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Haptic perception of softness is a unique feature of the human skin that relies on the concurrent measurements of the lateral deformation and compression of the skin during object manipulation. This is challenging to implement in robotics because of combined requirements in sensing modalities, skin format, robotic structures, and synthetic materials. A soft sensory skin supporting distributed and bimodal mechanical sensing over large surface area and suitable for robotic hand manipulation is reported. Resistive pressure and strain sensors are prepared with spray‐coated liquid metal films embedded in a silicone matrix. Object softness is computed through a calibrated model based on both sensor response curves and the stiffness of the carrier robot. The soft sensory skin enables localization and discrimination of softness that promise interesting future implementation for robotic palpation or precise teleoperation. [ABSTRACT FROM AUTHOR]

Abstract Only microstructures are used to improve the sensitivity of iontronic pressure sensors. By modulating the compressive modulus, a breakthrough in the sensitivity of the iontronic pressure sensor is achieved. Furthermore, it allows for programmatic tailoring of sensor performance according to the requirements of different applications. Such a new strategy pushes the sensitivity up to a record‐high of 25 548.24 kPa−1 and expands the linear pressure range from 15 to 127 kPa. Additionally, the sensor demonstrates excellent mechanical stability over 10 000 compression‐release cycles. Based on this, a well‐controlled robotic hand that precisely tracks the pressure behavior inside a balloon to autonomously regulate the gripping angle is developed. This paves the way for the application of iontronic pressure sensors in precise sensing scenarios.

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]

The emerging field of flexible tactile sensing systems, equipped with multi-physical tactile sensing capabilities, holds vast potential across diverse domains such as medical monitoring, robotics, and human–computer interaction. In response to the prevailing challenges associated with the limited integration and sensitivity of flexible tactile sensors, this paper introduces a versatile tactile sensing system capable of concurrently monitoring temperature and pressure. The temperature sensor employs carbon nanotube/graphene conductive paste as its sensitive material, while the pressure sensor integrates an ionic gel containing boron nitride as its sensitive layer. Through the application of cost-effective screen printing technology, we have successfully manufactured a flexible dual-mode sensor with exceptional performance, featuring high sensitivity (804.27 kPa − 1 ), a broad response range (50 kPa), rapid response time (17 ms), and relaxation time (34 ms), alongside exceptional durability over 5000 cycles. Furthermore, the resistance temperature coefficient of the sensor within the temperature range of 12.5 °C to 93.7 °C is −0.17% °C−1. The designed flexible dual-mode tactile sensing system enables the real-time detection of pressure and temperature information, presenting an innovative approach to electronic skin with multi-physical tactile sensing capabilities. [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]

Flexible electronic skins (e‐skins) have a wide range of applications in health monitoring, human–machine interfaces, and robotics. Herein, a novel architecture of e‐skins with a combination of multimode measurement and low‐cost implementation is proposed. A single electronic skin layer is used to integrate both the pressure and temperature sensing properties. An e‐skin membrane is first developed with poly(vinylidene) fluoride incorporated with silicon dioxide nanoparticles. When combined with electrodes, this simple architecture allows the implementation of multimode pressure and temperature sensing. This e‐skin exhibits excellent pressure sensitivity with a response time of 1.6 ms. This sensing performance can be attributed to the uniform distribution of the embedded nanoparticles, leading to an enhancement of the electroactive β phase. This e‐skin generates a voltage, from the finger movements, that can be used to detect precisely the minute changes of the finger movement. This electronic skin demonstrates the detection of a linear range of temperature which can be attributed to the phonon‐assisted hopping mechanism. A 4 × 4 pressure sensing array is demonstrated, which is able to map the inserted pressure as well as temperature stimuli. Thus, this study provides a new conceptual design for the next‐generation green electronic skins. [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]

The development of pressure sensors of high sensitivity and stable robustness over a broad range is indispensable for the future progress of electronic skin applicable to the detection of normal and shear pressures of various dynamic human motions. Herein, we present a flexible capacitive tactile sensing array that incorporates a porous dielectric layer with micro-patterned structures on the surface to enable the sensitive detection of normal and shear pressures. The proposed sensing array showed great pressure-sensing performance in the experiments, with a broad sensing range from several kPa to 150 kPa of normal pressure and 20 kPa of shear pressure. Sensitivities of 0.54%/kPa at 10 kPa and below, 0.45%/kPa between 10 kPa and 80 kPa, and 0.12%/kPa at 80 kPa and above were achieved for normal pressures. Meanwhile, for shear pressures, sensitivities up to 1.14%/kPa and 1.08%/kPa in x and y directions, respectively, and below 10 kPa, 0.73%/kPa, and 0.75%/kPa under shear pressure over 10 kPa were also validated. The performance of the finger-attached sensing array was also demonstrated, demonstrating which was a potential electronic skin to use in all kinds of wearable devices, including prosthetic hands, surgical robots, and other pressure monitoring systems. [ABSTRACT FROM AUTHOR]

