utilizing imperceptible electronics

Electrocardiogram (ECG) plays a vital role in the prevention, diagnosis, and prognosis of cardiovascular diseases (CVDs). However, the lack of a user-friendly and accurate long-term dynamic electrocardiogram (DCG) device in motion has made it challenging to perform many daily cardiovascular risk screenings and assessments, such as sudden cardiac arrest, resulting in additional economic burdens on society. Here, we present a motion-unrestricted dynamic electrocardiogram (MU-DCG) system, which employs skin-conformal, imperceptible electronics for long-term, comfortable, and accurate 12-lead DCG monitoring. To facilitate assembly for use on the skin, the MU-DCG system features a pressure-activated flexible skin socket for stably soft-connecting the on-skin soft module and the off-skin stiff module during dynamic movements. Crucially, blinded cardiologist evaluations confirm minimal motion artifacts in MU-DCG-acquired ECG signals. Our results demonstrate that the MU-DCG system, with large-area, ultra-thin on-skin electrodes/leads, and an off-skin module, accomplishes anti-motion interference acquisition and in-situ analysis while retaining wearing imperceptibility.

Interfacing with the Brain: How Nanotechnology Can Contribute

Interfacing artificial devices with the human brain is the central goal of neurotechnology. Yet, our imaginations are often limited by currently available paradigms and technologies. Suggestions for brain-machine interfaces have changed over time, along with the available technology. Mechanical levers and cable winches were used to move parts of the brain during the mechanical age. Sophisticated electronic wiring and remote control have arisen during the electronic age, ultimately leading to plug-and-play computer interfaces. Nonetheless, our brains are so complex that these visions, until recently, largely remained unreachable dreams. The general problem, thus far, is that most of our technology is mechanically and/or electrically engineered, whereas the brain is a living, dynamic entity. As a result, these worlds are difficult to interface with one another. Nanotechnology, which encompasses engineered solid-state objects and integrated circuits, excels at small length scales of single to a few hundred nanometers and, thus, matches the sizes of biomolecules, biomolecular assemblies, and parts of cells. Consequently, we envision nanomaterials and nanotools as opportunities to interface with the brain in alternative ways. Here, we review the existing literature on the use of nanotechnology in brain-machine interfaces and look forward in discussing perspectives and limitations based on the authors' expertise across a range of complementary disciplines─from neuroscience, engineering, physics, and chemistry to biology and medicine, computer science and mathematics, and social science and jurisprudence. We focus on nanotechnology but also include information from related fields when useful and complementary.

Recent Advances in Superspreading-Based Confined Synthesis and Assembly of Functional Nanomaterials

The rapid and complete spreading of liquids on surfaces, which is defined as superspreading, is of great importance in academic research and practical applications. The strong shear flow force during the superspreading process and the obtained confined stable and homogeneous thin liquid layers have great potential in the assembly of functional nanomaterials and confined synthesis. This review aims to summarize the fundamental understanding and emerging applications of superspreading-based confined synthesis and assembly of functional nanomaterials. First, several typical superspreading processes are briefly introduced, followed by highlighting the unique properties and design principles. Then, details about the confined superspreading liquid layers for highly efficient synthesis of functional thin films and the superspreading-induced shear flow to assembly nanomaterials into high-quality nanocomposite materials are presented. The following section then describes the emerging applications of the fabricated functional thin films and nanocomposites. Finally, an outlook for future development is also proposed.

Eco-Friendly Conductive Hydrogels: Towards Green Wearable Electronics

The rapid advancement of wearable electronics has catalyzed the development of flexible, lightweight, and highly conductive materials. Among these, conductive hydrogels have emerged as promising candidates due to their tissue-like properties, which can minimize the mechanical mismatch between flexible devices and biological tissues and excellent electrical conductivity, stretchability and biocompatibility. However, the environmental impact of synthetic components and production processes in conventional conductive hydrogels poses significant challenges to their sustainable application. This review explores recent advances in eco-friendly conductive hydrogels used in healthcare, focusing on their design, fabrication, and applications in green wearable electronics. Emphasis is placed on the use of natural polymers, bio-based crosslinkers, and green synthesis methods to improve sustainability while maintaining high performance. We discuss the incorporation of conductive polymers and carbon-based nanomaterials into environmentally benign matrices. Additionally, the article highlights strategies for improving the biodegradability, recyclability, and energy efficiency of these materials. By addressing current limitations and future opportunities, this review aims to provide a comprehensive understanding of environmentally friendly conductive hydrogels as a basis for the next generation of sustainable wearable technologies.

An ICU-grade breathable cardiac electronic skin for health, diagnostics, and intraoperative and postoperative monitoring

Cardiovascular digital health technologies potentially outperform traditional clinical equipment through their noninvasive, on-body, and portable monitoring with mass cardiac data beyond the confines of inpatient settings. However, existing cardiovascular wearables have difficulty with providing medical-grade accuracy with a chronically comfortable and stable patient/consumer device interface for reliable clinical decision-making. Here, we develop an intensive care unit (ICU)-grade breathable cardiac electronic skin system (BreaCARES) for real-time, wireless, continuous, and comfortable cardiac care. BreaCARES enables a novel digital cardiac care platform for health care, outpatient diagnostics, stable intraoperative monitoring during heart surgery, and continuous and comfortable inpatient postoperative cardiac care, exhibiting ICU-grade accuracy while having superior anti-interference stability, portability, and long-term on-skin biocompatibility to the clinically and commercially available cardiac monitors in cardiovascular ICUs.

Stretchable and adhesive bilayers for electrical interfacing

Integrated stretchable devices, containing soft modules, rigid modules, and encapsulation modules, are of potential use in implantable bioelectronics and wearable devices. However, such systems often suffer from electrical deterioration due to debonding failure at the connection between rigid and soft modules induced by severe stress concentration, limiting their practical implementation. Here, we report a highly conductive and adhesive bilayer interface that can reliably connect soft-soft modules and soft-rigid modules together by simply pressing without conductive pastes. This interface configuration features a nanoscale styrene-ethylene-butylene-styrene (SEBS) elastomer layer and a SEBS-liquid metal (LM) composite layer. The top SEBS layer enables a strong adhesion with different modules. The connections between soft-soft and soft-rigid modules can be stretched to high strains of 400% and 250%, respectively. Coupling electron tunneling through an ultrathin SEBS layer with LM particle networks in a SEBS-LM composite layer renders continuous pathways for electrical conductivity. Such a bilayer interface exhibits a strain-insensitive high conductivity (3.7 × 105 S m-1) over a wide strain range from 0 to 680%, which can be facilely fabricated in a self-organized manner by sedimentation of LM particles. We present a proof-of-concept demonstration of this bilayer interface as an electrode, interconnect, and self-solder for monitoring physiological signals.

