# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 2 State of the Art
### Magnesium Alloy WE43  
The magnesium alloy WE43 is classified among the ternary alloy systems and contains rare earths (Table 2) [3; 28]. It is considered biocompatible [29] and has a positive effect on bone growth [13]. As an additional positive effect, the alloy has an infection-inhibiting effect, which makes the material particularly attractive for use as an implant [30].  
[PERSON] et al. used a test rig for the degradation of magnesium WE43 round tensile samples, which were subsequently mechanically tested by means of tensile experiments. Within these tests, four different times (7, 14, 21, and 28 days) of degradation were compared with the initial state. It was established that the strength decreases over the period of degradation. In addition to assessing the mechanical properties at different degradation times, the change in geometry over time was also observed. For this purpose, computer tomography (CT) scans of the samples were taken and the change in depth was analysed. The analysis revealed that the samples exhibited surface corrosion as well as pitting corrosion. Over time, pitting corrosion formed smaller holes that coalesced into larger holes, with a sharp increase in depth observed between day 21 and day 28. In addition, the degradation rate was compared by measuring the H\({}_{2}\) evolution and by determining the volume loss based on the CT scans. The comparison indicated that the determination of the degradation rate using the H\({}_{2}\) evolution method yielded lower results than the method used for assessing volume loss via CT scans [26].  
In the study by [PERSON] et al., screws made of titanium were compared with MgYREZr (Magnezix(r) by Syntellix) screws for the treatment of hallux valgus [32]. The MgYREZr screws exhibited the same mechanical properties as the WE43 alloy. One group of patients was treated with the titanium screw, and the other group received the MgYREZr screw. The titanium screw was considered the gold standard and reference trial. No negative influence of the MgYREZr screw, such as allergic reaction, osteolysis, or foreign body reaction, was observed during the study period. The healing process of both groups was identical and fulfilled their function. These results were confirmed by the work of [PERSON] and supplemented by the information that normal bone function was present after the healing phase and degradation of the MgYREZr screw [30]. The advantage of the Mg screws was that they did not have to be removed again due to degradation and, therefore, had no negative influence on the patient's life later on. The presented results were confirmed in the work of [PERSON] et al. [33]. Titanium and magnesium screws were tested ex vivo in sawbones. The mechanical experiments involved applying a compressive load in two effective directions on the sawbones and the implant. No significant difference was found between the screws in these tests.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Y** & **Zr** & **Gd** & **Nd** & **Cu** & **Ni** & **Fe** & **Mg** \\ \hline
3.7–4.3 & 0.4–1.0 & 0.0–0.9 & 2.0–2.5 & \(\leq\)0.02 & \(\leq\)0.005 & \(\leq\)0.01 & rest \\ \hline \end{tabular}
\end{table}
Table 2: Chemical composition of WE43 by weight (%) (yttrium = Y; zirconium = Zr; gadolinium = Gd; neodymium = Nd; copper = Cu; nickel = Ni; iron = Fe; magnesium = Mg) [3; 31].