# Detachable Soft Actuators with Tunable Stiffness Based on Wire Jamming
## 3 Results and Discussions
### Applications  
In the previous section, we used three-point bending experiments and torsional stiffness experiments to study the stiffness performance of wire jamming structures. In this section, we first investigate the influence of the wire jamming structure on the bending and stiffness performance of a single assembled stiffness-tunable soft actuator, and then use the soft robotic gripper and wearable exoskeleton as application examples to demonstrate its load capacity and universal adaptability. Figure 5a,b illustrates the unloaded bending experiments of a fiber-reinforced soft actuator and an assembled stiffness-tunable soft actuator, respectively. The results show a significant decrease in bending performance after the soft actuator is assembled with a wire jamming structure (Figure 5c). For a bending angle of 90\({}^{\circ}\), the assembled soft actuator requires a positive air pressure of 145 kPa, while only about 87 kPa is required for the soft actuator alone. In order to explore the stiffness characteristics of the assembled soft actuator, we apply an external force to the tip of the actuator and record the force versus deflection curves at the contact point (Figure 5d,e). The experimental process is first to adjust the positive air pressure of the soft actuator to allow it to bend freely, then adjust the vacuum pressure of the wire jamming structure and finally adjust the initial position of the load cell so that it moves in a direction perpendicular to the contact surface. The experimental results show a phenomenon similar to the three-point bending experiment (Figure 5f). After the vacuum air pressure inside the jamming structure is switched from 0 to \(-\)85 kPa, the bending stiffness of the assembled soft actuator is remarkably enhanced. In addition, bending stiffness experiments are performed on a single wire jamming structure. The details of the experiments are shown in Figures S17 and S18 in the Supplementary Materials. Figure 5: Applications of an assembled soft actuator with tunable stiffness. (**a,b**) Experimental setup for a single soft actuator and an assembled soft actuator installed with a wire jamming structure, respectively. A nine-axis gyroscope (JY901S, WitMotion Co. Ltd., Shenzhen, China) is used to measure the bending angle with different inflation pressure. The gyroscope is attached to the tip of the soft actuator. (**c**) Angle versus positive air pressure \(P_{\rm in}\) curves of the soft actuator before and after assembly. (**d,e**) Bending stiffness experiments of the assembled soft actuator under two different positive air pressures. (**f**) Applied force versus deflection curves of the bending stiffness experiments. (**g**) Demonstration of the grasping process of the soft robotic gripper. (**h**) Comparison of maximum grasping mass at different positive air pressures. (**i**) An application example of a wearable exoskeleton, which only shows the wearing effect on the right arm. (**j**) The experiment of load capacity of a detachable soft glove, where the positive air pressure is 165 kPa, and the vacuum pressure is \(-85\) kPa. To further demonstrate the versatility of the soft assembly actuator with tunable stiffness, we developed a soft robotic gripper, which consists of three assembled soft actuators. The experimental scheme is to grasp a hollow plastic carrier at a confined positive air pressure, then set a specified vacuum pressure and finally increase the overall mass continuously by adding steel balls until the grasping fails (Figure 5g). A video of the grasping demonstration is available in Movie S1 in Supplementary Materials. The maximum mass successfully grasped is recorded and shown in Figure 5h. The maximum grasping mass of the soft gripper is increased by two times when the vacuum pressure is changed from 0 to \(-85\) kPa. Figure 5i shows an application example of a wearable exoskeleton, where the yellow detachable areas use loops fasteners.