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Neurofeedback training based on brain rhythm is appealing for both cognitive neuroscience and disorder treatment. However, electrodes that can integrate dual functions of recording and feedback without signal compromise still lack. Herein, an anisotropic cellulose carbon sponge (CCS) electrode by tailoring conductivity through the temperature that has the dual ability to record electrophysiological signals and sense pressures as feedback is developed. The electrode is fabricated via a gradient temperature annealing on CCS, which involves lower (300 °C) and higher (1000 °C) temperature treatments, namely CCS‐LT and CCS‐HT. CCS‐LT exhibits perpendicular resilience to the alignment direction of CCS, and CCS‐HT possesses lower sheet resistance (≈13 Ω sq−1) parallel to the alignment direction. As a pressure sensor, CCS‐LT can achieve excellent sensitivity (1.04 kPa−1), fast response time (27 ms), and reliable stability for 1000 cycles. CCS‐HT can serve as skin electrodes for electrophysiological sensing. The anisotropic functionality of annealed CCS allows it to be used in one sensing and regulation closed‐loop system driven by nerves, achieving accurate acquisition of human brain rhythm and machine movement information simultaneously. This not only helps rapid tracking of brain activity but also facilitates feedback regulation to enhance human brain function, having great potential applications in neurofeedback and disease rehabilitation. [ABSTRACT FROM AUTHOR]

To realize flexible pressure sensors with high sensitivity, surface‐textured soft films have often been adopted and the contact area can vary significantly depending on the applied pressure. However, the contact area modulation realized in such a way is subject to a limited dynamic range, and its infinitesimal zero‐pressure contact area raises concerns regarding durability. Herein, a flexible pressure sensor made of a texturing‐free piezocapacitive layer based on ion‐polymer networks is proposed. In this scheme, ion infiltration leads to electrical‐double‐layer modulation that gradually varies over a wide range of applied pressures. The proposed flexible pressure sensors with the optimal ion concentration are shown to exhibit both excellent mechanical durability and linear responses with high sensitivity over a wide pressure range up to 1 MPa. With the simple fabrication route, high performance, and reliability, the proposed approach may open up a new avenue for skin‐like pressure sensors ideal for many emerging applications. [ABSTRACT FROM AUTHOR]

In this work, a capacitive flexible tactile sensor based on the composite dielectric layer with a C-type symmetrical structure is proposed to improve the sensing performance through the introduction of a precise structure. Combined with simulations and experiments, the influence of the structural characteristics of the tactile sensor on its sensitivity is investigated, the correlation between the signal output of the sensor and the loading pressure is shown for different structural parameter designs, and the structure of the sensor is optimized. Data results display that the tactile sensor proposed in this work exhibits a lower detection limit (8.6 Pa) and an ultra-wide linear sensing range (8.6–500 kPa). In addition, from the 55 ms response time of the sensor and 2000 cycles of experiments, it can be concluded that the sensor possesses good repeatability and durability, and can achieve more accurate measurement results in motion detection, soft robots, and electronic skin. [ABSTRACT FROM AUTHOR]

Pressure sensors show significant potential applications in health monitoring, bio-sensing, electronic skin, and tactile perception. Consequently, tremendous research interest has been devoted to the development of high-performance pressure sensors. In this paper, recent progress on the polymer composite-based flexible pressure sensor is reviewed. The parameters of pressure sensors, including sensitivity, linear response range, detection limit, response speed, and reliability, are first introduced. Secondly, representative types of pressure sensors and relevant working principles are introduced and discussed. After that, the applications in human physiology monitoring, health monitoring, artificial skin, and self-powered smart system are listed and discussed in detail. Finally, the remaining challenges and outlook of polymer composite-based flexible sensors are summarized at the end of this review paper. This work should have some impact on the development of high-performance flexible pressure sensors. [ABSTRACT FROM AUTHOR]

Flexible sensors are the essential foundations of pressure sensing, microcomputer sensing systems, and wearable devices. The flexible tactile sensor can sense stimuli by converting external forces into electrical signals. The electrical signals are transmitted to a computer processing system for analysis, realizing real-time health monitoring and human motion detection. According to the working mechanism, tactile sensors are mainly divided into four types—piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. Conventional silicon-based tactile sensors are often inadequate for flexible electronics due to their limited mechanical flexibility. In comparison, polymeric nanocomposites are flexible and stretchable, which makes them excellent candidates for flexible and wearable tactile sensors. Among the promising polymers, conjugated polymers (CPs), due to their unique chemical structures and electronic properties that contribute to their high electrical and mechanical conductivity, show great potential for flexible sensors and wearable devices. In this paper, we first introduce the parameters of pressure sensors. Then, we describe the operating principles of resistive, capacitive, piezoelectric, and triboelectric sensors, and review the pressure sensors based on conjugated polymer nanocomposites that were reported in recent years. After that, we introduce the performance characteristics of flexible sensors, regarding their applications in healthcare, human motion monitoring, electronic skin, wearable devices, and artificial intelligence. In addition, we summarize and compare the performances of conjugated polymer nanocomposite-based pressure sensors that were reported in recent years. Finally, we summarize the challenges and future directions of conjugated polymer nanocomposite-based sensors. [ABSTRACT FROM AUTHOR]

