Nanomesh pressure sensor for monitoring finger manipulation without sensory interference

Nonlinear Conductive Graphene Composites for Pressure Sensing with a Linear Response and Voltage-Driven Thermal Correction

Thermal fluctuations pose a significant challenge to the signal stability of nanomaterial-based piezoresistive pressure sensors, limiting their effectiveness in applications such as electronic skin and robotics. Conventional temperature compensation strategies often rely on additional thermal sensors or complex calibration algorithms. Here, a flexible pressure sensor is reported featuring a nonlinear conductive graphene composite layer within a bilayer architecture, enabling bias voltage-controlled sensitivity without structural redesign. The sensor achieves ultra-high sensitivity (742.3 kPa-1), a broad linear sensing range of up to 800 kPa (R2 = 0.99913), and excellent long-term durability over 10 000 cycles. Crucially, the unique nonlinear characteristics enable the bias voltage to function as an internal remote control for correcting temperature drifts between 25 and 60 °C, as demonstrated by precise manipulation in robotic grippers under varying temperature conditions. This work offers a universal strategy for building environmentally adaptive sensors, advancing the development of robust and high-precision wearable electronics.

Unperceivable Designs of Wearable Electronics

Wearable smart electronics are taking an increasing part of the consumer electronics market, with applications in advanced healthcare systems, entertainment, and Internet of Things. The advanced development of flexible, stretchable, and breathable electronic materials has paved the way to comfortable and long-term wearables. However, these devices can affect the wearer's appearance and draw attention during use, which may impact the wearer's confidence and social interactions, making them difficult to wear on a daily basis. Apart from comfort, one key condition for user acceptance is that these new technologies seamlessly integrate into our daily lives, remaining unperceivable to others. In this review, strategies to minimize the visual impact of wearable devices and make them more suitable for daily use are discussed. These new devices focus on being unperceivable when worn and comfortable enough that users almost forget their presence, reducing psychological discomfort while maintaining accuracy in signal collection. Materials selection is crucial for developing long-term and unperceivable wearable devices. Recent developments in these unperceivable electronic devices are also covered, including sensors, transistors, and displays, and mechanisms to achieve unperceivability are discussed. Finally, the potential applications are summarized and the remaining challenges and prospects are discussed.

Fingertip-Inspired Spatially Anisotropic Inductive Liquid Metal Sensors with Ultra-Wide Range, High Linearity and Exceptional Stability

The advancement of robotic behavior and intelligence has led to an urgent demand for improving their sensitivity and interactive capabilities, which presents challenges in achieving multidimensional, wide-ranging, and reliable tactile sensing. Here an anisotropic inductive liquid metal sensor (AI-LMS) is introduced inspired by the human fingertip, which inherently possesses the capability to detect spatially multi-axis pressure with a wide sensing range, exceptional linearity, and signal stability. Additionally, it can detect very small pressures and responds swiftly to prescribed forces. Compared to resistive signals, inductive signals offer significant advantages. Further, integrated with a deep neural network model, the AI-LMS can decouple multi-axis pressures acting simultaneously upon it. Notably, the sensing range of Ecoflex and PDMS-based AI-LMS can be expanded by a factor of 4 and 9.5, respectively. For practical illustrations, a high-precision surface scanning reconstruction system is developed capable of capturing intricate details of 3D surface profiles. The utilization of biomimetic AI-LMS as robotic fingertips enables real-time discrimination of diverse delicate grasping behaviors across different fingers. The innovations and unique features in sensing mechanisms and structural design are expected to bring transformative changes and find extensive applications in the field of soft robotics.

Miniaturized Designs of Implantable and Wireless Hemodynamic Pressure Monitoring Capsules

OBJECTIVE

Hemodynamic pressure (HP) monitoring is critical for managing cardiovascular diseases. Clinical Doppler echocardiography and invasive catheter monitoring cannot realize remote continuous monitoring in daily life. Current implantable wireless equipment depends on custom chips or indirect sensing, presenting challenges in cost-effective and precise applications. Here, we present systematic design strategies for implantable, wireless, and battery-free capsule-like HP monitoring under near and middle-distance circumstances.

METHODS

The systems were composed of completely non-customized devices, with extremely compact volumes (<0.4 cm3). Near-distance monitoring utilized Near Field Communication with a piezoresistive sensor and foldable circuit designs. Middle-distance monitoring employed dual-winding antennas based on magnetic resonance (∼600 kHz) and Bluetooth. The power feedback circuit was optimized through human model electromagnetic simulations. Validation involved in vitro and in vivo experiments.

RESULTS

Near-distance system achieved 0.35 mmHg omnidirectional pressure accuracy under 5 mm tissue shielding. Middle-distance system attained the longest wireless power transfer distance (7.5 cm) via electromagnetic fields, supporting a capacitive sensor with 0.4 mmHg accuracy. In vitro tests in artificial tissue demonstrated stable data/energy transfer, accommodating axial misalignments up to ±45°. In vivo experiments on the beagle demonstrated real-time, wireless monitoring of left atrial pressure, whose rhythm synchronized with electrocardiograph recordings. The interatrial septum interventional installation was also validated.

CONCLUSION

The wireless and implantable capsules enable near and middle-distance hemodynamic pressure monitoring, even in dynamic swinging intracardiac situations. and has been validated in animal experiments.

SIGNIFICANCE

The designs provide a universal method for in vivo fully-implantable pressure monitor development.

Porous polymers: structure, fabrication and application

The porous polymer is a common and fascinating category within the vast family of porous materials. It offers valuable features such as sufficient raw materials, easy processability, controllable pore structures, and adjustable surface functionality by combining the inherent properties of both porous structures and polymers. These characteristics make it an effective choice for designing functional and advanced materials. In this review, the structural features, processing techniques and application fields of the porous polymer are discussed comprehensively to present their current status and provide a valuable tutorial guide and help for researchers. Firstly, the basic classification and structural features of porous polymers are elaborated upon to provide a comprehensive analysis from a mesoscopic to macroscopic perspective. Secondly, several established techniques for fabricating porous polymers are introduced, including their respective basic principles, characteristics of the resulting pores, and applied scopes. Thirdly, we demonstrate application research of porous polymers in various emerging frontier fields from multiple perspectives, including pressure sensing, thermal control, electromagnetic shielding, acoustic reduction, air purification, water treatment, health management, and so on. Finally, the review explores future directions for porous polymers and evaluates their future challenges and opportunities.

