Tuning Strain Sensor Performance via Programmed Thin-Film Crack Evolution.

With the rapid development of soft electronics, flexible and stretchable strain sensors are highly desirable. However, coupling of high sensitivity and stretchability in a single strain sensor remains a challenge. Herein, a kind of conductive elastomer is constructed with poly(dimethylsiloxane) (PDMS) and silylated cellulose nanocrystal (SCNC)/carbon nanotube (CNT) nanohybrids through a facile one-pot solution-casting method. The hydrophobic SCNCs can effectively facilitate the dispersion of CNTs in PDMS and synergistically improve the interfacial compatibility between CNTs and the PDMS matrix, resulting in favorable stress and electron transfer in the polymer network. Due to the outstanding electrical conductivity of CNTs and the excellent dispersity and high mechanical performance of SCNCs, combined with the good compatibility between SCNC-mediated carbon nanotubes (SCNC-CNTs) and PDMS, the resulting composite elastomer (SCNC-CNT/PDMS) shows high electrical conductivity (∼2.77 S m-1), tensile strength (∼5.72 MPa), and fatigue resistance properties. The strain sensor assembled by SCNC-CNT/PDMS demonstrates a high strain range above 100%, appealing strain sensitivity with a gauge factor of 37.11 at 50-100% strain, and long-term stability and durability, which is capable of monitoring both real-time human motions and acoustic vibrations. This work paves a new way for the design and controllable preparation of flexible and stretchable conductive elastomers, demonstrating promising applications in wearable devices and intelligent electronics.

In intelligent manufacturing and robotic technology, various sensors must be integrated with equipment. In addition to traditional sensors, stretchable sensors are particularly attractive for applications in robotics and wearable devices. In this study, a piezoresistive stretchable strain sensor based on laser-induced graphene (LIG) was proposed and developed. A three-dimensional, porous LIG structure fabricated from polyimide (PI) film using laser scanning was used as the sensing layer of the strain sensor. Two LIG pattern structures (parallel and vertical) were fabricated and integrated within the LIG strain sensors. Scanning electron microscopy, an X-ray energy dispersive spectrometer, and Raman scattering spectroscopy were used to examine the microstructure of the LIG sensing layer. The performance and strain sensing properties of the parallel and vertical stretchable LIG strain sensors were investigated in tensile tests. The relative resistance changes and the gauge factors of the parallel and vertical LIG strain sensors were quantified. The parallel strain sensor achieved a high gauge factor of 15.79 in the applied strain range of 10% to 20%. It also had high sensitivity, excellent repeatability, good durability, and fast response times during the tensile experiments. The developed LIG strain sensor can be used for the real-time monitoring of human motions such like finger bending, wrist bending, and throat swallowing.

Stretchable strain sensors that can detect and monitor human motion have attracted enormous attention in the field. To realize fully the translation of materials for stretchable strain sensors, it is important to make the fabrication way less complex and lessen the production cost. This paper investigated low-cost graphite-VHB strain sensors prepared by simple friction-transfer method. Designed by friction-transfer method, the graphite-VHB strain sensor possesses good flexibility, light weight, high stretchability and tunable range of GF. The gauge factor of the sample was 20 when strain rate was 3% and could be over 1000 when the strain rate was 50%. The addition of protection layer and pre-aging process have contributions to expand the GF of the sample. By attaching our strain sensor to the sample of mechanical arm, the resistance change of the sensor perfectly fitted to the deformation of the arm, which shows its potential in application of soft robotics and mechanical fields. The results showed the friction-transfer method is a simple and low-cost method, featured with environmental advantage that avoids chemical wastes.

Stretchable strain sensors with dentate groove structure for enhanced sensing recoverability

A highly flexible and stretchable strain sensor has been prepared by coating chemical reduction of graphene oxide on electrospun polyurethane nanofiber mats. The sensor exhibits an ohmic behavior regardless of applied strains and the current monotonically increases with the increase of the tensile strain. The morphology and stability of electrospun polyurethane nanocomposite mats were also studied. The flexible and stretchable strain sensor has great potential for practical application such as efficient human-motion detection. This cheap and simple process of graphene layer provides an effective fabrication for graphene stretchable electronic devices and strain sensors due to excellent stability and electrical proper.