Silicone elastomer composites with piezoelectric properties, conferred by incorporated polyimide copolymers, with pressure sensors similar to human skin and kinetic energy harvester capabilities, were developed as thin film (<100 micron thick) layered architecture. They are based on polymer materials which can be produced in industrial amounts and are scalable for large areas (m2). The piezoelectric properties of the tested materials were determined using a dynamic mode of piezoelectric force microscopy. These composite materials bring together polydimethylsiloxane polymers with customized poly(siloxane-imide) copolymers (2–20 wt% relative to siloxanes), with siloxane segments inserted into the structure to ensure the compatibility of the components. The morphology of the materials as free-standing films was studied by SEM and AFM, revealing separated phases for higher polyimide concentration (10, 20 wt%). The composites show dielectric behavior with a low loss (<10−1) and a relative permittivity superior (3–4) to pure siloxane within a 0.1–106 Hz range. The composite in the form of a thin film can generate up to 750 mV under contact with a 30 g steel ball dropped from 10 cm high. This capability to convert a pressure signal into a direct current for the tested device has potential for applications in self-powered sensors and kinetic energy-harvesting applications. Furthermore, the materials preserve the known electromechanical properties of pure polysiloxane, with lateral strain actuation values of up to 6.2% at 28.9 V/μm. [ABSTRACT FROM AUTHOR]

Flexible electronic technology is one of the research hotspots, and numerous wearable devices have been widely used in our daily life. As an important part of wearable devices, flexible sensors can effectively detect various stimuli related to specific environments or biological species, having a very bright development prospect. Therefore, there has been lots of studies devoted to developing high-performance flexible pressure sensors. In addition to developing a variety of materials with excellent performances, the microstructure designs of materials can also effectively improve the performances of sensors, which has brought new ideas to scientists and attracted their attention increasingly. This paper will summarize the flexible pressure sensors based on material microstructure designs in recent years. The paper will mainly discuss the processing methods and characteristics of various sensors with different microstructures, and compare the advantages, disadvantages, and application scenarios of them. At the same time, the main application fields of flexible pressure sensors based on microstructure designs will be listed, and their future development and challenges will be discussed. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors are essential components for wearable smart devices and intelligent systems. Significant progress has been made in this area, reporting on excellent sensor performance and fascinating sensor functionalities. Nevertheless, geometrical and morphological engineering of pressure sensors is usually neglected, which, however, is significant for practical application. Here, we present a digitized manufacturing methodology to construct a new class of iontronic pressure sensors with optionally defined configurations and widely modulated performance. These pressure sensors are composed of self-defined electrode patterns prepared by a screen printing method and highly tunable pressure-sensitive microstructures fabricated using 3D printed templates. Importantly, the iontronic pressure sensors employ an iontronic capacitive sensing mechanism based on mechanically regulating the electrical double layer at the electrolyte/electrode interfaces. The resultant pressure sensors exhibit high sensitivity (58 kPa−1), fast response/recovery time (45 ms/75 ms), low detectability (6.64 Pa), and good repeatability (2000 cycles). Moreover, our pressure sensors show remarkable tunability and adaptability in device configuration and performance, which is challenging to achieve via conventional manufacturing processes. The promising applications of these iontronic pressure sensors in monitoring various human physiological activities, fabricating flexible electronic skin, and resolving the force variation during manipulation of an object with a robotic hand are successfully demonstrated. [ABSTRACT FROM AUTHOR]

Electronic skins (e‐skins) are a promising design paradigm for health care systems and human–machine interactions. Piezoresistive sensors made with simple structures, high sensitivity, mass production methods, light weight, and comfort for long‐term wearing and physiological signal monitoring remain a challenge and are urgently desirable. Here, a breathable and lightweight all‐nanofiber piezoresistive (ANFP) sensor is presented, which is composed of three layers of electrospun nanofibers (NFs). A specific interpenetrating network of conductive polyvinylpyrrolidone NFs coated by polypyrrole (PVP@PPy) and insulating polyacrylonitrile NFs is constructed by controlling the vapor growth position of PPy to enhance the sensitivity. The ANFP sensor can achieve the real‐time monitoring of multiple parts of physiological signals, and a wireless detection system is designed for the online monitoring of human pulses. The NF network endows excellent breathability and heat dissipation to the ANFP sensors during practical application, which ensures comfort and device stability during long‐term wearing. Finally, a pressure sensing array with 5 × 5 pixels is fabricated to demonstrate the potential applications in spatial pressure detection. This work provides a viable strategy to improve the wearability of e‐skins, which can promote health care and human–machine interaction applications. [ABSTRACT FROM AUTHOR]

