Recent Advances in Flexible Pressure Sensors Based on MXene Materials

Predicting and Understanding Work Functions of Double Transition Metal MXenes via Interpretable Machine Learning Methods

In this study, we employed interpretable machine learning models to predict and understand the work functions of double transition metal MXenes with the formula (M1)2(M2)X2O2. We created a comprehensive data set of 242 structures covering 11 transition metals and two X elements (C, N) using first-principles calculations. Various machine learning methods, including linear regression, support vector regression, random forest regression, and artificial neural networks, were thoroughly evaluated. The random forest model achieved the best performance on the test set, with a mean absolute error of 0.17 ± 0.02 eV, root-mean-square error of 0.24 ± 0.03 eV, and R2 of 0.86 ± 0.03. The feature importance analysis revealed a hierarchical influence mechanism: the properties of the outer transition metal (M1) dominate the work function, followed by the X element, while the inner transition metal (M2) has minimal impact. Furthermore, we employed the Sure Independence Screening and Sparsifying Operator method to derive analytical expressions that relate element features to work functions, achieving comparable accuracy (R2 = 0.82 ± 0.04) while providing physical insights. Our findings not only enable rapid prediction of MXene work functions but also provide valuable guidance for the rational design of MXene-based materials.

Bio-Inspired Synthesis of Injectable, Self-Healing PAA-Zn-Silk Fibroin-MXene Hydrogel for Multifunctional Wearable Capacitive Strain Sensor

Conductive hydrogels have important application prospects in the field of wearable sensing, which can identify various biological signals for human motion monitoring. However, the preparation of flexible conductive hydrogels with high sensitivity and stability to achieve reliable signal recording remains a challenge. Herein, we prepared a conductive hydrogel by introducing conductive Ti3C2Tx MXene nanosheets into a dual network structure formed by Zn2+ crosslinked polyacrylic acid and silk fibroin for use as a wearable capacitive strain sensor. The prepared injectable hydrogel has a uniform porous structure and good flexibility, and the elongation at break can reach 1750%. A large number of ionic coordination bonds and hydrogen bond interactions make the hydrogel exhibit good structural stability and a fast self-healing property (30 s). In addition, the introduction of Ti3C2Tx MXene as a conductive medium in hydrogel improves the conductivity. Due to the high conductivity of 0.16 S/m, the capacitive strain sensor assembled from this hydrogel presents a high gauge factor of 1.78 over a wide strain range of 0-200%, a fast response time of 0.2 s, and good cycling stability. As a wearable sensor, the hydrogel can accurately monitor the activities of different joints in real-time. This work is expected to provide a new approach for wearable hydrogel electronic devices.

Flexible Piezoresistive Sensor Based on CNT/PVA Composite with Wide Linear Detection Range for Human Motion Monitoring

In recent years, flexible pressure sensors have attracted significant attention due to their extensive application prospects in wearable devices, healthcare monitoring, and other fields. Herein, we propose a flexible piezoresistive sensor with a broad detection range, utilizing a CNT/PVA composite as the pressure-sensitive layer. The effect of the CNT-to-PVA ratio on sensing performance was systematically investigated, revealing that the sensor's sensitivity initially increases and then decreases with rising CNT content. When the weight percentage of CNTs reaches 11.24 wt%, the sensing film exhibits optimal piezoresistive properties. A resistance model of the composite conductive material was established to elucidate the sensing mechanism associated with CNT content in detail. Furthermore, hill-like microstructures were fabricated on a PDMS substrate using sandpaper as a template to further enhance overall performance. The sensor demonstrates a sensitivity of 0.1377 kPa-1 (<90 kPa), a sensing range of up to 400 kPa, a response time of 160 ms, and maintains excellent stability after 2000 folding cycles. It can accurately detect human joint flexion and muscle activity. This work is expected to provide a feasible solution for flexible electronic devices applied in human motion monitoring and analysis, particularly offering competitive advantages in applications involving wide-range pressure detection.

Versatile core-shell MnO2@PANI nanocomposites: Bridging photo-assisted zinc-ion batteries and wearable strain sensors for self-powered systems

With the continuous development of self-powered sensing systems, achieving efficient energy self-supply and high-performance signal acquisition simultaneously has emerged as a main trend for next-generation sensors. However, developing functional materials for such sensing systems is still facing crucial challenges. Herein, a multifunctional MnO2@PANI (MP) composite material was designed to realize a synchronized "integration" strategy. Specifically, the MP serves as a cathode in photo-assisted zinc-ion batteries (PA-ZIBs), enabling solar energy conversion and storage. The p-n heterojunction formed between MnO2 and PANI promotes effective separation of photogenerated electron-hole pairs and enhances Zn2+ kinetics. Therefore, the PA-ZIBs deliver a high self-charging voltage of 1.08 V and 33 % enhancement in specific capacity (reaching 249.5 mAh g-1 at 0.1 A g-1) under illumination. Meanwhile, it also functions as the active layer of a flexible strain sensor, achieving efficient mechanical signal detection. The core-shell structure and composite component improve both structural stability and conductivity. As a result, the sensor exhibits high sensitivity, a fast response time of 0.4 s, and excellent durability over 2000 cycles. Furthermore, proof-of-concept demonstrations validate the device's capability to simultaneously harvest solar energy and detect physiological signals. This work offers a new solution for designing self-powered sensing systems and intelligent healthcare applications by merging energy-autonomous operation with multifunctional sensing capabilities.

Exploration of Two-Dimensional Conductance Along LaAlO3/SrTiO3 Interface for Pressure Sensing

Dominated by the pressure-origin of strain gradient, the sensitivity of pressure sensor is usually enhanced by reducing the bulk thickness. Considering the degraded robustness of the thin sensing block, it is anticipated to achieve the pressure sensing with high sensitivity and robustness. To address the trade-off between the sensitivity and stability, this investigation explores the two-dimensional (2D) conductance along the LaAlO3/SrTiO3 (LAO/STO) heterojunction as the pressure-sensing block. In details, by the pulsed laser deposition (PLD), LAO is synthesized on the (001) STO substrate and the oxygen vacancies are formed along the LAO/STO interface. These heterojunction vacancies exhibit 2D conductance in characterization about the magnetic-field orientation-dependent magnetoresistance. The deionization energy of the oxygen vacancy is estimated to be 0.03 eV, by which the Fermi level is lifted to enable the LAO/STO heterojunction with the metallic characteristic. Fabricated into a pressure sensor, the LAO/STO heterojunction exhibits the sensitivity of 2.9 × 10-6 Pa-1 which is robust during the repeatability tests more than 100 times. It is confirmed that the 2D conductance can be explored toward pressure detection with comparable sensitivity and durativity.

Gravity-Driven Air-Liquid Interface Flexible Sensor for Human Motion Detection

This study introduces a novel gravity-driven air-liquid interface flexible sensor (GALIFS) for detecting human motions. GALIFS leverages gravity-induced liquid flow to generate angle-dependent electrical signals, eliminating the need for material deformation (e.g., stretching or compression) during operation. Unlike conventional inertial sensors (limited by rigid designs causing discomfort) or existing flexible sensors (reliant on stress-induced signals and high material durability), GALIFS overcomes these constraints through its unique gravity-driven mechanism. Furthermore, GALIFS operates without requiring perfect skin adhesion, significantly enhancing user comfort. GALIFS achieves a wide angular detection range (0°-180°) with high stability (over 16000 cycles). Additionally, it can identify a diverse range of human motions, including neck bending, spine bending, squatting, jumping, walking, and running. A real-time lying posture monitoring system for bedridden patients is further developed, showcasing its medical potential. Following successful mitigation of liquid evaporation issues, GALIFS may have significant potential for applications in various scenarios, including medical rehabilitation and sports training.

