This review provides an overview of the current state‐of‐the‐art of the emerging field of flexible multifunctional sensors for wearable and robotic applications. In these application sectors, there is a demand for high sensitivity, accuracy, reproducibility, mechanical flexibility, and low cost. The ability to empower robots and future electronic skin (e‐skin) with high resolution, high sensitivity, and rapid response sensing capabilities is of interest to a broad range of applications including wearable healthcare devices, biomedical prosthesis, and human–machine interacting robots such as service robots for the elderly and electronic skin to provide a range of diagnostic and monitoring capabilities. A range of sensory mechanisms is examined including piezoelectric, pyroelectric, piezoresistive, and there is particular emphasis on hybrid sensors that provide multifunctional sensing capability. As an alternative to the physical sensors described above, optical sensors have the potential to be used as a robot or e‐skin; this includes sensory color changes using photonic crystals, liquid crystals, and mechanochromic effects. Potential future areas of research are discussed and the challenge for these exciting materials is to enhance their integration into wearables and robotic applications.

A switched inertance hydraulic system uses a fast switching valve to control flow or pressure and is potentially very efficient as it does not rely on dissipation of power by throttling. This article studies its performance using an analytical method which efficiently describes the system in the time domain and frequency domain. A lumped parameter model and a distributed parameter model have been used for investigation using different parameters and conditions. The analytical models have been validated in experiments and the results on a prototype device show a very promising performance. The proposed analytical models are effective for understanding, analysing and optimizing the characteristics and performance of a switched inertance hydraulic system.

This article reviews recent developments in fluid power engineering, particularly its market and research in China. The development and new techniques of the pump, valve, and actuator are presented in brief with a discussion of two typical modern fluid power systems, which are the switched inertance hydraulic system and the hydraulic quadruped robot. Challenges and recommendations are given in four aspects including efficiency, compactness and integration, cleanliness, and fluid power education.

Flexible material‐based soft robots are widely used in various areas. In many situations, the suitable soft robots should be rapidly fabricated to complete the urgent tasks (such as rescue), so the facile fabricating methods of the multifunctional soft robots are still in urgent needs. In this work, the origami structure is employed to design vacuum‐powered silicone rubber artificial muscles, which can perform multiple motions, including contraction, bending, twisting, and radial motions. Artificial muscles can be used for rapid reconfiguration of different soft robots, just like the “building bricks”. Based on these artificial muscles, four soft robots with different functions, including an omnidirectional quadruped robot, a flexible gripper, a flexible wrist, and a pipe‐climbing robot, are reconfigured to complete different tasks. The proposed origami artificial muscles offer a facile and rapid fabricating method of flexible material‐based soft robots, and also greatly improve the utilization rate of flexible materials.

Engineering materials and devices can be damaged during their service life as a result of mechanical fatigue, punctures, electrical breakdown, and electrochemical corrosion. This damage can lead to unexpected failure during operation, which requires regular inspection, repair, and replacement of the products, resulting in additional energy consumption and cost. During operation in challenging, extreme, or harsh environments, such as those encountered in high or low temperature, nuclear, offshore, space, and deep mining environments, the robustness and stability of materials and devices are extremely important. Over recent decades, significant effort has been invested into improving the robustness and stability of materials through either structural design, the introduction of new chemistry, or improved manufacturing processes. Inspired by natural systems, the creation of self‐healing materials has the potential to overcome these challenges and provide a route to achieve dynamic repair during service. Current research on self‐healing polymers remains in its infancy, and self‐healing behavior under harsh and extreme conditions is a particularly untapped area of research. Here, the self‐healing mechanisms and performance of materials under a variety of harsh environments are discussed. An overview of polymer‐based devices developed for a range of challenging environments is provided, along with areas for future research.

working. With the development of fabrication technology of soft robots, entirely flexible manipulator [9][10][11][12][13] and gripper [14][15][16][17][18] have been achieved. However, none of the existing soft actuators are appropriate for entirely flexible joint. Therefore, flexible twisting actuators with diverse functions and easy manufacture are needed to be designed.Pressurized air has been widely used as the main power source for soft actuators to achieve twisting or rotary motion, although an overpressure risk needs to be carefully considered in actuator design. [19][20][21][22][23][24][25] Lee et al., [19] Morin et al., [20] and Lazarus et al. [21] designed a range of twisting actuators powered by positive pressure with twisting angles of less than 62°. To improve performance, Connolly et al. [22] developed soft fluidic actuators reinforced by fibers, which can rotate up to 180°. They combined the actuators with different fiber angles in series to create a wormlike soft robot that could navigate through a pipe and insert prongs into holes. However, the actuator length needs to be increased to achieve larger twisting angles, which limits their application as flexible joints, since such structure requires a short length. Gorissen et al. [23] proposed a new soft actuator based on angled pneumatic balloon actuator arrays that can perform a large twisting angle of 71° without compromising an increase of actuator length. Four actuators were used to create a two degrees of freedom (DoFs) tilting mirror platform, which could turn at angles of ±25° and ± 29°. However, the actuator is not suitable for the development of soft robots due to its inherent sheet-like structure. A continuous rotary actuator driven by pressurized air was proposed by Gong et al. [24] who designed a pneumatic rotary actuator based on peristaltic motion of elastomeric materials. The actuator consisted of an inflatable stator that was paired with a rotor. A four-wheeled vehicle, which used a combination of the actuators, was prototyped and achieved a speed of 37 mm s −1 . The vehicle could travel over irregular terrains and survive high mechanical impact loads. The actuator was completely soft, but the cyclic fatigue behavior of the elastomeric bladders and delamination at the bonded interfaces were not clear and requires further investigation.Recently, pioneering studies employed the use of vacuum power to achieve torsional motion. [26][27][28] Yang et al. [26] exploited an elastomeric structure which contained a number of elastic beams and interconnected deformable cavities sealed within a Vacuum-powered soft pneumatic actuators (V-SPAs) are a promising enabling technology for a wide range of emerging applications, including artificial muscles, programmable locomotion, and flexible grippers. This is due to their flexible deformation, clean power supply, safe interaction with users, and high reliability compared with alternative actuators. A new vacuum-powered soft pneumatic twisting actuator (V-SPTA) is designed, which has a single seamless...

The triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are two recently developed technologies for effective harvesting of ambient mechanical energy for the creation of self-powered systems. The advantages of TENGs and PENGs which include large open-circuit output voltage, low cost, ease of fabrication, and high conversion efficiency enable their application as new flexible sensors, wearable devices, soft robotics, and machines. This perspective provides an overview of the current state of the art in triboelectric and piezoelectric devices that are used as self-powered sensors and energy harvesters for soft robots and machines; hybrid approaches that combine the advantages of both mechanisms are also discussed. To improve system performance and efficiency, the potential of providing self-powered soft systems with a degree of multifunctionality is investigated. This includes optical sensing, transparency, self-healing, water resistance, photo-luminescence, or an ability to operate in hostile environments such as low temperature, high humidity, or high strain/stretch. Finally, areas for future research directions are identified.

We have developed carbon fibre based flexible piezoresistive composites to fabricate a new pneumatic soft finger with an inherent sensing capability, much like a human finger.