Owing to air pollution and the pandemic outbreak, the need for quantitative pulmonary monitoring has greatly increased. The COVID-19 outbreak has aroused attention for comfortable wireless monitoring of respiratory profiles and more real-time diagnosis of respiratory diseases. Although respiration sensors have been investigated extensively with single-pixel sensors, 2D respiration profiling with a pixelated array sensor has not been demonstrated for both exhaling and inhaling. Since the pixelated array sensor allowed for simultaneous profiling of the nasal breathing and oral breathing, it provides essential respiratory information such as breathing patterns, respiration habit, breathing disorders. In this study, we introduced an air-permeable, stretchable, and a pixelated pressure sensor that can be integrated into a commercial face mask. The mask sensor showed a strain-independent pressure-sensing performance, providing 2D pressure profiles for exhalation and inhalation. Real-time 2D respiration profiles could monitor various respiratory behaviors, such as oral/nasal breathing, clogged nose, out-of-breath, and coughing. Furthermore, they could detect respiratory diseases, such as rhinitis, sleep apnea, and pneumonia. The 2D respiratory profiling mask sensor is expected to be employed for remote respiration monitoring and timely patient treatment. [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]

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.

Electronic skin (e-skin) has attracted considerable interests to endow robots the abundant perception abilities like human skin. However, multifunctional tactile feedbacks and poor wearability hinder the practical application towards compliant robot manipulations and friendly human-robot interaction (HRI). Here, a 3D-shaped e-skin integrated with hierarchically distributed flexible pressure, proximity, humidity sensors, and digital conversion circuits has been developed via the parting casting method. It can perfectly cover the non-developable and time-dynamic curved surface of a bionic hand and shows excellent wearability. The sensing data are collected by multichannel acquisition circuits and then sent to processing center to establish the mapping relations between multiple stimuli and movements of the bionic hand and arm. The multifunctional tactile feedbacks have been successfully demonstrated, which include non-contact obstacle avoidance, grasping force control, slip detection, and voice feedback. The e-skin shows great potential in the fields of HRI, artificial limbs, health care robots, and service robots. [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]

Highly sensitive capacitive pressure sensors with wide detection range are needed for applications such as human-machine interfaces, electronic skin in robotics, and health monitoring. However, it is challenging to achieve high sensitivity and wide detection range at the same time. Herein, we present an innovative approach to obtain a highly sensitive capacitive pressure sensor by introducing a zinc oxide nanowire (ZnO NW) interlayer at the polydimethylsiloxane (PDMS)/electrodes interface in the conventional metal-insulator-metal architecture. The ZnO NW interlayer significantly enhanced the performance with ~7 times higher sensitivity (from 0.81%kPa−1 to 5.6452%kPa−1 at a low-pressure range (0-10 kPa)) with respect to conventional capacitive sensors having PDMS only as the dielectric. The improvement in sensitivity is attributed to the enhanced charge separation and electric dipole generation due to the displacement of Zn+ and O− under applied pressure. Further, the orientation of ZnO NWs and their placement between the electrodes were investigated which includes either vertical or horizontal NWs near the electrodes, placing a third ZnO NW interlayer in the middle of dielectric PDMS and introducing an air gap between the ZnO NWs/electrode. Among various combinations, the introduction of air gap between the electrode and ZnO NW interlayer revealed a significant improvement in the device performance with ~50 times enhancement at a low-pressure range (0-10 kPa) and more than 200 times increase at a high-pressure range (10-200 kPa), in comparison with the conventional PDMS-based pressure sensor. [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]

[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]

In recent years, implantable electronics, electronic skin (e‐skin), and flexible wearable devices have been developed due to their extensive applications in health monitoring, intelligent robots, and human disease treatment. Tactile sensors are the keys necessary to build skin‐inspired electronics. This article reviews the latest progress of e‐skin‐based flexible pressure sensors, such as piezoresistivity, capacitance, triboelectricity, and piezoelectricity from 2018 up to now. The working principles, structure design, active materials, and performance of numerous flexible pressure sensors are covered in detail. Finally, insights are provided and challenges and future perspectives of flexible pressure sensors in practical applications are discussed. [ABSTRACT FROM AUTHOR]

[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]

