## 3 Results and Discussion
### Product Design with the Use of DfAM and Rapid Prototyping  
As indicated by the usability requirements, when designing the adapter geometry, it was necessary to take into account the geometric features of the full-face mask, the DAR filter, and the criteria presented in Table 2. After the measurements, it was found that the full-face mask has an internal thread RD 40 with a length of 20 mm, while the DAR filter has an outlet with a diameter of \(\mathcal{O}\) 22 mm and a length of 15 mm. After receiving the mask and the DAR filter from the hospital, a prototype adapter was designed and manufactured. Despite the advantage of the SLS method in the described application, at the prototyping stage, individual pieces of the product are produced, therefore, for economic reasons, the FDM method was applied using the Stratasys F170 machine with GrabCAD Print software. Adapter prototypes were printed using a \(\mathcal{O}\) 0.33 mm nozzle and a layer height of 0.33 mm. The filling density was set to 100%. The correctness of the prototype was tested by mounting it to the supplied mask and filter, thus ensuring that the minimum operational requirements were met. The adapter prototype was delivered to the hospital 22 h after the need emerged (Figure 6). After the adapter tests had been carried out, information was obtained that there were difficulties with screwing in/unscrewing the adapter from the mask. This indicates that the adapter cannot be fully screwed into the mask, which can in turn result in an increased distance between the mask and filter inlet (Figure 7). To facilitate the screwing in/unscrewing of the adapter from the mask, it was decided to add gripping elements. Two design variants were proposed with two and eight grips, and two other designs with two and eight gripping tongues. After further tests, it was \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Methodology**} \\ \hline
**Area** & **Criteria** & **ABS (FDM)** & **PA12 (SLS)** \\ \hline \multirow{8}{*}{Usability} & \multirow{2}{*}{ergonomics} & 0 & \multirow{2}{*}{4} \\  & & produces sharp edges & \\ \cline{2-3}  & & & \\ \cline{2-3}  & & functionality & 0 & \\ \cline{2-3}  & & possible leaks & 4 \\ \cline{2-3}  & sterilisation & 0 & 4 \\ \cline{2-3}  & cytotoxicity & 0 & 4 \\ \cline{2-3}  & life cycle & 0 & 4 \\ \cline{2-3}  & antibacterial & 0 & 4 \\ \hline \multirow{3}{*}{Eonomical and environmental} & price of the material & 0 & 4 \\ \cline{2-3}  & material availability & 4 & 4 \\ \cline{2-3}  & availability of machines & 4 & 0 \\ \cline{2-3}  & demand & 300 pcs & 300 pcs \\ \hline \multirow{3}{*}{Manufacturing} & technology/DfAM & 0 & 4 \\ \cline{2-3}  & productivity & 0 & 4 \\ \cline{2-3}  & scalability & 4 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Evaluation of the suitability of selected materials and technologies for the production of a full-face mask filter adapter. found that version 3 of the adapter is easier to screw in/unscrew. Sadly, the elements that facilitate the screwing in/unscrewing of the adapter in version 3 had sharp edges, which tore the disposable gloves. The sharp edges resulted directly from the limitation of the FDM technology and appeared at the point of contact of the model with the platform and at the seam. The authors of [22] presented a whole range of different PPEs produced with the use of FDM technology to fight against COVID-19. Moreover, the authors of [23] presented a model of an adapter for the full-face snorkel mask, which was manufactured with the FDM technology. However, the above publications did not consider a systematic approach that takes into account risk inducing factors, such as material cytotoxicity and antimicrobial activity properties. Due to the limitations of FDM technology, the produced parts are more susceptible to leakage. This is an important factor in the protection against COVID-19.