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![a) Schematic illustration of the shear force leading to the geometric distortions of the interlocked hairs. b) The change in the electrical resistance as a function of the applied shear force. Reproduced with permission.[¹⁴³] Copyright 2012, Springer Nature Publishing. c) Schematic illustration of the working principle of the capacitive‐type sensor with spine arrays for shear force monitoring. d) Dependence of the capacitance variation on the applied shear force. Reproduced with permission.[¹⁹¹] Copyright 2020, Royal Society of Chemistry. e) Schematic diagram of the e‐skin system with the fingerprint‐like TENG on the surface of the sensor. f) Outputted signals from TENG and pressure sensor can reflect the complex action from (b). Reproduced with permission.[¹⁹²] Copyright 2018, Elsevier.](publication/353374090/figure/fig9/AS:11431281173263138@1688808160367/a-Schematic-illustration-of-the-shear-force-leading-to-the-geometric-distortions-of-the.png)
a) Schematic illustration of the shear force leading to the geometric distortions of the interlocked hairs. b) The change in the electrical resistance as a function of the applied shear force. Reproduced with permission.[¹⁴³] Copyright 2012, Springer Nature Publishing. c) Schematic illustration of the working principle of the capacitive‐type sensor with spine arrays for shear force monitoring. d) Dependence of the capacitance variation on the applied shear force. Reproduced with permission.[¹⁹¹] Copyright 2020, Royal Society of Chemistry. e) Schematic diagram of the e‐skin system with the fingerprint‐like TENG on the surface of the sensor. f) Outputted signals from TENG and pressure sensor can reflect the complex action from (b). Reproduced with permission.[¹⁹²] Copyright 2018, Elsevier.
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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...
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The use of piezoelectric materials has been increased due to the growing demand for wearable devices. Herein, we report the development of new copolymer poly (vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE)-based reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MCNTs) loaded electrospun (E-Spun) nanofibers. The rGO-MCNTs loaded...
Citations
... In recent years, flexible pressure sensors have attracted considerable attentions because of their promising applications in wearable electronic [1][2][3][4], human-computer interface [5][6][7], and healthcare [8][9][10]. Based on different sensing principles, * Authors to whom any correspondence should be addressed. ...
Flexible pressure sensors have attracted wide attention because of their applications in wearable electronic, human-computer interface, and healthcare. However, it is still a challenge to design a pressure sensor with adjustable sensitivity in an ultrawide response range to satisfy the requirements of different application scenarios. Here, a laser patterned graphene pressure sensor (LPGPS) is proposed with adjustable sensitivity in an ultrawide response range based on the pre-stretched kirigami structure. Due to the out-of-plane deformation of the pre-stretched kirigami structure, the sensitivity can be easily tuned by simply modifying the pre-stretched level. As a result, it exhibits a maximum sensitivity of 0.243 kPa⁻¹, an ultrawide range up to 1600 kPa, a low detection limit (6 Pa), a short response time (42 ms), and excellent stability with high pressure of 1200 kPa over 500 cycles. Benefiting from its high sensitivity and ultrawide response range, the proposed sensor can be applied to detect physiological and kinematic signals under different pressure intensities. Additionally, taking advantage of laser programmable patterning, it can be easily configured into an array to determine the pressure distribution. Therefore, LPGPS with adjustable sensitivity in an ultrawide response range has potential application in wearable electronic devices.
... Additionally, he briefly introduced the representative synthesis methods and strategies for conductive hydrogels. In Chen's 2021 review [8], strategies for fabricating flexible strain sensors to achieve diverse functionalities in natural skin-like electronic skins (e-skins) were introduced. In 2022, Zhao [9] reviewed the latest research and developments in the sensing mechanisms, compositions, structural designs, and applications of typical ionic flexible sensors (IFS), especially focusing on novel ionic materials, structural designs, and biomimetic approaches. ...
... Temperature effect [104] measures the degree to which the sensor output signal is influenced by temperature changes, which is crucial for ensuring measurement accuracy and stability. Zero drift [8] indicates the stability of the sensor's output signal at zero strain, determining whether the sensor can maintain an accurate baseline value over time. Reproducibility [105] describes the ability of the sensor to generate similar outputs under multiple identical strain stimuli, reflecting the repeatability and consistency of the sensor. ...
Strain sensors, as electronic components, convert non-quantitative strain states into visually perceivable electrical signal variations using strain gauges. They have extensive applications in various fields such as materials science, medical diagnostics, structural mechanics, and environmental monitoring, making them crucial measurement tools. However, traditional strain sensors suffer from drawbacks such as low sensitivity, slow response speed, and susceptibility to interference, which impact their use in high-precision fields. This article systematically summarizes the research progress and preparation methods of polymer-based strain sensors in recent years, analyzes the challenges faced by strain sensors in their development process, and prospects future research directions to provide theoretical basis and foundation for the preparation of new strain sensors.