Enhanced Mechanical Properties and Sensing Performance of MXene-Based Dual-Crosslinked Hydrogel via EGCG Coating and Dynamic Covalent Bond

MXenes hold great promise for flexible sensors due to their outstanding electrical and mechanical properties. However, their practical application in aqueous environments is often compromised by oxidation susceptibility. Here, epigallocatechin gallate (EGCG), a naturally derived compound is introduced, as a protective coating for Ti₃C₂Tx MXene nanosheets. The catechol groups in EGCG form strong hydrogen bonds with MXene, significantly enhancing its oxidation resistance in aqueous environments for up to 40 days. By incorporating EGCG-coated MXene (MXene@EGCG) to form a dual-crosslinked hybrid network, a tough hydrogel with exceptional properties, including enhanced compressibility (>95%), high compressive strength (5.43 MPa), minimal residual strain (<1%), and rapid recovery within seconds is developed. Furthermore, the hydrogel exhibits superior sensing capabilities with a compressive gauge factor exceeding 10 and a stretch gauge factor of up to 3.72. This well-designed structure also endows it a low degree of hysteresis in compressive sensing. In vitro experiments confirm its great biocompatibility, desired self-adhesion properties, and practical utility as a sensing platform. This approach pioneers a versatile and transformative strategy for enhancing MXene stability and engineerability, unlocking new possibilities for fabricating high-performance hydrogel-based sensors capable of effectively sensing dynamic strains, which may find broad applications in the fields of multifunctional bioelectronics.

Detection of Positive and Negative Pressure in a Double-Chamber Underwater Thruster

The aim of this paper is to develop a compact, rapid-response pressure sensor for underwater propulsion. Flexible pressure sensors are widely utilized in human-computer interactions and wearable electronic devices; however, manufacturing capacitive sensors that offer a broad pressure range and high sensitivity presents significant challenges. Inspired by the dermal papillary microstructure, a capacitive pressure sensor was prepared by infusing polydimethylsiloxane (PDMS) inside an anodic aluminum oxide (AAO) template and then demolding it. The resulting pressure sensor exhibits several key characteristics: high linearity in the range of -5.2 to 6.3 kPa, a comprehensive range for both positive and negative pressure sensing in air or water environments, a quick response time of 52 ms, a recovery time of 40 ms, and excellent stability. The sensor presented in this work is innovatively applied to detect underwater negative pressure, and it is employed for the swift detection of positive and negative pressure changes in underwater thrusters. This work highlights the promising potential of biomimetic flexible capacitive pressure sensors across various applications.

Bionic learning in MXene-based actuators: An emerging frontier

Bionics offers valuable insights into the design and application of MXene-based soft actuators, which have garnered significant attention in the fields of flexible electronics and smart materials owing to their exceptional electrical conductivity, tunable interlayer spacing, and responsiveness to diverse external stimuli. This review begins with a comprehensive summary of the main response mechanisms of MXene-based soft actuators under various external stimuli. It presents a detailed analysis of the advantages and limitations of different actuation modes and discusses strategies for composite modification with other materials to enhance MXene performance under multi-stimulus conditions. Inspired by the sensory capabilities of animals and plants in nature, this work explores the potential for biomimetic design and identifies four key challenges for advancing the field: (1) the development of efficient and controllable material synthesis techniques, (2) the electrochemical stability and environmental robustness of devices, (3) the overall performance optimization of actuators, and (4) the nascent exploration of biomimetic learning mechanisms. Finally, future research directions are outlined, offering novel perspectives to promote the broader application of MXene-based soft actuators in biomimetic systems.

Mechano-Filtering Encapsulation: A Stitching-Based Packaging Strategy Implementing Active Noise Suppression in Piezoresistive Pressure Sensors

Flexible pressure sensors face the dual challenges of weak signal extraction and environmental noise suppression in wearable electronics and human-machine interfaces. This research proposes an intelligent pressure sensor utilizing chitosan/carbon nanotube/melamine sponge (CS/CNT/MS) composites, achieving high-performance sensing through a dual-stage noise reduction architecture that combines mechanical pre-filtration and electrical synergistic regulation. An innovative compressed-stitching encapsulation technique creates pressure sensors with equivalent mechanical low-pass filtering characteristics, actively eliminating interference signals below 3 kPa while maintaining linear response within the 3-20 kPa effective loading range (sensitivity: 0.053 kPa-1). The synergistic effects of CS molecular cross-linking and CNTs' three-dimensional conductive network endow the device with a 72 ms response time, 24 ms recovery speed, and over 3500-cycle compression stability. Successful applications in smart sport monitoring and tactile interactive interfaces demonstrate a material-structure-circuit co-design paradigm for mechanical perception in complex environments.

Flexible Pressure Sensors Enhanced by 3D-Printed Microstructures

3D printing has revolutionized the development of flexible pressure sensors by enabling the precise fabrication of diverse microstructures that significantly enhance sensor performance. These advancements have substantially improved key attributes such as sensitivity, response time, and durability, facilitating applications in wearable electronics, robotics, and human-machine interfaces. This review provides a comprehensive analysis of the sensing mechanisms of these sensors, emphasizing the role of microstructures, such as micro-patterned, microporous, and hierarchical designs, in optimizing performance. The advantages of 3D printing techniques, including direct and indirect fabrication methods, in the creation of complex microstructures with high precision and adaptability are highlighted. Specific applications, including human physiological signal monitoring, motion detection, soft robotics, and emerging applications, are explored to demonstrate the versatility of these sensors. Additionally, this review briefly discusses key challenges, such as material compatibility, optimization difficulties, and environmental stability, as well as emerging trends, such as the integration of advanced technologies, innovative designs, and multidimensional sensing as promising avenues for future advancements. By summarizing recent progress and identifying opportunities for innovation, this review provides critical insights into bridging the gap between research and real-world applications, helping to accelerate the evolution of flexible pressure sensors with sophisticated 3D-printed microstructures.

Design Strategies and Emerging Applications of Conductive Hydrogels in Wearable Sensing

Conductive hydrogels, integrating high conductivity, mechanical flexibility, and biocompatibility, have emerged as crucial materials driving the evolution of next-generation wearable sensors. Their unique ability to establish seamless interfaces with biological tissues enables real-time acquisition of physiological signals, external stimuli, and even therapeutic feedback, paving the way for intelligent health monitoring and personalized medical interventions. To fully harness their potential, significant efforts have been dedicated to tailoring the conductive networks, mechanical properties, and environmental stability of these hydrogels through rational design and systematic optimization. This review comprehensively summarizes the design strategies of conductive hydrogels, categorized into metal-based, carbon-based, conductive polymer-based, ionic, and hybrid conductive systems. For each type, the review highlights structural design principles, strategies for conductivity enhancement, and approaches to simultaneously enhance mechanical robustness and long-term stability under complex environments. Furthermore, the emerging applications of conductive hydrogels in wearable sensing systems are thoroughly discussed, covering physiological signal monitoring, mechano-responsive sensing platforms, and emerging closed-loop diagnostic-therapeutic systems. Finally, this review identifies key challenges and offers future perspectives to guide the development of multifunctional, intelligent, and scalable conductive hydrogel sensors, accelerating their translation into advanced flexible electronics and smart healthcare technologies.