One-step fabrication of ultrathin porous Janus membrane within seconds for waterproof and breathable electronic skin

It remains a challenge for a simple and scalable method to fabricate ultrathin porous Janus membranes for stretchable on-skin electronics. Here, we propose a one-step droplet spreading phase separation strategy to prepare an ultrathin and easily collected Janus thermoplastic polyurethane (TPU) membrane within seconds. The metal-ion solvation structure mitigated migration kinetics to delay TPU solution demixing, promoting the further penetration of the coagulating solvent. Consequently, the developed membranes, with an average preparation rate of 25.2 cm2 s-1, had a thickness of 5 μm, and the water vapor transmission rate was determined to be 663 g m-2 d-1. The small pore layer having an average pore size of 1.7 μm effectively blocked external liquid water. The porous Janus TPU membrane coated by liquid metal served as a building block to develop a new generation of monolithic stretchable electronics with simultaneous high permeability and waterproofness.

Dynamic multimodal information encryption combining programmable structural coloration and switchable circularly polarized luminescence

Multimodal optical-materials are highly desirable due to their advantages in enhancing information security, though independent modulation is challenging, especially accurately controlling the orthogonal relationship between the structural coloration (SC) and fluorescence (FL) pattern. Herein, we report a strategy which combines programmable structural coloration and switchable circularly polarized luminescence (CPL) for multimodal information encryption. Using photomask with aligned grating, programmable periodic patterns are fabricated on a polydiacetylene (PDA) gel film, which produces image in tunable structural colors. Introducing a chiral fluorescence layer containing perovskite nanocrystals and twisted-stacking Ag nanowires (NWs) bilayers, which provides stimuli-responsive FL and CPL with high dissymmetry factor (glum, up to 1.3). Importantly, the structural coloration information and FL patterns (including CPL pattern) can be independently modulated without mutual interference, even selectively concealed or exposed by varying microstructure design of the cross-linked PDA gel or by acetonitrile treatment.

Functional-hydrogel-based electronic-skin patch for accelerated healing and monitoring of skin wounds

Conductive hydrogels feature reasonable electrical performance as well as tissue-like mechanical softness, thus positioning them as promising material candidates for soft bio-integrated electronics. Despite recent advances in materials and their processing technologies, however, facile patterning and monolithic integration of functional hydrogels (e.g., conductive, low-impedance, adhesive, and insulative hydrogels) for all-hydrogel-based soft bioelectronics still poses significant challenges. Here, we report material design, fabrication, and integration strategies for an electronic-skin (e-skin) patch based on functional hydrogels. The e-skin patch was fabricated by using photolithography-compatible functional hydrogels, such as poly(2-hydroxyethyl acrylate) (PHEA) hydrogel (substrate), Ag flake hydrogel (interconnection; conductivity: ∼571.43 S/cm), poly(3,4-ethylenedioxythiophene:polystyrene) (PEDOT:PSS) hydrogel (working electrode; impedance: ∼69.84 Ω @ 1 Hz), polydopamine (PDA) hydrogel (tissue adhesive; shear strength: ∼725.1 kPa), and poly(vinyl alcohol) (PVA) hydrogel (encapsulation). The properties of these functional hydrogels closely resemble those of human tissues in terms of water content and Young's modulus, enabling stable tissue-device interfacing in dynamically changing physiological environments. We demonstrated the efficacy of the e-skin patch through its application to accelerated healing and monitoring of skin wounds in mouse models - efficient fibroblast migration, proliferation, and differentiation promoted by electric field (EF) stimulation and iontophoretic drug delivery, and monitoring of the accelerated healing process through impedance mapping. The all-hydrogel-based e-skin patch is expected to create new opportunities for various clinically-relevant tissue interfacing applications.

Emergence of Voronoi-Patterned Cellular Membranes via Confinement Transformation of Self-Assembled Metal-Organic Frameworks

The self-assembly of nanoparticles allows the fabrication of complex, nature-inspired architectures. Among these, Voronoi tessellations─intricate patterns found in many natural systems such as insect wings and plant tissues─have broad implications across materials science, biology, and geography. However, replicating these irregular yet organized features at the nanoscale through nanoparticle self-assembly remains challenging. Here, we introduce a confinement transformation method to generate two-dimensional (2D) Voronoi patterns by converting metal-organic frameworks, specifically zeolitic imidazolate framework-8 (ZIF-8), into layered hydroxides. The process begins with the self-assembly of ZIF-8 particles into densely packed monolayers at the liquid-air interface, driven by the Marangoni effect. Subsequent Ni2+-induced etching converts the floating ZIF-8 monolayer into a freestanding membrane composed of interconnected polygonal cells, closely resembling the geometric characteristics of Voronoi tessellations. We systematically investigate the parameters affecting the transformation of ZIF-8 particles, shedding light on the mechanism governing Voronoi pattern formation. Mechanical testing and simulations demonstrate that the resulting cellular membranes exhibit enhanced stress distribution and crack resistance, attributed to their Voronoi-patterned architecture. These robust, monolithic membranes composed of Ni-based hydroxides, when serving as catalyst support materials, can synergistically enhance the intrinsic activity of Pt catalysts for alkaline hydrogen evolution reaction by facilitating water dissociation. This work presents a promising approach for creating nature-inspired materials with optimal stress management, superior mechanical properties, and potential catalytic applications.