... 3 Sensitive, highly stretchable strain sensors can be attached to human skin to monitor pulse, heartbeat, blood pressure, muscle movement, vocalization, and facial expression. 4 Flexible or stretchable sensors can be directly applied to the skin surface and combined with clothes, 5 of which are highly adaptive. In addition, due to their simple preparation process and low cost, wearable sensors based on nanomaterials become one of the current research hotspots in the field of flexible electronics. ...
Flexible strain sensors have a wide range of electronic skin and health monitoring applications. In this paper, flexible strain sensors with unique direction designs were prepared using silver nanowires (AgNWs) and UV-curable acrylate elastomer films. They show an extensive strain range (tensile strain >50%), sensitivity up to 97 of gauge factor, and good reproducibility of up to 10% strain under cyclic tensile tests. The parallel and perpendicular placement of the sensors to strain direction allows us to detect wrist movement in a 360-degree direction with high accuracy.
... This sensing system is capable of detecting mechanical deformation caused by body movement, enabling operational control over machines or other devices. Such functionality could prove useful for applications in human-machine interface [44] and for intelligent electronic skin (E-skin) [45]. ...
Triboelectric nanogenerator (TENG) is one of the forefront technologies in energy harvesting, which can convert mechanical energy into electricity. Polydimethylsiloxane (PDMS) has been widely used as a friction layer for TENGs due to its high electron affinity and flexibility. In this work, a novel and green approach to fabricating a high-performance PDMS TENG is proposed by using yeast cells. Porous-structured PDMS produced by the formation of CO2 products of a fermentation reaction of baker’s yeast is found to significantly improve the TENG performance. The effects of yeast cell concentration in PDMS on morphologies, chemical composition, and TENG performance of the porous PDMS films are investigated. It is found that the average pore size formed in PDMS film depends on yeast cell concentration, which affects the electrical outputs of TENG. The modified PDMS TENG showed improved TENG performance with the highest power density at 5.14 w/m². The application of the fabricated porous PDMS to harness mechanical energy from body movement is demonstrated. Our work has presented a novel and effective technique using a biological approach to modify PDMS into a porous structure using yeast cells, which has the potential for flexible and wearable TENG to harvest mechanical energy from body movement.
Graphical abstract
... [6] Therefore, inspired by the human skin, electronic skin (e-skin), which is flexible, stretchable, and highly biocompatible, has emerged due to innovations in flexible materials and] processing technologies. [12][13][14][15][16] E-skin is a flexible wearable electronic device that imitates the characteristics and functions of human skin to sense various external signals and record them as different electrical signals, demonstrating enormous potential in health monitoring and personalized medical applications. [17][18][19][20][21] To achieve long-term and accurate health monitoring, eskin needs to possess the properties shown in Figure 1. ...
Electronic skin (e‐skin), a skin‐like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E‐skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e‐skin, laying the foundation for the application of next‐generation wearable medical technologies and devices. Herein, the properties required for e‐skin health monitoring devices to achieve long‐term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e‐skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e‐skin and health monitoring systems.
... Sensors are devices that obtain measurements and convert them into electrical signals or other information according to specific rules to enable information transmission, processing, storage, display, recording, and control. [1][2][3][4] They are core components of intelligent devices and can perceive touch, [1,5] taste, [6][7][8] vision, [9,10] hearing, [11,12] and smell, [13,14] similar to human senses (Figure 1a-e). [15] However, research on intelligent equipment has DOI: 10.1002/advs.202400816 ...
Integrating sensors and other functional parts in one device can enable a new generation of integrated intelligent devices that can perform self‐sensing and monitoring autonomously. Applications include buildings that detect and repair damage, robots that monitor conditions and perform real‐time correction and reconstruction, aircraft capable of real‐time perception of the internal and external environment, and medical devices and prosthetics with a realistic sense of touch. Although integrating sensors and other functional parts into self‐sensing intelligent devices has become increasingly common, additive manufacturing has only been marginally explored. This review focuses on additive manufacturing integrated design, printing equipment, and printable materials and stuctures. The importance of the material, structure, and function of integrated manufacturing are highlighted. The study summarizes current challenges to be addressed and provides suggestions for future development directions.
... Epidermal electronics, a type of flexible electronic system, can be applied to the body surface to perform tasks such as monitoring physiological signals, [1,2] facilitating human-machine interaction, [3][4][5] and providing assistive therapy. [6,7] This type of flexible electronic system can be classified into various forms, including electronic patches, electronic tattoos, and electronic ink, based on their physical characteristics. [8][9][10][11][12][13][14][15] Despite recent advancements in creating thin and well-integrated electronic patches, [16][17][18][19] they still face limitations regarding their inability to be customized in terms of shape and size for specific applications. ...
