## 2 Materials and Methods
### Manufacturing  
The designed prosthesis parts in their final version were manufactured using a Zortrax M300 Dual machine (Zortrax, Olsztyn, Poland). The M300 Dual is an upgraded version of the original Zortrax M300, offering dual extrusion capabilities. Key features of the Zortrax M300 Dual include dual extrusion, large build volume (265 \(\times\) 265 \(\times\) 300 mm, with a 0.4 mm diameter nozzle, resolution between 100-300 microns, max. temperature of the Table is 100 \({}^{\circ}\)C, and max. temperature of the heating block is 380 \({}^{\circ}\)C), and compatibility with variable materials, including Zortrax's proprietary filaments as well as third-party filaments that meet the required specifications. This machine can be classified as a semi-professional 3D printer, with an approximate purchase cost of USD 4490 (as of 2023).  
For manufacturing of mechanical parts of the prosthesis, ABS material was used (Spectrum Group, Pecice, Poland), in the form of 1.75 mm-diameter filament. Material processing characteristics (based on the material supplier data) are presented in Table 2.  
Constant material parameters were kept during manufacturing of all parts, i.e., layer thickness was 0.2 mm, and the internal filling was 30%. The temperatures and extrusion speeds were selected on the basis of the most suitable values recommended by the producer, slightly modified by authors' previous experiences (bringing the most stable process, without layer disjoint, under extrusion or other typical errors in the FDM process). The values of other manufacturing parameters (not shown in Table 1) were assumed standard as recommended by machine and material manufacturers.  
The printing of the prosthesis was divided into two batches, i.e., first the prosthetic socket was printed alone, and then the other elements. The programs were prepared in the Z-Suite program that was dedicated to work with Zortrax printers. The prosthetic socket was manufactured in the appropriate orientation so as to obtain the best possible quality of the inner surface, which is ultimately in direct contact with the residual limb. The expected print time was 21 h, and the estimated material consumption was 210 g. The remaining parts of the prosthesis (forearm with holes for electronics, C-handle, and Cardan) were printed simultaneously, which significantly reduced the production time. The expected print time was approx. 30 h, and the material consumption was 333 g. Figure 13 shows both prints as simulated in the Z-Suite software and also printer during the process.  
The manual post-processing of the obtained products was limited to the simplest activities: support removal, basic manual grinding, and thermal removal of excess strings of material. The produced parts were visually assessed during and after the process to check for major defects that would make them unusable and minor defects that would require certain processing in order to make the prosthesis functional or more comfortable. They were further used for assembly of complete prosthesis.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Properties** & **Process Parameters** \\ \hline \multirow{8}{*}{ABS (acrylonitrile-butadien–styrene) Red/black} & Density: 1.02 g/cm\({}^{3}\) & \\  & Extrusion temperature range: 240–270 \({}^{\circ}\)C & \\  & Glass transition temperature: 105 \({}^{\circ}\)C & \\  & Young’s modulus: 1.79–3.2 GPa & Extrusion temperature: 270 \({}^{\circ}\)C \\  & Tensile strength: 29.8–43 MPa & Build platform temperature: 90 \({}^{\circ}\)C \\  & Compressive strength: 76–78 MPa & Extrusion velocity: 60 mm/s \\  & Elongation at break: 10–50\% & Number of contours: 3 \\  & Flexural modulus: 2.1–7.6 GPa & Number of closing/opening layers: 4/4 \\  & Izod impact strength: 58 kJ/m\({}^{2}\) & \\  & Yield strength: 28–120 MPa & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characteristics of used materials and FDM process parameters.