Mechanical Compatibility in Stitch Configuration and Sensor Adhesion for High-Fidelity Pulse Wave Monitoring

Wearable electronics can achieve high-fidelity monitoring of pulse waveforms on the body surface enabling early diagnosis of cardiovascular diseases (CVDs). Textile-based wearable devices offer advantages in terms of high permeability and comfort. However, knitted strain sensors struggle to capture small-range deformation signals due to stress dissipation during friction and slip of yarns within the textiles. They are optimized for mechanical adaptability and adhesive capability. In this work, the stitch configurations of knitted structure are adjusted to optimize the energy dissipation ratio during deformation and waveform fitting performance. These electric-mechanical results enabled the selection of the most suitable knitted structure for the clinical diagnosis. On the other hand, the sensor's adhesion is optimized with respect to electrical-force-strain coupling and energy transfer efficiency at the interface between skin and sensor. The balance between the storage modulus and loss modulus are adjusted via the crosslinking degree of the polyacrylamide (PAAm) hydrogel network. As a result, the optimized knitted sensor enables stable collection of pulse waveforms from the radial and dorsalis pedis arteries. In human patient evaluations, the knitting-based strain sensor can distinguish patients with different potential CVD risks through extracted characteristic indicators.

Soft Materials and Devices Enabling Sensorimotor Functions in Soft Robots

Sensorimotor functions, the seamless integration of sensing, decision-making, and actuation, are fundamental for robots to interact with their environments. Inspired by biological systems, the incorporation of soft materials and devices into robotics holds significant promise for enhancing these functions. However, current robotics systems often lack the autonomy and intelligence observed in nature due to limited sensorimotor integration, particularly in flexible sensing and actuation. As the field progresses toward soft, flexible, and stretchable materials, developing such materials and devices becomes increasingly critical for advanced robotics. Despite rapid advancements individually in soft materials and flexible devices, their combined applications to enable sensorimotor capabilities in robots are emerging. This review addresses this emerging field by providing a comprehensive overview of soft materials and devices that enable sensorimotor functions in robots. We delve into the latest development in soft sensing technologies, actuation mechanism, structural designs, and fabrication techniques. Additionally, we explore strategies for sensorimotor control, the integration of artificial intelligence (AI), and practical application across various domains such as healthcare, augmented and virtual reality, and exploration. By drawing parallels with biological systems, this review aims to guide future research and development in soft robots, ultimately enhancing the autonomy and adaptability of robots in unstructured environments.

Iron-Supported Asymmetric Iontronic Pressure Sensors with High Sensitivity and Extended Linearity

Iontronic pressure sensors (IPSs) are emerging as promising candidates for integration into wearable electronics and healthcare monitoring systems due to their high sensitivity and low power consumption. However, achieving high sensitivity across a broad linear pressure range remains a significant challenge. This study presents a novel IPS device with an asymmetric sandwich structure, which includes a three-dimensional electrode made of nickel manganese oxide/carbon nanotubes (NMO/CNT) and an embedded iron needles ionic dielectric layer. The proposed device demonstrates exceptional linearity over 1700 kPa, with a sensitivity exceeding 7700 kPa-1. It exhibits rapid response and recovery times in the millisecond range and maintains a consistent capacitive response over 15,000 loading-unloading cycles. Moreover, the device enables noncontact sensing in response to magnetic field variations, broadening its potential applications. The innovative IPS design effectively balances high sensitivity and a wide linear pressure range, rendering it suitable for various applications such as nonverbal communication aids and healthcare monitoring systems.

Ultra-Stretchable Polymer Fibers Anchored with a Triple-Level Self-Assembled Conductive Network for Wide-Range Strain Detection

Numerous strategies have been demonstrated to enhance the mechanical stretchability of electromechanical sensors for widespread applications in wearable electronics. However, ranging from composite to microstructural materials, their electromechanical sensing performances are usually vulnerable to large stretching deformations due to the low-ductility of the infilled conductive components and the modulus mismatch between the flexible polymer substrate and conductive fillers. Here, a novel design strategy is proposed to fabricate ultra-stretchable electromechanical composites constructed by a triple-level interaction conductive network (Tri-LICN) in buckled-TPU microfibers for strain sensors. The Tri-LICN is established by bridging one-dimensional cellulose nanocrystals (CNC) with zero-dimensional gold-nanoparticles (AuNPs) and two-dimensional MXene sheets using interface self-assembly and ultrasound-assisted anchoring to eliminate the modulus mismatching between the conductive material and polymer substrate. The buckled-TPU microfibers are introduced to improve the mechanical stretchability of composites by the external-stimuli-induced imbalance of the stretching conformation of TPU macromolecules. The Tri-LICN MXene/CNC/AuNPs@TPU composite sensor displays an enhanced strain sensitivity (GF~2514) with a fast response time (~150 ms) over a wide operational strain up to 200% and excellent durability over 1000 tensile cycles. Our finding offers a promising approach to enhancing the performance of stretchable sensors based on polymer materials, providing new opportunities for the development of next-generation electronics.

Stretchable [2]rotaxane-bridged MXene films applicable for electroluminescent devices

Titanium carbide (Ti3C2TX) MXene has prominent mechanical properties and electrical conductivity. However, fabricating high-performance macroscopic films is challenging, as weak interlayer interactions limit their mechanical performance. Here, we introduce [2]rotaxane, a mechanically interlocked molecule, to enhance MXene films. Compared to pure MXene (fracture strain: 4.6%, toughness: 0.6 MJ/m3), [2]rotaxane-bridged MXene (RBM) films achieve record-high strain (20.0%) and toughness (11.9 MJ/m3) with only 3.6% [2]rotaxane by weight. Additionally, RBM films endure 500 stretch cycles (0 to 15% strain) with stable and reversible resistance alterations, making them ideal for stretchable electrodes. Notably, RBM films enable stretchable electroluminescent devices with reliable operation under 20% elongation and customizable luminescent patterns. This innovative use of mechanically interlocked molecules to cross-link MXene platelets advances MXene films and other two-dimensional materials in stretchable electronics.

Untethered Soft Robots Based on 1D and 2D Nanomaterials

Biological structures exhibit autonomous and intelligent behaviors, such as movement, perception, and responses to environmental changes, through dynamic interactions with their surroundings. Inspired by natural organisms, future soft robots are also advancing toward autonomy, sustainability, and interactivity. This review summarizes the latest achievements in untethered soft robots based on 1D and 2D nanomaterials. First, the performance of soft actuators designed with different structures is compared. Then, the development of basic locomotion forms, including crawling, jumping, swimming, rolling, gripping, and multimodal, mimicking biological motion mechanisms under dynamic stimuli, is discussed. Subsequently, various self-sustained movements based on imbalance mechanisms under static stimuli are introduced, including light tracking, self-oscillating, self-crawling, self-rolling, and flying. Following that, the progress in soft actuators integrated with additional functionalities such as sensing, energy harvesting, and storage is summarized. Finally, the challenges faced in this field and the prospects for future development are discussed.