Epidermal electronics has garnered significant research attention due to its promising applications in wearable human‐machine interfaces and intelligent healthcare sensing. However, their widespread use faces challenges due to complex manufacturing processes, high material costs, inadaptability to different skin surfaces, and inadequate reusability. Herein, inspired by the biological reshapability and environmental adaptability of amoeba, an ultra‐deformable (≈2600% strain), bioadhesive (adhesive strength ≈3 kPa), strong self‐healing (fastest recovery time ≈1s, maximum wound distance ≈5 mm), and electromechanical‐durable wearable electronic slime (E‐slime) is proposed, which can instantaneously form on‐skin electronics in situ to detect body motion and physiological signals. E‐slime demonstrates desired sensing performance with high sensitivity (gauge factor 2.95), wide sensing range (up to 400% strain), and low detection limit (≈1% strain), which can seamlessly adhere to the skin and can be easily reused multiple times (≈100 cycles usage). E‐slime also enables on‐the‐fly deployment of motion monitoring tasks at various body locations, showcasing its versatility and reliability for body motion recognition and personal health monitoring. This study holds potential for next‐generation green electronics, motion sensing devices, and wearable human‐machine interfaces, ultimately helping to ensure healthy lives and promote well‐being.
... In the current era marked by swift technological evolution, sensing technology occupies a pivotal position in diverse sectors, including advanced industrial processes [1], robotics [2], biomedical engineering [3][4][5][6], and civil engineering [7,8]. These sensors employ sophisticated structural design [9][10][11][12] and innovative material optimization [13,14] in their sensitive units to transform stimuli from objects into electrical or optical signals. ...
Machine learning and deep learning technologies are rapidly advancing the capabilities of sensing technologies, bringing about significant improvements in accuracy, sensitivity, and adaptability. These advancements are making a notable impact across a broad spectrum of fields, including industrial automation, robotics, biomedical engineering, and civil infrastructure monitoring. The core of this transformative shift lies in the integration of artificial intelligence (AI) with sensor technology, focusing on the development of efficient algorithms that drive both device performance enhancements and novel applications in various biomedical and engineering fields. This review delves into the fusion of ML/DL algorithms with sensor technologies, shedding light on their profound impact on sensor design, calibration and compensation, object recognition, and behavior prediction. Through a series of exemplary applications, the review showcases the potential of AI algorithms to significantly upgrade sensor functionalities and widen their application range. Moreover, it addresses the challenges encountered in exploiting these technologies for sensing applications and offers insights into future trends and potential advancements.
... Flexible piezoresistive sensors have gained extensive attention for their versatile applications. The sensors find use in various fields such as health monitoring, electronic skin, wearable electronics, and biomimetic prostheses [18][19][20][21][22][23]. One of the key advantages of flexible sensors is their high strain sensitivity coupled with excellent bendability, making them suitable for monitoring applications that involve dynamic and deformable surfaces. ...
In engineering measurements, metal foil strain gauges suffer from a limited range and low sensitivity, necessitating the development of flexible sensors to fill the gap. This paper presents a flexible, high-performance piezoresistive sensor using a composite consisting of graphene nanoplatelets (GNPs) and polydimethylsiloxane (PDMS). The proposed sensor demonstrated a significantly wider range (97%) and higher gauge factor (GF) (6.3), effectively addressing the shortcomings of traditional strain gauges. The microstructure of the GNPs/PDMS composite was observed using a scanning electron microscope, and the distribution of the conductive network was analyzed. The mechanical behavior of the sensor encapsulation was analyzed, leading to the determination of the mechanisms influencing encapsulation. Experiments based on a standard equal-strength beam were conducted to investigate the influence of the base and coating dimensions of the sensor. The results indicated that reducing the base thickness and increasing the coating length both contributed to the enhancement of the sensor's performance. These findings provide valuable guidance for future development and design of flexible sensors.
... The development of e-skin comprising various flexible sensors such as strain, pressure, shear force, and temperature sensors, integrated with sophisticated circuits, has emerged to mimic the sensing functionalities of human skin [128]. These tactile stimuli are typically converted into electrical signals, such as changes in resistance or capacitance, which can be collected and processed by computers [32]. ...
Soft robotics has received substantial attention due to its remarkable deformability, making it well-suited for a wide range of applications in complex environments, such as medicine, rescue operations, and exploration. Within this domain, the interaction of actuation and sensing is of utmost importance for controlling the movements and functions of soft robots. Nonetheless, current research predominantly focuses on isolated actuation and sensing capabilities, often neglecting the critical integration of these 2 domains to achieve intelligent functionality. In this review, we present a comprehensive survey of fundamental actuation strategies and multimodal actuation while also delving into advancements in proprioceptive and haptic sensing and their fusion. We emphasize the importance of integrating actuation and sensing in soft robotics, presenting 3 integration methodologies, namely, sensor surface integration, sensor internal integration, and closed-loop system integration based on sensor feedback. Furthermore, we highlight the challenges in the field and suggest compelling directions for future research. Through this comprehensive synthesis, we aim to stimulate further curiosity among researchers and contribute to the development of genuinely intelligent soft robots.
