# Additive Manufacturing of Bone Scaffolds Using PolyJet and Stereolithography Techniques
## 3 Results
### Experimentally Measured Permeability  
Figure 7 presents the experimentally measured permeability of the Polylet 3D-printed scaffold structures with cubic and hexagonal closed packed structures using tap water, 15% glycerol-water solution, and 20% glycerol-water solution. It can be observed from the figure that the experimentally measured permeability increased from lower to higher values in terms of the pore size, porosity, and viscosity of the test fluid. It was also noticed that the pore size had a greater effect on the permeability than the porosity and viscosity. The measured permeability values of cubic 3D-printed scaffold structures ranged between 1.05 and 2.83 \(\times\) 10\({}^{-10}\) m\({}^{2}\) (69% difference), while for hexagonal closed packed 3D-printed scaffold structures the values ranged between 0.46 and 2.75 \(\times\) 10\({}^{-10}\) m\({}^{2}\) (78% difference). Moreover, it was also observed that 3D-printed scaffold structures with the cubic pore shape had higher permeability values as compared to the 3D-printed scaffold structures with the hexagonal closed packed pore shape.  
Figure 7: Experimentally measured permeability values for Polylet 3D-printed scaffold structures using tap water, 15% glycerol-water solution, and 20% glycerol-water solution: (**a**) cubic structure; (**b**) hexagonal closed packed structure.  
The \(\mu\)SLA-printed 3D scaffold structures showed similar results as for the PolyJet-printed samples in terms of permeability. Figure 8 shows the experimentally measured permeability values for the \(\mu\)SLA 3D-printed scaffold structures with cubic and hexagonal closed packed structures using tap water, 15% glycerol-water solution, and 20% glycerol-water solution. The measured permeability results demonstrated higher values for higher pore size, porosity, and viscosity values, and it was observed that the pore sizes had greater effects on permeability. The measured permeability values for cubic-pore-shaped \(\mu\)SLA 3D-printed scaffold structures ranged between 0.52 and 2.23 \(\times\) 10\({}^{-10}\) m\({}^{2}\) (76% difference) and for hexagonal closed packed 3D-printed scaffold structures ranged between 1.05 and 1.99 \(\times\) 10\({}^{-10}\) m\({}^{2}\) (47% difference) at 30% porosity.  
Figure 9 shows a comparison between the experimentally measured permeability values for PolyJet and \(\mu\)SLA 3D-printed scaffold structures. As was mentioned in the development section, the \(\mu\)SLA-printed scaffold structures had greater precision because the \(\mu\)SLA-printed samples had higher permeability values as compared to the PolyJet-printed samples with lower pore sizes.  
Table 4 shows that the experimentally measured permeability was higher than the numerically calculated permeability for all cases. The variation between the measured and calculated permeability values could be due to the poor cleaning of 3D-printed scaffold structures or due to the parameters that were not included in the Kozeny-Carman equation, such as pressure drop across the sample, fluid viscosity, and surface energy; therefore, a combined model with the benefits of both experimental and calculated methods could be beneficial for measuring permeability more accurately.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Permeability** & \multicolumn{2}{c}{**PolyJet**} & \multicolumn{2}{c}{\(\mu\)**SLA**} \\ \cline{2-5}
**(\(\times\)10\({}^{-10}\) m\({}^{2}\))** & **C** & **H** & **C** & **H** \\ \hline Measured & 1.05–2.83 & 0.46–2.75 & 0.52–2.23 & 1.05–1.99 \\ Theoretical & 0.3–2.11 & 0.12–2.0 & 0.3–2.11 & 0.12–2.0 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison between the measured and calculated values for cubic and hexagonal closed packed 3D-printed scaffold structures.  
Figure 8: Experimentally measured permeability values for \(\mu\)SLA 3D-printed scaffold structures using tap water, 15% glycerol–water solution, and 20% glycerol–water solution at 30% porosity for both scaffold structures with cubic and hexagonal pore shapes.