Highly compressible lamellar graphene/cellulose/sodium alginate aerogel via bidirectional freeze-drying for flexible pressure sensor

Graphene exhibits exceptional electrical properties, and aerogels made from it demonstrate high sensitivity when used in sensors. However, traditional graphene aerogels have poor biocompatibility and sustainability, posing potential environmental and health risks. Moreover, the stacking of their internal structures results in low compressive strength and fatigue resistance, which limits their further applications. In this study, green and sustainable cellulose nanofibers/sodium alginate/reduced graphene oxide aerogels (BCSRA) were synthesized, featuring a well-defined lamellar structure and a fiber cross-linked network, employing techniques such as bidirectional freeze-drying, ionic cross-linking, and thermal annealing. The unique internal architecture of BCSRA results in a compressive strength of up to 64.55 kPa at 70 % compression deformation and an extremely low density of merely 7.21 mg/cm3. Furthermore, BCSRA displays outstanding fatigue resistance, maintaining 82.17 % of its stress after 100 compression cycles at 70 % compressive strain and 86.99 % after 1000 cycles at 50 % compressive strain. Remarkably, when utilized as a flexible pressure sensor, BCSRA achieves a sensitivity of 5.71 kPa-1 and endures over 2200 cycles at 40 % compression, all while ensuring consistent electrical signal output. These properties underscore its significant potential for application in wearable flexible pressure sensors, capable of detecting various human movements.

Superelastic bamboo cellulose nanofiber based carbon aerogel with layered network microstructure for high sensitivity piezoresistive sensor

Carbon aerogels, characterized by their high porosity and superior electrical performance, present significant potential for the development of highly sensitive pressure sensors. However, facile and cost-effective fabrication of biomass-based carbon aerogels that concurrently possess high sensitivity, high elasticity, and excellent fatigue resistance remains a formidable challenge. Herein, a piezoresistive sensor with a layered network microstructure (BCNF-rGO-CS) was successfully fabricated using bamboo nanocellulose fiber (BCNF), chitosan (CS), and graphene oxide (GO) as raw materials. The fabrication process involved directional ice-crystal growth and mild hydrothermal reduction methods where the directional ice-crystal growth technique imparted a stable network-like pore structure, while the mild hydrothermal reduction method ensured electrical conductivity without compromising the original properties of the CNF. Taking advantage of the stress transfer properties of the cross-linked network structure, BCNF-rGO-CS exhibited exceptional reversible compressibility (sustaining 80 % strain), high fatigue resistance (10,000 cycles at 60 % strain), and high stress retention (84.6 %) over long-term cycling. Furthermore, the BCNF-rGO-CS sensor exhibited notable low-pressure sensitivity, excellent response time (66/76 ms), and it was capable of responding to ultra-low pressures of 10 Pa. Based on these favorable characteristics, the piezoresistive sensor holds promising prospects for applications in body motion detection, health monitoring, and flexible electronic-skin.

Lignocellulose-Mediated Functionalization of Liquid Metals toward the Frontiers of Multifunctional Materials

Lignocellulose-mediated liquid metal (LM) composites, as emerging functional materials, show tremendous potential for a variety of applications. The abundant hydroxyl, carboxyl, and other polar groups in lignocellulose facilitate the formation of strong chemical bonds with LM surfaces, enhancing wettability and adhesion for improved interface compatibility. Beyond serving as a supportive matrix, lignocellulose can be tailored to optimize the microstructure of the composites, adapting them for diverse applications. This review comprehensively summarizes the fundamental principles and recent advancements in lignocellulose-mediated LM composites, highlighting the advantages of lignocellulose in composite fabrication, including facile synthesis, versatile interactions, and inherent functionalities. Key modulation strategies for LMs and innovative synthesis methods for functionalized lignocellulose composites are discussed. Furthermore, the roles and structure-performance relationships of these composites in electromagnetic shielding, flexible sensors, and energy storage devices are systematically summarized. Finally, the obstacles and prospective advancements pertaining to lignocellulose-mediated LM composites are thoroughly scrutinized and deliberated upon. This review is expected to provide basic guidance for researchers to boost the popularity of LMs in diverse applications and provide useful references for design strategies of state-of-the-art LMs.

Anchoring Ru single-atoms on MXene achieves dual-enzyme activities for mild photothermal augmented nanocatalytic therapy

Single-atom catalysts with abnormally high catalytic activity have garnered extensive attention and interest for their application in tumor therapy. Despite the advancements made with current nanotherapeutic agents, developing efficient systems for cancer treatment remains challenging due to low activity, uncontrollable behavior, and nonselective interactions. Herein, we have constructed Ru single-atom-anchored MXene nanozymes (Ru-Ti3C2Tx-PEG) with a mild photothermal effect and multi-enzyme catalytic activity for synergistic tumor therapy. Ru single atoms anchored on the surface of MXene nanosheets not only facilitate multi-enzyme catalytic activity but also amplify the photothermal performance owing to the localized surface plasmon resonance effect. The Ru single atoms could decompose H2O2 into toxic hydroxyl radicals (•OH) in response to the tumor microenvironment (TME) for enzyme catalytic therapy, and the heat produced by the nanozyme under near-infrared laser excitation enhanced the •OH generation yield. Moreover, the nanozyme exhibited oxygen formation and glutathione depletion capability in cancer cells, thereby regulating the TME and accelerating the •OH levels. The in vitro and in vivo studies in this work confirm that the two-dimensional Ru single-atom-anchored MXene nanozyme has an extraordinary tumor growth inhibition effect, thus presenting a rational therapeutic strategy for tumor ablation through the synergistic effect of photothermal activity and heat-promoted enzymatic catalysis.

Ga@MXene-based flexible wearable biosensor for glucose monitoring in sweat

Most wearable biosensors struggle to balance flexibility and conductivity in their sensing interfaces. In this study, we propose a wearable sensor featuring a highly stretchable, three-dimensional conductive network structure based on liquid metal. The sensor interface utilizes a patterned Ga@MXene hydrogel system, where gallium (Ga) grafted onto MXene provides enhanced electrical conductivity and malleability. MXene provides excellent conductivity and a three-dimensional layered structure. Additionally, the chitosan (CS) hydrogel, with its superior water absorption and stretchability, allows the electrode to retain sweat and closely stick to the skin. The sensor demonstrates a low limit of detection (0.77 μM), high sensitivity (1.122 μA⋅μM⁻1⋅cm⁻2), and a broad detection range (10-1,000 μM), meeting the requirements for a wide range of applications. Notably, the sensor can also induce perspiration in the wearer. The three-dimensional porous structure of the Ga@MXene/CS biosensor ensures excellent conductivity and flexibility, making it suitable for a variety of applications.

Revisiting the Interface Dynamics of MXene/Rubber Elastomers: Multiscale Mechanistic Insights into Collaborative Bonding for Robust Self-Healing Sensors

Sophisticated flexible strain sensors based on MXene/rubber with self-healing capabilities are poised to transform future deformable electronics by restoring impaired performance after repeated deformation. Despite their potential, integrating excellent self-healing properties with superior mechanical strength in a single system remains a significant challenge due to simplistic interface architectures with weak bonds and limited understanding of MXene/rubber interface dynamics. To address this, a novel metal coordination bonding scheme has been developed, synergizing with dynamic hydrogen bonding to enhance interface bonding strength, enabling both outstanding mechanical and self-healing properties. Using in situ synchrotron radiation techniques, a multiscale investigation of MXene/rubber interface dynamics provides valuable insights, linking bonding strength to mechanical performance. These findings not only deepen our understanding of interface evolution in deformable electrodes but also offer a promising path for designing advanced self-healable strain sensors with superior mechanical properties.