Paper has been extensively accepted as an ideal platform for fabricating low‐cost, flexible, and environmentally friendly electronics. However, current paper‐based pressure sensors have not fully demonstrated the unique merits of paper, such as cost efficiency, disposability, cuttability, and foldability, mainly because of the limitation of the applied metal electrodes and device configuration. Here, an all‐organic, all‐paper, cuttable, and foldable pressure sensor is demonstrated for the first time, with the high‐conductivity polypyrrole (PPy) printing paper as electrode and the low‐conductivity PPy tissue paper as active layer. Hollow and 3D all‐paper sensors are realized through fabricating the kirigami or origami structure since the device can be freely cut and folded, presenting a universal strategy promising for flexible device design. The cuttability and foldability of device create a unique 3D perception capability. The devices show high sensitivity (4.8 kPa−1 at < 5.5 kPa, 1.7 kPa−1 at 5.5–40 kPa) and wide detection range (up to 40 kPa), providing a capability for full‐range detection of human physiological and motion signals. These results open a feasible route to realize hollow and 3D sensors and fully demonstrate the potential of paper sensors for diverse applications to new‐generation green electronics and portable electronics. [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]

ZnO nanorods (NRs) are nanomaterials with a wide range of applications (photocatalysis, optoelectronics, catalysis, etc). One peculiar property of ZnO NRs is their piezoelectricity, which opens up a wealth of possibilities in the field of pressure sensors. In fact, thanks also to the recent availability of low cost hydrothermal growth, it is already possible to fabricate flexible, large area, self‐powered, distributed pressure sensors, with a high potential for use in robotics and prosthetics as "electronic skins". This review focuses hence on ZnO NRs grown by the hydrothermal method, with an eye on the relationship between the reaction parameters and the resulting NRs morphology, and on their specific application in pressure sensing in terms of device design and performance. [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]

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.

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]

A flexible pressure sensor with high performances is one of the promising candidates for achieving electronic skins (E‐skin) related to various applications such as wearable devices, health monitoring systems, and artificial robot arms. The sensitive response for external mechanical stimulation is fundamentally required to develop the E‐skin which imitates the function of human skin. The performance of capacitive pressure sensors can be improved using morphologies and structures occurring in nature. In this work, highly sensitive capacitive pressure sensors based on a porous structure of polydimethylsiloxane (PDMS) thin film, inspired on the natural multilayered porous structures seen in mushrooms, diatoms, and spongia offilinalis, have been developed and evaluated. A bioinspired porous dielectric layer is used, resulting in high‐performance pressure sensors with high sensitivity (0.63 kPa−1), high stability over 10 000 cycles, fast response and relaxation times, and extremely low‐pressure detection of 2.42 Pa. Additionally, the resulting pressure sensors are demonstrated to fabricate multipixel arrays, thus achieving successful real‐time tactile sensing of various touch shapes. The developed high‐performance flexible pressure sensors may open new opportunities for innovative applications in advanced human‐machine interface systems, robotic sensory systems, and various wearable health monitoring devices. [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]

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]

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]

• 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]

Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft pressure sensors, but such a nonlinearity issue still exists and the sensors are only effective within a very narrow strain range. Herein, we fabricated a highly sensitive multi-channel pressure sensor array by using a simple thermal evaporation process of conducting nanomembranes onto a stretchable substrate. A rigid-island structure capable of dissipating accumulated strain energy induced by external mechanical stimuli was adopted for the sensor. The performance of the sensor was precisely controlled by optimizing the thickness of the stretchable substrate and the number of serpentines of an Au membrane. The fabricated sensor exhibited a sensitivity of 0.675 kPa−1 in the broad pressure range of 2.3–50 kPa with linearity (~0.990), and good stability (>300 Cycles). Finally, we successfully demonstrated a mapping of pressure distribution. [ABSTRACT FROM AUTHOR]

Recently, owing to their excellent flexibility and adaptability, skin-like pressure and strain sensors integrated with the human body have the potential for great prospects in healthcare. This review mainly focuses on the representative advances of the flexible pressure and strain sensors for health monitoring in recent years. The review consists of five sections. Firstly, we give a brief introduction of flexible skin-like sensors and their primary demands, and we comprehensively outline the two categories of design strategies for flexible sensors. Secondly, combining the typical sensor structures and their applications in human body monitoring, we summarize the recent development of flexible pressure sensors based on perceptual mechanism, the sensing component, elastic substrate, sensitivity and detection range. Thirdly, the main structure principles and performance characteristic parameters of noteworthy flexible strain sensors are summed up, namely the sensing mechanism, sensitive element, substrate, gauge factor, stretchability, and representative applications for human monitoring. Furthermore, the representations of flexible sensors with the favorable biocompatibility and self-driven properties are introduced. Finally, in conclusion, besides continuously researching how to enhance the flexibility and sensitivity of flexible sensors, their biocompatibility, versatility and durability should also be given sufficient attention, especially for implantable bioelectronics. In addition, the discussion emphasizes the challenges and opportunities of the above highlighted characteristics of novel flexible skin-like sensors. [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]