Unveiling Ultrafast Vibration Detection from Nanostructures: Cluster Arrays Achieving Precise Responses without Direct Interparticle Mechanical Interaction

Sensitive materials assembled with nanostructures respond to subjected mechanical stimuli by modulating the internal electron transport through their intrinsic deformation. However, this deformation inherently entails a sufficient delay to overcome mechanical interactions between nanostructures to propagate within materials, thereby limiting the timely responsiveness of sensitive materials to ultrafast mechanical stimuli. Here, we propose a novel sensing array composed of isolated clusters, where majority of the clusters maintain nanoscale separations from each other. These interparticle separations effectively eliminate direct mechanical interactions within clusters, permitting the sensing array to respond to ultrafast deformations without additional delay. Furthermore, the nanoscale separations facilitate electron transport between clusters via quantum tunneling, achieving an ultrasensitive response to subtle mechanical stimuli. This engineered cluster array can be developed for vibration-sensing applications, capable of detecting a wide frequency range from 0.1 Hz to 60 kHz, providing characterizations of vibration details including amplitude, phase, and symmetry. The broad measurement range and precise detecting capability ensure that cluster array-based devices can find extensive applications such as mechanical inspections and medical diagnostics.

Biointerface engineering of flexible and wearable electronics

Biointerface sensing is a cutting-edge interdisciplinary field that merges conceptual and practical aspects. Wearable bioelectronics enable efficient interaction and close contact with biological components such as tissues and organs, paving the way for a wide range of medical applications, including personal health monitoring and medical intervention. To be applicable in real-world settings, the patches must be stable and adhere to the skin without causing discomfort or allergies in both wet and dry conditions, as well as other desirable features such as being ultra-soft, thin, flexible, and stretchable. Biosensors have emerged as promising tools primarily used to directly detect biological and electrophysiological signals, enhancing the efficacy of personalized medical treatments and enabling accurate tracking of human well-being. This review highlights the engineering of skin-tissue surfaces/interfaces and their interactions with wearable patches, aiming for both a broad and in-depth understanding of the mechanical and physicochemical properties required for the advancement of flexible and wearable skin patches. Specifically, the advantages of flexible bioelectronics and sensors with optimized surface geometry for long-term diagnosis are discussed. This insight aims to guide the future development of functional materials that can interact with human tissue in a controlled manner. Finally, we provide perspectives on the challenges and potential applications of biointerface engineering in wearable devices.

3D printing of wearable sensors with strong stretchability for myoelectric rehabilitation

Myoelectric biofeedback (EMG-BF) is a widely recognized and effective method for treating movement disorders caused by impaired nerve function. However, existing EMG-feedback devices are almost entirely located in large medical centers, which greatly limits patient accessibility. To address this critical limitation, there is an urgent need to develop a portable, cost-effective, and real-time monitoring device that can transcend the existing barriers to the treatment of EMG-BF. Our proposed solution leverages polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as core materials, ingeniously incorporating wood pulp nano celluloses (CNF-P)-Na+ to enhance the structural integrity. Additionally, the inclusion of nano-silica particles further augments the sensor's capabilities, enabling the creation of a stress-sensitive mineral ionization hydrogel sensor. This innovative approach not only capitalizes on the superior rheological properties of the materials but also, through advanced 3D printing technology, facilitates the production of a micro-scale structural hydrogel sensor with unparalleled sensitivity, stability, and durability. The potential of this sensor in the realm of human motion detection is nothing short of extraordinary. This development can potentially improve the treatment landscape for EMG-BF offering patients more convenient and efficient therapeutic options.

Electromagnetic Functions Modulation of Recycled By-Products by Heterodimensional Structure

One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic (EM) wave jamming and the recycling of defensive shields. The synergistic effect of heterodimensional materials can effectively enable the manipulation of EM waves by altering the nanostructure. Here we propose a novel approach for upcycling by-products of silver nanowires that can fabricate shape-tunable aerogels which enable the modulation of its interaction with microwaves by heterodimensional structure of by-products. By-product heterodimensionality was used to design EM-wave-jamming-dissipation structures and therefore two typical tunable aerogel forms were studied. The first tunable form was aerogel film, which shielded EM interference (EMI shielding effectiveness (EMI SE) > 89 dB) and the second tunable form was foam, which performed dual EM functions (SE > 30 dB& reflective loss (RL) < -35 dB, effective absorption bandwidth (EAB) > 6.7 GHz). We show that secondary recycled aerogels retain nearly all of their EM protection properties, making this type of closed-loop cycle an appealing option. Our findings pave the way for the development of adaptive EM functions with nanoscale regulation in a green and closed-loop cycle, and they shed light on the fundamental understanding of microwave interactions with heterodimensional structures.

Dynamic Liquid Metal-Microfiber Interlocking Enables Highly Conductive and Strain-insensitive Metastructured Fibers for Wearable Electronics

Stretchable fibers with high conductivity are vital components for smart textiles and wearable electronics. However, embedding solid conductive materials in polymers significantly reduces conductive pathways when stretched, causing a sharp drop in conductivity. Here, a stretchable metastructured fiber with dynamic liquid metal-microfiber interlocking interface is reported to realize highly conductive yet ultrastable conductance. The Cu-EGaIn mixture is partially embedded within the porous microfiber mat, thereby enabling its roll-up into a spiral-layered metastructured fiber with self-compensating conductive pathways. The metastructured fiber shows outstanding performance, including high conductivity of 1.5 × 106 S m-1, large stretchability up to 629%, and ultrastable conductance with only 16% relative resistance change at 100% strain, which far surpasses the theoretical value. Moreover, these fibers have served as versatile platforms for wearable temperature-visualizing electrothermal fiber heaters and fully stretchable smart sensing-display fabrics. This dynamic solid-liquid interfacial interlocking strategy is promising for stretchable electronics.

Electrospun multifunctional nanofibers for advanced wearable sensors

The multifunctional extension of fiber-based wearable sensors determines their integration and sustainable development, with electrospinning technology providing reliable, efficient, and scalable support for fabricating these sensors. Despite numerous studies on electrospun fiber-based wearable sensors, further attention is needed to leverage composite structural engineering for functionalizing electrospun fibers. This paper systematically reviews the research progress on fiber-based multifunctional wearable sensors in terms of design concept, device fabrication, mechanism exploration, and application potential. Firstly, the basics of electrospinning are briefly introduced, including its development, principles, parameters, and material selection. Tactile sensors, as crucial components of wearable sensors, are discussed in detail, encompassing their performance parameters, transduction mechanisms, and preparation strategies for pressure, strain, temperature, humidity, and bioelectrical signal sensors. The main focus of the article is on the latest research progress in multifunctional sensing design concepts, multimodal decoupling mechanisms, sensing mechanisms, and functional extensions. These extensions include multimodal sensing, self-healing, energy harvesting, personal thermal management, EMI shielding, antimicrobial properties, and other capabilities. Furthermore, the review assesses existing challenges and outlines future developments for multifunctional wearable sensors, highlighting the need for continued research and innovation.