Porous Carbon Nanoparticle Composite Paper Fiber with Laser-Induced Graphene Surface Microstructure for Pressure Sensing

In recent years, flexible pressure sensors have played an increasingly important role in human health monitoring. Inspired by traditional papermaking techniques, we have developed a highly flexible, low-cost, and ecofriendly flexible pressure sensor using shredded paper fibers as the substrate. By combining the properties of laser-induced graphene with the structure of paper fibers, we have improved the internal structure of pressure-sensitive paper and designed a conical surface microstructure, providing new insights into nanomaterial engineering. It features low resistance (424.44 Ω), low energy consumption of only 0.367 μW under a pressure of 1.96 kPa, high sensitivity (1.68 kPa-1), and a wide monitoring range (98 Pa-111.720 kPa). The pressure-sensitive paper with surface microstructure (MFTG) developed in this study has a total thickness comparable to A4 paper, is soft and bendable, can be cut into any shape like paper to fit the human body, and holds great potential for continuous monitoring of human activity status and physiological information.

Wearable Resistive-Type Stretchable Strain Sensors: Materials and Applications

The rapid advancement of wearable electronics over recent decades has led to the development of stretchable strain sensors, which are essential for accurately detecting and monitoring mechanical deformations. These sensors have widespread applications, including movement detection, structural health monitoring, and human-machine interfaces. Resistive-type sensors have gained significant attention due to their simple design, ease of fabrication, and adaptability to different materials. Their performance, evaluated by metrics like stretchability and sensitivity, is influenced by the choice of strain-sensitive materials. This review offers a comprehensive comparison and evaluation of different materials used in resistive strain sensors, including metal and semiconductor films, low-dimensional materials, intrinsically conductive polymers, and gels. The review also highlights the latest applications of resistive strain sensors in motion detection, healthcare monitoring, and human-machine interfaces by examining device physics and material characteristics. This comparative analysis aims to support the selection, application, and development of resistive strain sensors tailored to specific applications.

Designing Silk Biomaterials toward Better Future Healthcare: The Development and Application of Silk-Based Implantable Electronic Devices in Clinical Diagnosis and Therapy

Implantable medical electronic devices (IMEDs) have attracted great attention and shown versatility for solving clinical problems ranging from real-time monitoring of physiological/ pathological states to electrical stimulation therapy and from monitoring brain cell activity to deep brain stimulation. The ongoing challenge is to select appropriate materials in target device configuration for biomedical applications. Currently, silk-based biomaterials have been developed for the design of diagnostic and therapeutic electronic devices due to their excellent properties and abundant active sites in the structure. Herein, the aim is to summarize the structural characteristics, physicochemical properties, and bioactivities of natural silk biomaterials as well as their derived materials, with a particular focus on the silk-based implantable biomedical electronic devices, such as implantable devices for invasive brain-computer interfaces, neural recording, and in vivo electrostimulation. In addition, future opportunities and challenges are also envisioned, hoping to spark the interests of researchers in interdisciplinary fields such as biomaterials, clinical medicine, and electronics.

Exploring chiral and achiral properties of novel multilayer 3D polymers: synthesis and characterization

This study reports the novel synthesis of multilayered 3D polymers via the 1,3,5-position coupling of 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene with 1,8-dibronaphthalene, a previously unreported method. The resulting polymers exhibit both achiral and chiral characteristics, offering a unique platform for structural and functional exploration. Comprehensive characterization using gel permeation chromatography, UV-vis spectroscopy, fluorescence measurements, circular dichroism, and scanning electron microscopy revealed intriguing optical properties and morphological features, promoting potential applications in photonics, sensors, and materials science.

Ti3C2Tx MXene Composite with Much Improved Stability for Superior Humidity Sensors

MXenes have attracted tremendous attention in electromagnetic interference shielding, energy storage, and gas and humidity detections because of their ultralarge surface area and abundant functional groups. However, their poor stability against hydration and oxidation makes them challenging for long-term storage and applications. Herein, we proposed and demonstrated a Ti3C2Tx MXene composite-based humidity sensor, of which the stability is pronouncedly enhanced by introducing an O2 adsorption competitor of extracted bentonite (EB). All the results of TEM, XPS, and Raman spectroscopy show that the oxidation of the Ti3C2Tx MXene is significantly suppressed by the introduction of EB. Its excellent performance in humidity detection further confirms the effectiveness of EB in improving the stability. An ultrahigh response value of 6400% and an ultrafast response time of 1 s at 85% RH are observed, suggesting promising prospects for superior humidity detection of the Ti3C2Tx MXene composite. Furthermore, its feasibility for flexible humidity detection was also examined on a PET substrate, which exhibited high flexibility and excellent discrimination in speaking words.

Highly Elastic Spongelike Hydrogels for Impedance-Based Multimodal Sensing

Hydrogel-based sensors have been widely studied for perceiving the environment. However, the simplest type of resistive sensors still lacks sensitivity to localized strain and other extractable data. Enhancing their sensitivity and expanding their functionality to perceive multiple stimuli simultaneously are highly beneficial yet require optimal material design and proper testing methods. Herein, we report a highly elastic, sponge-like hydrogel and its derived multimodal iontronic sensor. By unidirectional freeze casting of poly(vinyl alcohol) (PVA) with electrospun cellulose nanofibers (CNF), a hierarchical structure with aligned PVA channels supported by interlaced CNF tangles is created. The structure ensures both efficient mass transport and good elasticity, enhancing reversible compressibility and ionic conductivity. Combining this sponge hydrogel with impedance-based measurement methods allows the development of multimodal sensors capable of detecting local strain, position, and material type of object-in-contact. Integrating these sensing capabilities, a two-dimensional small motion monitor, a 3D input interface, and a material identification gripper are demonstrated. This study provides a simple approach to versatile multimodal sensors.

Multifunctional pressure and humidity sensor modulated by electrostatic interactions and hydrogen bonds for wearable health monitoring

Breathing and urination, are vital physiological activities of the human body, continuous real-time monitoring of these physiological behaviors could offer timely feedback on an individual's health status. However, current monitoring techniques predominantly rely on cumbersome and intricate medical apparatuses, posing challenges in adapting to the diverse requirements of multi-scenario detection. Consequently, there is a growing interest in developing wearable devices capable of monitoring breathing and urination. In this work, we developed a multifunctional sensor integrating humidity and pressure sensing modes using a simple dip-coating process. By introducing sodium carboxymethyl cellulose and conductive polyaniline hybrid intercalation between MXene layers, a stable conductive network is established through hydrogen bonds and electrostatic interactions among materials. The overall electromechanical properties of the composites will be well improved. And, the effects of different conductive filler ratios and the number of dipping times on the construction of conductive networks are investigated. The multifunctional sensor exhibited improved sensing characteristics, including detecting pressures up to 532 kPa and a sensitivity of 19.58 kPa-1. Furthermore, it also demonstrates good humidity-sensing capabilities. Tests on volunteers demonstrated the potential in the detection of breathing and urination. In addition, the sensors are capable of transmitting Morse code. This interesting application will offer the possibility of normal communication for people with speech impairments. Given its utility and sustainability, the sensor has potential for applications in wearable health monitoring, intelligent life and telemedicine.

