A majority of soft‐body creatures evolve armor or shells to protect themselves. Similar protection demand is for flexible electronics working in complex environments. Existing works mainly focus on improving the sensing capabilities such as electronic skin (E‐skin). Inspired by snakeskin, a novel electronic armor (E‐armor) is proposed, which not only possesses mechanical flexibility and electronic functions similar to E‐skin, but is also able to protect itself and the underlying soft body from external physical damage. The geometry of the kirigami mechanical metamaterial (Kiri‐MM) ensures auxetic stretchability and meanwhile large areal coverage for sufficient protection. Moreover, to suppress the inherent but undesired out‐of‐plane buckling of conventional Kiri‐MMs for conformal applications, soft hinges are used to form a distinct soft (hinges)‐rigid (tiles) configuration. Analytical, computational, and experimental studies of the mechanical behaviors of the soft‐hinge Kiri‐MM E‐armor demonstrate the merits of this design, i.e., stretchability, conformability, and protectability, as applied to flexible electronics. Deploying a conductive soft material at the hinges enables facile wiring strategies for large‐scale circuit arrays. Functional E‐armor systems for controllable display and sensing purposes provide simple examples of a wide spectrum of applications of this concept.

With exceptional performance, flexible sensors have found broad applications, including human health monitoring, motion detection, human-machine interaction, smart wearable technology, and robot control. Crack-sensitive structures based on animal bionics have also caught increasing attention because of their extraordinary sensitivity. Crack-based flexible sensors, which combine the flexibility of the flexible sensors and the high sensitivity of the crack sensing structures, have seen rapid development in recent years. In this review, we summarize the sensing mechanisms of the flexible sensors based on the crack disconnection-reconnection process. The effects of crack type, depth, and density on sensor performance are explored in detail. We also discuss the performance characteristics and applications of the crack-based flexible sensors with various materials, design structures, and crack generation procedures. Finally, the main challenges of the crack-based flexible sensors are also reviewed, and several research directions are proposed.

The facial expressions are a mirror of the elusive emotion hidden in the mind, and thus, capturing expressions is a crucial way of merging the inward world and virtual world. However, typical facial expression recognition (FER) systems are restricted by environments where faces must be clearly seen for computer vision, or rigid devices that are not suitable for the time-dynamic, curvilinear faces. Here, we present a robust, highly wearable FER system that is based on deep-learning-assisted, soft epidermal electronics. The epidermal electronics that can fully conform on faces enable high-fidelity biosignal acquisition without hindering spontaneous facial expressions, releasing the constraint of movement, space, and light. The deep learning method can significantly enhance the recognition accuracy of facial expression types and intensities based on a small sample. The proposed wearable FER system is superior for wide applicability and high accuracy. The FER system is suitable for the individual and shows essential robustness to different light, occlusion, and various face poses. It is totally different from but complementary to the computer vision technology that is merely suitable for simultaneous FER of multiple individuals in a specific place. This wearable FER system is successfully applied to human-avatar emotion interaction and verbal communication disambiguation in a real-life environment, enabling promising human-computer interaction applications.

Advances in fabric strain sensors have established a route to comfortableto-wear flexible electronics with particularly remarkable permeability and low modulus due to their porous fabric microstructure. A key challenge that remains unsolved is to regulate the sensor response via on-demand design for a variety of application scenarios to sufficiently exploit the highest possible sensitivity. While recent reports have described a variety of options in varying the material and orientation of the overall fiber mat, the development of approaches where multiple sensors with different responses can be integrated on a single substrate without affecting macroscopic mechanical properties remains an area of continued interest. Herein, a simple mechanical strategy is reported, which plates the patterned functional material on the fabric mat at a pre-stretched state in the prescribed direction, and control of direction and prestrain forms either sensors with different responses or strain-insensitive interconnects. A systematic study has revealed the underlying mechanism of this strategy, which can serve as a guideline for the on-demand design and fabrication of fabric strain sensors. Demonstration applications in motion monitoring bandages and gesture recognition gloves illustrate capabilities in functional epidermal sensing devices.

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