# Detachable Soft Actuators with Tunable Stiffness Based on Wire Jamming
## Materials and Methods
### Fabrication  
The fabrication process of the wire jamming structure is divided into three main steps. As shown in Figure 3a, the first major step is to cut wires into a specified length (i.e., 150 mm) using a commercial laser cutting machine (T1, Diaotu Industrial Co. Ltd., Shanghai, China). Due to the different packing and delivery methods (e.g., reel and carbboard), wires or ropes require pre-cutting before being fixed on the working platform. The second major step is to fabricate the airtight envelopes with rectangular cross-sections. Considering the layout and bending state of wire jamming structures, high-density polyethylene (HDPE) is adopted as the envelope material (see Section S3 in the Supplementary Materials for details). The HDPE film has high ductility and toughness, puncture resistance and excellent chemical resistance, as well as low friction, and is often applied to agricultural greenhouses. In Figure 3b, the HDPE film is cut into four strips and then the strips are combined into a rectangular cross-section structure using a heat-sealing machine (FKR200, Yinuo Packaging Material Co. Ltd., Shanghai, China). The third major step focuses on sealing the wires into the airtight envelope (Figure 3c). The specific method is to insert the wires from one side of the rectangular cross-section structure and seal one end. Following the gradient effect solution discussed in Section 2.1, we trim wires and seal the other end. Finally, a plastic hose coupler is installed on the wire jamming structure for air tube connection.  
An important issue that we also need to consider is how to combine the actuator unit with the tunable stiffness structure. The traditional approaches are integrated designs or permanent adhesion [22; 23; 26]. These approaches reduce the reliability and versatility of the whole structure. For example, the whole structure needs to be replaced after leakage and fouling, as well as in the case of applications where multiple jamming structures are required. Therefore, the modular concept is introduced into the design of the soft actuator with tunable stiffness, where the key factor is the use of Velcro strips (a.k.a., \"hook-and-loop fastener\"). Because the loop side fastener is covered with dense fibers, it can be robustly bonded to the silicone rubber, which offers numerous possibilities for combining rigid and soft materials. In order to confirm the advantages of Velcro, a set of tensile tests are performed to compare the different attaching methods  
Figure 3: Fabrication processes of the wire jamming structure. (**a**) Illustration of cutting process of wires. (**b**) Heat sealing process of rectangular cross-section structure using HDPE films (film thickness 0.08 mm). (**c**) Assembly process of trimmed wires and airtight envelope. (**d**) Illustration of the soft pneumatic actuator based on wire jamming structure, including local details of double-sided Velcro strip and knit loop fastener with pressure-sensitive adhesive.  
(Figures S9 and S10, Supplementary Materials). Here, we use double-sided hook and loop fasteners (ONE-WRAP 29, Velcro USA Inc., Manchester, NH, USA) as a strain-limiting layer of the fiber-reinforced soft actuator, in which the main silicone body is cured on the loop side (Figure 3d). The details of fabrication processes are available in Section S6 and Figure S11 in the Supplementary Materials. In addition, knitted loop fasteners (velour 3165, Velcro USA Inc., Manchester, NH, USA) with an adhesive coating on the opposite side are used for the wire jamming structure. Finally, with the detachable support of Velcro strips, soft actuators based on jamming structures are capable of handling a variety of applications.