Cilia-Inspired Bionic Tactile E-Skin: Structure, Fabrication and Applications

The rapid advancement of tactile electronic skin (E-skin) has highlighted the effectiveness of incorporating bionic, force-sensitive microstructures in order to enhance sensing performance. Among these, cilia-like microstructures with high aspect ratios, whose inspiration is mammalian hair and the lateral line system of fish, have attracted significant attention for their unique ability to enable E-skin to detect weak signals, even in extreme conditions. Herein, this review critically examines recent progress in the development of cilia-inspired bionic tactile E-skin, with a focus on columnar, conical and filiform microstructures, as well as their fabrication strategies, including template-based and template-free methods. The relationship between sensing performance and fabrication approaches is thoroughly analyzed, offering a framework for optimizing sensitivity and resilience. We also explore the applications of these systems across various fields, such as medical diagnostics, motion detection, human-machine interfaces, dexterous robotics, near-field communication, and perceptual decoupling systems. Finally, we provide insights into the pathways toward industrializing cilia-inspired bionic tactile E-skin, aiming to drive innovation and unlock the technology's potential for future applications.

Fabricating a SFMA/BAChol/PAA/ZnCl2 Hydrogel with Excellent Versatile Comprehensive Properties and Stable Sensitive Freezing-Tolerant Conductivity for Wearable Sensors

Flexible wearable sensors have obtained tremendous interest in various fields and conductive hydrogels are a promising candidate. Nevertheless, the insufficient mechanical properties, the low electrical conductivity and sensitivity, and the limited functional properties prevent the development of hydrogels as wearable sensors. In this study, an SFMA/BAChol/PAA/ZnCl2 hydrogel was fabricated with high mechanical strength and versatile comprehensive properties. Specifically, the obtained hydrogel displayed excellent adhesion and mechanical stability, cryophylactic ability, stable sensitive freezing-tolerant conductivity, and feasible electrical conduction under a wide temperature range, demonstrating the high application potential as a flexible wearable sensor for movement behavior surveillance, even under harsh environments. Furthermore, the mechanical strength of the hydrogel could easily be regulated by varying the copolymer content. The molecular mechanisms of the hydrogel formation and the reversible adhesion during the wet-dry transition were proposed. The non-covalent interactions, including the electrostatic interaction, hydrogen bond interaction and hydrophobic association, and coordination interaction, were dynamically presented in the hydrogel network and hence supported the versatile comprehensive properties of the hydrogel. This study provides a strategy for designing novel hydrogels to promote the development of flexible sensors with stable sensitive freezing-tolerant conductivity.

Development of a Dual-Epitope Nanobody-Based Immunosensor with MXenes@CNTs@AuNPs for Ultrasensitive Detection of Rotavirus

Immunoassays have become essential tools for detecting infectious viruses. However, traditional monoclonal antibody-dependent immunoassays are costly, fragile, and unstable, especially in complex media. To overcome these challenges, we have developed cost-effective, robust, and high-affinity nanobodies as alternatives to monoclonal antibodies for rapid detection applications. We engineered dual-epitope nanobody (NB) pairs and incorporated them into a sandwich immunosensor design to detect transmitted rotaviruses in rectal swabs and wastewater samples. To further enhance sensitivity, we synthesized an advanced two-dimensional material, MXenes@CNTs@AuNPs, which offers an extensive specific surface area that supports the enrichment and immobilization of NBs. This integration with catalase-modified magnetic probes facilitates signal generation. Subsequently, our sensor achieved a detection limit of 0.0207 pg/mL for the rotavirus VP6 antigen, significantly outperforming commercial antigen kits with a sensitivity enhancement of 3.77 × 105-fold. The exceptional sensor performance extended to specificity, repeatability, stability, and accuracy across various sample types, establishing it as a promising tool for rotavirus detection. This research outlines a viable strategy for creating a robust and ultrasensitive analytical nanoprobe, thereby addressing the critical need for efficient and reliable viral detection methods in various environments.

Recent advances in MXene-based composites for piezoelectric sensors

Piezoelectric sensors are crucial in medical, industrial, and consumer electronics applications, yet their performance and sensitivity often fall short due to the limitations in current piezoelectric materials. To address these deficiencies, significant research has been directed towards developing composite materials that enhance piezoelectric properties by integrating piezoelectric materials with various fillers. MXenes, a novel class of 2D transition metal carbides/nitrides, exhibit remarkable properties such as high electrical conductivity, mechanical strength, and chemical stability. These characteristics, along with a high surface area and hydrophilicity, make MXenes an ideal additive for preparing piezoelectric composites with improved properties. Despite existing reviews on MXenes in sensor applications, only a few have systematically explored their role in piezoelectric sensors. This review provides a comprehensive analysis of MXene-based piezoelectric sensors, examining the impact of different composites on piezoelectric properties, synthesis methods, structural designs, and application areas. While promising, challenges such as scalability, reproducibility, and environmental stability must be addressed to fully realize the potential of MXene-based composites. This comprehensive analysis highlights the advancements, opportunities for further development, and the transformative potential of MXenes in the next generation of high-performance, multifunctional piezoelectric sensors.

Flexible Pressure, Humidity, and Temperature Sensors for Human Health Monitoring

The rapid advancements in artificial intelligence, micro-nano manufacturing, and flexible electronics technology have unleashed unprecedented innovation and opportunities for applying flexible sensors in healthcare, wearable devices, and human-computer interaction. The human body's tactile perception involves physical parameters such as pressure, temperature, and humidity, all of which play an essential role in maintaining human health. Inspired by the sensory function of human skin, many bionic sensors have been developed to simulate human skin's perception to various stimuli and are widely applied in health monitoring. Given the urgent requirements for sensing performance and integration of flexible sensors in the field of wearable devices and health monitoring, here is a timely overview of recent advances in pressure, humidity, temperature, and multi-functional sensors for human health monitoring. It covers the fundamental components of flexible sensors and categorizes them based on different response mechanisms, including resistive, capacitive, voltage, and other types. Specifically, the application of these flexible tactile sensors in the area of human health monitoring is highlighted. Based on this, an extended overview of recent advances in dual/triple-mode flexible sensors integrating pressure, humidity, and temperature tactile sensing is presented. Finally, the challenges and opportunities of flexible sensors are discussed.

Bioinspired Ultrasensitive Flexible Strain Sensors for Real-Time Wireless Detection of Liquid Leakage

Liquid leakage of pipeline networks not only results in considerable resource wastage but also leads to environmental pollution and ecological imbalance. In response to this global issue, a bioinspired superhydrophobic thermoplastic polyurethane/carbon nanotubes/graphene nanosheets flexible strain sensor (TCGS) has been developed using a combination of micro-extrusion compression molding and surface modification for real-time wireless detection of liquid leakage. The TCGS utilizes the synergistic effects of Archimedean spiral crack arrays and micropores, which are inspired by the remarkable sensory capabilities of scorpions. This design achieves a sensitivity of 218.13 at a strain of 2%, which is an increase of 4300%. Additionally, it demonstrates exceptional durability by withstanding over 5000 usage cycles. The robust superhydrophobicity of the TCGS significantly enhances sensitivity and stability in detecting small-scale liquid leakage, enabling precise monitoring of liquid leakage across a wide range of sizes, velocities, and compositions while issuing prompt alerts. This provides critical early warnings for both industrial pipelines and potential liquid leakage scenarios in everyday life. The development and utilization of bioinspired ultrasensitive flexible strain sensors offer an innovative and effective solution for the early wireless detection of liquid leakage.

