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Filter Test Kits for 3D-printed Reusable Masks

The BEmask is still evolving toward meeting the requirements for a medical N95 mask. Functional design barriers to overcome include (1) providing an airtight seal around the face and nose for a large range of users, (2) user comfort with respect to the weight and bulk in comparison to disposable masks and (3) breathing ease for available filter materials that will meet N95 requirements.

The BE masks are being tested in 3 sizes (S, M, L) in either rigid or flexible materials. PLA is a rigid material that is easy to print and the user can be easily custom fit the nose area by thermoforming with hot water. TPU is compliant and forms a softer interface with the skin of the user, but it is more tricky to print.

Comfort regarding the weight and bulk has been addressed by using a 3D printed variation of a head strap arrangement that was used by 3M for their bulky industrial respirators (see https://www.youmagine.com/designs/comfortable-head-strap-for-reusable-respirators-and-medical-masks#information).

Our filter test kits are special variations of the BEmasks to study the effects of different filter materials, their thickness and their surface area on the ease of breathing in a 3D printed mask.

Specifically, we have found that for commercially available HEPA filters with a MERV rating of 15 (found in some vacuum cleaner bags), two layers of filter may be required to meet the N95 standards. We would like to know how large such filters must be in order for the user to breathe with an acceptable level of comfort.

To study this, we have designed a filter holding box that can adjust the filter area by masking off a portion with the blue tape (familiar to users of 3D printers). The adapter has two filter compartments for a standard (2 1/2 inch) filter size. Therefore, the user can evaluate the breathing comfort with up to double the filter size for single-layer and for double-layer filters.

The 3 mask sizes (S, M, L) have been modified so that they easily accept the filter holding box. The evolution of the design can be followed on our website https://bemask.org/.

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