Sign-Switchable Poisson's Ratio Design for Bimodal Strain-to-Electrical Signal Transducing Device

Stretchable electronic devices that conduct strain-related electronic performances have drawn extensive attention, functioning as mechanical sensors, actuators, and stretchable conductors. Although strain-insensitive or strain-responsive nature is well-achieved separately, it remains challenging to combine these two characteristics in one single device, which will offer versatile adaptability in various working situations. Herein, a hybrid material with sign-switchable Poisson's ratio (SSPR) is developed by combining a phase-change gel based reentrantreentrant honeycomb pattern and a polydimethylsiloxane film. The phase-change gel featuring thermally-regulated Young's modulus enables the hybrid material to switch between negative and positive Poisson's ratios. After integrating with a pre-stretched silver nanowires film, the obtained stretchable device performs bimodal strain-to-electrical signal transducing (Bi-SET) functions, in which the SSPR-dominated strain-resistance response switches between strain-dependent and strain-insensitive behaviors. As a proof of concept, a mode-switchable grasping system is constructed using a Bi-SET device-based controller, enabling the adaptation of grasping behaviors to various target objects.

3D printable and myoelectrically sensitive hydrogel for smart prosthetic hand control

Surface electromyogram (sEMG) serves as a means to discern human movement intentions, achieved by applying epidermal electrodes to specific body regions. However, it is difficult to obtain high-fidelity sEMG recordings in areas with intricate curved surfaces, such as the body, because regular sEMG electrodes have stiff structures. In this study, we developed myoelectrically sensitive hydrogels via 3D printing and integrated them into a stretchable, flexible, and high-density sEMG electrodes array. This electrode array offered a series of excellent human-machine interface (HMI) features, including conformal adherence to the skin, high electron-to-ion conductivity (and thus lower contact impedance), and sustained stability over extended periods. These attributes render our electrodes more conducive than commercial electrodes for long-term wearing and high-fidelity sEMG recording at complicated skin interfaces. Systematic in vivo studies were used to investigate its efficacy to control a prosthetic hand by decoding sEMG signals from the human hand via a multiple-channel readout circuit and a sophisticated artificial intelligence algorithm. Our findings demonstrate that the 3D printed gel myoelectric sensing system enables real-time and highly precise control of a prosthetic hand.

Enhanced Anticancer Efficacy of Alkaline Plasma-Activated Water through Augmented RONS Production

Despite notable advances in anticancer drug development, their manufacture and use pose environmental and health risks due to toxic byproducts, drug residue contamination, and cytotoxicity to normal cells. Therefore, developing cost-effective anticancer treatments with fewer toxic side effects and higher selectivity is essential to the advancement of highly effective anticancer therapies. Plasma-activated water (PAW) offers a green alternative to conventional chemical treatments as it reverts to water within days. However, the limited duration and dose of reactive oxygen and nitrogen species (RONS) in acidified PAW restrict its clinical deployment and the full understanding of their mechanism. In this study, we propose alkaline PAW as an innovative enhancement of the RONS technology. The alkaline PAW generated markedly superior RONS, with about 10 times higher levels of NO2-, H2O2, and ONOO-/O2•- than acidic PAW. The possible RONS generation pathways in alkaline PAW are analyzed by scavengers. In conventional acidic PAW, 70% of the H2O2 concentration is contributed by •OH but only about 20% in alkaline PAW. ONOO- is mainly formed through the reaction of O2•- with NO in alkaline pH, while in acidic PAW, it mainly forms from NO2- and H2O2. The results unveiled the synergistic and formidable anticancer effects of alkaline PAW against cancer cells, typified by an increase in intracellular ROS/RNS levels. Furthermore, alkaline PAW injection also effectively prevented xenograft tumor growth in mice. We systematically investigated this high-dose anticancer solution without using noble gases, toxic reagents, or extra energy consumption and successfully demonstrated the possibility of alkaline PAW being an effective and environmentally friendly therapeutic technology. The activity is closely linked to the RONS dose, and the generation pathway provides much-needed insight into the fundamental aspects of PAW chemistry required for the optimization of the biochemical activity of PAW.

Vertical-Structure Overcomes the Strain Limit of Stretchable Organic Electrochemical Transistors

Intrinsically stretchable organic electrochemical transistors (IS-OECTs), utilizing organic mixed ionic-electronic conductors (OMIECs) as their channel materials, have drawn great attention recently because of their potential to enable seamless integration between bioelectronic devices and living systems. However, the fabrication of IS-OECTs presents challenges due to the limited availability of OMIEC materials that possess the desired combination of mechanical and electrical properties. In this work, 1) we report the first successful fabrication of a vertical intrinsically stretchable OECT (VIS-OECT), achieved by using elastoadhesive electrodes; 2) we experimentally proved that vertical architecture can push the strain limit of an IS-OECT from 20% to 50%; and 3) the above finding introduces an unconventional design concept: the strain limit of an IS-OECT can surpass the intrinsic stretchability of the constituent OMIECs by employing vertical structure.

Recent Advances in Nanomaterial-Based Biosignal Sensors

Recent research for medical fields, robotics, and wearable electronics aims to utilize biosignal sensors to gather bio-originated information and generate new values such as evaluating user well-being, predicting behavioral patterns, and supporting disease diagnosis and prevention. Notably, most biosignal sensors are designed for body placement to directly acquire signals, and the incorporation of nanomaterials such as metal-based nanoparticles or nanowires, carbon-based or polymer-based nanomaterials-offering stretchability, high surface-to-volume ratio, and tunability for various properties-enhances their adaptability for such applications. This review categorizes nanomaterial-based biosignal sensors into three types and analyzes them: 1) biophysical sensors that detect deformation such as folding, stretching, and even pulse, 2) bioelectric sensors that capture electric signal originating from human body such as heart and nerves, and 3) biochemical sensors that catch signals from bio-originated fluids such as sweat, saliva and blood. Then, limitations and improvements to nanomaterial-based biosignal sensors is depicted. Lastly, it is highlighted on deep learning-based signal processing and human-machine interface applications, which can enhance the potential of biosignal sensors. Through this paper, it is aim to provide an understanding of nanomaterial-based biosignal sensors, outline the current state of the technology, discuss the challenges that be addressed, and suggest directions for development.

