## 3 Results and Discussion
### Characterization of the 3D-Printed Bioceramics  
Figure 5 shows the 2D confocal Raman maps acquired on the cross-sections of the printed biocercamics. According to the results, Mg\({}_{2}\)SiO\({}_{4}\) is the main component of all samples, but when using 5% of HPMC or 5% of CMC, some MgSiO\({}_{3}\) is also present, mostly accumulated on the surface (colored in green in Figure 5). Thus, the use of different cellulose derivatives (HPMC or CMC), fundamental for achieving satisfactory printing parameters, did not influence the composition of the forming biocercamics. At the same time, it is important to note here that 3D scaffolds made of pure forsterite could be prepared only  
Figure 4: XRD patterns of cements after 2 days of hydration. Figure 3: (**A**) Top view black/white images of 2D printed cements prepared at different printing velocities; (**B**) pictures of a good (**top**) and bad (**bottom**) 3D printed cement. when using 10% of HPMC/CMC, suggesting that the amount of cellulose influences the forming phases. This result can be attributed to the water regulatory effect of these cellulose derivatives, which are expected to affect the water availability in the cement formulations, thus influencing the hydration reaction of MgO/SiO\({}_{2}\), which in turn impacts the biocercamics forming upon thermal treatment of M-S-H. In fact, at the sub-nanometric level, M-S-H can resemble a mixture of chrysotile (Mg\({}_{3}\)Si\({}_{2}\)O\({}_{5}\)(OH)\({}_{4}\)) and talc (Mg\({}_{3}\)Si\({}_{4}\)O\({}_{10}\)(OH)\({}_{2}\)) [22], and the water-carrying capacity of HPMC/CMC could influence these hydration products forming when MgO/SiO\({}_{2}\) reacts with water to form M-S-H. Figure 6 shows the SEM images collected on the cross-sections of the printed biocercamics. In all cases, the morphology of the samples is homogeneous, and at small magnification (Figure 6, images on the left), we can see the macro-porous nature of the samples' morphology. At higher magnification (Figure 6, images on the right), we can observe polydisperse agglomerated objects, ascribable to forsterite and, eventually, clinoenstatite phases [14; 16; 63]. The topography of the printed biocercamics was also studied through AFM (Figure 7), to gain information on the roughness of the investigated samples, taking into account that micro/nano-topographies resembling the structure of natural bone could improve the biological performances. The results confirm the presence of rounded, agglomerated phases, as observed by means of SEM, with sizes ranging from tens of nm to a few \(\upmu\)m. Table 2 reports the average values of roughness (Ra, arithmetic mean roughness) calculated on different maps. According to the results, the samples display varying roughness levels, indicating that the cellulose derivatives can affect this important parameter. In particular, when using 10% of HPMC or CMC, the surfaces display smaller particles (see Figure 7) and lower Ra values (Table 1), which could be appropriate for the successful deposition of  
Figure 5: Confocal Raman maps collected on the cross-sections of printed samples HPMC_5 (**A**), HPMC_10 (**B**), CMC_5 (**C**), and CMC_10 (**D**); and Raman spectra of CMC_5 bulk (top) and surface (bottom) (**E**), where the red and green regions highlight the peaks of forsterite and clinoenstatite selected for the mapping, respectively. All mapped samples (**A**–**D**) expose the external surfaces on the left. hydroxapatite and thus for the preparation of scaffolds with good biocompatibility, since scaffolds containing forsterite and displaying similar values of roughness were recently reported for the successful deposition of hydroxyapatite [64,65]. The porosity of the microstructure and the structural features were further investigated by means of gas porosimetry and compressive strength tests (see Table 2). We observed that higher amounts of HPMC/CMC lead to scaffolds with lower specific surface areas and total pore volumes, which could be ascribed to an enhanced hydration reaction.