3D printing human heads key to a new approach for relieving PPE backlogs.
They may be in less demand today than during the COVID-19 pandemic but N95 respirators continue to be a crucial piece of personal protective equipment (PPE). For millions of people worldwide – from healthcare and construction workers to the immunocompromised and their families —having access to high-quality masks is simply nonnegotiable.
Given those stakes, N95 mask tests must be not only reliable but also quick enough to keep up with demand – which isn’t the case with existing systems. But this month, a team of engineers and scientists at Sandia National Laboratories revealed a promising new approach. Combining creative design with 3D printing, it could be the foundation of an all-in-one testing system that produces safer masks, faster.
Problems with the Current Approach to N95 Mask Testing
The core of an N95 respirator is a fine mesh of nonwoven polypropylene fabric produced by melt blowing, which forms an inner layer to filter out hazardous particles. Traditional testing of this core is “very time-consuming and not as efficient as it could be,” Michael Omana, an aerosol scientist at Sandia National Laboratories in Albuquerque, New Mexico, said in a press release. It involves using hot wax or putty to attach a mask to a flat plate enclosed in a box, introducing a test aerosol, and then measuring penetration levels. Because National Institute for Occupational Safety and Health requires 20 masks in each batch to be tested before the batch can be approved for use, the testing phase represents major bottleneck in the supply chain.
Beyond being time-consuming, this approach only tests the mask’s inner layer. “It doesn’t test geometry, how the respirator fits on a face, how it’s moved on and off multiple times, how the straps perform, how the nose bridge performs, how the mask can wear over time,” said Todd Barrick, one of the engineers on the research team. Added Omana: “I think there were a lot of lessons learned with everyone suddenly looking at what the industry standards were.”
Testing N95 Respirators Holistically
To begin, the Sandia team replaced the flat plate with a 3D-printed model of a human face that can be loaded into a commercial filter test system. According to engineer and team member Brad Salzbrenner, the idea is to test more performance factors at once, such as how the mask fits. Using 3D printing enabled the team to make the model pliable to more closely resemble human skin.
This was a good start, but it didn’t fully account for real-world usage, so the team developed a more complete model of a human head that can be placed in an airtight box and then loaded into the testing machine. Salzbrenner and Barrick wanted to go even further, creating a way to test N95 masks for reuse—a common practice during the height of the pandemic but for which there is no testing standard.
“We developed the chamber version to automate donning and doffing (putting on and taking off an item) to test respirator function over time, a predominant factor in wear on a mask,” Salzbrenner said. “It also mimics how a mask is set on the face and shows you any gaps that air and particles can get past.”
The hope is that these two methods can be combined into an all-in-one tester that accounts for all the aspects of the mask. As Omana explained, the current approach to testing doesn’t account for all the other potential points of failure besides the filter media. This new holistic test gets much closer to how N95 masks are used in the field.
The Sandia team is currently working on further refining their approach, with the goal of licensing the science to a company that can produce their all-in-one testers on a commercial level.