[Display omitted] Applying a multi-modal sensing algorithm to a skin-like dual-channel self-powered sensor, which accurately detects real-time and continuous changes in pressure on the skin in response to variations in finger-applied force, while mitigating errors induced by temperature fluctuations. • A multimodal sensing algorithm compensating errors induced by temperature fluctuations. • Oxidation-stable metal-elastomer thermoelectric composite with a high pressure-sensitivity. • A self-powered sensor accurately detecting real-time continuous pressure changes. In the rapidly evolving field of electronic skins (e-skins), the development of self-powered sensors has emerged as a promising solution to providing continuous and reliable power sources for embedded sensors. This study introduces a novel approach that incorporates spike-shaped nickel (Ni) microparticles into a styrene-ethylene-butylene-styrene (SEBS) matrix, resulting in a thermoelectric material that functions as both an energy harvester and a pressure sensor, and a multimodal sensing algorithm designed to mitigate pressure sensing errors arising from temperature fluctuations in the thermoelectric self-powered pressure sensor. The Ni-SEBS composite, with a sensing mechanism that identifies changes in the Ni particle percolation state induced by compressive strain, exhibited a high sensitivity of 0.6234 kPa−1. Based on this composite, a dual-channel self-powered sensor was fabricated using the proposed algorithm and attached to the skin; the sensor successfully detected various forms of external pressure applied to the skin without errors due to temperature changes. [ABSTRACT FROM AUTHOR]

Wearable piezoresistive sensors are being developed as electronic skins (E‐skin) for broad applications in human physiological monitoring and soft robotics. Tactile sensors with sufficient sensitivities, durability, and large dynamic ranges are required to replicate this critical component of the somatosensory system. Multiple micro/nanostructures, materials, and sensing modalities have been reported to address this need. However, a trade‐off arises between device performance and device complexity. Inspired by the microstructure of the spinosum at the dermo epidermal junction in skin, a low‐cost, scalable, and high‐performance piezoresistive sensor is developed with high sensitivity (0.144 kPa‐1), extensive sensing range (0.1–15 kPa), fast response time (less than 150 ms), and excellent long‐term stability (over 1000 cycles). Furthermore, the piezoresistive functionality of the device is realized via a flexible transparent electrode (FTE) using a highly stable reduced graphene oxide self‐wrapped copper nanowire network. The developed nanowire‐based spinosum microstructured FTEs are amenable to wearable electronics applications. [ABSTRACT FROM AUTHOR]

In the article "Gradual Electrical-Double-Layer Modulation in Ion-Polymer Networks for Flexible Pressure Sensors with Wide Dynamic Range," Hanul Moon, Seunghyup Yoo, and their colleagues propose a method for creating flexible pressure sensors with high sensitivity over a wide range of pressures. The sensors utilize a porous polymer network filled with ionic gels to enable gradual electrical-double-layer modulation. These sensors have potential applications in various fields, from artificial skins to robotics and underwater environments. [Extracted from the article]

[Display omitted] • Integration of two distinctly sized 2D nanosheets forms a synergistic dual 3D network. • The synergistic effect of MXOH and hBN boosts electrical conductivity and network stability. • The modified hydrogel showed mechanical and electrical self-healing properties. • It showed a linear response (0–80 kPa) in pressure sensing with minimal hysteresis. • It is employed in wearables, e.g., touchscreens and thread-based motion sensors. Next-generation wearable electronic devices rely on electronic skin for its high flexibility, wearability, and ability to monitor vital health signs. Despite these advantages, developing flexible strain sensors for full-range human activity detection remains challenging. A solution involves thread-based motion sensors seamlessly integrated into clothing. This study employs a synergistic dual three-dimensional network using hydroxyl-functionalized MXene (MXOH) and hexagonal boron nitride (hBN) to modify poly(vinyl alcohol) (PVA) hydrogels, showcasing promising advancements in wearable technology. The hydrogel, incorporating MXOH with its larger lateral size and hBN with its smaller lateral size, forms a robust 3D network that reinforces the percolation network of MXOH nanosheets. This strategic combination ensures stability in the conductive pathway, minimizing electrical hysteresis during mechanical stress. The completion of the 3D network in PVA, facilitated by hBN, significantly enhances electrical conductivity due to the ion conduction properties of hBN. Moreover, the incorporation of non-conductive hBN nanosheets amplifies overall conductivity compared to MXOH alone, contributing to network stability. Rheological tests demonstrate the pronounced impact of increasing hBN weight percentage on the storage modulus, indicating the formation of a 3D network upon percolation. Additionally, MXOH and hBN exhibit self-healing characteristics through hydrogen bonding with the PVA chain, with hBN displaying higher mobility and faster self-healing compared to MXOH. These hydrogel-based flexible sensors exhibit mechanical stability and responsiveness across a wide pressure range (0 to 80 kPa) and find versatile applications in touch screens, thread-based motion sensors, and wearable electronics, promising transformative advances in handwriting-to-digital translation and smart textile technologies. [ABSTRACT FROM AUTHOR]