An 8-Micrometer-Thick Film Strain Sensor with Conformal 3D Microstructure for Accurate Detection of Body Motion and Air Leakage

Elastomer-based resistive super-thin film strain sensors show great application potentials in electronic skins, human-machine interaction systems, wearable devices for healthcare, and machine learning algorithms. However, it is challenging to accurately monitor the deformation of human body joints and organs with curved surfaces (e.g., knees, throats, finger joints) by only taking advantage of material thickness and elasticity of conventional 2D film strain sensors. Herein, a simple strategy is developed to fabricate conformal elastomeric thin film sensors with periodic 3D microstructure inspired by the ridges and valleys of human skin for accurate signal acquisition. Specifically, an 8-micrometer-thick elastic film strain sensor with 3D microstructure is fabricated via thermoforming followed by in situ chemical growth of silver nanoparticles. The 3D film strain sensors exhibit excellent signal linearity (R2 = 0.99) and relatively high sensitivity (gauge factor = 14) over a relatively wide strain range (≈43%), with an ultra-low strain detection limit of 0.025%, enabling potential applications in human healthcare monitoring and air leakage detection. Thus, this study unveils a simple methodology to process microstructure-enabled conformable 3D film strain sensors, which show good conformability and multiple mechanical sensing functions for advancing the development of next-generation flexible strain sensors.

A crosslinked eutectogel for ultrasensitive pressure and temperature monitoring from nostril airflow

Accurate detection of nostril airflow is vital for real-time respiratory monitoring. However, the developed methods only rely on single stimulus sensing for nostril airflow, which is extremely susceptible to interference in the complex environment, and severely affects the accuracy of detection results. Here, a multimodal integrated eutectogel sensor is explored to simultaneously sense the pressure and temperature stimuli of nostril airflow, by independently outputting capacitance and resistance, respectively, without cross-coupling. The completely physical crosslinking and the synergistic interaction of hydroxyapatite and tannic acid within the network endow this eutectogel with extremely low modulus, remarkable self-healing efficiency, robust adhesion, good environmental stability, and bio-compatibility. A multimodal sensor is developed by integrating this synthetic eutectogel with circuit design, which exhibits superior pressure sensitivity compared to other reported gel-based sensors. As a proof of concept, this sensor is further explored to diagnose the traditional respiratory disease of obstructive sleep apnea syndrome by simultaneously detecting five kinds of stimuli in the sleeping process, greatly improving the accuracy and reliability of the detection results. This work provides a highly effective strategy for achieving ultrasensitive respiratory monitoring and forecasting respiratory diseases.

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.

Hierarchical Synergetic Strategy for Iontronic Pressure Sensors with High Sensitivity and Broad Linearity Range

Flexible iontronic pressure sensors have attracted extensive attention in intelligent robots and wearable healthcare devices for their flexible properties and sensing functions. Introducing surface microstructures in iontronic pressure sensors has remarkably enhanced sensitivity, whereas achieving flexible pressure sensors with high sensitivity over a broad linear range remains challenging. Here, we propose a hierarchical synergetic strategy for flexible iontronic pressure sensors by combining hemisphere and porous microstructure, realizing high sensitivity (9.27 kPa-1), fast response speed (<15 ms), and linear pressure response (R2 = 0.998) over a broad range (10 Pa-400 kPa). The high linearity of the pressure sensor is attributed to the porous hemispherical microstructure, which improves compressibility and compensates for the effect of structural stiffening. The excellent application potential of our pressure sensors in healthcare monitoring and spatial pressure distribution is demonstrated. The porous hierarchical hemispherical microstructure provides a general strategy expected to be applied to other types of pressure sensors calling for both high sensitivity and high linearity.

Electrochromic Pressure-Sensitive Device for In Situ and Instantaneous Pressure Visualization

High sensitivity and spatial recognition of pressure sensors are important for application of the sensors in electronic skins, and in situ visualization is a practical and effective approach to identifying pressure information. Here, we present a facial strategy to achieve in situ pressure information recognition that is visible to the naked eye in coloring form by designing an H3PO4/PVA film with hemispheric microstructures in an integrated electrochromic pressure sensor. The device can be applied for different stress scenarios within the range of 0-250 kPa by adjusting the spacing of hemispheric microstructures and can identify the magnitude, position, shape, and duration of the pressure. Furthermore, the device can be used repeatedly by erasing under a 1 V bias, and more obvious information can be displayed under strong sunlight compared with light-emitting equipment. This strategy provides new insight into the design of flexible electronics for in situ and instantaneous pressure visualization in the future.

Mechanosensing of Stimuli Changes with Magnetically Gated Adaptive Sensitivity

Inspired by biological sensors that characteristically adapt to varying stimulus ranges, efficiently detecting stimulus changes sooner than the absolute stimulus values, we propose a mechanosensing concept in which the resolution can be adapted by magnetic field (H) gating to detect small pressure-changes under a wide range of compressive stimuli. This is realized with resistive sensing by pillared H-driven assemblies of soft ferromagnetic electrically conducting particles between planar electrodes under a voltage bias. By modulation of H, the pillars respond with mechanically adaptable sensitivity. Higher H enhances current resolution, while it increases scatter among repeating measurements due to increased magnetic structural jamming between colloids in their assembly. To manage the trade-off between electrical resolution and scatter, machine learning is introduced for searching optimum H gatings, thus facilitating efficient pressure prediction. This approach suggests bioinspired pathways for developing adaptive stimulus-responsive mechanosensors, detecting subtle changes across varying stimuli levels with enhanced effectiveness through machine learning.

Toward Stretchable Flexible Integrated Sensor Systems

Skin-like flexible sensors hold great potential as the next generation of intelligent electronic devices owing to their broad applications in environmental monitoring, human-machine interfaces, the Internet of Things, and artificial intelligence. Flexible electronics inspired by human skin play a vital role in continuous and real-time health monitoring. This review summarizes recent progress in skin-mountable electronics developed by designing flexible electrodes and substrates into different structures, including serpentine, microcrack, wrinkle, and kirigami. Furthermore, this review briefly discusses advances in wearable integrated sensor systems that mimic the flexibility of human skin, as well as multisensing functions. In the future, innovations in stretchable integrated sensor systems will be crucial to develop next-generation intelligent skin-based sensors for practical applications such as medical diagnosis, treatment, and environment monitoring.

