Janus and Heteromodulus Elastomeric Fiber Mats Feature Regulable Stress Redistribution for Boosted Strain Sensing Performance.

Stretchable strain sensors play a vital role in monitoring human body movements and have been widely applied in human–machine interface (HMI) systems. Conventional planarfabricated sensors attached to curved surfaces often suffer from low fabrication efficiency and reduced measurement accuracy due to poor conformability. This study presents a laser direct writing–based approach for the direct fabrication of double‐layer strain sensor arrays, interconnects and electrodes on complex curved, stretchable substrates. The resulting strain sensor exhibits a high gauge factor of 10⁶ at 80% strain and a minimum detectable strain as low as 0.1%, enabling precise monitoring of joint motion across a bending range of 0° to 90°. Additionally, tuning the material composition and structural design enables precise control over the sensor's electromechanical responses to suit various HMI applications. As a demonstration, an HMI with integrated strain sensors and interconnect arrays is directly fabricated onto the 3D surfaces of a glove. This system enables the robotic hand to accurately mimic multiple human gestures, highlighting its potential for advanced human–machine interaction.

Flexible and stretchable strain sensors have attracted growing interest for applications in health monitoring and human-machine interfaces. Conventional crack-based resistive strain sensors can achieve high sensitivity and large strain ranges by exploiting the opening and closing of randomly distributed microcracks. However, the uncontrolled evolution of these cracks during prolonged use often leads to performance degradation and poor reliability. In this work, we present a novel resistive strain sensor featuring predefined hourglass-shaped cracks that precisely regulate resistance variations through controlled crack opening and closure under stretching and release. A serpentine array of hourglass-shaped cracks is laser-cut into a 3D-printed conductive TPU film, after which the crack gaps are closed by releasing a pre-stretched elastomer substrate. Through geometric design, crack contact and evolution are precisely controlled, enabling the cracks to open stably and symmetrically under tensile strain, thereby producing predictable and linear resistance changes. This design enables high sensitivity over a broad linear operating range. The sensor also exhibits excellent recoverability after overstretching well beyond its working window and shows negligible resistance variation under bending, highlighting its robustness for wearable applications. To demonstrate its practical utility, the sensor was integrated into athletes' strength-training tasks, and the acquired signals were analyzed using machine learning algorithms to recognize motion patterns and provide early warnings of over-exercise. These capabilities support real-time load adjustment and fatigue-risk management, underscoring the sensor's strong potential for wearable health monitoring and human-machine interface applications.

Wearable strain sensors have attracted research interest owing to their potential within digital healthcare, offering smarter tracking, efficient diagnostics, and lower costs. Unlike rigid sensors, fiber‐based ones compete with their flexibility, durability, adaptability to body structures as well as eco‐friendliness to environment. Here, the sustainable fiber‐based wearable strain sensors for digital health are reviewed, and material, fabrication, and practical healthcare aspects are explored. Typical strain sensors predicated on various sensing modalities, be it resistive, capacitive, piezoelectric, or triboelectric, are explained and analyzed according to their strengths and weaknesses toward fabrication and applications. The applications in digital healthcare spanning from body area sensing networks, intelligent health management, and medical rehabilitation to multifunctional healthcare systems are also evaluated. Moreover, to create a more complete digital health network, wired and wireless methods of data collection and examples of machine learning are elaborated in detail. Finally, the prevailing challenges and prospective insights into the advancement of novel fibers, enhancement of sensing precision and wearability, and the establishment of seamlessly integrated systems are critically summarized and offered. This endeavor not only encapsulates the present landscape but also lays the foundation for future breakthroughs in fiber‐based wearable strain sensor technology within the domain of digital health.

High performance strain sensors have recently attracted considerable attention because of their applications in human motion detection, soft robotics, and human-machine interface. However, it remains some challenges in achieving satisfactory features (e.g., high sensitivity, high stretchable, linearity, and easy fabrication) for soft strain sensors. Inspired by the working principle of the eye's adaptation to different light luminance, this paper presents an ultra-stretchable, highly sensitive and high linear strain sensor based on the photoelectric effect. The sensor has a simple structure which is made of light-emitting diode (LED), photosensitive element, silicone rod, and sensor shell. When the silicone rod is stretched, the light's shielding area becomes larger, causing the increase of light luminous received by the photosensitive element. Hence, the sensitivity of the sensor can be tuned by changing luminance of LED and the amplification factor. Experiments demonstrate that the sensor has a high sensitivity (the maximum gauge factor was 1050), wide strain-sensing range (the max sensing range was up to 800%), high linearity range (from 100% to 300%), good repeatability (decreased by 5.48% over 5000 cycles at the wide tensile strain of 0 - 300%), low drift, and high signal-to-noise ratio (over 60dB). The proposed strain sensor has been applied in the bending detection of the wrist and finger, the recording of the human moving patterns, and the human's pulse counting. The sensor can be further fabricated into a data glove for detecting the human hand movement.