Materials in Radiative Cooling Technologies

Radiative cooling (RC) is a carbon-neutral cooling technology that utilizes thermal radiation to dissipate heat from the Earth's surface to the cold outer space. Research in the field of RC has garnered increasing interest from both academia and industry due to its potential to drive sustainable economic and environmental benefits to human society by reducing energy consumption and greenhouse gas emissions from conventional cooling systems. Materials innovation is the key to fully exploit the potential of RC. This review aims to elucidate the materials development with a focus on the design strategy including their intrinsic properties, structural formations, and performance improvement. The main types of RC materials, i.e., static-homogeneous, static-composite, dynamic, and multifunctional materials, are systematically overviewed. Future trends, possible challenges, and potential solutions are presented with perspectives in the concluding part, aiming to provide a roadmap for the future development of advanced RC materials.

Machine-Learning Mental-Fatigue-Measuring μm-Thick Elastic Epidermal Electronics (MMMEEE)

Electrophysiological (EP) signals are key biomarkers for monitoring mental fatigue (MF) and general health, but state-of-the-art wearable EP-based MF monitoring systems are bulky and require user-specific, labeled data. Ultrathin epidermal electrodes with high performance are ideal for constructing imperceptive EP sensing systems; however, the lack of a simple and scalable fabrication delays their application in MF recognition. Here, we report a facile, scalable printing-welding-transferring strategy (PWT) for printing μm-thickness micropatterned silver nanowires (AgNWs)/sticky polydimethylsiloxane, welding the AgNWs via plasmonic effect, and transferring the electrode to skin as tattoos. The PWT provides electrodes with conformability, comfort, and stability for EP sensing. Leveraging the facile and scalable PWT, we develop plug-and-play wireless multimodal epidermal electronics integrated with an unsupervised transfer learning (UTL) scheme for MF recognition across various users. The UTL adaptively minimizes the intersubject difference and achieves high accuracy, without demand of expensive computation and labels from target users.

Soft Cardiac Patch Using a Bifacial Architecture of Adhesive/Low‐Impedance Hydrogel Nanocomposites and Highly Conductive Elastomer Nanocomposites

Soft implantable multichannel cardiac electrode arrays that establish direct monolithic interfaces with the heart are key components for advanced cardiac monitoring and electrical modulation. A significant technological advancement in this area is the development of stretchable conductive nanocomposites, fabricated through the integration of metallic nanomaterials and elastic polymers, aimed at achieving both high electrical conductivity and mechanical elasticity. Despite these advances, further progress in material performance and device designs is required to ensure seamless, reliable, biocompatible, and high‐fidelity cardiac interfacing. Herein, the development of a soft multichannel cardiac patch based on a bifacial architecture of adhesive/low‐impedance hydrogel nanocomposites and highly conductive elastomer nanocomposites is reported. The bifacial design facilitates the integration of the cardiac patch between the heart and other tissues/organs can be achieved. The hydrogel nanocomposite layer, positioned on the epicardial side, provides stable adhesion to the target cardiac tissue and enables low‐impedance biocompatible interfacing with the heart, while the elastomer nanocomposite layer, positioned on the opposite side, offers high electrical conductivity for facile electrophysiological signal transfer and a low‐friction surface minimizing unwanted interactions with surrounding tissues. The effectiveness of this bifacial patch in multiple applications involving various cardiac signal recordings and electromechanical modulation demonstrations is showcased.

Recent advances in gold Janus nanomaterials: Preparation and application

Gold Janus nanomaterials have a tremendous significance for the novel bifunctional materials, significantly expanding the application scope of gold nanomaterials, especially Janus gold-thiol coordination polymer due to their exceptional biological characteristics, stability, plasmon effect, etc. The recent research on Janus gold nanoparticles and monolayer films of preparation and application has been summarized and in this review. To begin, we briefly introduce overview of Janus nanomaterials which received intense attention, outline current research trends, and detail the preparation and application of gold nanomaterials. Subsequently, we present comprehensively detailing fabrication strategies and applications of Janus gold nanoparticles. Additionally, we survey recent studies on the Janus gold nano-thickness films and point out the outstanding advantage of application on the tunable surface plasmon resonance, high sensitivity of surface-enhanced Raman scattering and electrical analysis fields. Finally, we discuss the emerging trends in Janus gold nanomaterials and address the associated challenges, thereby providing a comprehensive overview of this area of research.

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.

Active Stratification of Colloidal Mixtures for Asymmetric Multilayers

Stratified films offer high performance and multifunctionality, yet achieving fully stratified films remains a challenge. The layer-by-layer method, involving the sequential deposition of each layer, has been commonly utilized for stratified film fabrication. However, this approach is time-consuming, labor-intensive, and prone to leaving defects within the film. Alternatively, the self-stratification process exploiting a drying binary colloidal mixture is intensively developed recently, but it relies on strict operating conditions, typically yielding a heterogeneous interlayer. In this study, an active interfacial stratification process for creating completely stratified nanoparticle (NP) films is introduced. The technique leverages NPs with varying interfacial activity at the air-water interface. With the help of depletion pressure, the lateral compression of NP mixtures at the interface induces individual desorption of less interfacial active NPs into the subphase, while more interfacial active NPs remain at the interface. This simple compression leads to nearly perfect stratified NP films with controllability, universality, and scalability. Combined with a solvent annealing process, the active stratification process enables the fabrication of stratified films comprising a polymeric layer atop a NP layer. This work provides insightful implications for designing drug encapsulation and controlled release, as well as manufacturing transparent and flexible electrodes.