On the Breathability of Epidermal Polymeric-Printed Tattoo Electrodes

Tattoo sensors offer many of the features of next-generation epidermal devices. They are ultrathin and conformable electrodes that have been shown to record high-quality biosignals from the skin. Moreover, they can be fabricated through large-area processing such as printing. Here, we report on printed poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) tattoo electrodes breathability. Epidermal devices require a breathable interface to ensure a physiological transepidermal water loss for reduced skin inflammation and discomfort of the user. In this work, we deeply examine the polymeric tattoo sensor's permeability properties with complementary experiments. By assessing the water permeance, the water-vapor transmission rate, and the impedance spectroscopy of polymeric tattoo electrodes, we show that they are intrinsically breathable, establishing a dry interface with the skin. The stability of such a dry interface is shown through the recording of muscle activity during sport when the sweat rate is much higher. While breathability is often hindered in conventional epidermal sensors, in PEDOT:PSS tattoo electrodes, it lies at the core of a stable sensor performance.

Advances in Soft Strain and Pressure Sensors

Soft strain and pressure sensors represent a breakthrough in material engineering and nanotechnology, providing accurate and reliable signal detection for applications in health monitoring, sports management, human-machine interface, or soft robotics, when compared to traditional rigid sensors. However, their performance is often compromised by environmental interference and off-axis mechanical deformations, which lead to nonspecific responses, as well as unstable and inaccurate measurements. These challenges can be effectively addressed by enhancing the sensors' specificity, making them responsive only to the desired stimulus while remaining insensitive to unwanted stimuli. This review systematically examines various materials and design strategies for developing strain and pressure sensors with high specificity for target physical signals, such as tactility, pressure distribution, body motions, or artery pulse. This review highlights approaches in materials engineering that impart special properties to the sensors to suppress interference from factors such as temperature, humidity, and liquid contact. Additionally, it details structural designs that improve sensor performance under different types of off-axis mechanical deformations. This review concludes by discussing the ongoing challenges and opportunities for inspiring the future development of highly specific electromechanical sensors.

Scalable magnetoreceptive e-skin for energy-efficient high-resolution interaction towards undisturbed extended reality

Electronic skins (e-skins) seek to go beyond the natural human perception, e.g., by creating magnetoperception to sense and interact with omnipresent magnetic fields. However, realizing magnetoreceptive e-skin with spatially continuous sensing over large areas is challenging due to increase in power consumption with increasing sensing resolution. Here, by incorporating the giant magnetoresistance effect and electrical resistance tomography, we achieve continuous sensing of magnetic fields across an area of 120 × 120 mm2 with a sensing resolution of better than 1 mm. Our approach enables magnetoreceptors with three orders of magnitude less energy consumption compared to state-of-the-art transistor-based magnetosensitive matrices. A simplified circuit configuration results in optical transparency, mechanical compliance, and vapor/liquid permeability, consequently permitting its imperceptible integration onto skins. Ultimately, these achievements pave the way for exceptional applications, including magnetoreceptive e-skin capable of undisturbed recognition of fine-grained gesture and a magnetoreceptive contact lens permitting touchless interaction.

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.

Advanced Morphological and Material Engineering for High-Performance Interfacial Iontronic Pressure Sensors

High-performance flexible pressure sensors are crucial for applications such as wearable electronics, interactive systems, and healthcare technologies. Among these, iontronic pressure sensors have garnered particular attention due to their superior sensitivity, enabled by the giant capacitance variation of the electric double layer (EDL) at the ionic-electronic interface under deformation. Key advancements, such as incorporating microstructures into ionic layers and employing diverse materials, have significantly improved sensor properties like sensitivity, accuracy, stability, and response time. This review highlights advancements in flexible EDL pressure sensors, focusing on structural designs and material engineering. These strategies are tailored to optimize key metrics such as sensitivity, detection limit, linearity, stability, response speed, hysteresis, transparency, wearability, selectivity, and multifunctionality. Key fabrication techniques, including micropatterning and externally assisted methods, are reviewed, along with strategies for sensor comparison and guidelines for selecting appropriate sensors. Emerging applications in healthcare, environmental and aerodynamic sensing, human-machine interaction, robotics, and machine learning-assisted intelligent sensing are explored. Finally, this review discusses the challenges and future directions for advancing EDL-based pressure sensors.

Fully 3D-Printed Soft Capacitive Sensor of High Toughness and Large Measurement Range

Soft capacitive sensors are widely utilized in wearable devices, flexible electronics, and soft robotics due to their high sensitivity. However, they may suffer delamination and/or debonding due to their low interfacial toughness. In addition, they usually exhibit a small measurement range resulting from their limited stiffness variation range. In this paper, soft silicone-based capacitive sensors are developed by using a customized multimaterial 3D printer. By curing silicone materials simultaneously, the continuous conductive and dielectric layers achieve a substantial interfacial toughness of 1036 J·m-2. The sensor with tilted thin-plate dielectrics exhibits interfacial toughness of 645 J·m-2 or 339 J·m-2 in the transverse or longitudinal direction, respectively. Additionally, the sensors demonstrate a broad measurement range from 0.85 Pa to 5000 kPa. This extended range is facilitated by the significant stiffness variation of the separated tilted thin-plate dielectrics, ranging from 0.56 kPa to 19.76 MPa. Two applications of these fully printed soft sensors, including an intelligent sensorized insole and a robotic hand combining both soft actuators and soft sensors are showcased. It is believed that the strategy, employing 3D printing for soft microstructured sensors, is a general approach not only applicable for improving the performance of soft sensors, but also conducive to designing powerful soft functional devices.