Artificial hydrogel electronic skin (E-skin) sensing systems have received considerable attention due to their ability in providing tactile perception. Recent advancements in hydrogel E-skin have allowed for simultaneous sensing of touch position and pressure through construction of sensor arrays. However, the fabrication process is complex, and the sensing resolution is limited by the size and number of array cells. Here, we report a multi-modal sensory E-skin based on a polyvinyl alcohol (PVA) hydrogel embedded with carbon nano-materials, which can recognize touch position and pressure simultaneously without constructing arrays. Combining the advantages of high electron transfer efficiency of 1D nanotube and 2D graphene nanosheet, the 3D hierarchical cross-linked polydopamine (PDA) modified reduced graphene oxide (rGO)/carboxylic multiwalled carbon nanotube (MWCNT-COOH) composites were proposed as a conductive filler, which was added by nano-doping to hydrogel substrate to gain an elastic modulus and stretchability of the hydrogel similar to that of human skin. Meanwhile, a surface-capacitive touch (SCT) system and piezoresistive technology were adopted to sense touch position and pressure due to the stability of conductive networks and the piezoresistive properties of carbon nanomaterials. Our E-skin device demonstrates superior sensing performance and provides a new direction for designing novel E-skin sensor devices. In order to bring the perception of E-skin closer to that of human skin, an integral E-skin achieves simultaneous recognition of touch position and pressure without constructing pressure sensor array. The mussel-inspired polydopamine (PDA) materials "bond" reduced graphene oxide (rGO) and carboxylic multiwalled carbon nanotube (MWCNT-COOH) together to form a stable conductive network. Surface-capacitive touch (SCT) system and piezoresistive technology were adopted to sense touch position and pressure. The application prospects of this flexible E-skin have well been validated in the fields of smart prosthetics and human-computer interaction electronics. [Display omitted] • An integral E-skin achieves simultaneous recognition of touch position and pressure to bring the perception of the E-skin closer to that of human skin. • The 3D hierarchical cross-linked of conductive filler provides the E-skin with a stable conductive network. • The mechanical properties of the hydrogel are tuned by nano-doping. [ABSTRACT FROM AUTHOR]

[Display omitted] The bionic application of electronic skin (e-skin) requires a high resolution close to that of human skin, while its long-term attachment to human body or robotic skin requires a porous structure that is air permeable and enables hair growth. To simultaneously meet the requirements of high resolution and porous structure, as well as improve the sensing performance, we propose a fully 3D printed e-skin with high-resolution and air permeable porous structure. The flexible substrate and electrodes are 3D printed by a direct ink writing extrusion printer. The sensitive material is 3D printed by a self-made low-viscosity liquid extrusion 3D print module. This e-skin has a high sensor density of 100/cm2, which is close to the resolution of the human fingertip skin. The piezoresistive sensor units of e-skin exhibit a highly linear resistance response and a relatively performance consistency between devices. Owing to the porous and breathable structure, better human comfort and mechanical heat dissipation are realized. This high-resolution e-skin is successfully applied to identify small-sized objects with complex contours. [ABSTRACT FROM AUTHOR]

Inspired by the human skin, electronic skins (e-skins) composed of various flexible sensors, such as strain sensor, pressure sensor, shear force sensor, temperature sensor, and humility sensor, and delicate circuits, are emerged to mimic the sensing functions of human skins. In this review, the strategies to realize the versatile functionalities of natural skin-like e-skins, including strain-, pressure-, shear force-, temperature-and humility-sensing abilities, as well as self-healing ability and other functions are summarized. Some representative examples of high-performance e-skins and their applications are outlined and discussed. Finally, the outlook of the future of e-skins is presented. [ABSTRACT FROM AUTHOR]

Compliance sensation is a unique feature of the human skin that electronic devices could not mimic via compact and thin formfactor devices. Due to the complex nature of the sensing mechanism, up to now, only high-precision or bulky handheld devices have been used to measure compliance of materials. This also prevents the development of electronic skin that is fully capable of mimicking human skin. Here, we developed a thin sensor that consists of a strain sensor coupled to a pressure sensor and is capable of identifying compliance of touched materials. The sensor can be easily integrated into robotic systems due to its small form factor. Results showed that the sensor is capable of classifying compliance of materials with high sensitivity allowing materials with various compliance to be identified. We integrated the sensor to a robotic finger to demonstrate the capability of the sensor for robotics. Further, the arrayed sensor configuration allows a compliance mapping which can enable humanlike sensations to robotic systems when grasping objects composed of multiple materials of varying compliance. These highly tunable sensors enable robotic systems to handle more advanced and complicated tasks such as classifying touched materials. [ABSTRACT FROM AUTHOR]

Electronic skin (e-skin) has shown great application prospects in many fields due to its multiple advantages. Previous studies have illustrated that the structure with a dielectric layer sandwiched between two electrodes had good pressure-sensing abilities, and microstructures in the dielectric layer could improve the sensitivity. In this paper, we proposed mechanical models of e-skin sensing unit with different microstructures (flat, trapezoidal, half-cylinder, and pyramids) in the dielectric layer. Then, we performed finite element method simulations and experiments to validate the model. Finally, we demonstrated its application as the pressure-sensing unit for human hands, showing its great potentials in sensors of artificial prosthesis or soft robots in the future. [ABSTRACT FROM AUTHOR]

