WikiJournal Preprints/Design and Manufacturing of an Aerosol Box for Clinical Personal Protection

Introduction
Photos, services, and an abbreviated medical publication on the internet are sharing new designs for aerosol boxes  to aid in the intubation of patients adversely affected by COVID-19. The abbreviated medical publication showing the dispersion of a simulated cough also suggests that aerosol boxes may reduce the risk of transmission of disease (see video ). While the efficacy of these new designs will eventually benefit from methodical testing, current clinical needs are motivating the adoption of materials and devices in healthcare settings, which are not normally permissible.

Going further, there may be an existing supply of materials from more than 4,100 large hardware stores in North America to fabricate thousands of boxes for some of the 7,000+ hospitals across the region. In this article, we show an approach to the design and manufacture of an aerosol box with minimal cutting for fast adoption by healthcare providers and volunteers. Again, the authors claim no responsibility and make no claims concerning the efficacy of devices fabricated using the content of this article.

Materials
The materials to fabricate aerosol box include the following:


 * Four 24" x 18" sheets of acrylic (polymethylmethacrylate or PMMA) with a thickness of 0.22" (commonly found at hardware stores in North America)
 * Gorilla Super Glue (commonly found at hardware stores in North America)
 * 70% isopropyl alcohol or another cleaner to prepare areas receiving glue
 * Cotton swabs, rags, or paper towels
 * Thin pieces of plastic (e.g., food wrap) on which to rest two corners of the drying box to avoid sticking to the floor.Sheets super glue 20200404 042727 cropped.jpg

Design
We lay out designs as shown in the schematics. In the first design with all three back edges/faces flush against each other, the side sheets have dimensions of 18" x 17.78" with the long edge in the vertical direction. The front sheet with holes requires cutting of two holes with a diameter of 4". The 24" x 18" top sheet (uncut) sits on the three supporting sheets with their outward facing sheets flush against three of the side edges of the top sheet. The side sheets have one of their side edges with a length of 18" flush against the back side of the front sheet and another other side edge with a length of 17.78" is flush against the bottom of the top sheet. This design requires the four cuts (one for each side sheet and the holes in the front sheet) when employing four acrylic 24" x 18" sheets and is also applicable to any other four-sided "box" starting with sheets of uniform size.

A second design leaves all the outer dimensions of the four sheets at 24"x18". The only cuts are for the two holes with a diameter of 4". The side sheets go past the back of the top sheet. This design requires a minimal number of cuts (only holes in the front sheet) when employing four acrylic 24" x 18" sheets and is also applicable to any other four-sided "box" starting with sheets of uniform size.

Fabrication
For the "first" design, the side sheets require a single cut in two of the 24" x 18" sheets to shorten their length from 24" to 17.78". The front sheet requires cutting of holes. For a laser cutter, we provide pdf files for the front sheet with holes and the side sheets. There are black lines and red lines in the pdf files. The black lines are for alignment and the red lines are for vector cutting. On a 50-Watt Universal Laser System, settings for vector cutting were approximately 77% for power, 3% for speed, and 500 pulses per inch. Two passes with these settings cut the material cleanly, and we avoided moving the samples between passes. Laser cutters with lower power should work and may require more passes or slower speeds. The footprint of the Universal Laser System in this study was 24"x18", which dictated the selected size of the acrylic sheets and modification of the previously published design of an aerosol box. We fabricated nine boxes with this "first" design in a few hours before letting the glue cure. The "second" design requires cutting the two holes in the front sheet/panel before assembly, and there is no need to perform additional cuts to reduce the length or width of the sheet. A 4" hole saw mounted to the end of a handheld electric drill is capable of cutting through the 0.22" acrylic sheets, but this process requires more time and manual effort than cutting with a laser cutter. Nonetheless, a handheld drill and 4" hole saw (also available at commercial hardware stores) are the only required tools (i.e., no laser cutter or hack, table, or band saws required as long as you have four sheets of the appropriate stock). To facilitate easier manipulation and handling, the side sheets were also offset approximately 0.5" from the outer edges of the top and front sheets. We fabricated two boxes with this "second" design in a few hours before letting the glue cure.

