# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 3 Materials and Methods  
### Experimental Setup and Preparation of the Experiments  
An experimental setup was designed and constructed before the experiments were carried out, which is shown schematically in Figure 3. The aim was to have three independently running experimental chambers (three in one box), each with identical but autonomously operating sensor technology. Three experimental chambers were aimed for, allowing multiple independent experiments to be conducted simultaneously. The construction of an immersion test (an experiment to evaluate chemical resistance) [16], which determines mass loss using the gravimetric method [6], was considered to be the most effective in the context of this work. The advantage is that, for example, the gases produced do not have to be collected in an extra container for volume measurement. This ensures that different sample geometries can also be analysed at different locations in the experimental chamber. By using the immersion experiment, it is possible to create a bone-like environment. In this environment, for example, there are no high flow properties as in blood vessels (artery 30-40 cm/s [2]) or high temperature fluctuations as on the skin. Furthermore, it was necessary to implement a flow in the fluid by using pumps. A circulation pump (Micro Centrifugal Liquid Pump Range from TCS Micropumps Ltd, UK) was used to maintain a constant fluid volume, eliminating the need for an additional reservoir. The pumps are each attached to one end of the test chamber with a flow rate of 330 mL/min, based on information provided by the manufacturer (left side in Figure 3). The inlet and outlet of the pump were positioned at the same vertical height to ensure that the flow behaviour was not affected by any additional gravitational influences. In order to simulate the flowing environment, which represents an abstraction for later use as an osteosynthesis implant, a suitable flow was selected. A flow rate was targeted, ranging from a minimum of 7.065 mL/min to 706.5 mL/min, based on typical mid-sized veins due to the lack of available measurements within bones [2]. This enables the simulation on a laboratory scale of the degradation of the implant by the body's own processes. The sensor technology includes a temperature controller (heating rod from Schego, Schemel & Goetz GmbH & Co KG, Offenbach, Germany), each equipped with its own temperature sensor (Hobby Biotherm, Dohse Aquaristik GmbH & Co. KG, Gelsdorf, Germany), within each experimental chamber. In addition, each experimental chamber has a pH sensor (Gravity compatible with Raspberry Pi (DFRobot, Shanghai, China)) and another temperature sensor (DEBO LK-Temp compatible with Raspberry Pi (Reichelt Elektronik GmbH, Sande, Germany)). These are each connected to the Raspberry Pi for storing the results. The data storage of the Raspberry Pi can be varied and was set to a frequency of 3600 s for longer experiments. The temperature sensors, as well as the pH sensor, are positioned opposite the pump side to effectively monitor temperature and pH value development. Consideration was given to positioning the pH sensor away from the direct exposure outlet to the pump to ensure accurate measurements. Each experimental chamber measures 114 \(\times\) 296 \(\times\) 126 mm (width \(\times\) length \(\times\) height (w \(\times\) 1 \(\times\) h)) and is made of polymethyl methacrylate (PMMA). The box around the three experimental chambers was made of PMMA with the dimensions 550 \(\times\) 400 \(\times\) 195 mm (w \(\times\) 1 \(\times\) h) for thermal insulation and further protection against leakage. The temperature was set to 37.0 \(\pm\) 0.2 \({}^{\circ}\)C for all experiments to simulate human body temperature [34]. Temperature regulation, such as heating, was carried out via the respective heating rod joint with the temperature sensor. Validation was carried out by comparing the temperature display, which is joined to the heating rod, with the independent temperature recorded on the Raspberry.