Absence of Additional Stretching-Induced Electron Scattering in Highly Conductive Cross-linked Nanocomposites with Negligible Tunneling Barrier Height and Width

The intrinsic resistance of stretchable materials is dependent on strain, following Ohm's law. Here the invariable resistance of highly conductive cross-linked nanocomposites over 53% strain is reported, where additional electron scattering is absent with stretching. The in situ generated uniformly dispersed small silver nanosatellite particles (diameter = 3.6 nm) realize a short tunneling barrier width of 4.1 nm in cross-linked silicone rubber matrix. Furthermore, the barrier height can be precisely controlled by the gap state energy level modulation in silicone rubber using cross-linkers. The negligible barrier height (0.01 eV) and short barrier width, achieved by the silver nanosatellite particles in cross-linked silicone rubber, dramatically increase the electrical conductivity (51 710 S cm-1) by more than 4 orders of magnitude. The high conductance is also maintained over 53% strain. The quantum tunneling behavior is observed when the barrier height is increased, following the Simmons approximation theory. The transport becomes diffusive, following Ohm's law, when the barrier width is increased beyond 10.3 nm. This study provides a novel strain-invariant resistance mechanism in highly conductive cross-linked nanocomposites.

Core-Sheath Heterogenous Interlocked Stretchable Conductive Fiber Induced by Adhesive MXene Modulated Interfacial Soldering

Whereas high electrical conductivity and mechanical stretchability are both essentially required for flexible electronics, simultaneously achieving them remains a great challenge due to the "trade-off" effect. Herein, an ultrastretchable conductor with core-sheath heterogeneous interlocked structure was developed, induced by interfacial soldering silver nanowires (AgNWs) which gradually evolved into elastic conductive fiber. Adhesive polydopamine-functionalized MXene (PDM) was proposed as an interfacial solder to assemble AgNWs along fibers while induced strong cold-welding effect soldered them into superelastic interconnected network. In situ coaxial heterogeneous interlocking between core AgNWs and sheath PDM network gradually formed during the interfacial soldering process, which enables elastic conductor simultaneously owning large mechanical stretchability and high electrical conductivity. Stretchable conductive fiber with core-sheath heterogeneous interlocking structure not only exhibits excellent electrical conductivity (1.13 × 105 S/m) but also could maintain stability (ΔR/R0 < 0.19) even under large mechanical deformations (300%). Ultrastretchable fibrous conductor with core-sheath heterogeneous interlocked microstructure induced by adhesive PDM interfacial soldering holds great promise in soft electronics.

Highly elastic relaxor ferroelectrics for wearable energy storage

Polymer-based relaxor ferroelectrics with high dielectric constant are pivotal in cutting-edge electronic devices, power systems, and miniaturized pulsed electronics. The surge in flexible electronics technology has intensified the demand for elastic ferroelectric materials that exhibit excellent electrical properties and mechanical resilience, particularly for wearable devices and flexible displays. However, as an indispensable component, intrinsic elastomers featuring high dielectric constant and outstanding resilience specifically tailored for elastic energy storage remain undeveloped. Elastification of relaxor ferroelectric materials presents a promising strategy to obtain high-dielectric elastomers. In this study, we present a strain-insensitive, high elastic relaxor ferroelectric material prepared via peroxide crosslinking of a poly(vinylidene fluoride) (PVDF)-based copolymer at low temperature, which exhibits an intrinsic high dielectric constant (∼20 at 100 Hz) alongside remarkable thermal, chemical, and mechanical stability. This relaxor ferroelectric elastomer maintains a stable energy density (>8 J cm-3) and energy storage efficiency (>75%) under strains ranging from 0 to 80%. This strain-insensitive, high elastic relaxor ferroelectric elastomer holds significant potential for flexible electronic applications, offering superior performance in soft robotics, smart clothing, smart textiles, and electronic skin.

PEDOT-based stretchable optoelectronic materials and devices for bioelectronic interfaces

The rapid development of wearable and implantable electronics has enabled the real-time transmission of electrophysiological signals in situ, thus allowing the precise monitoring and regulation of biological functions. Devices based on organic materials tend to have low moduli and intrinsic stretchability, making them ideal choices for the construction of seamless bioelectronic interfaces. In this case, as an organic ionic-electronic conductor, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has low impedance to offer a high signal-to-noise ratio for monitoring bioelectrical signals, which has become one of the most promising conductive polymers. However, the initial conductivity and stretchability of pristine PEDOT:PSS are insufficient to meet the application requirements, and there is a trade-off between their improvement. In addition, PEDOT:PSS has poor stability in aqueous environments due to the hygroscopicity of the PSS chains, which severely limits its long-term applications in water-rich bioelectronic interfaces. Considering the growing demands of multi-function integration, the high-resolution fabrication of electronic devices is urgent. It is a great challenge to maintain both electrical and mechanical performance after miniaturization, particularly at feature sizes below 100 μm. In this review, we focus on the combined improvement in the conductivity and stretchability of PEDOT:PSS, as well as the corresponding mechanisms in detail. Also, we summarize the effective strategies to improve the stability of PEDOT:PSS in aqueous environments, which plays a vital role in long-term applications. Finally, we introduce the reliable micropatterning technologies and PEDOT:PSS-based stretchable optoelectronic devices applied at bio-interfaces.

A fully integrated breathable haptic textile

Wearable haptics serve as an enhanced media to connect humans and VR/robots. The inevitable sweating issue in all wearables creates a bottleneck for wearable haptics, as the sweat/moisture accumulated in the skin/device interface can substantially affect feedback accuracy, comfortability, and create hygienic problems. Nowadays, wearable haptics typically gain performance at the cost of sacrificing the breathability, comfort, and biocompatibility. Here, we developed a fully integrated breathable haptic textile (FIBHT) to solve these trade-off issues, where the FIBHT exhibits high-level integration of 128 pixels over the palm, great stretchability of 400%, and superior permeability of over 657 g/m2/day (moisture) and 40 mm/s (air). It is a stand-alone haptic system totally composed of stretchable, breathable, and bioadhesive materials, which empowers it with precise, sweating/movement-insensitive and dynamic feedback, and makes FIBHT powerful for virtual touching in broad scenarios.