After cutting the sheets, we use cotton swabs, rags, or paper towels to prepare and clean the bonding regions of the acrylic sheets with isopropyl alcohol. We then use a small dispenser to apply adhesive to the edges of the sheets that mate flush against a neighboring face of an adjacent sheet. This process requires patience and care, and we place little pieces of disposable plastic/paper under the front two edges of the boxes to keep the boxes from sticking to the ground when adhesive leaks down from the front vertical joints. Note: a small bottle (15 g) of Gorilla Super Glue is enough to fabricate two boxes.

The sheets were not perfectly flat, which contributed to mixed quality in the resulting bonded interfaces. Nonetheless, we did not need to discard or re-cut any sheets, and boxes bonded with Gorilla Super Glue held together well enough for shipping within 12-16 hours of bonding.

Results
The completed boxes using Gorilla Super Glue with less than 16 hours of drying were sturdy enough to lift and pack in a car for delivery to a local hospital on March 25th, 2020. There were some messy regions where glue spilled or dripped down the sides, but the boxes left the Makerspace intact. How long the boxes will last in a clinical setting is still unclear, but boxes with super glue lasted over a week.

Using a laser cutter with the "first design," a small team of 2-3 individuals was able to design, acquire materials, fabricate, and deliver nine boxes in less than 24 hours. We made 5 boxes with Gorilla Construction Adhesive and 4 boxes with Gorilla Super Glue. One of the boxes with construction adhesive broke during delivery, at least one other with construction adhesive broke at a hospital, and the boxes with super glue appear to be holding up well.

Using a handheld drill with a 4" hole saw with the "second design," a single person made two boxes in a few hours. These boxes have yet to undergo use at a local hospital.

For both designs, we recommend Gorilla Super Glue for bonding the sheets together at this point in time.

Feedback from clinicians matches that stated by Canelli et al. in that the box can restrict motion during removal of a stylet. Also, the designs in this article have an internal height (18") less than the 50-cm vertical dimension (19.7") in the original design posted on the internet. With a width of 24" (no cutting of the outer dimensions of the stock material), these boxes fit well on beds in an emergency room but may have difficulty fitting on a table in an operating room with a standard width of 50 cm.

Conclusions
This article describes a technique for rapid fabrication of aerosol boxes as a form of PPE to reduce the spread of disease associated with intubation. The concept is the same as that provided in photos by Hsien Yung Lai, and we provide information concerning how to design a box amenable to manufacture from materials found in a hardware store. Using a laser cutter, a small team of 2-3 individuals was able to design, acquire materials and fabricate nine boxes in less than 24 hours using the "first design." These boxes have been used in an emergency room setting on patients, and there is demand for more boxes. Using a handheld drill with a 4" hole saw with the "second design," a single person fabricated two of these boxes in a few hours.

These initial prototypes are a modest step toward designs that might lead to an array of solutions for PPE to combat COVID-19. With more than 4,100 large hardware stores in North America, there may be an existing supply of materials to fabricate thousands of boxes for some of the 7,000+ hospitals across the region. These designs continue to evolve weighing functionality, simplicity of fabrication, durability, and portability.

Acknowledgements
We are grateful for the support of the College Ave. Makerspace at the Rutgers Honors College, which permitted the use of a $$\mathrm{CO_2}$$ laser cutter to produce the designs described in this article. We are also grateful for ongoing support from the Rutgers Honors College, the Rutgers Department of Mechanical and Aerospace Engineering, and the Rutgers Department of Biomedical Engineering. Troy Shinbrot, Joshua Prasad, Sameer Sood, Renee Riggs-Fiesseler, and Kelvin Kwong Eisenstein facilitated communication and provided feedback on the fabricated aerosol boxes.

Competing interests
The authors have no competing interests.

Ethics statement
The designs continue for the aerosol boxes continue to evolve. The authors claim no responsibility and make no claims concerning the efficacy of devices fabricated using the content of this article.