## 3 Results and Discussion
### Concerning the Dissolution Tests of the PLA Specimens  
During the dissolution tests, 3D-printed PLA samples with a thickness of 0.4 mm were immersed in solutions with pH values of 12 and 12.55. Each specimen was submerged in 50 mL of solution, covered, and kept for four weeks (28 days). Preventing evaporation was key, as it ensured that the pH of the solution remained constant throughout the measurement. The observation was a subjective process; therefore, the evaluations were conducted based on a custom assessment system. During the observations, only the first week of the dissolution tests was observed for a full seven days since the rate of change in the test samples slowed down after the first week. Table 6 summarizes the one-week-long 24 h observations of the dissolution tests on the specimens and contains the list of symbols used. During the 168 h observation period of the dissolution tests, the GYP specimens exhibited the most significant and noticeable changes and reactions to the solution. In the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Material** & **Solution pH** & **Day 1** & **Day 2** & **Day 3** & **Day 4** & **Day 5** & **Day 6** & **Day 7** \\ \hline ESD & 12 & NC & C & C & C, P & C, I & C, CRP & C, CRP, I \\ ENG & 12 & NC & C, P & C, I & C, I & C, I & C, CRP, S & C, CRP, S, I \\ HI & 12 & NC & C, P & C, I & C, I & C, I & C, CRP, S & C, CRP, S, I \\ ABS & 12 & NC & C, P & C, I & C, I & C, I & C, CRP & C, CRP, I \\ GYP & 12 & NC & C, P & C, I & C, I & C, I & C, CRP, S & C, CRP, S, I \\ \hline ESD & 12.55 & NC & C & C, P & C, P & C, I & C, I & C, CRP \\ ENG & 12.55 & NC & C & C, I & C, I & C, I & C, CRP, S & C, CRP, S, I \\ HI & 12.55 & NC & C, P, F & C, F, I & C, F, I & C, F, I & C, F, CRP, S & C, CRP, S, I \\ ABS & 12.55 & NC & C & C, P & C, I & C, I & C, CRP & C, CRP, I \\ GYP & 12.55 & C & C, P & C, I & C, I & C, CRP & C, CRP, S, W & C, CRP, S, W, I \\ \hline \hline \multicolumn{8}{l}{**Remarks**} \\ \hline The solution does not run off the surface, covering it evenly—C. & & & & & & & \\ The solution runs off the surface, no coverage—NC. & & & & & & & \\ Faded surface where the specimen was in contact with the solution—F. & & & & & & \\ Small amount of white substance that forms as a solid deposit, resembling powder on the surface—P. & & & & & & \\ Increase in the amount of precipitation—I. & & & & & & & \\ Precipitation occurred in the solution as tiny particles—S. & & & & & & \\ Precipitation occurred on the wall of the measuring cup—W. & & & & & & \\ White crystal-like precipitation in continuous lines, parallel to the printing direction—CRP. & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Summary of observations during the dissolution tests with the list of symbols. first 24 h of the test, the solution uniformly coated the surface of the GYP specimens while it rolled off the surface of the other specimens. By the second day, all specimens tested in the pH 12.55 and pH 12 solutions were uniformly coated by the solution. In the pH 12.55 solution, a small amount of white substance that formed as a solid deposit, resembling powder, was observed on the GYP and HI specimens, whereas in the pH 12 solution, similar precipitation was observed on the ENG, HI, ABS, and GYP specimens. This type of precipitation could occur due to the crystallization of dissolved compounds when the solution became oversaturated, a chemical reaction between solutes, or environmental factors such as changes in temperature or pH. The appearance and composition of this precipitation can vary depending on the specific compounds involved, but it typically consists of solid particles that settle or adhere to surfaces. Additionally, in the pH 12.55 solution, the black surface of the HI specimens where they contacted the solution had faded to gray. Figure 14 illustrates the fading of the color observed on the surface of the HI specimen in the 12.55 pH solution. On the third day, a small amount of white precipitation appeared on the ESD specimen immersed in the pH 12.55 solution.