High-Performance Stretchable Strain Sensors Based on Auxetic Fabrics for Human Motion Detection

Wearable strain sensors play a pivotal role in real-time human motion detection and health monitoring. Traditional fabric-based strain sensors, typically with a positive Poisson's ratio, face challenges in maintaining sensitivity and comfort during human motion due to conflicting resistance changes in different strain directions. In this work, high-performance stretchable strain sensors are developed based on graphene-modified auxetic fabrics (GMAF) for human motion detection in smart wearable devices. The proposed GMAF sensors, with a negative Poisson's ratio achieved through commercially available warp-knitting technology, exhibit an 8-fold improvement in sensitivity compared to conventional plain fabric sensors. The unique auxetic fabric structure enhances sensitivity by synchronizing resistance changes in both wale and course directions. The GMAF sensors demonstrate excellent washability, showing only slight degradation in auxeticity and an acceptable increase in resistance after 10 standard wash cycles. The GMAF sensors maintain stability under different strain levels and various motion frequencies, emphasizing their dynamic performance. The sensors exhibit superior conformability to joint movements, which effectively monitor a full range of motions, including joint bending, sports activities, and subtle actions like coughing and swallowing. The research underscores a promising approach to achieve industrial-scale production of wearable sensors with improved performance and comfort through fabric structure design.

Antifouling Asymmetric Block Copolymer Nanofilms via Freestanding Interfacial Polymerization for Efficient and Sustainable Water Purification

Membrane materials that resist nonspecific or specific adsorption are urgently required in widespread practical applications, such as water purification, food processing, and life sciences. In water purification, inevitable membrane fouling not only limits membrane separation performance, leading to a decline in both permeance and selectivity, but also remarkably increases operation requirements, and augments extra maintenance costs and higher energy consumption. In this work, we report a freestanding interfacial polymerization (IP) fabrication strategy for in situ creation of asymmetric block copolymer (BCP) nanofilms with antifouling properties, greatly outperforming the conventional surface post-modification approaches. The resultant free-standing asymmetric BCP nanofilms with highly-dense, highly-hydrophilic polyethylene glycol (PEG) brushes on one side, can be readily formed via a typical IP process of a well-defined double-hydrophilic BCP composed of a highly-efficient antifouling PEG block and a membrane-forming multiamine block. The asymmetric BCP nanofilms have been applied for efficient and sustainable natural water purification, demonstrating extraordinary antifouling capabilities accompanied with superior separation performance far beyond commercial polyamide nanofiltration membranes. The antifouling behaviors of asymmetric BCP nanofilms derived from the combined effect of the hydration layer, electrostatic repulsion and steric hindrance were further elucidated by water flux and fouling resistance in combination with all-atom molecular dynamics (MD) simulation. This work opens up a new avenue for the large-scale and low-cost creation of broad-spectrum, asymmetric membrane materials with diverse functional "defect-free" surfaces in real-world applications.

Highly Conductive and Stretchable Hydrogel Nanocomposite Using Whiskered Gold Nanosheets for Soft Bioelectronics

The low electrical conductivity of conductive hydrogels limits their applications as soft conductors in bioelectronics. This low conductivity originates from the high water content of hydrogels, which impedes facile carrier transport between conductive fillers. This study presents a highly conductive and stretchable hydrogel nanocomposite comprising whiskered gold nanosheets. A dry network of whiskered gold nanosheets is fabricated and then incorporated into the wet hydrogel matrices. The whiskered gold nanosheets preserve their tight interconnection in hydrogels despite the high water content, providing a high-quality percolation network even under stretched states. Regardless of the type of hydrogel matrix, the gold-hydrogel nanocomposites exhibit a conductivity of ≈520 S cm-1 and a stretchability of ≈300% without requiring a dehydration process. The conductivity reaches a maximum of ≈3304 S cm-1 when the density of the dry gold network is controlled. A gold-adhesive hydrogel nanocomposite, which can achieve conformal adhesion to moving organ surfaces, is fabricated for bioelectronics demonstrations. The adhesive hydrogel electrode outperforms elastomer-based electrodes in in vivo epicardial electrogram recording, epicardial pacing, and sciatic nerve stimulation.

Needle-Like Multifunctional Biphasic Microfiber for Minimally Invasive Implantable Bioelectronics

Implantable bioelectronics has attracted significant attention in electroceuticals and clinical medicine for precise diagnosis and efficient treatment of target diseases. However, conventional rigid implantable devices face challenges such as poor tissue-device interface and unavoidable tissue damage during surgical implantation. Despite continuous efforts to utilize various soft materials to address such issues, their practical applications remain limited. Here, a needle-like stretchable microfiber composed of a phase-convertible liquid metal (LM) core and a multifunctional nanocomposite shell for minimally invasive soft bioelectronics is reported. The sharp tapered microfiber can be stiffened by freezing akin to a conventional needle to penetrate soft tissue with minimal incision. Once implanted in vivo where the LM melts, unlike conventional stiff needles, it regains soft mechanical properties, which facilitate a seamless tissue-device interface. The nanocomposite incorporating with functional nanomaterials exhibits both low impedance and the ability to detect physiological pH, providing biosensing and stimulation capabilities. The fluidic LM embedded in the nanocomposite shell enables high stretchability and strain-insensitive electrical properties. This multifunctional biphasic microfiber conforms to the surfaces of the stomach, muscle, and heart, offering a promising approach for electrophysiological recording, pH sensing, electrical stimulation, and radiofrequency ablation in vivo.

Highly elastic relaxor ferroelectric via peroxide crosslinking

Relaxor ferroelectrics are well-known for their high dielectric constants, low dielectric losses, and excellent electromechanical properties, making them valuable for various electronic devices. Despite recent efforts to enhance the durability of ferroelectrics through chemical cross-linking, achieving elasticity in relaxor ferroelectric materials remains a significant challenge. These materials inherently possess traits such as low crystallinity and small crystal size, while chemical crosslinking tends to diminish polymer crystallinity considerably. Thus, a key obstacle to making relaxor ferroelectric polymers elastic lies in safeguarding their crystalline regions from the effects of slight crosslinking. To tackle this issue, we selected P(VDF-CTFE-DB) with highly reactive C[double bond, length as m-dash]C double bonds as crosslinking sites, reducing the amount of cross-linking agents added and thereby lessening their impact on crystallinity. Through peroxide crosslinking, we transformed linear P(VDF-CTFE-DB) into a network structure, successfully producing a resilient relaxor ferroelectric material with maintained polarization intensity for ferroelectricity. Notably, this elastic relaxor ferroelectric was synthesized at relatively low temperatures, exhibiting a remarkable dielectric constant, superior resilience, fatigue resistance, and a stable ferroelectric response even under strains of up to 80%. Our approach paves the way for developing low-cost, high-dielectric-constant elastomers suitable for wearable electronics and related applications.