High resolution screen-printing of carbon black/carbon nanotube composite for stretchable and wearable strain sensor with controllable sensitivity

Owing to their potential applicability in wearable devices and intelligent robots, stretchable strain sensors have been widely investigated. However, fabricating sensors with high sensitivity, wide sensing range, high repeatability, robustness, and capability for continuous production remains challenging. Herein, a deterministic‐contact‐resistance braided structure (DCRBS)‐based stretchable strain sensor is proposed. The polyester yarns in the sensor tightly trap the silver fibers with the latex thread substrate to form a periodic “Y” structure to avoid slippage of the fibers, thereby facilitating deterministic contact and separation between the silver fibers during cyclic stretching. Owing to this braided structure, the strain sensor exhibits high repeatability (repeatability error = 3.74%), high sensitivity (gauge factor up to 140), wide sensing range (50%), and high robustness (washability, insensitivity to micro‐defects). Additionally, the strain sensor can be continuously mass produced using mature raw materials and processing technology. Because of its demonstrated excellent performance, the strain sensor can find applications in human motion monitoring, rehabilitation medicine, and robotic control.

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.

Silver nanowires (AgNWs), having excellent electrical conductivity, transparency, and flexibility in polymer composites, are reliable options for developing various sensors. As transparent conductive electrodes (TCEs), AgNWs are applied in optoelectronics, organic electronics, energy devices, and flexible electronics. In recent times, research groups across the globe have been concentrating on developing flexible and stretchable strain sensors with a specific focus on material combinations, fabrication methods, and performance characteristics. Such sensors are gaining attention in human motion monitoring, wearable electronics, advanced healthcare, human-machine interfaces, soft robotics, etc. AgNWs, as a conducting network, enhance the sensing characteristics of stretchable strain-sensing polymer composites. This review article presents the recent developments in resistive stretchable strain sensors with AgNWs as a single or additional filler material in substrates such as polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), polyurethane (PU), and other substrates. The focus is on the material combinations, fabrication methods, working principles, specific applications, and performance metrics such as sensitivity, stretchability, durability, transparency, hysteresis, linearity, and additional features, including self-healing multifunctional capabilities.

3D microprinting of QR-code integrated hydrogel tactile sensor for real-time E-healthcare

Detecting dynamic multi-scale human motion requires the stretchable strain sensor to possess outstanding properties in every aspect. Unlike conventional strain sensors which focus on changing conductive materials and preparing methods, we introduce a novel mechanical structure design to control the performance of the strain sensor. The performance of the device can be simply controlled by the structural design rather than complex materials adjustments. So the complexity of the material preparation will be greatly reduced, thus promotes the materials translation and production. By designing an asymmetric structure of elastomer substrate and protect layer with different adjustable parameters, the strain distribution in elastomer can be controlled, which finally change the performance of strain sensors. The experiment results illustrated our works on changing the stretchablity and sensitivity of the strain sensors. Application tests on human body including subtle-scale strain like pulse and large-scale strain like elbow bending are conducted to prove our capability for multi-scale motion detecting.

A sparse-dense hierarchical structured conductive elastomer composites for highly sensitive and stretchable strain sensor

Wrinkled, cracked and bridged carbon networks for highly sensitive and stretchable strain sensors

Human-machine interfaces (HMIs) are essential tools facilitating effective interactions between users and intelligent systems. However, current wearable HMIs, particularly smart gloves, often face challenges in precisely recognizing subtle finger movements and delivering real-time tactile feedback, limiting their operational effectiveness and user immersion. To overcome these challenges, we propose an intelligent glove system integrating highly stretchable liquid metal-based strain sensors and programmable electromagnetic feedback actuators to realize closed-loop immersive human-machine interaction. The strain sensors achieve superior stretchability (over 200%), linear response, minimal hysteresis, and robust durability, effectively capturing complex hand movements. Gesture recognition, performed by a convolutional neural network, achieves an accuracy of 98% across common gestures, demonstrating exceptional precision and robustness. Furthermore, the glove integrates soft programmable electromagnetic actuators that generate an output force greater than 0.25 N, providing adjustable and precise tactile feedback via pulse-width modulation. This allows users to intuitively perceive tactile sensations in human-machine interaction scenarios, including robotic manipulation and motion guidance tasks. Comprehensive experiments confirm the intelligent glove system’s superior real-time responsiveness and adaptability in dynamic environments. This advanced closed-loop HMI glove significantly enhances operator immersion, operational accuracy, and interaction realism, demonstrating strong potential in robotics, virtual reality, and remote teleoperation applications.

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