In this paper, we propose a set of novel tactile descriptors to enable robotic systems to extract robust tactile information during tactile object explorations, regardless of the number of the tactile sensors, sensing technologies, type of exploratory movements, and duration of the objects’ surface exploration. The performance and robustness of the tactile descriptors are verified by testing on four different sensing technologies (dynamic pressure sensors, accelerometers, capacitive sensors, and impedance electrode arrays) with two robotic platforms (one anthropomorphic hand and one humanoid), and with a large set of objects and materials. Using our proposed tactile descriptors, the Shadow Hand, which has multimodal robotic skin on its fingertips, successfully classified 120 materials (100% accuracy) and 30 in-hand objects (98% accuracy) with regular and irregular textural structure by executing human-like active exploratory movements on their surface. The robustness of the proposed descriptors was assessed further during the large object discrimination with a humanoid. With a large sensing area on its upper body, the humanoid classified 120 large objects with multiple weights and various textures while the objects slid between its sensitive hands, arms, and chest. The achieved 90% recognition rate shows that the proposed tactile descriptors provided robust tactile information from the large number of tactile signals for identifying large objects via their surface texture regardless of their weight. [ABSTRACT FROM AUTHOR]

Artificial “electronic skin” is of great interest for mimicking the functionality of human skin, such as tactile pressure sensing. Several important performance metrics include mechanical flexibility, operation voltage, sensitivity, and accuracy, as well as response speed. In this Letter, we demonstrate a large-area high-performance flexible pressure sensor built on an active matrix of 16 × 16 carbon nanotube thin-film transistors (CNT TFTs). Made from highly purified solution tubes, the active matrix exhibits superior flexible TFT performance with high mobility and large current density, along with a high device yield of nearly 99% over 4 inch sample area. The fully integrated flexible pressure sensor operates within a small voltage range of 3 V and shows superb performance featuring high spatial resolution of 4 mm, faster response than human skin (<30 ms), and excellent accuracy in sensing complex objects on both flat and curved surfaces. This work may pave the road for future integration of high-performance electronic skin in smart robotics and prosthetic solutions. [ABSTRACT FROM AUTHOR]

The rational design of high-performance flexible pressure sensors attracts attention because of the potential applications in wearable electronics and human-machine interfacing. For practical applications, pressure sensors with high sensitivity and low detection limit are desired. Here, ta simple process to fabricate high-performance pressure sensors based on biomimetic hierarchical structures and highly conductive active membranes is presented. Aligned carbon nanotubes/graphene (ACNT/G) is used as the active material and microstructured polydimethylsiloxane (m-PDMS) molded from natural leaves is used as the flexible matrix. The highly conductive ACNT/G films with unique coalescent structures, which are directly grown using chemical vapor deposition, can be conformably coated on the m-PDMS films with hierarchical protuberances. Flexible ACNT/G pressure sensors are then constructed by putting two ACNT/G/PDMS films face to face with the orientation of the ACNTs in the two films perpendicular to each other. Due to the unique hierarchical structures of both the ACNT/G and m-PDMS films, the obtained pressure sensors demonstrate high sensitivity (19.8 kPa−1, <0.3 kPa), low detection limit (0.6 Pa), fast response time (<16.7 ms), low operating voltage (0.03 V), and excellent stability for more than 35 000 loading-unloading cycles, thus promising potential applications in wearable electronics. [ABSTRACT FROM AUTHOR]

It is a challenge to manufacture pressure-sensing materials that possess flexibility, high sensitivity, large-area compliance, and capability to detect both tiny and large motions for the development of artificial intelligence products. Herein, a very simple and low-cost approach is proposed to fabricate versatile pressure sensors based on microcrack-designed carbon black (CB)@polyurethane (PU) sponges via natural polymer-mediated water-based layer-by-layer assembly. These sensors are capable of satisfying the requirements of ultrasmall as well as large motion monitoring. The versatility of these sensors benefits from two aspects: microcrack junction sensing mechanism for tiny motion detecting (91 Pa pressure, 0.2% strain) inspired by the spider sensory system and compressive contact of CB@PU conductive backbones for large motion monitoring (16.4 kPa pressure, 60% strain). Furthermore, these sensors exhibit excellent flexibility, fast response times (<20 ms), as well as good reproducibility over 50 000 cycles. This study also demonstrates the versatility of these sensors for various applications, ranging from speech recognition, health monitoring, bodily motion detection to artificial electronic skin. The desirable comprehensive performance of our sensors, which is comparable to the recently reported pressure-sensing devices, together with their significant advantages of low-cost, easy fabrication, especially versatility, makes them attractive in the future of artificial intelligence. [ABSTRACT FROM AUTHOR]

Fiber-based, flexible pressure-sensing systems have attracted attention recently due to their promising application as electronic skins. Here, a new kind of flexible pressure-sensing device based on a polydimethylsiloxane membrane instrumented with double-twisted smart threads (DTSTs) is reported. DTSTs are made of two conductive threads obtained by coating cotton threads with carbon nanotubes. One thread is coated with a homogeneous thickness of single-walled carbon nanotubes (SWCNTs) to detect the intensity of an applied load and the other is coated with a graded thickness of SWCNTs to identify the position of the load along the thread. The mechanism and capacity of DTSTs to accurately sense an applied load are systematically analyzed. Results demonstrate that the fabricated 1D, 2D, and 3D sensing devices can be used to predict both the intensity and the position of an applied load. The sensors feature high sensitivity (between ≈0.1% and 1.56% kPa) and tunable resolution, good cycling resilience (>104 cycles), and a short response time (minimum 2.5 Hz). The presented strategy is a viable alternative for the design of simple, low-cost pressure sensors. [ABSTRACT FROM AUTHOR]