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Stretchable Electrodes for Interconnects in Soft Electronics

Soft electronics have significantly enhanced user convenience and data accuracy in wearable devices, implantable devices, and human-machine interfaces. However, a persistent challenge in their development has been the disconnection between the rigid and soft components of devices due to the substantial difference in modulus and stretchability. To address this issue, establishing a durable and flexible connection that smoothly links components of varying stiffness to signal-capturing sections with a lower stiffness is essential. In this study, we developed a novel stretchable interconnect that strongly adheres to various materials, facilitating electrical connections effortlessly by applying minimal finger pressure. Capable of stretching up to 1000% while maintaining electrical integrity, this interconnect proves its applicability across multiple domains, including electrocardiogram (ECG), electromyography (EMG), and stretchable light-emitting diode (LED) circuits. Its versatility is further demonstrated through its compatibility with various manufacturing techniques such as 3D printing, painting, and spin coating, highlighting its adaptability in soft electronics.

Phase-separated porous nanocomposite with ultralow percolation threshold for wireless bioelectronics

Realizing the full potential of stretchable bioelectronics in wearables, biomedical implants and soft robotics necessitates conductive elastic composites that are intrinsically soft, highly conductive and strain resilient. However, existing composites usually compromise electrical durability and performance due to disrupted conductive paths under strain and rely heavily on a high content of conductive filler. Here we present an in situ phase-separation method that facilitates microscale silver nanowire assembly and creates self-organized percolation networks on pore surfaces. The resultant nanocomposites are highly conductive, strain insensitive and fatigue tolerant, while minimizing filler usage. Their resilience is rooted in multiscale porous polymer matrices that dissipate stress and rigid conductive fillers adapting to strain-induced geometry changes. Notably, the presence of porous microstructures reduces the percolation threshold (Vc = 0.00062) by 48-fold and suppresses electrical degradation even under strains exceeding 600%. Theoretical calculations yield results that are quantitatively consistent with experimental findings. By pairing these nanocomposites with near-field communication technologies, we have demonstrated stretchable wireless power and data transmission solutions that are ideal for both skin-interfaced and implanted bioelectronics. The systems enable battery-free wireless powering and sensing of a range of sweat biomarkers-with less than 10% performance variation even at 50% strain. Ultimately, our strategy offers expansive material options for diverse applications.

Metal nanowire-based transparent electrode for flexible and stretchable optoelectronic devices

High-quality transparent electrodes are indispensable components of flexible optoelectronic devices as they guarantee sufficient light transparency and electrical conductivity. Compared to commercial indium tin oxide, metal nanowires are considered ideal candidates as flexible transparent electrodes (FTEs) owing to their superior optoelectronic properties, excellent mechanical flexibility, solution treatability, and higher compatibility with semiconductors. However, certain key challenges associated with material preparation and device fabrication remain for the practical application of metal nanowire-based electrodes. In this review, we discuss state-of-the-art solution-processed metal nanowire-based FTEs and their applications in flexible and stretchable optoelectronic devices. Specifically, the important properties of FTEs and a cost-benefit analysis of existing technologies are introduced, followed by a summary of the synthesis strategy, key properties, and fabrication technologies of the nanowires. Subsequently, we explore the applications of metal-nanowire-based FTEs in different optoelectronic devices including solar cells, photodetectors, and light-emitting diodes. Finally, the current status, future challenges, and emerging strategies in this field are presented.

Microneedle Patches-Integrated Transdermal Bioelectronics for Minimally Invasive Disease Theranostics

Wearable epidermal electronics with non- or minimally-invasive characteristics can collect, transduce, communicate, and interact with accessible physicochemical health indicators on the skin. However, due to the stratum corneum layer, rich information about body health is buried under the skin stratum corneum layer, for example, in the skin interstitial fluid. Microneedle patches are typically designed with arrays of special microsized needles of length within 1000 µm. Such characteristics potentially enable the access and sample of biomolecules under the skin or give therapeutical treatment painlessly and transdermally. Integrating microneedle patches with various electronics allows highly efficient transdermal bioelectronics, showing their great promise for biomedical and healthcare applications. This comprehensive review summarizes and highlights the recent progress on integrated transdermal bioelectronics based on microneedle patches. The design criteria and state-of-the-art fabrication techniques for such devices are initially discussed. Next, devices with different functions, including but not limited to health monitoring, drug delivery, and therapeutical treatment, are highlighted in detail. Finally, key issues associated with current technologies and future opportunities are elaborated to sort out the state of recent research, point out potential bottlenecks, and provide future research directions.

Electronic Skin: Opportunities and Challenges in Convergence with Machine Learning

Recent advancements in soft electronic skin (e-skin) have led to the development of human-like devices that reproduce the skin's functions and physical attributes. These devices are being explored for applications in robotic prostheses as well as for collecting biopotentials for disease diagnosis and treatment, as exemplified by biomedical e-skins. More recently, machine learning (ML) has been utilized to enhance device control accuracy and data processing efficiency. The convergence of e-skin technologies with ML is promoting their translation into clinical practice, especially in healthcare. This review highlights the latest developments in ML-reinforced e-skin devices for robotic prostheses and biomedical instrumentations. We first describe technological breakthroughs in state-of-the-art e-skin devices, emphasizing technologies that achieve skin-like properties. We then introduce ML methods adopted for control optimization and pattern recognition, followed by practical applications that converge the two technologies. Lastly, we briefly discuss the challenges this interdisciplinary research encounters in its clinical and industrial transition.

Simulated skin model for in vitro evaluation of insertion performance of microneedles: design, development, and application verification

Microneedles, as a new efficient and safe transdermal drug delivery technology, has a wide range of applications in drug delivery, vaccination, medical cosmetology, and diagnostics. The degree of microneedles penetration into the skin determines the reliability of the delivery dose, but its evaluation is not yet well-established, which is one of the major constraints in the commercialization of microneedles. In this paper, a novel visual simulated skin model was developed with reference to the physical properties of real skin. The simulated skin model was well-designed and its prescription was optimized to make the thickness, hardness, elasticity, and other parameters close to those of real skin. It not only meets the need to assess the degree of insertion of microneedles but also provides a visual observation of the insertion state of microneedles.