Top-down architecture of magnetized micro-cilia and conductive micro-domes as fully bionic electronic skin for de-coupled multidimensional tactile perception

Electronic skin (E-skin) has attracted considerable attention for simulating the human sensory system for use in prosthetics, human-machine interactions, and healthcare monitoring. However, it is still challenging to fully mimic the skin function that can de-couple stimuli such as normal/tangential forces, contact/non-contact behaviors, and react to high-frequency inputs. Herein, we propose fully bionic E-skin (FBE-skin), which consists of a magnetized micro-cilia array (MMCA), a micro-dome array (MDA), and flexible electrodes to completely duplicate the hairy layer, epidermis/dermis interface, and subcutaneous mechanoreceptors of human skin. The optimized MDA and interdigital electrode enable the FBE-skin to perceive static forces with a linear sensitivity of 96.6 kPa-1 up to 100 kPa, while the branch of electromagnetic induction allows the FBE-skin to sensitively capture dynamic stimuli with vibrating signals up to 100 Hz. The top-down integration of MDA and MMCA not only replicates the three-dimensional structure of human skin, but also synergistically provides the FBE-skin with bionic rapidly adapting (RA) and slowly adapting (SA) receptors. Consequently, the FBE-skin is capable of perceiving dynamic/static, normal/tangential, and contact/non-contact stimuli with a broad range of working pressures and frequencies. We expect that the design of FBE-skin will be promising for widespread applications from intelligent sensing to human-machine interactions.

Mechano-Graded Contact-Electrification Interfaces Based Artificial Mechanoreceptors for Robotic Adaptive Reception

Triboelectrification-based artificial mechanoreceptors (TBAMs) is able to convert mechanical stimuli directly into electrical signals, realizing self-adaptive protection and human-machine interactions of robots. However, traditional contact-electrification interfaces are prone to reaching their deformation limits under large pressures, resulting in a relatively narrow linear range. In this work, we fabricated mechano-graded microstructures to modulate the strain behavior of contact-electrification interfaces, simultaneously endowing the TBAMs with a high sensitivity and a wide linear detection range. The presence of step regions within the mechanically graded microstructures helps contact-electrification interfaces resist fast compressive deformation and provides a large effective area. The highly sensitive linear region of TBAM with 1.18 V/kPa can be effectively extended to four times of that for the devices with traditional interfaces. In addition, the device is able to maintain a high sensitivity of 0.44 V/kPa even under a large pressure from 40 to 600 kPa. TBAM has been successfully used as an electronic skin to realize self-adaptive protection and grip strength perception for a commercial robot arm. Finally, a high angle resolution of 2° and an excellent linearity of 99.78% for joint bending detection were also achieved. With the aid of a convolutional neural network algorithm, a data glove based on TBAMs realizes a high accuracy rate of 95.5% for gesture recognition in a dark environment.

An intelligent hybrid-fabric wristband system enabled by thermal encapsulation for ergonomic human-machine interaction

Human-machine interaction has emerged as a revolutionary and transformative technology, bridging the gap between human and machine. Gesture recognition, capitalizing on the inherent dexterity of human hands, plays a crucial role in human-machine interaction. However, existing systems often struggle to meet user expectations in terms of comfort, wearability, and seamless daily integration. Here, we propose a handwriting recognition technology utilizing an intelligent hybrid-fabric wristband system. This system integrates spun-film sensors into textiles to form the smart fabric, enabling intelligent functionalities. A thermal encapsulation process is proposed to bond multiple spun-films without additional materials, ensuring the lightweight, breathability, and stretchability of the spun-film sensors. Furthermore, recognition algorithms facilitate precise accurate handwriting recognition of letters, with an accuracy of 96.63%. This system represents a significant step forward in the development of ergonomic and user-friendly wearable devices for enhanced human-machine interaction, particularly in the virtual world.

Multifunctional Porous Soft Bioelectronics

Soft bioelectronics, seamlessly interfacing with the human body to enable both recording and modulation of curvilinear biological tissues and organs, have significantly driven fields such as digital healthcare, human-machine interfaces, and robotics. Nonetheless, intractable challenges persist due to the onerous demand for imperceptible, burden-free, and user-centric comfortable bioelectronics. Porous soft bioelectronics is a new way to a library of imperceptible bioelectronic systems, that form natural interfaces with the human body. In this review, we provide an overview of the development and recent advances in multifunctional porous engineered soft bioelectronics, aiming to bridge the gap between living biotic and stiff abiotic systems. We first discuss strategies for fabricating porous, soft, and stretchable bioelectronic materials, emphasizing the concept of materials-level porous engineering for breathable and imperceptible bioelectronics. Next, we summarize wearable bioelectronics devices and multimodal systems with porous configurations designed for on-skin healthcare applications. Moving beneath the skin, we discuss implantable devices and systems enabled by porous bioelectronics with tissue-like compliance. Finally, existing challenges and translational gaps are also proposed to usher further research efforts towards realizing practical and clinical applications of porous bioelectronic systems; thus, revolutionizing conventional healthcare and medical practices and opening up unprecedented opportunities for long-term, imperceptible, non-invasive, and human-centric healthcare networks.

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.

A neurocognitive pathway for engineering artificial touch

Artificial haptics has the potential to revolutionize the way we integrate physical and virtual technologies in our daily lives, with implications for teleoperation, motor skill acquisition, rehabilitation, gaming, interpersonal communication, and beyond. Here, we delve into the intricate interplay between the somatosensory system and engineered haptic inputs for perception and action. We critically examine the sensory feedback's fidelity and the cognitive demands of interfacing with these systems. We examine how artificial touch interfaces could be redesigned to better align with human sensory, motor, and cognitive systems, emphasizing the dynamic and context-dependent nature of sensory integration. We consider the various learning processes involved in adapting to artificial haptics, highlighting the need for interfaces that support both explicit and implicit learning mechanisms. We emphasize the need for technologies that are not only physiologically biomimetic but also behaviorally and cognitively congruent with the user, affording a range of alternative solutions to users' needs.

Ultrathin rubbery bio-optoelectronic stimulators for untethered cardiac stimulation

Untethered electrical stimulation or pacing of the heart is of critical importance in addressing the pressing needs of cardiovascular diseases in both clinical therapies and fundamental studies. Among various stimulation methods, light illumination-induced electrical stimulation via photoelectric effect without any genetic modifications to beating cells/tissues or whole heart has profound benefits. However, a critical bottleneck lies in the lack of a suitable material with tissue-like mechanical softness and deformability and sufficient optoelectronic performances toward effective stimulation. Here, we introduce an ultrathin (<500 nm), stretchy, and self-adhesive rubbery bio-optoelectronic stimulator (RBOES) in a bilayer construct of a rubbery semiconducting nanofilm and a transparent, stretchable gold nanomesh conductor. The RBOES could maintain its optoelectronic performance when it was stretched by 20%. The RBOES was validated to effectively accelerate the beating of the human induced pluripotent stem cell-derived cardiomyocytes. Furthermore, acceleration of ex vivo perfused rat hearts by optoelectronic stimulation with the self-adhered RBOES was achieved with repetitive pulsed light illumination.