With the rapid development of intelligent wearable electronics, flexible shielding electronic skin is highly desired to monitor physiological signals and protect human beings from electromagnetic radiation. One primary concern is the synergetic improvement of electromagnetic interference (EMI) shielding effectiveness and piezoresistive sensitivity that meet the demands above. Here, we report a bifunctional electrospun nanofiber membrane decorated with MXene nanosheets and Fe 3 O 4 nanoparticles (NPs) that possess desired properties. Notably, this electrospun composite membrane (thicknesses of 33 μm) demonstrates excellent specific shielding effectiveness (SSE/t) of 9212.1 dB cm2 g−1 in a broad waveband range (8–26.5 GHz), owing to the combined effects of favorable porous structure, magnetic loss from Fe 3 O 4 NPs and dielectric loss from MXene. The bifunctional membrane exhibited high sensitivity of 5.53 kPa−1 in a broad pressure regime (0–2.5 kPa), with a rapid response time and long-term stability. This pressure sensor can achieve noninvasive health monitoring of pulse, laryngeal movement, and other physiological signals. This work provides a new avenue toward wearable electromagnetic wave protection and human-machine interfaces. [Display omitted] • A flexible electrospun MXene-Fe 3 O 4 nanofiber membrane with a 0D-1D-2D structure. • The bifunctional membrane is developed for EMI shielding and pressure sensor. • It displays excellent EMI SSE/t value of 9212.1 dB cm2 g−1 in wide waveband range. • The pressure sensor shows high sensitivity (5.53 kPa−1), fast response time (62.2 ms). • The sensor achieves noninvasive health monitoring of physiological signals. [ABSTRACT FROM AUTHOR]

This report demonstrates a wearable elastomer-based electronic skin including resistive sensors for monitoring finger articulation and capacitive tactile pressure sensors that register distributed pressure along the entire length of the finger. Pressure sensitivity in the order of 0.001 to 0.01 kPa−1 for pressures from 5 to 405 kPa, which includes much of the range of human physiological sensing, is achieved by implementing soft, compressible silicone foam as the dielectric and stretchable thin-metal films. Integrating these sensors in a textile glove allows the decoupling of the strain and pressure cross-sensitivity of the tactile sensors, enabling precise grasp analysis. The sensorized glove is implemented in a human-in-the-loop system for controlling the grasp of objects, a critical step toward hand prosthesis with integrated sensing capabilities. [ABSTRACT FROM AUTHOR]

• The sensor achieves favorable trade-off between sensitivity (S max > 450 kPa−1) and sensing range (250 kPa). • The sensor shows an excellent self-cleaning attribute. • Flexible circuit board was successfully integrated with the sensor to transmit the force signal. A wearable integrated tactile sensory system consisting of self-cleaning flexible pressure sensors with ultrahigh sensitivity (S max > 450 kPa−1) and flexible circuit board can wirelessly transmit the force signals. [Display omitted] Flexible tactile sensors (FTS), which have been extensively used in force sensing devices, are gaining tremendous attentions in various application fields, such as robots, electronic skin (E-Skin), human-machine interaction (HMI), and many other rapidly developing frontier technologies. However, fabricating FTS achieving both high sensitivity and broad sensing range remains a great challenge. Moreover, the integration of FTS with flexible circuit boards has long been a hot topic due to its potential applications in flexible hybrid electronics (FHEs). Here, we report a novel flexible tactile sensor with ultrahigh sensitivity and wide sensing range and its application in a self-cleaning and fully integrated wearable tactile sensing system for real-time analysis. Benefiting from the conductive sensing materials composed of fine inverted pyramid arrays and double-covered sensing layers, the sensor exhibits a superior sensitivity of 451.292 kPa−1, a wide working range up to 250 kPa, and a fast response time of 31 ms, as well as long-term durability. Furthermore, the sensor system can accurately monitor the grasped force in real-time and easily be fixed on a flexible clamping jaw or human hands. Our design concept and experimental approach, either for the flexible sensor or the whole system, potentially push further the wearable electronics toward practical applications. [ABSTRACT FROM AUTHOR]

Soft biomimetic electronic devices primarily comprise an electronic skin (e-skin) capable of implementing various wearable/implantable applications such as soft human–machine interfaces, epidermal healthcare systems, and neuroprosthetics owing to its high mechanical flexibility, tissue conformability, and multifunctionality. The conformal contact of the e-skin with living tissues enables more precise analyses of physiological signals, even in the long term, as compared to rigid electronic devices. In this regard, e-skin can be considered as a promising formfactor for developing highly sensitive and transparent pressure sensors. Specifically, to minimize the modulus mismatch at the biotic–abiotic interface, transparent-conductive hydrogels have been used as electrodes with exceptional pressing durability. However, critical issues such as dehydration and low compatibility with elastomers remain a challenge. In this paper, we propose a skin-like transparent polymer-hydrogel hybrid pressure sensor (HPS) with microstructures based on the polyacrylamide/sodium-alginate hydrogel and p-PVDF-HFP-DBP polymer. The encapsulated HPS achieves conformal contact with skin due to its intrinsically stretchable, highly transparent, widely sensitive, and anti-dehydrative properties. We believe that the HPS is a promising candidate for a robust transparent epidermal stretchable-skin device. [ABSTRACT FROM AUTHOR]