Highly Flexible and Compressible 3D Interconnected Graphene Foam for Sensitive Pressure Detection

A flexible pressure sensor, capable of effectively detecting forces exerted on soft or deformable surfaces, has demonstrated broad application in diverse fields, including human motion tracking, health monitoring, electronic skin, and artificial intelligence systems. However, the design of convenient sensors with high sensitivity and excellent stability is still a great challenge. Herein, we present a multi-scale 3D graphene pressure sensor composed of two types of 3D graphene foam. The sensor exhibits a high sensitivity of 0.42 kPa-1 within the low-pressure range of 0-390 Pa and 0.012 kPa-1 within the higher-pressure range of 0.4 to 42 kPa, a rapid response time of 62 ms, and exceptional repeatability and stability exceeding 10,000 cycles. These characteristics empower the sensor to realize the sensation of a drop of water, the speed of airflow, and human movements.

Hybrid biological macromolecules spider-silk fibroin optical patches for efficient wound healing

Efforts toward developing wound dressings that effectively monitor healing have become at the forefront of the field of wound healing. However, monofunctionality, biotoxicity, and passive therapy constrain wound patches. Herein, a hypoallergenic wound patch integrating moisture monitoring, motion sensing and electrical stimulation for wound healing is presented. Microstructured patches composed of silk proteins and spider silk proteins (MIS) fused together were structurally transformed and crosslinked by spin-coating a mixture of silk proteins (SFs) and spider silk proteins (SPs) with water-soluble polyurethane (PU), creating MIS patches with microstructures by hot embossing. This is attributed to stable SF-SP hydrogen bonding, which provides an extremely rapid response to humidity and endows the patch with superior motion sensing tensile properties. Notably, β-folding and α-helical structures confer SP toughness and strength, producing electrical charges under electrical stimulation occurring with motor stretching, thereby enabling electrical stimulation for quicker wound healing. Specifically, The MIS is sensitive to changes in humidity, which is reflected in changes in the colour of its surface patches. Also it enhances the strength of the electrical stimulation signal more effectively as the thickness of the film layer increases. These characteristics indicate the high potential of the MIS for wound management.

Intelligent Song Recognition via a Hollow-Microstructure-Based, Ultrasensitive Artificial Eardrum

Artificial ears with intelligence, which can sensitively detect sound-a variant of pressure-and generate consciousness and logical decision-making abilities, hold great promise to transform life. However, despite the emerging flexible sensors for sound detection, most success is limited to very simple phonemes, such as a couple of letters or words, probably due to the lack of device sensitivity and capability. Herein, the construction of ultrasensitive artificial eardrums enabling intelligent song recognition is reported. This strategy employs novel geometric engineering of sensing units in the soft microstructure array (to significantly reduce effective modulus) along with complex song recognition exploration leveraging machine learning algorithms. Unprecedented pressure sensitivity (6.9 × 103 kPa-1) is demonstrated in a sensor with a hollow pyramid architecture with porous slants. The integrated device exhibits unparalleled (exceeding by 1-2 orders of magnitude compared with reported benchmark samples) sound detection sensitivity, and can accurately identify 100% (for training set) and 97.7% (for test set) of a database of the segments from 77 songs varying in language, style, and singer. Overall, the results highlight the outstanding performance of the hollow-microstructure-based sensor, indicating its potential applications in human-machine interaction and wearable acoustical technologies.

Releasing Au Electrons to Mo Site for Weakened Mo─H Bond of Mo2C MXene Cocatalyst Toward Improved Photocatalytic H2 Production

Mo2C MXene (Mo2CTx) is one of the most promising noble-metal-free cocatalysts for photocatalytic H2 production because of its excellent electron transport capacity and abundant Mo sites. However, Mo2CTx typically exhibits a strong Mo─Hads bond, resulting in that the produced H2 difficultly desorbs from the Mo surface for the limited activity. To effectively weaken the Mo─Hads bond, in this paper, a regulation strategy of electron donor Au releasing electrons to the d-orbitals of Mo sites in Mo2CTx is proposed. Herein, the Mo2CTx-Au/CdS photocatalysts are prepared through a two-step process, including the initial loading of Au nanoparticles on the Mo2CTx surface and the subsequent in situ growth of CdS onto the Mo2CTx-Au surface. Photocatalytic measurements indicate that the maximal H2-production rate of Mo2CTx-Au/CdS reaches up to 2799.44 µmol g-1 h-1, which is 30.99 and 3.60 times higher than that of CdS and Mo2CTx/CdS, respectively. Experimental and theoretical data corroborate that metallic Au can transfer free electrons to Mo2CTx to generate electron-enriched Moδ- sites, thus causing the increased antibonding-orbital occupancy state and the weakened Mo─Hads bond for the boosted H2-production efficiency. This research provides a promising approach for designing Mo2CTx-based cocatalysts by regulating the antibonding-orbital occupancy of Mo sites for improved photocatalytic performance.

A Flexible Smart Healthcare Platform Conjugated with Artificial Epidermis Assembled by Three-Dimensionally Conductive MOF Network for Gas and Pressure Sensing

The rising flexible and intelligent electronics greatly facilitate the noninvasive and timely tracking of physiological information in telemedicine healthcare. Meticulously building bionic-sensitive moieties is vital for designing efficient electronic skin with advanced cognitive functionalities to pluralistically capture external stimuli. However, realistic mimesis, both in the skin's three-dimensional interlocked hierarchical structures and synchronous encoding multistimuli information capacities, remains a challenging yet vital need for simplifying the design of flexible logic circuits. Herein, we construct an artificial epidermal device by in situ growing Cu3(HHTP)2 particles onto the hollow spherical Ti3C2Tx surface, aiming to concurrently emulate the spinous and granular layers of the skin's epidermis. The bionic Ti3C2Tx@Cu3(HHTP)2 exhibits independent NO2 and pressure response, as well as novel functionalities such as acoustic signature perception and Morse code-encrypted message communication. Ultimately, a wearable alarming system with a mobile application terminal is self-developed by integrating the bimodular senor into flexible printed circuits. This system can assess risk factors related with asthmatic, such as stimulation of external NO2 gas, abnormal expiratory behavior and exertion degrees of fingers, achieving a recognition accuracy of 97.6% as assisted by a machine learning algorithm. Our work provides a feasible routine to develop intelligent multifunctional healthcare equipment for burgeoning transformative telemedicine diagnosis.

Bioinspired Photoluminescent "Spider Web" as Ultrafast and Ultrasensitive Airflow-Acoustic Bimodal Sensor for Human-Computer Interaction and Intelligent Recognition

Nature provides massive biomimetic design inspiration for constructing structural materials with desired performances. Spider webs can perceive vibrations generated by airflow and acoustic waves from prey and transfer the corresponding information to spiders. Herein, by mimicking the perception capability and structure of a spider web, an ultrafast and ultrasensitive airflow-acoustic bimodal sensor (HOF-TCPB@SF) is developed based on the postfunctionalization of hydrogen-bonded organic framework (HOF-TCPB) on silk film (SF) through hydrogen bonds. The "spider web-like" HOF-TCPB@SF possesses light weight and high elasticity, endowing this airflow sensor with superior properties including an ultralow detection limit (DL, 0.0076 m s-1), and excellent repeatability (480 cycles). As an acoustic sensor, HOF-TCPB@SF exhibits ultrahigh sensitivity (105140.77 cps Pa-1 cm-2) and ultralow DL (0.2980 dB), with the greatest response frequency of 375 Hz and the ability to identify multiple sounds. Moreover, both airflow and acoustic sensing processes show an ultrafast response speed (40 ms) and multiangle recognition response (0-180°). The perception mechanisms of airflow and acoustic stimuli are analyzed through finite element simulation. This bimodal sensor also achieves real-time airflow monitoring, speech recognition, and airflow-acoustic interoperability based on human-computer interaction, which holds great promise for applications in health care, tunnel engineering, weather forecasting, and intelligent textiles.