The fabrication of strain sensors with high sensitivity, large sensing range and excellent stability is highly desirable because of their promising applications in human motion detection, human-machine interface and electric skin, etc. Herein, by introducing a highly conductive silver nanowire (AgNW) layer between two serried silver nanoparticle (AgNP) layers, forming a sandwich structure, a strain sensor with high sensitivity (a large gauge factor of 2.8 × 105), large sensing range (up to 80% strain) and excellent stability (over 1000 cycles) can be achieved. A combination of experimental and mechanism studies shows that the high performance of the obtained strain sensor is ascribed to the synergy of the highly conductive AgNW layer, astatic AgNP layers and the presence of large cracks in stretching. As a proof-of-concept application, the obtained strain sensor can be used for highly effective human motion detection ranging from large scale motions, i.e. kneel bending and wrist flexion, to subtle scale motions, i.e. pulse and swallowing.

Flexible wearable sensors are emerging as next-generation tools to collect information from the human body and surroundings in a smart, friendly, and real-time manner. A new class of such sensors with various functionality and amenability for the human body is essential for this goal. Unfortunately, the majority of the wearable sensors reported so far in the literature were of a single function (mostly strain sensors) and just a prototype without thinking of continuous mass production. In this paper, we report a series of multifunctional conductive hydrogel/ thermochromic elastomer hybrid fibers with core-shell segmental configuration and their application as flexible wearable strain and temperature sensors to monitor human motion and body/surrounding temperatures. Specifically, a conductive reduced-graphene-oxide-doped poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylamide (rGO-poly(AMPS-co-AAm)) hydrogel and a thermochromic elastomer containing silicon rubber and thermochromic microcapsules are chosen as strain-sensitive and thermosensitive materials, respectively. A core-shell segmental structure is realized by programming the extrusion of either conductive hydrogel precursor solution or a thermochromic elastomer prepolymer as a core layer via dual-core coaxial wet spinning. Depending on the assembly order and length of the conductive hydrogel and the thermochromic elastomer, the as-prepared hybrid fibers can be used for different purposes, i.e., human-motion monitoring, body or room temperature detection, and color decoration. The strategy described above, i.e., fabrication of core-shell segmental fibers via the wet-spinning method, is especially suitable for mass production in industry and can be further extended to fabricate flexible wearable devices with more components and more functions such as transistors, sensors, displays, and batteries.

The booming prosperity of strain sensors promotes the regeneration of wearable electronics. However, strain sensors featured with both large workable range and superb sensitivity are still less than satisfaction. Softness and practicality are also of vital importance for wearable electronics. In this work, a flexible wearable strain sensor based on carbonized cotton fabric coated with reduced graphene oxide (rGO) through polydopamine (rGO/PDA/CCF) modification was fabricated, which exhibits fascinating electrical mechanical performance including a large workable range and superb sensitivity. rGO/PDA/CCF was characterized using scanning electron microscopy (SEM), Raman scattering spectroscopy, and X-ray diffraction (XRD) patterns. The electromechanical performance of the rGO/PDA/CCF strain sensor was evaluated. The strain sensors of rGO/PDA/CCF exhibit a large workable strain range (0–120%) and superb sensitivity with strong durability over 800 cycles. The rGO/PDA/CCF strain sensor has a low detection limit down to 0.01% with a good gauge factor (GF) of 132 within the strain range of 0–1%, and also displays fantastic property in terms of sensitivity in other workable range (GF of 26 and 8 within in a strain range of 1–30% and 30–60%, respectively). rGO/PDA/CCF strain sensor was then applied to track the signal of human motions in real time. rGO/PDA/CCF flexible strain sensor can be utilized in detecting almost all human motions with various dimensions. Additionally, the hydrophobicity and the stability at different temperatures endow the rGO/PDA/CCF strain sensor with high efficiency in various usage, which shows its potential for application in health monitor and wearable electronics.

This paper summarizes recent advances in the design and realization of PDMS-based, high-performance conductive hydrogel-based, MXene-based, CNT-GNP-based and Ultra-thin gold nanowires-based sensors. Wearable strain sensors are widely used in medical detector, dynamic monitoring, and human-computer interaction due to their excellent stretchability, sensitivity, and durability. At this stage, technologies such as graphene and nanocellulose thin film mosaic, neuron-like structures, GNP-CNT hybrid films, and ultrathin gold nanowire fabrication have been successfully utilized in the development of higher performance and higher quality wearable strain sensors. Different strain sensors have different advantages in terms of different mechanical properties. The text compares the advantages of strain sensors made of different materials applied to different devices. Finally, it looks at the future prospects of wearable strain sensors. Although sensors have made great progress in the application of products in medicine, life and other aspects, it is still not possible to put these products into use on a large scale. Corresponding products still face problems and challenges to improve and enhance their performance.

