# Sintering Behavior of a Six-Oxide Silicate Bioactive Glass for Scaffold Manufacturing
## 3 Results and Discussion
However, a drop in mechanical properties was observed at 800 \({}^{\circ}\)C as a result of a decrease in structure density. However, even including the samples treated at 800 and 850 \({}^{\circ}\)C, the overall strength-T\({}_{\rm s}\) relationship still remains linear with R\({}^{2}\) = 0.8393 (Figure 5). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sintering Temperature** & **Apparent Density** & **Total Porosity** & **Maximum Shrinkage** & **Compressive Strength** \\ T/\({}^{\circ}\)C & \(\rho_{\rm s}\)/g/cm\({}^{3}\) & \(\epsilon_{\theta}\) & **AH/\%** & \(\sigma_{\rm max}\)/MPa \\ \hline
600 & 0.62 \(\pm\) 0.06 & 0.76 \(\pm\) 0.2 & 24 & 0.49 \(\pm\) 0.08 \\
650 & 0.72 \(\pm\) 0.07 & 0.72 \(\pm\) 0.03 & 28 & 1.02 \(\pm\) 0.44 \\
700 & 0.41 \(\pm\) 0.02 & 0.85 \(\pm\) 0.01 & 27 & 1.47 \(\pm\) 0.09 \\
750 & 0.87 \(\pm\) 0.03 & 0.67 \(\pm\) 0.01 & 18 & 1.93 \(\pm\) 0.06 \\
800 & 0.47 \(\pm\) 0.01 & 0.82 \(\pm\) 0.01 & 21 & 1.61 \(\pm\) 0.29 \\
850 & 0.69 \(\pm\) 0.03 & 0.73 \(\pm\) 0.01 & 29 & 2.09 \(\pm\) 1.02 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physical and structural parameters of 47.5B-based bioactive glass and glass-ceramic scaffolds sintered at different temperatures within the 600–850 \({}^{\circ}\)C range. Figure 4: SEM images of 47.5B glass and glass-ceramic scaffolds sintered at different temperatures: 600 \({}^{\circ}\)C (**a**), 650 \({}^{\circ}\)C (**b**), 700 \({}^{\circ}\)C (**c**), 750 \({}^{\circ}\)C (**d**), 800 \({}^{\circ}\)C (**e**) and 850 \({}^{\circ}\)C (**f**). Despite the higher sintering temperature, it should be noticed that the total porosity \(\varepsilon_{0}\) of scaffolds sintered at 800 \({}^{\circ}\)C was remarkably higher with respect to the sample treated at 750 \({}^{\circ}\)C, but comparable to that sintered at 700 \({}^{\circ}\)C. It is also interesting to underline that, although it was reasonable to assume higher crystallinity levels in scaffolds sintered at 800 \({}^{\circ}\)C, the \(\sigma_{\max}\) values were comparable in samples with comparable values of \(\varepsilon_{0}\), regardless of crystallinity. This suggests that the porous architecture, compared to the nucleation and growth of crystalline phases, played a predominant role in defining the mechanical performances of the scaffolds under compressive loads. This hypothesis could be further supported by comparing the 47.5B foam-replicated scaffolds, characterized in the present study, with 47.5B glass-ceramic scaffolds produced by dolomite foaming, as described in a previous work [20]. Specifically, it is interesting to notice how both dolomite-foamed and polymer-replicated scaffolds treated at 800 \({}^{\circ}\)C, with \(\varepsilon_{0}\) = 83.0 vol. %, exhibited comparable compressive strength \(\sigma_{\max}\) of \(1.3\pm 0.4\) MPa [20] and \(1.6\pm 0.3\) MPa, respectively, while the dolomite-foamed scaffolds treated at 850 \({}^{\circ}\)C exhibited lower porosity (\(65.5\pm 7.1\) vol. % [20]) and higher compressive strength (\(3.9\pm 0.9\) MPa) with respect to the scaffolds sintered at 850 \({}^{\circ}\)C described in the present study.