# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 4 Results and Discussion
### Results from the Degradation Experiments
Sample geometry 1 exhibited a higher mass loss of 0.09%, whereas sample geometry 2 experienced a mass loss of 0.06%. A similar trend can also be seen in the degradation rate (Figure 13b). Again, sample geometry 2 shows a lower degradation rate (0.25 mm/y) compared to sample geometry 1 (0.75 mm/y). The degradation rate was calculated using the linear relationship between mass loss and density (Equation (1)). Overall, it can be stated here that an influence of the sample geometry can be recognised. Although both sample geometries lose a similar mass in percentage terms, different degradation rates are calculated due to the different surface areas exposed to the medium. Both rates fall within the targeted degradation range of 0.2-0.5 mm/y, which is recommended for bone healing [20]. Consequently, both geometries could be replaced by the alloy WE43 in future applications. For sample geometry 1, one half was covered with parafilm before the experiments (Figure 14). During the optical measurement, the influence of the degradation is made clear by a difference in the height between the covered (left half) and uncovered side (right half) (Figure 14a). Before conducting the measurements, the degradation layer was removed to prevent any distortion of the results. It can be seen that on the covered half is a smooth and even surface, which is used as a reference plane for determining the height differences. It is evident that this area was not in contact with HBSS due to the application of Parafilm, indicating that no degradation process occurred. On the uncovered half, height differences  
Figure 13: Mass development (**a**) as well as the degradation rate (**b**) of position \(X_{2}\) for sample geometry 1 and 2.  
ranging from 0.02 mm to \(-\)0.05 mm are measured. On one hand, a slight uniform reduction in height is observable on the exposed side, where even degradation occurred. On the other hand, there is significant height reduction, indicative of localised degradation, in certain areas, which is highlighted by the blue regions. In some areas around the strong height reduction, there is a punctual height increase. This may indicate the accumulation of possible degradation products or measurement inaccuracies, as the height increase is very small (0.02 mm). The observed results from the optical measurement can also be seen in the top view in Figure 14b. In this instance as well, the difference between covered and uncovered areas is distinctly observable due to a variation in colour. Furthermore, both the almost uniform and the punctual/local degradation can be seen. With the help of the microscope, different areas of the sample were examined more closely (Figure 14c). Firstly, a covered area (left side) was examined in more detail. Clear scratches are visible due to the previous polishing of the sample. These observations correspond to the analyses before the start of the experiment (Figure 7). It can therefore be concluded that the Parafilm protected the part of the sample from the contact with HBSS. Moreover, areas exposed to HBSS are also analysed (right side). In Figure 14c, the scratches are less clearly visible due to the degradation of this sample area. In addition, the local degradation is visible in the lower right area of the image. Due to the depth of the degradation, it was not possible to visualise the area completely in focus. For sample geometry 2, the left half of the specimen was also covered with parafilm before the start of the experiments (Figure 15). The optical measurement clearly shows the difference due to the influence of degradation between the covered and uncovered sides (Figure 15a). Overall, similar results are achieved here between the covered and uncovered sides compared to sample geometry 1. Increased degradation can be seen in the area of the hole. An almost uniform degradation can be recognised between the two boreholes in the uncovered area. In the far-right area, more pronounced localised grooves can be seen, which are mainly concentrated in the area of the hole.