There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin‐mountable, and wearable strain sensors are needed for several potential applications including personalized health‐monitoring, human motion detection, human‐machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin‐mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.

Transition metal dichalcogenides (TMDs) layers of molecular thickness, in particular molybdenum disulfide (MoS 2 ), become increasingly important as active elements for mechanically flexible/stretchable electronics owing to their relatively high carrier mobility, wide bandgap, and mechanical flexibility. Although the superior electronic properties of TMD transistors are usually integrated into rigid silicon wafers or glass substrates, the achievement of similar device performance on flexible substrates remains quite a challenge. The present work successfully addresses this challenge by a novel process architecture consisting of a solution‐based polyimide (PI) flexible substrate in which laser‐welded silver nanowires are embedded, a hybrid organic/inorganic gate insulator, and multilayers of MoS 2 . Transistors fabricated according to this process scheme have decent properties: a field‐effect‐mobility as high as 141 cm 2 V −1 s −1 and an I on / I off ratio as high as 5 × 10 5 . Furthermore, no apparent degradation in the device properties is observed under systematic cyclic bending tests with bending radii of 10 and 5 mm. Overall electrical and mechanical results provide potentially important applications in the fabrication of versatile areas of flexible integrated circuitry.

On page 2426, C. P. Grigoropoulos, S. Kim, Y. K. Hong, and co-workers demonstrate a novel process architecture for flexible electronics. The multilayer molybdenum disulfide thin-film transistor array fabricated according to this scheme exhibits not only outstanding device performances, but also no apparent degradation under various mechanical stresses. These results could provide important applications in the fabrication of flexible integrated circuitry for various versatile functions.

A transparent and flexible force sensor film based on polymer-waveguide is proposed as described by K. U. Kyung and co-workers on page 4474. Microscale transparent structures enable the sensor to work on curvilinear surfaces such as human skin or flexible displays

A polymer-waveguide-based transparent and flexible force sensor array is proposed, which satisfies the principal requirements for a tactile sensor working on curvilinear surfaces, such as thinfilm architecture (thickness < 150 μm), localized force sensing (ca. 0-3 N), multiple-point re cognition (27 points), bending robustness (10.8% degradation at R = 1.5 mm), and fast response (bandwidth > 16 Hz).

Haptic affection plays a crucial role in user experience, particularly in the automotive industry where the tactile quality of components can influence customer satisfaction. This study aims to accurately predict the affective property of a car door by only watching the force or torque profile of it when opening. To this end, a deep learning model is designed to capture the underlying relationships between force profiles and user-defined adjective ratings, providing insights into the door-opening experience. The dataset employed in this research includes force profiles and user adjective ratings collected from six distinct car models, reflecting a diverse set of door-opening characteristics and tactile feedback. The model’s performance is assessed using Leave-One-Out Cross-Validation, a method that measures its generalization capability on unseen data. The results demonstrate that the proposed model achieves a high level of prediction accuracy, indicating its potential in various applications related to haptic affection and design optimization in the automotive industry.

This study introduces the soft tactile electromagnetic (STEM) actuator, a compact and wearable haptic device designed to deliver multimodal tactile feedback in virtual environments. The actuator employs soft materials as both an energy-storing and encasing structure, enabling out-of-plane deformations in response to arbitrary input signals while ensuring high wearability. Magnetic reinforcements, including a soft magnetic cap and a ferromagnetic pole piece, minimize magnetic flux leakage, effectively amplifying output force along with protrusion to enable precise and varied haptic feedback. The actuator generates multimodal tactile stimuli, including force, impulse, and vibration, surpassing conventional vibrotactile devices in delivering more varied and dynamic feedback. Experimental evaluation of the actuator's mechanical performance demonstrates its ability to produce both low- and high-frequency tactile feedback. A user study evaluating perception thresholds and signal recognition accuracy found that participants identified eight distinct tactile signals with an average accuracy of 91%, confirming the actuator's capacity to deliver distinguishable multimodal feedback. These findings underscore the feasibility of the STEM actuator for immersive haptic interactions and highlight its potential applications in virtual reality.

