## Materials and Methods
### Design  
The design and fabrication followed a completely free and open source software toolchain, which maximizes the ability for the replication of the results. All of the 3-D printable components are designed by using the open source CAD software, FreeCAD [41], and can be further edited to customize the equipment for any scientific lab. They were designed to provide the mechanical integrity necessary for the component while still being 3-D printable without support. Exported STL files were sliced with the open source slicer, Cura [42]. Most of the components are printed using PLA, which is the most popular 3-D printing material, being available for the majority of 3-D printing supplies vendors. PLA has been shown to be a safer alternative to toxic acrylonitrile butadiene styrene (ABS) plastic fumes, the second most widely available 3-D printing material [43; 44]. PLA has a relatively low melting point (150 \({}^{\circ}\)C to 160 \({}^{\circ}\)C), so it may not be appropriate for high temperature applications. For such applications, a higher melting point thermoplastic such as ABS or polycarbonate can be substituted and printed in a fume hood or a well-ventilated area by using the same designs shown here. All of the PLA filament designs were printed using a MOST Delta 3-D printer [45] running Franklin [46], which is a RepRap [1; 2; 3]. All of the PLA components were built with the following print settings: infill 25%, layer height 0.25 mm, shell thickness 1 mm, print temperature 185 \({}^{\circ}\)C, and 70 mm/s print speed (with the exception of the rod that was printed with 0.15 mm layer height and 35% infill to improve the mechanical properties). The slit and dimpled mat were printed using Ninja Flex on a commercial RepRap, the Lulzbot Mini with a Flexystruder Extruder (Aleph Objects, Loveland, CO, USA) [47; 48], with print settings: infill 20%, layer height 0.325 mm, shell thickness 0.6 mm, print speed 14 mm/s, and print temperature 230 \({}^{\circ}\)C. The final design for the 3-D printable components focused on minimizing the filament quantity used while still achieving high torque despite the offset of the rotating axis. If the design needs to be scaled up, all of the components can be scaled, as well until the limit of the DC motor is reached and then will need to be substituted for a higher torque DC motor. Figure 1 shows all of the 3-D printed parts that are required for the open source nutating mixer. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sr. No.** & **Component** & **3-D Printing Material** & **Quantity** & **Mass (g)** & **Cost (USS)** \\ \hline
1 & Rod & PLA & 1 & 7 & 0.15 \\
2 & Bearing holder & PLA & 1 & 8 & 0.18 \\
3 & Base & PLA & 1 & 60 & 1.32 \\
4 & Cover & PLA & 1 & 126 & 2.77 \\
5 & Platform & PLA & 1 & 76 & 1.67 \\
6 & Dimpled Bed & Ninja Flex & 1 & 67 & 5.80 \\
7 & Slit & Ninja Flex & 1 & 4 & 0.34 \\  & & Total Filament Cost & & 12.23 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Bill of materials (BOM) for three-dimensional (3-D) printed components including material, mass and cost. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sr. No.** & **Component** & **Qty** & **Cost (USS)** \\ \hline
1 & Skateboard bearing [36] & 1 & 0.73 \\
2 & DC barrel connector [37] & 1 & 1.00 \\
3 & Switch DPDT [38] & 1 & 1.19 \\
4 & 12 Volt DC Motor—25 RPM [39] & 1 & 13.95 \\
5 & DC adapter [40] & 1 & 6.99 \\
6 & M3 Fasteners (2 M3 7 mm, 2 6 mm, 3 M3 16 \\  & mm and 1 M3 10 mm and bolts) & 1 & \textless{}1.00 \\  & Total Ordered Material Cost & & 24.86 \\  & **Total Cost of Equipment (Tables 1 and 2)** & **37.09** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: BOM for ordered components. The functionality for each 3-D printed component is described below:  
1. Base (Figure 2): The base of the equipment holds the 12 V 25 RPM DC geared motor, which is the main load bearing component of the equipment. 2. Bearing holder (Figure 3): The bearing holder is designed at a 20-degree tilt angle.