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.

Stabilizing Metal Coating on Flexible Devices by Ultrathin Protein Nanofilms

The significant modulus difference between a metal coating and a polymer substrate leads to interface mismatches, seriously affecting the stability of flexible devices. Therefore, enhancing the adhesion stability of a metal layer on an inert polymer substrate to prevent delamination becomes a key challenge. Herein, an ultrathin protein nanofilm (UPN), synthesized by disulfide-bond-reducing protein aggregation, is proposed as a strong adhesive layer to enhance adhesion between polymer substrate and metal coating. Unlike traditional biopolymer adhesives with micrometer-scale thicknesses, the UPN layer is minimized to nanometer/single-molecular scale. Such UPN thereby effectively enhances the interfacial adhesive strength and reduces the cohesion contribution in the entire adhesion system by directly connecting two interfaces with a nearly single-molecular thickness. Using UPN as the adhesive layer, a multifunctional metal coating could be reliably adhered on flexible polymer substrates by ion sputtering, delivering unprecedented adhesion stability even under repetitive mechanical deformation. Applications of this design include reversible transparency control, tension-responsive encryption, reusable optical sensing, and wearable capacitive touch sensors. This work highlights UPN's potential to create strong bonding strength between flexible polymers and metal coatings, offering a biocompatible solution with high surface activity and low cohesion, facilitating the development of hybrid devices with stable metal nano-coating.

Research Progress of Flexible Electronic Devices Based on Electrospun Nanofibers

Electrospun nanofibers have become an important component in fabricating flexible electronic devices because of their permeability, flexibility, stretchability, and conformability to three-dimensional curved surfaces. This review delves into the advancements in adaptable and flexible electronic devices using electrospun nanofibers as the substrates and explores their diverse and innovative applications. The primary development of key substrates for flexible devices is summarized. After briefly discussing the principle of electrospinning, process parameters that affect electrospinning, and two major electrospinning techniques (i.e., single-fluid electrospinning and multifluid electrospinning), the review shines a spotlight on the recent breakthroughs in multifunctional and stretchable electronic devices that are based on electrospun substrates. These advancements include flexible sensors, flexible energy harvesting and storage devices, flexible accessories for electronic devices, and flexible environmental monitoring devices. In particular, the review outlines the challenges and potential solutions of developing electrospun nanofibers for flexible electronic devices, including overcoming the incompatibility of multiple interfaces, developing 3D microstructure sensor arrays with gradient geometry for various imperceptible on-skin devices, etc. This review may provide a comprehensive understanding of the rational design of application-oriented flexible electronic devices based on electrospun nanofibers.

Biointerface Fiber Technology from Electrospinning to Inflight Printing

Building two-dimensional (2D) and three-dimensional (3D) micro- and nanofibril structures with designable patterns and functionalities will offer exciting prospects for numerous applications spanning from permeable bioelectronics to tissue engineering scaffolds. This Spotlight on Applications highlights recent technological advances in fiber printing and patterning with functional materials for biointerfacing applications. We first introduce the current state of development of micro- and nanofibers with applications in biology and medical wearables. We then describe our contributions in developing a series of fiber printing techniques that enable the patterning of functional fiber architectures in three dimensions. These fiber printing techniques expand the material library and device designs, which underpin technological capabilities from enabling fundamental studies in cell migration to customizable and ecofriendly fabrication of sensors. Finally, we provide an outlook on the strategic pathways for developing the next-generation bioelectronics and "Fiber-of-Things" (FoT) using nano/micro-fibers as architectural building blocks.

Smart Green Cotton Textiles with Hierarchically Responsive Conductive Network for Personal Healthcare and Thermal Management

Whereas cotton as an abundant natural cellulose has been widely used for sustainable and skin-friendly textiles and clothes, developing cotton fabrics with smart functions that could respond to various stimuli is still eagerly desired while remaining a great challenge. Herein, smart multiresponsive cotton fabric with hierarchically copper nanowire interwoven MXene conductive networks that are seamlessly assembled along a 3D woven fabric template for efficient personal healthcare and thermal comfort regulation is successfully developed. The robust hierarchically interwoven conductive network was "glued" and protected by organic conductive polymer poly(3,4-ethylenedioxythiophene) along a 3D interconnected fabric template to enhance interfacial adherent and environmental stability. Benefiting from the robust multiresponsive hierarchically interwoven conductive network, smart cotton fabric exhibits real-time response to various external stimuli (light/electrical/heat/temperature/stress), and the details of human activities can be accurately recognized and monitored. Furthermore, the porous structure of 3D smart fabric induced strong capillary force and confinement to phase change materials PEG, which exhibits a wide range of phase transition temperatures for efficient thermal comfort regulation. After further encapsulation with transparent fluorosilicone resin, the smart cotton fabric exhibits excellent self-cleaning performance with water/oil repellent. The smart multiresponsive cotton fabrics hold great promise in next-generation wearable systems for efficient personal healthcare and thermal management.

Ultrathin crystalline silicon-based omnidirectional strain gauges for implantable/wearable characterization of soft tissue biomechanics

Monitoring soft-tissue biomechanics is of interest in biomedical research and clinical treatment of diseases. An important focus is biointegrated strain gauges that track time-dependent mechanics of targeted tissues with deforming surfaces over multidirections. Existing methods provide limited gauge factors, tailored for sensing within specific directions under quasi-static conditions. We present development and applicability of implantable/wearable strain gauges that integrate multiple ultrathin monocrystalline silicon-based sensors aligned with different directions, in stretchable formats for dynamically monitoring direction angle-sensitive strain. We experimentally and computationally establish operational principles, with theoretical systems that enable determination of intensities and direction of applied strains at an omnidirectional scale. Wearable evaluations range from cardiac pulse to intraocular pressure monitoring of eyeballs. The device can evaluate cardiac disorders of myocardial infarction and hypoxia of living rats and locate the pathological orientation associated with infarction, in designs with possibilities as biodegradable implants for stable operation. These findings create clinical significance of the devices for monitoring complex dynamic biomechanics.