Multi-functional electronic skin is of paramount significance for wearable electronics in health monitoring, medical analysis, and human-machine interfacing systems. In order to achieve the function of natural skin, mechanical sensing with high sensitivity is an important feature of electronic skin. Inspired by the spinosum structure under the skin, herein, we fabricate a new capacitive pressure sensor with two-dimensional transition-metal carbides and nitrides (MXene) and ferroelectric polymer (P(VDF-TrFE-CFE)) as an active layer and micropatterned Cr-Au deposited on polydimethylsiloxane as flexible electrodes. Such a method is facile, effective, easily operated, and low-cost. The device design provides great capacitive change as a consequence of large deformation under pressure. Benefiting from the randomly distributed microstructure and high dielectric constant of the active layer, the device demonstrates high sensitivity with great linearity (16.0 kPa−1 for less than 10 kPa), that is, a low detection limit of 8.9 Pa, and quick response. A series of dynamic physiological signals, including typing, knuckle motion, and voice recognition can be facilely detected, making it a competitive candidate in the field of wearable electronics. [ABSTRACT FROM AUTHOR]

Electronic skin imitates the function of human skin. The flexible pressure sensor is an important sensor of electronic skin. Although the flexible pressure sensor has made some progress, electronic skin is still a challenging subject with good pressure resolution, high sensitivity, and fast response ability in biomedical, human motion detection, personal health monitoring, and other fields. The PEDOT:PSS/GR/SWCNTs multicomponent solution was directly written on the flexible PDMS substrate by the near-field electrohydrodynamic direct-writing method, a serpentine shaped pressure sensitive unit was prepared, which was encapsulated with the PDMS thin film, and the flexible pressure sensor was fabricated. The sensitivity of the flexible pressure sensor is about 0.39 kPa−1 at 0–0.5 kPa and 1.04 kPa−1 at 0.5–2.4 kPa, and the response/recovery speed is 75 ms/150 ms, respectively. The fabricated flexible pressure sensor can detect a small pressure of about 6.4 Pa. The experimental results show that the fabricated flexible pressure sensor has high sensitivity, fast response capability, and low detection limit. The flexible pressure sensor for electronic skin demonstrates good performance in the application of finger joint movement and word pronunciation recognition, which indicates that it has great potential application in human motion detection and personal health monitoring. Image 1 • Flexible pressure sensitive unit fabricated by using near-field electrohydrodynamic direct-writing method. • Patterns of flexible pressure sensitive unit were fabricated into a serpentine shape to improve the performance. • The fabricated flexible pressure sensor has high sensitivity, fast response capability, and low detection limit. • The fabricated sensor has good performance in the application of finger joint motion and speech recognition. [ABSTRACT FROM AUTHOR]

As an essential role in electronic skins, flexible pressure sensors have attracted wide attention for their applications in human-machine interaction and intelligent prosthetic, etc. Whereas, in general, it is difficult for most flexible pressure sensors to acquire high accuracy, especially under multi-modal interference (temperature, humidity and deformation). Herein, a novel stretchable flexible pressure sensor was presented by direct writing, which was capable of weakening the strain effect, fending off humidity interference and restraining thermal influence by using a double layer raised island structure substrate, a covering layer and a Wheatstone bridge-configuration of the sensing element. The sensor kept robust under multi-modal interference of strain about 0–20%, temperature of 30–80 °C and humidity in 20–90%, owning high and stable sensitivity of 2.6 kPa−1–14.05 kPa−1 under 0–74 kPa. Two demonstrations of grabbing a bottle with different temperatures and a kid's catching behavior on a opisthenar of a carer verified that such sensor possessed a great potential in many non-structured applications and will be a promising candidate for stretchable flexible pressure sensors in future. Image 1 • A robust pressure sensor which can restrain the interference of deformation, temperature and humidity was presented. • A double layer raised island structure substrate was used to weaken the strain effect. • A Wheatstone bridge configuration of four same sensing elements was elaborated to eliminate the thermal impact. • Two applications including grabbing a bottle and a kid's catching behavior have been demonstrated. [ABSTRACT FROM AUTHOR]

