# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 1 Introduction  
Due to an ageing society, medicine and biomedical technology are facing new challenges. These include an increasing number of operations, which relate to orthopaedic care and consequently a higher risk of side effects or subsequent illnesses [1]. In the field of implantology, in particular, the orthopaedic treatment of deformities or fractures, metallic materials are frequently applied. The natural regeneration process in cases of patient fractures or deformities is facilitated through the use of these implants. Implants can be differentiated into permanent and temporary implants [2]. The latter have a significant benefit in the application and are further differentiated into temporarily non-resorbable and temporarily resorbable implants. Temporarily resorbable implants eliminate the need for a second operation to remove the implant [3]. As regards temporarily resorbable materials, options include degradable metallic materials such as magnesium, as well as polymers, composite materials, and bioceramics. Materials are chosen based on the area of application and the specific objective, making different groups of the listed materials appropriate [4].  
In addition to the necessary mechanical properties, these materials are subject to extensive requirements with regard to their biocompatibility. From a fundamental point of view, all elements present in the implant material are released into the organism during degradation. Therefore, it must be ensured that this does not have any negative side effects on the human body [5]. According to [PERSON] et al., biocompatibility is described as the compatibility between a technical and a biological system, whereby no toxic or allergic reactions are caused [2].  
The focus of this work is on magnesium alloys, as pure magnesium is unsuitable for use in medical technology due to its high degradation rate [6]. Due to their special material properties, such as biocompatibility or stimulation of bone growth (osteoconductivity), these alloys are increasingly becoming the focus of research questions. In the field of implantology, these alloys are also attractive due to their ability to dissolve in the body (degradation) and to be decomposed [3]. Based on numerous in vivo studies, magnesium and its alloys have been found to be a resorbable material with great biocompatibility [7; 8; 9]. Moreover, orthopaedic implants made of magnesium alloys have been shown to have a positive effect on new bone tissue and blood vessel formation [10]. For instance, the suitability of magnesium for use as a screw has been evaluated both numerically and through simplified experimental trials, and it has been identified as feasible [11]. Therefore, magnesium alloys could be widely used for orthopaedic purposes [12].  
For the application as implant materials, the materials must be analysed through degradation experiments. Consequently, various degradation test setups have been developed, each study emphasising a different aspect; however, a dedicated setup specifically for osteosynthesis implants has not yet been established. In this work, the magnesium alloy WE43 was investigated in greater detail for its potential use as an orthopaedic implant in a body replacement fluid. To provide an initial assessment, an appropriate degradation setup was established, which continuously recorded parameters such as temperature and pH value throughout the experiment's duration. Within this setup, three different positions were evaluated for their suitability as sample sites. The experiments were analysed in terms of surface roughness and prevailing flow conditions. Additionally, the effect of two different sample geometries on degradation was investigated. The results were evaluated in terms of degradation phenomena and degradation rates and assessed for their suitability as osteosynthesis implants. To further assess the applicability in this area, the mechanical properties of the degradation layer were determined and compared with the base material.