## 3 Results
### Experiment Verification and Analysis
#### 3.3.3 Verifying and Analyzing the Elastic Bands  
In this study, elastic bands were used to generate the stent's self-expanding force, enabling the stent to expand to the required diameter after being implanted in the AVF. The total recovery force of the elastic bands was designed to match the measured compression force of the stent, as described in Section 3.3.1. The dimensions of the TPU elastic bands for the enlarged stent and original-size stent were designed separately. The TPU elastic bands for the enlarged stent were 100 \(\times\) 15 \(\times\) 1.5 mm, while those for the original-size stent were 28.5 \(\times\) 0.3 \(\times\) 0.2 mm. Figure 16 shows the relationship between stretch displacement and force for the TPU elastic band test piece used in the enlarged stent. The experimental values, indicated on the figure, represent the average of five repeated measurements, with two standard deviations shown. The results reveal that as the stretch displacement increased, the recovery force of the TPU elastic band also increased. Furthermore, the simulation values closely matched the experimental results, confirming that the simulated scenarios accurately predicted the actual force and deformation of the TPU elastic bands. Figure 13: Stent (**a**) expanded with a taper rod; (**b**) compressed and inserted into a silicone tube. Figure 16: Relationship between stretch displacement and force for the enlarged stent’s TPU elastic band (single-layer stent). Figure 14: PLA stent being released from the silicone tube and reverting to its original size: (**a–d**) the compressed stent was ejected from the silicone tube using a metal rod and immediately expanded to the original diameter; (**e**) the released stent; (**f**) the measured diameter 3.98 mm. Figure 15: Relationship between simulated compression displacement, compression force, and expansion displacement in the original-size stent. Both ends of the TPU elastic band were attached to disc grooves on the stretching mechanism, and the nuts were rotated to stretch the band to 4.3 mm before installing it inside the enlarged stent (Figure 17a). At this point, the recovery force of the TPU elastic band exceeded 3.283 N (Figure 16), which was greater than the compression force of 2.656 N required by a single stent structure at 0.8 mm compression displacement. This recovery force caused the stent to expand. As the TPU elastic band contracted to 3.5 mm, its recovery force reduced to approximately 2.6 N, equal to the stent's compression force, achieving equilibrium. At this point, the stent maintained an expanded state with a diameter of 28 mm (Figure 17b). If the stent needs to be returned to its original diameter, the TPU elastic band should be stretched back to 4.3 mm. Figure 15 presents the simulation analysis results for the compression displacement, compression force, and expansion displacement of the single-layer structure of the original-size stent. The data show that, when compressed by 0.2 mm, the stent structure experienced a compression force of 0.983 N and a radial expansion displacement of 2.345 mm, meaning the stent could expand from its original diameter of 4 mm to 6.345 mm. Therefore, the compression force of the original-size stent (0.983 N) divided by 8 equals the compression force required by a single structure of the stent, which is 0.123 N. The simulation analysis results for the TPU elastic band used in the original-size stent are shown in Figure 18.  
Figure 17: (**a**) Stretching and loading the TPU elastic band onto the interior of the enlarged stent; (**b**) diameter of the self-expanded, enlarged stent when the TPU elastic band was not stretched. Figure 18: Relationship between stretch displacement and force in the original-size stent’s TPU test piece. The original-sized stent was designed with a two-layer structure, where each layer consists of eight diamond-shaped units. The design incorporated an elastic TPU band stretched across the diamond-shaped units, which connect the upper and lower layers of the stent.