# Solution Extrusion Additive Manufacturing of Biodegradable Polycaprolactone
## 3 Results
### Effects of Processing Parameters on Part Strength  
Figure 5A shows the stress-strain curves of parts prepared using different PCL/DCM ratios, while Figure 5B shows the maximum tensile strengths. The elongation at break generally increased with the volume of DCM. The maximum tensile strengths also increased as the volume of DCM increased. Parts manufactured using a ratio of 5 g/7.2 mL exhibited the greatest tensile strength, while fabricated parts with a ratio of 5 g/6.8 mL showed the worst mechanical properties. Figure 9 shows the surface images of manufactured parts. Incompletely sealed orifices can be seen on surfaces of the solution extrusion manufactured products in the profile projector image. Small orifices were observed on the part surface, which mainly resulted from the evaporation of solvent. Better healing is observed in Figure 9A (5 g/7.2 mL) than in Figure 9B (5 g/6.8 mL), not only in the same layer but also across layers. Since the part made with the 5 g/6.8 mL solution showed greater pore sizes than parts made with 5 g/7.2 mL, it shows worse mechanical properties. Figure 6A shows the stress-strain curves of parts manufactured using different fill densities. Clearly, the maximum strength and elongation at break increased with the fill density. Figure 6B shows the influence of fill density on the maximum tensile strength of the fabricated parts. Parts with 80% fill density exhibited the greatest tensile strength, while parts fabricated with 65% exhibited the lowest mechanical properties. Figure 10A,B show the surface images of parts manufactured with 80% and 65% fill density, respectively. The surface of parts manufactured with 80% fill density are almost completely healed, but huge pores could still be seen on the surface of parts prepared with 65% fill density. Parts manufactured with a lower fill density showed larger pores, which may lead to stress concentrations during the tensile tests. Thus, they demonstrated lower mechanical strength. Figure 7A shows the tensile test curves of parts manufactured with various speeds of the dispensing tip. Figure 7B shows the effect of the tip's moving speed on the maximum tensile strength. The tensile strength decreased generally with the tip's speed. Parts prepared using a speed of 40 mm/s exhibited the greatest tensile strength, while parts fabricated with a speed of 70 mm/s showed the lowest mechanical properties. Figure 11A,B show the surface images of parts manufactured using tip speeds of 40 mm/s and 70 mm/s, respectively. Again, all parts exhibit a fused surface with many incompletely healed small pores. Furthermore, parts manufactured with a tip speed of 70 mm/s showed pores of greater size than those fabricated with a tip speed of 40 mm/s. Thus, they showed worse mechanical properties. Figure 8A shows the stress-strain curves of parts manufactured using different orientations of 30\({}^{\circ}\), 45\({}^{\circ}\), 75\({}^{\circ}\), and 90\({}^{\circ}\), and Figure 8B shows the maximum tensile strength of these samples. The specimen manufactured with an orientation of 90\({}^{\circ}\) showed the greatest tensile strength, while 45\({}^{\circ}\) resulted in the lowest mechanical properties. Figure 12 shows the surface images of the parts manufactured with orientations of 90\({}^{\circ}\) and 45\({}^{\circ}\). Obviously, 45\({}^{\circ}\) resulted in more large pores on the surface. Furthermore, compared to 90\({}^{\circ}\), 45\({}^{\circ}\) resulted in sharp rectangular pores. Meanwhile, due to the different print orientation of infill, the interlayer fusion of PCL strips might be different, which in turn leads to various bonding intensities and relevant mechanical strengths. This might explain why the strength of the 30\({}^{\circ}\) manufactured part is higher than that of the 45\({}^{\circ}\). When these pores are subjected to external forces, stress concentrations may occur and lead to fractures. The strength decreased accordingly.