Flexible Integrated Air Pressure Sensors for Monitoring Positive and Negative Pressure Distribution

Barometric pressure monitoring typically depends on conventional rigid microelectromechanical systems (MEMS) for single-point measurements. However, applications such as fluid dynamics require mapping barometric pressure distribution to study phenomena such as pressure variations on an aircraft wing during flight. In this study, we developed a mechanically flexible, multichannel air pressure sensor sheet using laser-induced graphene (LIG). This air pressure sensor sheet is designed to be mechanically flexible, allowing it to conform to nonplanar objects. First, the crystallinity change of LIG is studied by monitoring the bottom and top surfaces, revealing the presence of multilayered graphene and amorphous-like carbon in the formation of LIG. This explains the crystallinity change before and after the transfer process. Using LIG with optimal structures, negative and positive pressure detection is achieved, enabling its use as an air pressure sensor. Finally, as a proof-of-concept for the multichannel air pressure sensor sheet, the pressure distribution on the surface of an aircraft wing model is successfully mapped out.

Development of a Highly Sensitive and Stretchable Charge-Transfer Fiber Strain Sensor for Wearable Applications

Wearable electronics have significantly advanced the development of highly stretchable strain sensors, which are essential for applications such as health monitoring, human-machine interfaces, and energy harvesting. Fiber-based sensors and polymeric materials are promising due to their flexibility and tunable properties, although balancing sensitivity and stretchability remains a challenge. This study introduces a novel composite strain sensor that combines poly(3-hexylthiophene) and tetrafluoro-tetracyanoquinodimethane to form a charge-transfer complex (CTC) with carbon nanotubes (CNTs) on a styrene-butadiene-styrene substrate. The CTC improves conductivity through effective charge transfer, while CNTs provide mechanical reinforcement and maintain conductive paths, preventing cracks under large strains. Purposefully introduced wrinkles in the structure enhance the detection of small strains. The sensor demonstrated a broad strain-sensing range from 0.01 to 200%, exhibiting high sensitivity to both minor and major deformations. Mechanical tests confirmed strong stress-strain performance, and electrical tests indicated significant conductivity improvements with CNT integration. These results highlight the potential of the sensor for applications in health monitoring, human-machine interfaces, and energy harvesting, effectively mimicking the tactile sensing abilities of human skin.

Nanoscale Strategies for Enhancing the Performance of Adhesive Dry Electrodes for the Skin

High-quality electrophysiological monitoring requires electrodes to maintain a compliant and stable skin contact. This necessitates low impedance, good skin compliance, and strong adhesion to ensure continuous and stable contact under dynamic conditions. In this context, adhesive epidermal dry electrodes are advancing rapidly, which is promising for long-term applications in clinical diagnosis, wearable health monitoring, and human-machine interfaces. However, challenges persist, as conventional technologies usually fall short of meeting the high standards required for electrophysiological electrodes. This Perspective discusses four key aspects for high-performance epidermal electrodes from an adhesive perspective: initial adhesion, water resistance, dynamic stability, and removal simplicity. We review recent nanoscale strategies addressing these issues, providing a comprehensive guideline to enhance the application performance of epidermal dry electrodes. Additionally, we explore key nanoscale strategies and their associated functions, future technology roadmaps, and prospects for dry adhesive epidermal electrodes.

Advancements in Flexible Electronics Fabrication: Film Formation, Patterning, and Interface Optimization for Cutting-Edge Healthcare Monitoring Devices

Flexible electronics can seamlessly adhere to human skin or internal tissues, enabling the collection of physiological data and real-time vital sign monitoring in home settings, which give it the potential to revolutionize chronic disease management and mitigate mortality rates associated with sudden illnesses, thereby transforming current medical practices. However, the development of flexible electronic devices still faces several challenges, including issues pertaining to material selection, limited functionality, and performance instability. Among these challenges, the choice of appropriate materials, as well as their methods for film formation and patterning, lays the groundwork for versatile device development. Establishing stable interfaces, both internally within the device and in human-machine interactions, is essential for ensuring efficient, accurate, and long-term monitoring in health electronics. This review aims to provide an overview of critical fabrication steps and interface optimization strategies in the realm of flexible health electronics. Specifically, we discuss common thin film processing methods, patterning techniques for functional layers, interface challenges, and potential adjustment strategies. The objective is to synthesize recent advancements and serve as a reference for the development of innovative flexible health monitoring devices.

Mechanically Active Materials and Devices for Bio-Interfaced Pressure Sensors-A Review

Pressures generated by external forces or by internal body processes represent parameters of critical importance in diagnosing physiological health and in anticipating injuries. Examples span intracranial hypertension from traumatic brain injuries, high blood pressure from poor diet, pressure-induced skin ulcers from immobility, and edema from congestive heart failure. Pressures measured on the soft surfaces of vital organs or within internal cavities of the body can provide essential insights into patient status and progression. Challenges lie in the development of high-performance pressure sensors that can softly interface with biological tissues to enable safe monitoring for extended periods of time. This review focuses on recent advances in mechanically active materials and structural designs for classes of soft pressure sensors that have proven uses in these contexts. The discussions include applications of such sensors as implantable and wearable systems, with various unique capabilities in wireless continuous monitoring, minimally invasive deployment, natural degradation in biofluids, and/or multiplexed spatiotemporal mapping. A concluding section summarizes challenges and future opportunities for this growing field of materials and biomedical research.

Wearable and implantable biosensors: mechanisms and applications in closed-loop therapeutic systems

This review article examines the current state of wearable and implantable biosensors, offering an overview of their biosensing mechanisms and applications. We also delve into integrating these biosensors with therapeutic systems, discussing their operational principles and incorporation into closed-loop devices. Biosensing strategies are broadly categorized into chemical sensing for biomarker detection, physical sensing for monitoring physiological conditions such as pressure and temperature, and electrophysiological sensing for capturing bioelectrical activities. The discussion extends to recent developments in drug delivery and electrical stimulation devices to highlight their significant role in closed-loop therapy. By integrating with therapeutic devices, biosensors enable the modulation of treatment regimens based on real-time physiological data. This capability enhances the patient-specificity of medical interventions, an essential aspect of personalized healthcare. Recent innovations in integrating biosensors and therapeutic devices have led to the introduction of closed-loop wearable and implantable systems capable of achieving previously unattainable therapeutic outcomes. These technologies represent a significant leap towards dynamic, adaptive therapies that respond in real-time to patients' physiological states, offering a level of accuracy and effectiveness that is particularly beneficial for managing chronic conditions. This review also addresses the challenges associated with biosensor technologies. We also explore the prospects of these technologies to address their potential to transform disease management with more targeted and personalized treatment solutions.

