## 2 Materials and Methods
### 3D Printing and Cost Model  
Three ISO/ASTM 3D printing processes, namely vat photopolymerization (VP), material extrusion (ME), and powder bed fusion (PBF), are most commonly used to produce parts in the COVID-19 pandemic. The ME process is the most widespread 3D printing technology to date. The VP process is widely used in the medical field to print biocompatible materials. The PBF process is broadly used for producing functional prototypes, end-use parts, and rapid tooling. Table 2 lists the 3D printing machines and materials that are currently being used, or that can otherwise maintain the functional integrity of the respective products. Further, alternative materials can also be used as stated in Table 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Description** & **Users** & **Pandemic Demand** & **3D Model Source** \\ \hline Face mask & Frontline workers: hospital staff, paramelics, law & Very high & & \\ (filter is attached separately) & enforcement authorities, etc.—individual people & \(>\) 10 billion & & [[https://amaskforall.com/](https://amaskforall.com/)]([https://amaskforall.com/](https://amaskforall.com/)) \\ \hline \multirow{2}{*}{Face shield (3D printed holder)} & Frontline workers: hospital staff, paramelics, law & & \\  & enforcement authorities, etc.—some & & Very high & [[https://www.prussaprinters.org/prints/25857-pruss-face-shield](https://www.prussaprinters.org/prints/25857-pruss-face-shield)]([https://www.prussaprinters.org/prints/25857-pruss-face-shield](https://www.prussaprinters.org/prints/25857-pruss-face-shield)) \\  & individual people & \(>\) 1 billion & & [https://www.3 dsystems.com/covid-19-response/face-Shield](https://www.3 dsystems.com/covid-19-response/face-Shield) \\ \hline \multirow{2}{*}{Nasal swab} & Hospital staff, paramelics, law enforcement & Very high & & \\  & authorities, etc.—every person to be tested & \(>\) 100 million & & \\ \hline \multirow{2}{*}{Venturi valve} & Hospitals—shortage of parts & Medium & & \\  & & & \(>\) 10 million & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Products currently being manufactured using 3D printing in the COVID-19 pandemic. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**ISO/ASTM** & **Equipment \& Material** & **Layer** & **Notes** & **Steilization** & **Alternatives** \\ \hline \multirow{2}{*}{VAT Photopolymerization} & Form 2\({}^{\text{TM}}\) \& Dental SG. & \multirow{2}{*}{0.1 mm} & \multirow{2}{*}{Biocompatible material, needs post-curing and autoclaving} & \multirow{2}{*}{Autoclave} & \multicolumn{1}{c}{Vat photopolymerization} \\  & (Formlabs Inc., USA) & & & & & \\ \hline \multirow{2}{*}{Material Extrusion} & uPrint\({}^{\text{TM}}\) SE Plus \& ABS & \multirow{2}{*}{0.33 mm} & Material not medically approved, product might not be airtight & \multirow{2}{*}{Isopropyl} & \multirow{2}{*}{Other material extrusion equipment and materials, approved material} \\  & (Stratasys Ltd., Israel) & & & & & \\ \hline \multirow{2}{*}{Powder Bed Fusion} & Ultmaker\({}^{\text{TM}}\) \& ABS & \multirow{2}{*}{0.1 mm} & Material not medically approved, product might not be airtight & & \\  & (Ultimaker BV, Dutch) & & & & \\ \hline \multirow{2}{*}{Powder Bed Fusion} & 3 DSystems\({}^{\text{TM}}\) Prox SLS 500 \& \multirow{2}{*}{0.1 mm} & \multirow{2}{*}{Biocompatible material} & \multirow{2}{*}{Autoclave} & Powder bed fusion technologies with approved material for medical use \\  & DuraFormProx PA (3D Systems Inc., USA) & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: 3D Printing technologies and alternatives. The build volume of the respective 3D printing machines is often packed/nested in a manner that aims to fully maximize the number of parts within the build area, while maintaining a high probability of a successful print.