## 4 Discussion
In contrast, despite the layer-by-layer construction process of 3D, it still achieved a relatively smooth surface, with only occasional granular features that might be related to specific printing parameters and material deposition mechanisms [28]. The reduction of demolding-related defects in CM samples highlighted the importance of optimizing processing temperatures and demolding strategies. ATR-FTIR spectroscopy was employed to identify the characteristic chemical groups present in the chemical structure of the processed PCUs. On the other hand, it was also used to examine potential structural changes that may occur during the reprocessing of PCUs. The FTIR results in this study revealed that the final specimens of PCUs with different hardness, obtained through three different molding methods, exhibited the same functional groups without any damage. These results were consistent with the PCU molecular structure reported in the literature [29; 30; 31; 32], indicating that the material did not undergo degradation or introduce impurities during the molding process, and the molded specimens were identical. [PERSON] et al. [33] also conducted a study on different PCU grades using various molding methods and found that there was no significant difference in the degree of phase separation between IM and 3D-molded PCU materials for any hardness of PCU. This suggested that different molding methods did not cause damage to the material's functional groups, which agreed with the findings of this study. All tensile tests in this study utilized A1 specimens. Due to the measurement range limitations of the testing equipment, the specimens reached the maximum capacity of the equipment at a 300% elongation. Therefore, all data processing was conducted using 300% strain as the upper limit. Fracture testing could not be performed, and thus, the ultimate tensile strength and elongation at break of the PCUs could not be obtained. However, the stress-strain curves of the PCUs processed through different molding methods within 300% elongation were consistent with the research by [PERSON] et al. [34]. The modulus of the PCUs significantly increased with the increase in hard segment content. Furthermore, the PCUs exhibited classic elastomer behavior, with the typical plateau region diminishing as the hard segment content increased, which also validated the findings of [PERSON] et al. [35] that the mechanical behavior of the PCU materials was the same under IM and 3D processing. A comparison of the elongation in our study revealed that the tensile properties of PCU processed by IM were inferior to those of PCU processed by CM and 3D printing. Additionally, the tensile properties of PCU processed by CM were inferior to those of PCU processed by 3D printing. Therefore, considering tensile properties, 3D printing was found to be the optimal molding method, followed by CM and IM. This was consistent with the findings of [PERSON] et al. [33], which demonstrated that 3D-processed specimens exhibited significantly larger failure strain during tension compared to IM-processed specimens. In the compression process of this study, PCU exhibited linear behavior before reaching 40% strain, but subsequently demonstrated non-linear behavior, with a rapid increase in compressive modulus. This was somewhat inconsistent with the findings of [PERSON] et al. [36], who observed that PCU material exhibited linear behavior throughout the entire compression process. The possible reason for this discrepancy is that their study primarily focused on the application of PCU in cartilage and did not investigate the material's behavior under larger compressive strains. In our study, when processed by IM, the average stress levels of PCU with all hardness levels were above 0.9 MPa, theoretically satisfying the load-bearing requirements of the intervertebral disc. However, the stress level of 55D was excessively high, failing to meet the shock absorption requirements of the disc, and thus it was excluded from material selection.