Toward an AI Era: Advances in Electronic Skins

Electronic skins (e-skins) have seen intense research and rapid development in the past two decades. To mimic the capabilities of human skin, a multitude of flexible/stretchable sensors that detect physiological and environmental signals have been designed and integrated into functional systems. Recently, researchers have increasingly deployed machine learning and other artificial intelligence (AI) technologies to mimic the human neural system for the processing and analysis of sensory data collected by e-skins. Integrating AI has the potential to enable advanced applications in robotics, healthcare, and human-machine interfaces but also presents challenges such as data diversity and AI model robustness. In this review, we first summarize the functions and features of e-skins, followed by feature extraction of sensory data and different AI models. Next, we discuss the utilization of AI in the design of e-skin sensors and address the key topic of AI implementation in data processing and analysis of e-skins to accomplish a range of different tasks. Subsequently, we explore hardware-layer in-skin intelligence before concluding with an analysis of the challenges and opportunities in the various aspects of AI-enabled e-skins.

Transformable 3D curved high-density liquid metal coils - an integrated unit for general soft actuation, sensing and communication

Rigid solenoid coils have long been indispensable in modern intelligent devices. However, their sparse structure and challenging preparation of flexible coils for soft robots impose limitations. Here, a transformable 3D curved high-density liquid metal coil (HD-LMC) is introduced that surpasses the structural density level of enameled wire. The fabrication technique employed for high-density channels in elastomers is universally applicable. Such HD-LMCs demonstrated excellent performance in pressure, temperature, non-contact distance sensors, and near-field communication. Soft electromagnetic actuators thus achieved significantly improved the electromagnetic force and power density. Moreover, precise control of swinging tail motion enables a bionic pufferfish to swim. Finally, HD-LMC is further utilized to successfully implement a soft rotary robot with integrated sensing and actuation capabilities. This groundbreaking research provides a theoretical and experimental basis for expanding the applications of liquid metal-based multi-dimensional complex flexible electronics and is expected to be widely used in liquid metal-integrated robotic systems.

Skin-Mountable Functional Electronic Materials for Bio-Integrated Devices

Skin-mountable electronic materials are being intensively evaluated for use in bio-integrated devices that can mutually interact with the human body. Over the past decade, functional electronic materials inspired by the skin are developed with new functionalities to address the limitations of traditional electronic materials for bio-integrated devices. Herein, the recent progress in skin-mountable functional electronic materials for skin-like electronics is introduced with a focus on five perspectives that entail essential functionalities: stretchability, self-healing ability, biocompatibility, breathability, and biodegradability. All functionalities are advanced with each strategy through rational material designs. The skin-mountable functional materials enable the fabrication of bio-integrated electronic devices, which can lead to new paradigms of electronics combining with the human body.

Tailor-Made Gold Nanomaterials for Applications in Soft Bioelectronics and Optoelectronics

In modern nanoscience and nanotechnology, gold nanomaterials are indispensable building blocks that have demonstrated a plethora of applications in catalysis, biology, bioelectronics, and optoelectronics. Gold nanomaterials possess many appealing material properties, such as facile control over their size/shape and surface functionality, intrinsic chemical inertness yet with high biocompatibility, adjustable localized surface plasmon resonances, tunable conductivity, wide electrochemical window, etc. Such material attributes have been recently utilized for designing and fabricating soft bioelectronics and optoelectronics. This motivates to give a comprehensive overview of this burgeoning field. The discussion of representative tailor-made gold nanomaterials, including gold nanocrystals, ultrathin gold nanowires, vertically aligned gold nanowires, hard template-assisted gold nanowires/gold nanotubes, bimetallic/trimetallic gold nanowires, gold nanomeshes, and gold nanosheets, is begun. This is followed by the description of various fabrication methodologies for state-of-the-art applications such as strain sensors, pressure sensors, electrochemical sensors, electrophysiological devices, energy-storage devices, energy-harvesting devices, optoelectronics, and others. Finally, the remaining challenges and opportunities are discussed.

Three-dimensional micro strain gauges as flexible, modular tactile sensors for versatile integration with micro- and macroelectronics

Flexible tactile sensors play important roles in many areas, like human-machine interface, robotic manipulation, and biomedicine. However, their flexible form factor poses challenges in their integration with wafer-based devices, commercial chips, or circuit boards. Here, we introduce manufacturing approaches, device designs, integration strategies, and biomedical applications of a set of flexible, modular tactile sensors, which overcome the above challenges and achieve cooperation with commercial electronics. The sensors exploit lithographically defined thin wires of metal or alloy as the sensing elements. Arranging these elements across three-dimensional space enables accurate, hysteresis-free, and decoupled measurements of temperature, normal force, and shear force. Assembly of such sensors on flexible printed circuit boards together with commercial electronics forms various flexible electronic systems with capabilities in wireless measurements at the skin interface, continuous monitoring of biomechanical signals, and spatial mapping of tactile information. The flexible, modular tactile sensors expand the portfolio of functional components in both microelectronics and macroelectronics.

