Manufacturing and Assembly

Printed Components

The core component is the 3D printed mask itself. It comes in four sizes, Small, Medium, Medium-Large, and Large. The other printed components are the two sides of the 3D-printed strap buckle, found at https://3dprint.nih.gov/discover/3dpx-015331.

Print Settings

The mask can be printed by standing it up on the circular “snout” and using supports. We used a standard 0.4mm nozzle and SunLu PLA+ material; some type of PLA Plus is recommended because the mask is fairly thin, and could break if made of normal PLA. Three shell layers and a layer height less than 0.2mm is recommended. Infill settings should be irrelevant.

The strap buckle has two parts, a “male” and a “female”. Once again, three shell layers and a layer height less than 0.2mm is recommended. Infill of 10-30% should be ideal. We found that for best results, the “female” side should be printed out of PETG, because it contains a bending beam element. (Brittle PLA materials are not suited for repeated bending). The “male” side can be printed from PLA or PETG. 

Non-Printed Materials

In addition to the printed parts, you will need:

• A rectangle of thin (2-4mm) silicone rubber of the following dimensions corresponding to mask size:

Mask Size

Silicone Rectangle Size

Small

115 x 50 mm

Medium

110 x 50 mm 

Medium-Large

100 x 50 mm

Large

120 x 40 mm

• A thin clothespin to pin the silicone square into place while it’s being glued. (Recommended: https://www.thingiverse.com/thing:339768, scaled up 200% in X and Y but not Z)
• Roughly 85 linear cm of one-inch (25mm) wide elastic band material. Cut one “top strap” approximately 35cm long, and two “bottom straps” approximately 25cm long. 
  • (Users with smaller heads may be able to use less, users with very large heads may need more). 
• Roughly 35cm of insulated, solid copper wire, thin enough that two strands can pass side-by-side through the nose bridge loops on the mask.
• Silicone caulk or glue.
• Masking or duct tape.

Assembly

1. Insert the nose bridge wire and twist it into place.
2. Spread silicone glue around the perimeter of the silicone rectangle.
3. Place the rectangle inside the mask and pin it in place with one or multiple clothespins.
4. Wait for the glue to harden.
5. Put the top elastic strap through the top strap loops, leaving one side loose and securing the other by folding the elastic strap over and taping it.
6. Put in the two bottom straps through the bottom strap loops, leaving them both loose to be adjusted. Attach the “male” strap buckle to one and the “female” strap buckle to the other, securing both with tape.
7. Put on the mask and adjust the straps until they’re tight, then secure them in place with tape.
8. Trim the excess material off the ends of the straps.

Air Intake Manifold

We also developed an air intake manifold that fits the front of the mask and allows air to be pumped in through a one-inch flexible hose. The design can be found at https://3dprint.nih.gov/discover/3DPX-015330. We used a flexible one-inch hose from McMaster-Carr and secured it to the manifold with smooth hose clamps from McMaster-Carr.

Air Intake Printing

We printed the manifold from high-temperature PLA; high-temperature PLA or PLA Plus is recommended because the weight of the hose makes the manifold a load-bearing part. Three shell layers, a layer height less than 0.2mm, and an infill of at least 20% is recommended. 

We found that the manifold is best printed with the cup facing upwards and the hose barb facing sideways, with supports touching the build plate only. 

Air intake installation 

Spread silicone glue around the top of the outer wall of the intake cylinder:

Then put the manifold over the cylinder with the hose barb pointing down and to the side at a roughly 45% angle. (User handedness and ergonomic preference can determine which side it points to). 

Once the glue is fully hardened, you can attach a one-inch hose using appropriate hose clamps. 

PAPR blower

We attempted to develop a low-cost improvised PAPR blower from an N95 mask, an air mattress pump, and printed parts. However, none of our prototypes could sustain acceptable levels of airflow for more than a few minutes, making them dangerous to use in a COVID-19 context. We instead recommend sourcing PAPR blowers from elsewhere and connecting them to our PAPR mask.