Li et al. designed a wearable assistive device for the hip joint during walking using a plasticized polyvinyl chloride (PVC) gel and meshed electrode-based DEA [83]. The device had a control and power system for outdoor walking, as shown in Figure 9a, and exhibited biological muscle behaviour with high deformation (>10%), high stress (>90 kPa) and variable stiffness. A multi-layer structure was introduced to increase the output force. When actuated, the DEA contracts and generates a moment on the hip joint to move the thigh forward, see Figure 9a. The maximum output force was 94 N, and the weight of the device was 2 kg. In a preliminary evaluation, a hemiparetic stroke patient successfully performed a 10 m to-and-fro straight-line walking task at a walking speed of 0.8 m/s. This assistive device facilitates the natural movement of the patient, increases the step length, and decreases muscle activity; it also has the advantages of a lightweight nature, fast response time, and low drive voltage (400 V).
In addition to mimicking the contractive behaviour of skeleton muscles, DEAs are also able to provide a high compression pressure. Disorders associated with the lower extremity venous system significantly affect the quality of life of people. These disorders often cause orthostatic hypotension, oedema, deep vein thrombosis and other conditions related to insufficient venous blood return. A DEA-based active compression bandage (ACB) for assisting the human lower extremity venous system was designed, prototyped and tested by Pourazadi et al. [84]; see Figure 9b. A customised calf prototype was developed to measure the pressure applied by the compression of DEAs fabricated using silicone substrates and copper electrodes. A finite element model (FEM) was developed to simulate the electromechanical behaviour of the DEA. The compression range of the ACB was approximately 15 - 20 mmHg (2000 - 2670 Pa) from knee to ankle, which is similar to the mildest grade of compression stockings. The relationship of the actuation pressure (Pa) and the applied electric field for ACBs at different calf regions is shown in Figure 9c.