# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 4 Results and Discussion
### Results from the Degradation Experiments
The observations from the optical measurement can also be recognised in the top view of the sample (Figure 15b). With the help of the microscope, different areas were also analysed in this sample geometry (Figure 15c). Firstly, the covered area of the sample is examined (left image). In this image, the scratches can be detected due to the pre-treatment of the sample prior to the experiments, which clearly indicates the absence of contact with HBSS. In addition, areas that had been exposed to HBSS are analysed in more detail (right image). An uneven surface is evident, with localised deeper extrema, which, as previously, cannot be fully rendered in sharp detail due to the height differences in the image. Figure 14: Optical analysis results of sample geometry 1 after five days in the HBSS by **(a)** optical measurement **(b)** overview image and **(c)** microscope images. Homogeneous degradation was observed globally across both sample geometries. However, significantly stronger, locally confined degradation in the form of pitting corrosion was also evident. This behaviour of local degradation can be explained by the phase distribution in the alloy, which was also investigated in more detail in the work by [PERSON] et al. [18]. In their work, it was found that the \(\alpha\)-Mg phases on the surface of the samples degrade first. In addition, individual inclusions in the alloy were observed in this work through the confocal microscope images. It is assumed that the degradation had spread along the phases and that \(\alpha\)-Mg phases had dissolved first according to the work of [PERSON] et al. [18]. To summarise the results, it was observed that the shortest distance (X\({}_{1}\)) to the pump led to the greatest increase in the roughness R\({}_{2}\). Due to the increase in the R\({}_{x}\) value, there was also a greater scattering of the measured values for all sample positions. Position X\({}_{1}\) showed the highest scatter for both sample geometries. For position X\({}_{2}\), only sample geometry 1 showed a greater scatter compared to sample position X\({}_{3}\). If the location of a possible bone implant is also taken into account, it is obvious that a purely flowing state is not suitable as an abstraction for the planned location of the application. Accordingly, the middle distance (X\({}_{2}\)) in the experimental chamber should be targeted for further experiments. This corresponds more to a mixture of dynamic uniform flowing and static state, which corresponds to an abstraction of the state in the bone. At the same time, the influence of the sample geometry on the degradation rate should be investigated in more detail. This becomes clear from the fact that although sample geometry 2 shows the same or similar percentage loss compared to sample geometry 1, it has a lower degradation rate. The mass loss rate in mm/(cm\({}^{2}\)* day) is included in the calculation of the degradation rate. Accordingly, the lower value results from the lower initial mass and the larger surface area also plays a role.