The smart sensor is an effective way to detect damage and improve structural safety in structural health monitoring. Microcapsule‐based visualization sensors stand out from the smart sensors. Here, the research progress of microcapsule visualization materials in recent years is summarized and the sensing principles, influence factors, performances, applications, and future prospects are introduced. The way to achieve the visualizing function of microcapsule visualization sensors is the fabrication of microcapsules that are encapsulated with solutions of dyes or indicator. When the protective shell of microcapsules is broken, the dyes will be released and activated under optical, chemical, or mechanical conditions. These visualized microcapsules can be added to the interior of the structure or prepared as a coating to provide structural health monitoring of the interior and surface of the structure. They can accurately detect microcracks and highlight them in bright colors. Additionally, the structural health monitoring applications of microcapsule visualization sensing coatings in concrete, asphalt, and steel are presented with detailed examples. The development and application of these microcapsule visualization sensors are of great significance in improving the structural life and avoiding structural failure in engineering.

A visual microcapsule sensor for concrete damage detection by color variation without the requirement for additional activators.

To avoid conductive failure due to the cracks of the metal thin film under external loads for the wearable strain sensor, a stretchable metal/polymer composite film embedded with silver nanowires (AgNWs) was examined as a potential candidate. The combination of Ag film and AgNWs enabled the fabrication of a conductive film that was applied as a high sensitivity strain sensor, with gauge factors of 7.1 under the applied strain of 0–10% and 21.1 under the applied strain of 10–30%. Furthermore, the strain sensor was demonstrated to be highly reversible and remained stable after 1000 bending cycles. These results indicated that the AgNWs could act as elastic conductive bridges across cracks in the metal film to maintain high conductivity under tensile and bending loads. As such, the strain sensor engineered herein was successfully applied in the real-time detection and monitoring of large motions of joints and subtle motions of the mouth.

Wearable health monitoring smart systems based on flexible metal films are considered to be the next generation of devices for remote medical practice. However, cracks on the metallic surface of the films and difficulty in repeatability are the key issues that restrict the application of such wearable strain sensors. In this work, a flexible wearable strain sensor with high sensitivity and good repeatability was fabricated based on a patterned metal/polymer composite material fabricated through nanoimprint lithography. The mechanical properties were measured through cyclic tension and bending loading. The sensor exhibited a small ΔR/R0 error line for multiple test pieces, indicating the good mechanical stability and repeatability of the fabricated device. Moreover, the sensor possesses high sensitivity with gauge factors of 10 for strain less than 50% and 40 for strain from 50% to 70%. Various activities were successfully detected in real-time, such as swallowing, closing/opening of the mouth, and multi-angle bending of elbow, which illustrates the proposed sensor’s potential as a wearable device for the human body.

During the fabrication of metal/polymer bilayer gratings by nanoimprint lithography, adhesion and friction forces at the interfaces can deform and damage the transferred pattern of the bilayer grating during the demoulding process. To improve the quality of bilayer gratings, the effects of the aspect ratio and metal layer thickness on deformation and stress during the demoulding process in the nanoimprinting of bilayer gratings were investigated. This information was used to determine the optimal grating parameters. The results for the von Mises stress and deformation of bilayer gratings are discussed in detail. The effects of the aspect ratio and metal layer thickness on the grating quality are then considered.