## 2 Materials and Methods
### Experimental Setup  
The solution extrusion printing was conducted on a novel, lab-exploited, solution-type 3D printer. As shown in Figure 1, the printer was a modified version of commercially available FDM printer (UMaker, Hertz Information, Taipei, Taiwan). By keeping the main structure intact and only installing a new solution-type plunger-actuated feeding system, stepper motors and motion components (Figure 2), a solution extrusion 3D printer was thus available for part printing (Figure 3). A free and open-source Cura interface (Ultimaker B.V., Geldermalsen, The Netherlands) was adopted to control the entire printing process (Figure 4). Before printing, a predetermined weight of PLA was first dissolved in DCM. The solution was then loaded into the solution-type feeder (a syringe) equipped with a plastic nozzle (needle) with an inner diameter of 0.18 mm for printing. During printing, the feeder was actuated by a computer-controlled servo motor and extruded the PLA solution onto the print bed. After the evaporation of DCM, a PLA bead of around 0.2 mm in diameter was deposited onto the printer bed surface layer-by-layer. Meanwhile, the setup utilised for the melt extrusion 3D printing was a commercially-available FDM printer (CR8, Taipei, Taiwan) that has a printing resolution of 200 \(\upmu\)m.  
Figure 1: Photo of the lab-exploited solution extrusion type 3D printer, which was a modified version of commercially available fused-deposition modelling (FDM) printer.  
Figure 3: Photo of the solution extrusion 3D printer.  
Figure 2: Schematically, the lab-exploited solution extrusion type 3D printer, (**A**) components of solution-type plunger-actuated feeding system and the feeding syringe (rightmost), (**B**) assembly of the system.  
Both the melt extrusion and solution extrusion printers were placed in an oven equipped with a forced-air circulation that has a temperature control accuracy of \(\pm 0.2\)\({}^{\circ}\)C. Following the ASTM D638 standard, a dumbbell-shaped geometry was selected for the parts. Figure 5 shows the layout and dimensions of the part. A solid modelling computer-aided design (CAD) computer program (Solidworks, Waltham, MA, USA) that runs primarily on Microsoft Windows was adopted to generate the code that was needed for the microcontroller to controls the movement of print heads.  
To evaluate the effect of residual solvent on printed products, a few test trials were first completed to print samples of square geometry (\(20\) mm \(\times\) 20 mm) (Figure 6), and the weights of printed parts were estimated after being put in a ventilation chamber at ambient temperature for different times. The measured weights (weight reduction percentages) at days 0, 1, 2, 3, 4, 5, 6, and 7 post printing were measured to be 0.264 g (17.58%), 0.218 g (18.18%), 0.216 g (18.56%), 0.212 g (19.69%), 0.212 g (19.69%), 0.212 g (19.69%), and 0.212 g (19.69%), respectively. The weight reductions were mainly attributable to the evaporation of residual solvents in the parts. Furthermore, the weight reduction and part shrinkage levelled off after 3 days and the final dimension of printed part shrank by approximately 10%.  
Figure 4: The Cura interface used to control the printing process.  
Figure 5: Layout and dimension of the dumbbell part.  
All printed dumbbell-shaped parts were first placed in the ventilation chamber for 7 days so as to minimize influence of the solvents. The mechanical properties of 3D-printed parts were then assessed by a Lloyd tensiometer (AMETEK, Berwyn, PA, USA) equipped with a 2500 N load cell. The pulling rate of the clamps was set at a rate of 50 mm/min. Measurements were taken five times for each part.