Highly sensitive, direction-aware, and transparent strain sensor based on oriented electrospun nanofibers for wearable electronic applications

Lightweight, stretchable, and wearable strain sensors have recently been widely studied for the development of health monitoring systems, human-machine interfaces, and wearable devices. Herein, highly stretchable polymer elastomer-wrapped carbon nanocomposite piezoresistive core-sheath fibers are successfully prepared using a facile and scalable one-step coaxial wet-spinning assembly approach. The carbon nanotube-polymeric composite core of the stretchable fiber is surrounded by an insulating sheath, similar to conventional cables, and shows excellent electrical conductivity with a low percolation threshold (0.74 vol %). The core-sheath elastic fibers are used as wearable strain sensors, exhibiting ultra-high stretchability (above 300%), excellent stability (>10 000 cycles), fast response, low hysteresis, and good washability. Furthermore, the piezoresistive core-sheath fiber possesses bending-insensitiveness and negligible torsion-sensitive properties, and the strain sensing performance of piezoresistive fibers maintains a high degree of stability under harsh conditions. On the basis of this high level of performance, the fiber-shaped strain sensor can accurately detect both subtle and large-scale human movements by embedding it in gloves and garments or by directly attaching it to the skin. The current results indicate that the proposed stretchable strain sensor has many potential applications in health monitoring, human-machine interfaces, soft robotics, and wearable electronics.

This letter presented a pencil-on-paper-based ecofriendly capacitive touchpad fabricated through a low-cost lab- and solvent-free fabrication process. Economical, readily available, and biodegradable materials, such as pencil and paper, have been used for sensor fabrication. A touchpad based on five such sensors has been developed and evaluated by using it as a user control interface to on/off LEDs and displaying results on LCD and mobile app. The graphite sensors in the user interface have been shielded from the direct interaction of humans and the environment using changeable cling film to make the interface reliable and reusable. The interface can be used in different conditions and users by changing the shielding film. Simultaneously, the system's functionality will remain consistent and functioned similarly to the conventional touch sensors and buttons. These recyclable and easily arrayed touch sensor-based keypads can contribute to future developments in disposable and lightweight interfaces for human-machine interface, medical and healthcare applications, smart packaging, security monitoring, and consumer products.

Wearable and stretchable strain sensors have potential values in the fields of human motion and health monitoring, flexible electronics, and soft robotic skin. The wearable and stretchable strain sensors can be directly attached to human skin, providing visualized detection for human motions and personal healthcare. Conductive polymer composites (CPC) composed of conductive fillers and flexible polymers have the advantages of high stretchability, good flexibility, superior durability, which can be used to prepare flexible strain sensors with large working strain and outstanding sensitivity. This review has put forward a comprehensive summary on the fabrication methods, advanced mechanisms and strain sensing abilities of CPC strain sensors reported in recent years, especially the sensors with superior performance. Finally, the structural design, bionic function, integration technology and further application of CPC strain sensors are prospected.

Flexible strain sensors are attracting more and more attentions in wearable devices and electronic skins. Currently, the fabrication of flexible strain sensor with features of high sensitivity and wide linear working range is still a great challenge. Herein, a stretchable and wearable strain sensor is fabricated with the ZnO nanoparticles (NPs)/graphene nanoplatelets nanocomposite (ZnO/GNP NC) as both the sensing element and reinforcement phase. The ZnO/GNP NC strain sensor exhibits fascinating performance, including high mechanical properties (fracture strength of 0.6 MPa and elongation of ~ 90%), large working range of 0–44%, high sensitivity (gauge factor of 8.8–12.8), and good reproducibility over 1700 cycles. Importantly, the ZnO/GNP NC strain sensor holds perfect linearity (R2 = 0.999) in the whole working range, which can be attributed to the coupling effect between the ZnO NPs and the GNP. The ZnO/GNP NC strain sensor can not only detect large human motions such as elbow rotation, wrist rotation, clenching fist, and waving badminton racket, but also monitor subtle human motions in real time, such as pulse, phonation, coughing, and swallowing. The wide linear working range of the ZnO/GNP NC strain sensor makes it a potential choice for the application of wearable devices.

Ultrasensitive and highly stretchable bilayer strain sensor based on bandage-assisted woven fabric with reduced graphene oxide and liquid metal

Due to their growing adaptability, there has been an increased awareness and interest in artificial intelligence and wearable strain sensors across various fields of study and industry. Researchers are developing new instruments to investigate novel gadgets, electronic skins, wearable wellness care, and robotics for precise detection needs. Machine learning and AI techniques are gaining attention for their ability to enhance analytical procedures. This review examines the benefits of using AI techniques and wearable sensors to modernize and optimize data analysis tasks. Developing wearable strain sensor technology is crucial in overcoming the current challenges and achieving breakthroughs in nanotechnology. Wearables with AI have the potential to enhance early detection, intelligent diagnosis, and lifelong monitoring for improved well-being. There's great potential in wearable strain sensors, particularly those with flexible features such as stretchability and high detection power. The growing interest in skin-attachable wearable devices is fueled by their diverse applications in human-machine systems, healthcare, and AI. This review provides a brief overview of flexible wearable strain sensing systems, existing challenges, and prospects.