Final Design

Respirator

Respirator design consists of five parts: (1) filter cartridge, (2) connection piece, (3) silicone body, (4) silicone seal, and (5) strap
The silicone facepiece will be manufactured by injecting a hard silicone mixture into the molds created by the 3D printer. The silicone facepiece is responsible for retaining the general structure of the respirator, as well as the straps that go around the head of the user.
There are two components that connected to the silicone body. The first component is the strap connector. The second component is the cartridge.
The silicone for the outer facepiece is slightly different from the silicone used for the inner facepiece, the inner facepiece will be made of softer silicone. The design intent is that the facepiece material will be friendly to human skin. In addition, the soft silicone has greater flexibility and elasticity, so it can adhere to different face shapes easily.

Since this project only resulted in a prototype of the respirator design, some design decisions were made on the manufacturability of the prototype with limited equipment. For silicone molding, the 3D printed mold can be replaced by an industrial molding process. As a result, the flexible part of the respirator can be molded as one piece with two different types of silicone. The rigid pieces of the respirator design, which were 3D printed in this prototype, can be injection molded through injection mold that are designed with expertise.

Filter material is pressed between two pieces.
the seealing groove ensures that filter material is tightly stack in the cartridge, which make air only pass through the filter material.
The cartrige is replacable. Users can easily replace the cartridge based on filter materials' effective time.

There are two designs for the strap connector. The major difference is that one connector uses slide-in and fit press connection, and the other uses a magnetic alignment and press fit connection. Both designs enable users to easily adjust straps by one hand. The main purpose of designing two strap connectors is to fit a different using environment. The magnetic alignment strap connector can shorten the wearing time by automatically aligning the strap to the right position. However, due to the restriction in some medical facilities (e.g. MRI), Health care workers may not be allowed to carry magnets. Thus, users may need to choose the slide-in and fit press connection strap connectors.

Both designs have a locking bar on right and left side, so that, after locking them, the strap will not fall of. Also, users can lock one side first, and then use one hand to attach the strap to another side. The sequence of locking can completely based on users' need. For instance, left handers can lock right side first, and use their left hand to wrap the strap around their heads.

Testbed

The goal of the testbed is to simulate the quantitative testing standards set forth by using different 3-D printed head shapes from OSHA. Based on the five head shapes provided by our sponsor, if our designed respirator can measure a passing fit factor value for all five head shapes then our respirator design should be able to fit the majority of the population's head shapes therefore eliminating the need for multiple sizes.

The test box is designed of clear acrylic to allow for clear visibility of the uses.
The air pump has the direction of airflow alternating between positive and negative pressure in order to simulate the normal breathing rate of a wearer.
If the respirator is designed properly then the concentration of aerosol particles between the head model and respirator will be very small in comparison to the aerosol concentration within the rest of the testbed.

The head model is covered by silicon mask, which can mimic the texture of face skin

The chamber inside the testbed can be open to put electrical components (sensor and Arduino). Also, it can be sealed.

Other components:

The test box consists of two parts, the main body and the sealing lid.
On the two longer sides of the test box, two holes are cut out to accommodate additional parts. One of the holes is intended for an aerosol adapter which allows particles to enter the box from an outside aerosol generator. The other hole is intended to install a dual-USB panel mount, which can connect the arduino boards from inside of the box to outside laptops without any leaks occurring within the box.

Summary of performance results:

As the plot has shown, the numbers of PM2.5 particles counted inside the respirator at 30 seconds are highest for the surgical mask, followed by the respirator prototype. The N95 mask has the lowest PM2.5 particles count at 30 seconds. The respective values are 1273 for the surgical mask, 1090 for the respirator prototype, and 860 for the N95 mask. By comparing the number of PM2.5 particles in each trial with different masks, a conclusion can be drawn that the prototype respirator performs better than the surgical mask, but slightly worse than the N95 mask.

Interpretation of the raw data

By reading from the full spectrum of data produced by the arduino program, which are shown in below figures, there was one interesting discovery or trend the team noticed. For the surgical mask, the readings for PM2.5, PM4.0 and PM10.0 are different and vary with great discrepancies. However, the respective readings for N95 mask and the respirator prototype are the same for these particles with different sizes.

Assumptions and findings:

The fact that PM4.0 and PM10.0 readings are greater than PM2.5 reading clearly indicates the gap in fitment of the surgical mask, as particles of size 4 micrometers or more in diameter will only go inside the mask through the gap assuming the filter is functioning as expected.
There are almost no particles greater than 2.5 micrometers in diameter entering both the N95 mask and the respirator prototype. From here, the team concludes that the respirator prototype achieves at least the same performance of sealing as the N95 mask.
In conclusion of the test performance, the team managed to identify that the respirator prototype achieved at least the same level of sealing as the N95 mask. The difference in data readings between N95 mask and the respirator prototype can be attributed to the underperformance of KN95 filter and the porous surface of 3D printed parts.

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