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Mask making on a pandemic sabbatical

How the MNmask Style 3 went from idea to reality

Rhonda Franklin was on sabbatical leave when the coronavirus pandemic hit. Borders closed, planes were grounded, and stay-at-home orders took effect. She had been eager to present some invited talks and attend conferences—but like many, she adapted. Franklin, an electrical and computer engineering professor, ended up leading a University of Minnesota team in developing a general-purpose face mask inspired by hospital procedure masks.

“I was sitting in front of the TV, watching what, in my mind, was the world about to collapse,” she recalled. “I couldn’t imagine what my colleagues on campus were facing. I felt like I needed to contribute something.”

She immediately contacted John Bischof, director of the University of Minnesota Institute for Engineering in Medicine (IEM), wondering if there were any mask-making projects she could join. Bischof, who is also the Carl and Janet Kuhrmeyer Chair in Mechanical Engineering at the College of Science and Engineering, connected her to fellow mechanical engineering professor Will Durfee, the technical lead for the MNmask project funded by IEM.

Durfee sent her some reading material and invited her to a group meeting.

“I thought I could sew a few masks and call it a day,” said Franklin, who started sewing in high school.

A few days later, however, she was in charge of creating “Style 3.” Durfee’s team had already created two face mask designs from repurposed air filtration material donated by Cummins. Both of them, the single-use foam mask and the reusable anesthesia mask with a disposable filter, were intended for clinical use. Now, the inventors were looking to round out their MNmask family with one that could serve a wider audience.

Simplicity is key

Over the next three weeks, Franklin—recently named an IEM Abbott Professor in Innovative Education—threw herself into all aspects of product design and development.

Her closest collaborators were Joan Bechtold, professor in the Departments of Orthopedic Surgery and Biomedical Engineering and a researcher with the Hennepin Healthcare Research Institute (HHRI); and two certified industrial hygienists at the University of Minnesota—Susan Arnold, assistant professor and director of the Exposure Science and Sustainability Institute in the School of Public Health; and Neil Carlson, with the Department of Environmental Health and Safety.

“Simplicity was extremely important to me,” Franklin said. 

And all their models had to incorporate the tenets of effective respiratory protection that Arnold shared with her in a phone call. These include a snug seal to your face and ease of breathability.

“We prototyped 10 styles using different materials and made each style two ways,” Franklin explained. “One with a sewing machine and another with a stapler.”

Bechtold, who’s been sewing since junior high and could whip out a prototype in five minutes with her 1950s Singer machine, landed the stitching job. Franklin got stapling duty.

According to Bechtold, their two-prong approach was necessary to evaluate efficacy against today’s common face coverings—namely, the home-sewn mask and the standard mask healthcare workers wear when performing patient procedures outside the operating room.

“Because of the pace of our project, we didn't have the time to do all the comparisons we'd normally like to do—to better tease out the effect of mask design, mask fabrication method, and mask material,” she said. “So, we narrowed it down. We needed to have something that is known in practice, tested the same way.”

Bechtold, an alumna of CSE’s mechanical engineering graduate program, isn’t new to emergency mask designs. In fact, she shared some ideas with the MNmask team. She had started to study them in HHRI because of her work with orthopedic surgeons at Hennepin County Medical Center.

Tests, and more tests

The 20 prototypes landed in Arnold’s lab at Boynton Health Center. There, her PortaCount respirator fit testing equipment by TSI Inc., a company founded by biomedical engineering alumnus Leroy Fingerson, collected the preliminary data they needed.

“It simultaneously measures the number of particles inside and outside the mask [after a person wearing the mask is put through a series of moving, breathing, and talking exercises],” Arnold said. “This tells us how effective a respirator or mask, in our case, is. We are particularly interested in blocking particles that are the right size from getting deep into the lungs.”

In addition to Franklin, Carlson was roped in to try the masks.

“We needed his expert opinion and a second face,” Franklin said. “One stapled prototype—what we now call Style 3—consistently outperformed the other models we tested.” 

“This design was based on Linsey’s origami mask with key design edits to simplify construction,” she noted, “and it proved to be the better combination of filtering material and fit of the 10 styles.”

Linsey Griffin, assistant professor and co-director of the Human Dimensioning Laboratory in the College of Design, invented Style 1. That MNmask features a heat-sealed contour, foam for comfort and fit, and versatile band placement for a complete seal.

After three rounds of testing, which saw them eliminating designs and changing the band on the mask to a latex-free option, the team had a lone model to move forward.

“We were pleasantly surprised by how well the mask performed, when it was donned and adjusted properly,” Arnold said.

Stand on your head, but use the ruler

The “100 mask” experiment came next. The goal was to see if others could replicate the winning mask—made by Franklin (then Bechtold) with a stapler, a nose wire, rubber band, and the same Cummins air filters used in Style 1 and Style 2.

“We provided five people we knew written instructions, a how-to video, and materials they needed in a kit,” Franklin said. “We were also curious to see if people get better the more they make.”

Well, it turns out they don’t. People will consistently make things the same way without feedback.

“What matters is how they start,” she noted. “One of the quirks we found was in the instructions. It didn’t occur to me to describe the exact placement of the staples. Your staples must form a T shape to correctly secure the form of the mask. Some people had L-shaped staples. So those masks did not fit right.”

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To build the Style 3 mask so it fits correctly or snug on a face, the staples must form a T shape (left image) and not an "L" shape (right image). Photos courtesy of Rhonda Franklin.

That discovery led to modifications in the instructions. Plus, further human experiments.

In May, the MNmask team recruited nearly 60 undergraduate and graduate student volunteers to assemble 6,000 Style 1 masks for M Health Fairview’s crisis stockpile. About 15 of those students volunteered to wear the Style 3 masks.

More findings emerged from the increased face samples. They added a ruler to the final mask-making kit.

“The staples were introducing variability,” Franklin said. “Personality types was another factor. All this got me thinking, ‘who’s going to make these masks?’ and will they be as methodical and slow as I am or quick and creative as Joanie? My hope is that the ruler, with only two key dimensions, gives everyone the same reference point.”

“What’s great about this mask when it’s made correctly,” she added, “is that it fits a wide range of faces very nicely.” 

“So,” Franklin said, “I don’t care how you make it—you can stand on your head to do it—but I need you to get the dimensions right.”

Last month, 50,000 Style 3 masks were packaged into kits. They sit ready in Anderson Labs for distribution to faculty, staff, and students. Effective July 1, the University of Minnesota began requiring face coverings to be worn indoors (including in classrooms) across all five campuses, as part of its larger effort to prevent the spread of COVID-19.

A student with face mask and gloves standing at a table, with a stack of boxes behind him.
A volunteer placing a card-stock ruler with two dimensions (2 cm and 9 cm) into a bag. A total of 500 MNmask Style 3 kits were assembled at Anderson Labs last month. Photo credit: Ben Guengerich

“The project was definitely a team effort,” Franklin said. “Our interdisciplinary knowledge and backgrounds are what allowed this mask to come about. I enjoyed the chance to work with experts in the Medical School and School of Public Health—amazing colleagues I might never have run across otherwise. This has turned out to be a very memorable sabbatical.”

More information

Learn more about the MNmask, and download designs, on the UMN Institute for Engineering in Medicine website or UMN Technology Commercialization licensing webpage

Read about the Style 3 mask-kit assembly in the Clifford I. and Nancy C. Anderson Student Innovation Labs at “50,000 masks and counting.”


If you'd like to support this work and other COVID-19-related activities, visit the CSE Response Fund.