Microstructured CNTs/Cellulose Aerogel for a Highly Sensitive Pressure Sensor

Flexible sensors have been applied in human health monitoring and biomedical research, but producing high-performance piezoresistive sensors at low cost is still challenging. To address these shortcomings, we proposed a microstructured carbon nanotube (CNT)/cellulose aerogel-based pressure sensor. The sensor consists of three parts, i.e., cellulose/poly(vinyl alcohol)/CNT aerogel-based sensing layer and top and bottom thermoplastic polyurethane elastomer (TPU)/silver nanowire (Ag NW) nanofiber electrode. The aerogel is fabricated using a simple freeze-drying method and an easy electrospinning method to obtain the nanofiber-based electrode. Two TPU/Ag NW nanofiber electrodes sandwiched the aerogel with a microstructure in the middle. Benefiting from the microcone and micropore structures on the nanofiber electrode, the assembled sensors show a high sensitivity of 66.4 kPa-1, a significant detection boundary of 50 kPa, and an excellent response speed of 10 ms. The high sensing performance enables the sensor to monitor physiological signals, Morse code interactions, and gesture recognition. With the help of machine learning, the success rate of gesture recognition is as high as 98.8%. The preparation of this pressure sensor based on an aerogel shows excellent health and environmental monitoring potential as an artificial skin.

Flexible Tactile Sensors with Gradient Conformal Dome Structures

The trade-off between high sensitivity and wide detection range remains a challenge for flexible capacitive pressure sensors. Gradient structure can provide continuous deformation and lead to a wide sensing range. However, it simultaneously augments the distance between two electrodes, which diminishes the variation in the relative distance and results in a decreased sensitivity. Herein, a conformal design is introduced into the gradient structure to construct a flexible capacitive pressure sensor. The gradient conformal dome structure is fabricated by a simple reverse dome adsorption process. Taking advantage of the progressive deformation behavior of the gradient dielectric, and the significant improvement of relative distance variation between two electrodes from the conformal design, the sensor achieves a sensitivity of 0.214 kPa-1 in an ultrabroad linear range up to 200 kPa. It maintains high-pressure resolution under the preload of 10 and 100 kPa. Benefiting from the rapid response and excellent repeatability, the sensor can be used for physiological monitor and human motion detection, including arterial pulse, joint bending, and motion state. The gradient conformal design strategy may pave a promising avenue to develop pressure sensors with high sensitivity and wide linear range.

Flexible Ti3C2Tx-Polyurethane Electrodes for Versatile Wearable Applications

With the development of science and technology, wearable electronics are increasingly widely used in medical, environmental monitoring, and other fields. Thus, the demand for flexible electrodes is increasing. The two-dimensional material Ti3C2Tx has attracted much attention in the manufacture of flexible electrodes due to its excellent mechanical and electrical properties. However, the brittleness of pure Ti3C2Tx films has become a major obstacle for their use as flexible electrodes in wearable devices. Therefore, solving the brittleness problem of flexible electrodes based on Ti3C2Tx while maintaining the excellent performance of Ti3C2Tx has become an urgent problem. To solve this problem, Ti3C2Tx was compounded with waterborne polyurethane (WPU), and a Ti3C2Tx-WPU composite film with a hierarchical structure was constructed by evaporation-assisted self-assembly. The Ti3C2Tx-WPU composite film not only retains the excellent electrical conductivity of Ti3C2Tx (100 S m-1) but also has flexibility (20 MJ m-3). Furthermore, the Ti3C2Tx-WPU composite film is applied to functional devices such as contact pressure sensors and non-contact proximity sensors. Finally, the Ti3C2Tx-WPU composite film wearable device demonstrates its practical application potential in the field of wearable devices.

Realization of hydrogenation-induced superconductivity in two-dimensional Ti2N MXene

Two-dimensional (2D) MXene superconductors have been currently attracting considerable interest due to their unique electronic properties and diverse applicability. Utilizing first-principles computational methods, we have designed two distinct configurations of hydrogenated 2D Ti2N MXene materials, namely Ti2NH2 and Ti2NH4, and have conducted an exhaustive analysis of their structural stability, electronic characteristics, and superconductivity. Hydrogenation endows monolayer Ti2N with inherent metallic characteristics, as evidenced by an elevated density of states (DOS) at the Fermi level (Ef). Notably, Ti2NH4 exhibits a superconducting critical temperature (Tc) of 15.8 K, which is predominantly ascribed to the electronic contributions stemming from the Ti 3d orbitals. Analysis of phonon dispersion underscores the pivotal role that diverse lattice vibrational modes play in electron-phonon coupling (EPC), particularly the significance of low-frequency vibrations for facilitating electron pairing and the emergence of superconductivity. Furthermore, strain engineering can effectively modulate the superconducting properties of Ti2NH4, with a 2% tensile strain enhancing the EPC strength (λ) to 0.857 and increasing Tc to 18.7 K. This research elucidates the superconducting mechanisms of hydrogenated Ti2N structures, offering valuable insights for the development of novel 2D superconducting materials.

MXenes for Wearable Physical Sensors toward Smart Healthcare

The gradual rise of personal healthcare awareness is accelerating the deployment of wearable sensors, whose ability of acquiring physiological vital signs depends on sensing materials. MXenes have distinct chemical and physical superiorities over other 2D nanomaterials for wearable sensors. This review presents a comprehensive summary of the latest advancements in MXenes-based materials for wearable physical sensors. It begins with an introduction to special structural features of MXenes for sensing performance, followed by an in-depth exploration of versatile functionalities. A detailed description of different sensing mechanisms is also included to illustrate the contribution of MXenes to the sensing performance and its improvement. In addition, the real-world applications of MXenes-based physical sensors for monitoring different physiological signs are included as well. The remaining challenges of MXenes-based materials for wearable physical sensors and their promising opportunities are finally narrated, in conjunction with a prospective for future development.

Electronic Skin for Health Monitoring Systems: Properties, Functions, and Applications

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

Flexible Nanofiber Pressure Sensors with Hydrophobic Properties for Wearable Electronics

In recent years, flexible pressure sensors have received considerable attention for their potential applications in health monitoring and human-machine interfaces. However, the development of flexible pressure sensors with excellent sensitivity performance and a variety of advantageous characteristics remains a significant challenge. In this paper, a high-performance flexible piezoresistive pressure sensor, BC/ZnO, is developed with a sensitive element consisting of bacterial cellulose (BC) nanofibrous aerogel modified by ZnO nanorods. The BC/ZnO pressure sensor exhibits excellent mechanical and hydrophobic properties, as well as a high sensitivity of -15.93 kPa-1 and a wide range of detection pressure (0.3-20 kPa), fast response (300 ms), and good cyclic durability (>1000). Furthermore, the sensor exhibits excellent sensing performance in real-time monitoring of a wide range of human behaviors, including mass movements and subtle physiological signals.