Gait event detection is a requirement for clinical diagnosis and control strategies for power exoskeletons and rehabilitation robots. Smart insoles are widely used in gait research as they are easy to wear. However, current sensor insoles still have some problems, such as being easily affected by temperature, low sensor sensitivity and discomfort while wearing. To solve these problems, in this work we developed a fully flexible insole based on a high-sensitivity capacitive sensor. High sensitivity was achieved by preparing the dielectric material with a porous structure and full flexibility was obtained by using customized compliant electrodes. The porous structure was produced by mixing xylitol with silicone rubber and the compliant electrode was manufactured by mixing conductive carbon nanotubes into plasticized polyvinyl chloride. The mechanical and sensing properties of the sensor were studied. The results show that our sensor has high sensitivity, a good dynamic response, a fast response time (about 80 ms), a large pressure detection range (0–500 kPa), good durability (>1000 cycles) and is little influenced by temperature. We integrated the sensors into the self-made flexible silicone insole. A wireless data transmission measurement module was developed for ease of use. Finally, we found that the prepared sensor insole is able to detect gait events.

The rapid development of robotics technology and human-machine interaction has created a growing demand for accurate and reliable three-dimensional force measurement. Flexible force sensors, known for their high sensitivity, bendability, and customizability, offer an effective solution for achieving accurate three-dimensional force measurements. This review aims to comprehensively assess the research progress of flexible force sensors in the field of three-dimensional force detection and explore their potential applications in various areas. Firstly, the working principles and structural characteristics of flexible three-dimensional force sensors are introduced. Then, the materials utilized by these sensors are discussed. After that, the decoupling methods of three-dimensional force sensors are summarized. Finally, the review summarizes the current applications of flexible three-dimensional force sensors in robotics, adjuvant therapy, human monitoring field, and controllers. By comprehensively analyzing existing literature and research results, this review offers important guidance for further advancing the application of flexible force sensors in the field of three-dimensional force detection. With the continuous development of technology, flexible three-dimensional force sensors are expected to increasingly play a significant role in the critical task of achieving accurate three-dimensional force detection.

Flexible strain sensors based on liquid metal have great application potential in wearable devices, biomedicine and soft robots due to their huge deformability, low hysteresis and high durability. However, the existing fabrication method for the sensor faced with some challenges such as high cost, cumbersome process and long preparation time, which affect the development of the flexible sensors. Herein, this paper reported a flexible strain sensor based on liquid metal (FSS-LM) through atomizing spraying process. We optimized the spraying process, remarkably improving spraying quality. On the basis of the optimized spraying process, we quickly fabricated the FSS-LM with low cost. The sensor shows low hysteresis (1.18%), fast response (212ms), long durability (2000 stretching and releasing cycles), excellent dynamic and static performance, as well as good repeatability. Finally, the developed sensor was used to detect a variety of activities, including the bending of human joints and robot fingers, expansion of the balloon and the growth of plant stems. The results show that the FSS-LM exhibits great potential in the field of wearable devices.

Microchannel-type flexible strain sensors have aroused great interest in the fields of medical devices, artificial skin, and soft robotics due to their high stretchability, low hysteresis, and excellent durability. However, they are often limited in practical applications because of low sensitivity. In this paper, a novel liquid metal-based sensor with non-uniform strain distribution was developed, aimed at enhancing the sensor sensitivity. The sensor was designed with localized changes in cross-sectional area using 3D printed molds. Compared with the traditional microchannel-type flexible strain sensors with uniform strain distribution, the sensitivity of our developed sensor increased by 18%, demonstrating a good improvement. In addition, the sensor exhibits low hysteresis (0.59%), fast response and recovery time (184 ms), long durability (1000 cycles of stretching/releasing at 100% strain), and excellent dynamic and static performance. Finally, the sensor was applied to a robotic joint and human body joints such as the neck, elbow, knee, and wrist to capture various activities. The results indicate that the developed flexible strain sensor exhibits outstanding performance, making it a promising candidate for wearable devices.