Nanoengineering Ultrathin Flexible Pressure Sensors with Superior Sensitivity and Wide Range via Nanocomposite Structures

Flexible pressure sensors have attracted great interest due to their bendable, stretchable, and lightweight characteristics compared to rigid pressure sensors. However, the contradictions among sensitivity, detection limit, thickness, and detection range restrict the performance of flexible pressure sensors and the scope of their applications, especially for scenarios requiring conformal fitting, such as rough surfaces such as the human skin. This paper proposes a novel flexible pressure sensor by combining the nanoengineering strategy and nanocomposite structures. The nanoengineering strategy utilizes the bending deformation of nanofilm instead of the compression of the active layer to achieve super high sensitivity and low detection limit; meanwhile, the nanocomposite structures introduce distributed microbumps that delay the adhesion of nanofilm to enlarge the detection range. As a result, this device not only ensures an ultrathin thickness of 1.6 μm and a high sensitivity of 84.29 kPa-1 but also offers a large detection range of 20 kPa and an ultralow detection limit of 0.07 Pa. Owing to the ultrathin thickness as well as high performance, this device promotes applications in detecting fingertip pressure, flexible mechanical gripping, and so on, and demonstrates significant potential in wearable electronics, human-machine interaction, health monitoring, and tactile perception. This device offers a strategy to resolve the conflicts among thickness, sensitivity, detection limit, and detection range; therefore, it will advance the development of flexible pressure sensors and contribute to the community and other related research fields.

Fabrication, sustainability, and key performance indicators of bioelectronics via fiber building blocks

Bioelectronics provide efficient information exchange between living systems and man-made devices, acting as a vital bridge in merging the domains of biology and technology. Using functional fibers as building blocks, bioelectronics could be hierarchically assembled with vast design possibilities across different scales, enhancing their application-specific biointegration, ergonomics, and sustainability. In this work, the authors review recent developments in bioelectronic fiber elements by reflecting on their fabrication approaches and key performance indicators, including the life cycle sustainability, environmental electromechanical performance, and functional adaptabilities. By delving into the challenges associated with physical deployment and exploring innovative design strategies for adaptability, we propose avenues for future development of bioelectronics via fiber building blocks, boosting the potential of "Fiber of Things" for market-ready bioelectronic products with minimized environmental impact.

Blade-Coated Porous 3D Carbon Composite Electrodes Coupled with Multiscale Interfaces for Highly Sensitive All-Paper Pressure Sensors

Flexible and wearable pressure sensors hold immense promise for health monitoring, covering disease detection and postoperative rehabilitation. Developing pressure sensors with high sensitivity, wide detection range, and cost-effectiveness is paramount. By leveraging paper for its sustainability, biocompatibility, and inherent porous structure, herein, a solution-processed all-paper resistive pressure sensor is designed with outstanding performance. A ternary composite paste, comprising a compressible 3D carbon skeleton, conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), and cohesive carbon nanotubes, is blade-coated on paper and naturally dried to form the porous composite electrode with hierachical micro- and nano-structured surface. Combined with screen-printed Cu electrodes in submillimeter finger widths on rough paper, this creates a multiscale hierarchical contact interface between electrodes, significantly enhancing sensitivity (1014 kPa-1) and expanding the detection range (up to 300 kPa) of as-resulted all-paper pressure sensor with low detection limit and power consumption. Its versatility ranges from subtle wrist pulses, robust finger taps, to large-area spatial force detection, highlighting its intricate submillimeter-micrometer-nanometer hierarchical interface and nanometer porosity in the composite electrode. Ultimately, this all-paper resistive pressure sensor, with its superior sensing capabilities, large-scale fabrication potential, and cost-effectiveness, paves the way for next-generation wearable electronics, ushering in an era of advanced, sustainable technological solutions.

Designs and Applications for the Multimodal Flexible Hybrid Epidermal Electronic Systems

Research on the flexible hybrid epidermal electronic system (FHEES) has attracted considerable attention due to its potential applications in human-machine interaction and healthcare. Through material and structural innovations, FHEES combines the advantages of traditional stiff electronic devices and flexible electronic technology, enabling it to be worn conformally on the skin while retaining complex system functionality. FHEESs use multimodal sensing to enhance the identification accuracy of the wearer's motion modes, intentions, or health status, thus realizing more comprehensive physiological signal acquisition. However, the heterogeneous integration of soft and stiff components makes balancing comfort and performance in designing and implementing multimodal FHEESs challenging. Herein, multimodal FHEESs are first introduced in 2 types based on their different system structure: all-in-one and assembled, reflecting totally different heterogeneous integration strategies. Characteristics and the key design issues (such as interconnect design, interface strategy, substrate selection, etc.) of the 2 multimodal FHEESs are emphasized. Besides, the applications and advantages of the 2 multimodal FHEESs in recent research have been presented, with a focus on the control and medical fields. Finally, the prospects and challenges of the multimodal FHEES are discussed.

MXene-Based Pressure Sensor with a Self-Healing Property for Joule Heating and Friction Sliding

As a kind of flexible electronic device, flexible pressure sensor has attracted wide attention in medical monitoring and human-machine interaction. With the continuous deepening of research, high-sensitivity sensor is developing from single function to multi-function. However, Current multifunctional sensors lack the ability to integrate joule heating, detect sliding friction, and self-healing. Herein, a MXene/polyurethane (PU) flexible pressure sensor with a self-healing property for joule heating and friction sliding is fabricated. The MXene/PU sensitive layer with special spinosum structure is prepared by a simple spraying method. After face-to-face assembly of the sensitive layers, the MXene/PU flexible pressure sensor is obtained and showed excellent sensitivity (150.65 kPa-1), fast response/recovery speed (75.5/63.9 ms), and good stability (10 000 cycles). Based on the self-healing property of PU, the sensor also has the ability to heal after mechanical damage. In addition, the sensor realizes the joule heating function under low voltage, and has the real-time monitoring ability of sliding objects. Combined with low cost and simple manufacturing method, the multi-functional MXene/PU flexible sensor shows a wide range of application potential in human activity monitoring, thermal management, and slip recognition.

Creep-free polyelectrolyte elastomer for drift-free iontronic sensing

Artificial pressure sensors often use soft materials to achieve skin-like softness, but the viscoelastic creep of soft materials and the ion leakage, specifically for ionic conductors, cause signal drift and inaccurate measurement. Here we report drift-free iontronic sensing by designing and copolymerizing a leakage-free and creep-free polyelectrolyte elastomer containing two types of segments: charged segments having fixed cations to prevent ion leakage and neutral slippery segments with a high crosslink density for low creep. We show that an iontronic sensor using the polyelectrolyte elastomer barely drifts under an ultrahigh static pressure of 500 kPa (close to its Young's modulus), exhibits a drift rate two to three orders of magnitude lower than that of the sensors adopting conventional ionic conductors and enables steady and accurate control for robotic manipulation. Such drift-free iontronic sensing represents a step towards highly accurate sensing in robotics and beyond.