In this article, a mobile robot equipped with magnetic tracks was developed to explore the corrugated ceilings of shipping containers. To address instability caused by uneven surfaces, we designed magnetic auxiliary wheels based on static force analysis and finite-element method simulations. These auxiliary wheels facilitate the robot’s ability to steer, enabling both translational and rotational movements to any location on the ceiling. Experimental performance evaluations show that the robot can achieve a linear speed faster than 0.1 m/s while carrying a load of 30 kg, which is 1.86 times its own weight. Moreover, the robot can rotate beyond 23° at over 8.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\ }^ \circ }/\mathrm{s}$</tex-math></inline-formula> with a 15-kg load and move diagonally on the corrugated ceiling. We also demonstrate that the robot can navigate to an arbitrary target point on a real 40-ft shipping container ceiling using a kinematic model-based algorithm. This confirms the feasibility of applying the robot in actual shipping container environments and supports its potential for future autonomous operation.

This study presents the design, optimization, and evaluation of an optical fiber-based force myography (FMG) sensor for hand gesture and grasping force estimation, with potential haptic applications for realistic human-robot interaction (HRI). The sensor, with a diameter of 10 mm and a thickness of 2 mm, is designed to be flexible and easily integrated into clothing or sleeves. Utilizing the principle of light loss due to touch in bent optical fibers, the sensor demonstrates high sensitivity and stability. Through simulation, the sensor design parameters, such as the bending radius and the number of weavings, were optimized to achieve a high signal-to-noise ratio and sensitivity. The fabricated sensor showed excellent performance in various experiments, including high sensitivity, repeatability, and accurate force estimation. A wearable system with four embedded sensors achieved 91% hand gesture recognition accuracy using long short-term memory neural network and grasping force estimation exhibited high linearity across different ball grip types. These findings demonstrate the sensor practicality, with future research focusing on improving durability and exploring broader applications in haptics and HRI.

There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin‐mountable, and wearable strain sensors are needed for several potential applications including personalized health‐monitoring, human motion detection, human‐machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin‐mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.

Transition metal dichalcogenides (TMDs) layers of molecular thickness, in particular molybdenum disulfide (MoS 2 ), become increasingly important as active elements for mechanically flexible/stretchable electronics owing to their relatively high carrier mobility, wide bandgap, and mechanical flexibility. Although the superior electronic properties of TMD transistors are usually integrated into rigid silicon wafers or glass substrates, the achievement of similar device performance on flexible substrates remains quite a challenge. The present work successfully addresses this challenge by a novel process architecture consisting of a solution‐based polyimide (PI) flexible substrate in which laser‐welded silver nanowires are embedded, a hybrid organic/inorganic gate insulator, and multilayers of MoS 2 . Transistors fabricated according to this process scheme have decent properties: a field‐effect‐mobility as high as 141 cm 2 V −1 s −1 and an I on / I off ratio as high as 5 × 10 5 . Furthermore, no apparent degradation in the device properties is observed under systematic cyclic bending tests with bending radii of 10 and 5 mm. Overall electrical and mechanical results provide potentially important applications in the fabrication of versatile areas of flexible integrated circuitry.

On page 2426, C. P. Grigoropoulos, S. Kim, Y. K. Hong, and co-workers demonstrate a novel process architecture for flexible electronics. The multilayer molybdenum disulfide thin-film transistor array fabricated according to this scheme exhibits not only outstanding device performances, but also no apparent degradation under various mechanical stresses. These results could provide important applications in the fabrication of flexible integrated circuitry for various versatile functions.

A transparent and flexible force sensor film based on polymer-waveguide is proposed as described by K. U. Kyung and co-workers on page 4474. Microscale transparent structures enable the sensor to work on curvilinear surfaces such as human skin or flexible displays