# Production of Synthetic Models for Neuro-Oncology Training by Additive Manufacturing
## 2 Materials and Methods
### Model Manufacturing  
The final models were manufactured by material extrusion AM. An Atom (ALT Design, Taiwan) and Ender3 (Creality 3D, Shenzhen, China) 3D printers were used with the corresponding selected materials and infill densities. Regarding the printing parameters, a 0.4 mm nozzle was used for the extruders, with a manual width of 0.6 mm (also for the first layer), a layer height of 0.3 mm, 3 wall perimeters, and 3 top and bottom solid layers. The nozzle temperature was 200 \({}^{\circ}\)C for Smartfli(r) PLA and 210 \({}^{\circ}\)C for Smartfli(r) EP. The default printing speed was 60 mm/s for Smartfli(r) PLA and 40 mm/s for Smartfli(r) EP, with a movement speed in the \(x/y\)-axis of 100 mm/s and 40 mm/s in the \(z\)-axis (for both materials). The layer fan was set at 100% from layer 2, and the supports were defined with 30% infill density with no dense support layers. The bed temperature was 60 \({}^{\circ}\)C for both materials. No retractions were applied for the Smartfli(r) EP filament, while in the case of Smartfli(r) PLA, the retraction distance was 8 mm at 40 mm/s. Additionally, in the case of Smartfli(r) EP, a cleaning process was applied after every print, especially in the extruder gears. This filament is more fragile due to the ceramic content, leading to powder accumulation in the gear teeth. If this powder is not removed from time to time, filament jams may occur.  
Figure 6 shows the 3D printed models.  
Figure 5: Features performed in SolidWorks to obtain the skull (**a**), the brain mold (**b**), the mold to define the working area inside the brain mold (**c**), and the tumor mold (**d**).  
Once the different models were produced, the silicon pouring was carried out. In the case of the brain that was manufactured with two different mixtures, the mold to define the working area (area surrounding the tumor) was placed inside the brain mold and a first pouring was made inside this mold with the chosen mixture, i.e., 1:1:3 (A:B:Slacker). Then, when the silicone had cured, the rest of the mix without Slacker was poured into the brain mold. In the case of the tumor, the chosen mixture 1:1 (A:B) with the red pigments and the crushed Smartfil(r) PLA was poured into the tumor mold. Finally, in the case of the dura mater, the chosen mixture 1:1 (A:B) was expanded on a surface to left a thin sheet. The results obtained by pouring the different silicone mixtures are shown in Figure 7.  
Once all the models were manufactured using AM and the silicone casting pours, the final assembly was carried out, as shown in Figure 8. Ten replicas of the model were produced and screwed on to the corresponding fixation mechanism, which allowed the desired orientation for the intervention. Finally, these models were used as training materials in a neuro-oncology workshop for medicine students during the second BRAIN IT summer school.  
Figure 6: 3D printed skull (the visible layers were due to the slicing height of the CT scan, which was 2 mm in the vertical or z-axis) (**a**), the brain mold (**b**), the mold to define the working area inside the brain mold (**c**), and the tumor mold (**d**). Approximate dimensions: (**a**) skull with 180 mm length and 150 mm width from the top view, (**b**) brain mold with 205 mm length and 159 mm width from the top view, (**c**) mold inside brain mold with 155 mm length from the top view, and (**d**) tumor mold with 90 mm length and 70 mm width from the top view.  
Figure 8: Final assembly: (**a**) brain with tumor and (**b**) complete model.  
Figure 7: Casting of the different silicones in different proportions for the brain (**a**), tumor (**b**), and dura mater (**c**) models.