Electronic skin (e-skin), which is an electronic surrogate of human skin, aims to recreate the multifunctionality of skin by using sensing units to detect multiple stimuli, while keeping key features of skin such as low thickness, stretchability, flexibility, and conformability. One of the most important stimuli to be detected is pressure due to its relevance in a plethora of applications, from health monitoring to functional prosthesis, robotics, and human-machine-interfaces (HMI). The performance of these e-skin pressure sensors is tailored, typically through micro-structuring techniques (such as photolithography, unconventional molds, incorporation of naturally micro-structured materials, laser engraving, amongst others) to achieve high sensitivities (commonly above 1 kPa−1), which is mostly relevant for health monitoring applications, or to extend the linearity of the behavior over a larger pressure range (from few Pa to 100 kPa), an important feature for functional prosthesis. Hence, this review intends to give a generalized view over the most relevant highlights in the development and micro-structuring of e-skin pressure sensors, while contributing to update the field with the most recent research. A special emphasis is devoted to the most employed pressure transduction mechanisms, namely capacitance, piezoelectricity, piezoresistivity, and triboelectricity, as well as to materials and novel techniques more recently explored to innovate the field and bring it a step closer to general adoption by society. [ABSTRACT FROM AUTHOR]

Considering electronic skin applications, a pressure sensor based on periodic structure of graphene oxide-reduced graphene oxide (GO-rGO) has been designed and fabricated based on a low cost direct laser writing technique by utilizing the laser diode of DVD drive's pickup head. The optimization of sensor structure has been performed using computational modelling through Finite Element Method (FEM) in the COMSOL environment. The optimized structure is fabricated based on the deposition of thin layer of GO on the surface of Kapton and the pattering is performed by laser irradiation. The fabricated sensor structure has been characterized structurally and functionally. The results show that the fabrication method is successful in the formation of periodic structure of GO-rGO and the sensor has an acceptable response in the range of 1.5–40 kPa. Image 1 [ABSTRACT FROM AUTHOR]

Electronic skin (e‐skin) integrating pressure sensors and strain sensors has shown great potential applications in smart robotics and healthcare monitoring for their flexibility and wearability. However, making the sensor low cost and highly durable for industrialization and commercialization is still a problem to be addressed. An embedded 3D printing technology is developed based on novel thermosetting printing ink which is prepared using the Ecoflex and carbon nanoparticles. The properties of the printing ink including printability and electrical conductivity are first studied and then optimized. By using this technology, a glove‐shaped e‐skin integrating both strain sensors and pressure sensors is fabricated, and the properties of the sensors are studied. Both types of sensors have excellent stability and reliability which are verified by multiple long‐term measurements (10 000 testing cycles). Specifically, the sensors possess a great shock resistance and high durability which are significant for application in real life. Furthermore, some applications for human activity monitoring and personal healthcare are demonstrated, including complex gesture recognition using 15 strain sensors, hardness sensing using pressure sensors coupled with strain sensors, and arterial pulse measurement using pressure sensors, which are promising for smart robotic sensing and wearable biomedical devices. [ABSTRACT FROM AUTHOR]

Electronic skin (e‐skin) is an important building block to achieve human–machine interfaces, functional prostheses, and health monitoring devices. While high pressure and temperature sensitivity with visible indication are important for e‐skins, such multifunctionality often requires complex fabrication and integration processes, which hinders practical applications. Here, a simple solution is shown to fabricate a bimodal e‐skin sensor array that is capable of changing color as a response to a range of temperatures (26–40 °C) with an ability to sense finger tap (≈20 kPa pressure) as a pressure sensor. The bimodal functionality of thermochromic response and tactile sensing is achieved by judicial material selection of our custom‐developed elastomer composite containing thermochromic dye, which is sandwiched by tough and transparent stretchable electrodes of ion‐containing polyampholyte hydrogels. The e‐skin array is potentially promising for applications in internet‐of‐things and soft robotics. [ABSTRACT FROM AUTHOR]

Remarkable research efforts have been devoted to replicate the tactile sensitivity of human skin. Unfortunately, so far flexible pressure sensors reported barely fit the tactile requirements for fingertips, which could endure a pressure over 100 kPa and also can sense a gentle touch. It is vital to develop flexible pressure sensors which can ensure high sensitivity and wide operation range simultaneously, to satisfy the demands of mimicking the pressure sensing function of fingertips. In this work, a mini-size, light-weight but high-performance graphene film based pressure sensor is presented. Owing to the advanced structure with fluctuations on surface and fluffy-layered structure in cross-section of the graphene film, this pressure sensor shows an extraordinary performance of high sensitivity of 10.39 kPa-1 (0–2 kPa), ultra-wide operation range up to 200 kPa, impressively stable repeatability, high working frequency, rapid response and recovery time. Moreover, the demonstrated results of the detection of traditional Chinese medicine wrist-pulse waveform and the bionic fingertip tactile sensors, suggest the great application potential of the obtain device in biomedical field and bionic skins field. • Free-standing graphene film as active material of pressure sensors. • Widest operation range among flexible piezoresistive pressure sensors. • High sensitivity of 10.39 kPa-1 in 0–2 kPa. • Practicable applications for whist pulse detection and bionic fingertips. [ABSTRACT FROM AUTHOR]

In article number 1800284, Jang‐Yeon Kwon and co‐workers demonstrate highly sensitive tactile sensors using a pyramid‐plug structure that enables them to detect pressure, shear force, and torsion. The wide operating range of the sensor, from soft breathing to arbitrary multiplex touching, makes it particularly promising for future applications. [ABSTRACT FROM AUTHOR]