Physician innovators and engineers partner on a low-cost mask filtration testing device in response to COVID-19

Huan Song
10/15/2020 10:03:08 AM

The COVID-19 pandemic has triggered a global surge in demand for personal protective equipment (PPE), especially surgical masks and N95 respirators. Supply chain disruptions have further resulted in a shortage of PPE for healthcare professionals on the front lines.

Filtration efficiency measurement setup
Filtration efficiency measurement setup
Clinicians, medical students and researchers from the University of Illinois teamed up to develop a low-cost conversion of existing hospital equipment to measure filtration efficiencies of alternative mask materials. This testing setup, which required less than $300 of additional materials, can approximate the National Institute for Occupational Safety and Health (NIOSH) testing standards. Furthermore, the team proposes possible alternative materials that can achieve filtration efficiencies close to that of N95 respirators in a healthcare setting. The findings are published in PLOS ONE

Healthcare professionals require different types of PPE depending on their level of contact with the virus. When people speak, cough or sneeze, they expel droplets that may contain the virus. A mask primarily prevents the spread of the wearer's own droplets whereas a respirator protects the wearer from inhaling smaller aerosol particles in their surroundings. The filtration efficiency (FE), or the ability of the material to filter out particles, is a quantitative measurement of the effectiveness of the face covering. Most home-made masks do not take FE into consideration. 

During the pandemic, labs with specialized equipment to measure FE are in high demand with long wait times. As a response to this shortage, the research team designed an alternative device that combined standard hospital equipment - a respirator fit-test apparatus and a particle generator - with the hospital's vacuum and some low-cost materials from the hardware store. The particle generator creates aerosolized NaCl particles that are pumped through the filter material. NaCl particles are then measured downstream using the fit-test particle counter which enables the team to calculate the FE, or the percentage of particles blocked by the respirator. 

This study benchmarked materials against the 3M 1870 and 1860 N95 respirators, which have an FE of 99.43% ± 0.18 and 98.89% respectively. Test samples included healthcare-grade materials like sterilization wraps and consumer-grade materials like cotton fabrics and vacuum bags. The team also examined a combination of materials, multiple layers of materials and their impacts on breathability.

The tests showed that two layers of heavy sterilization wrap achieved a FE level that exceeded the N95 certification requirement.  "We demonstrated a FE of 96.49% and a pressure drop of 25.4 mmH20 for a double-layer of heavy sterilization wrap used in surgical suites and a FE of 90.37% for a combination of consumer-grade materials," said Ian Berg, a bioengineering Ph.D. candidate and a co-author of the study. Specifically for the consumer-grade materials, the team used a combination of two layers of Smart Fab, a common arts and crafts supply, with a layer of vacuum bag.  

"The excellent filtration characteristics of the former demonstrate potential utility for emergent situations when N95 respirators are not available, while those of the latter demonstrates that a high FE can be achieved using publicly available materials," Berg said. The results from this study show the possibility to perform preliminary triage of materials for masks and respirators.

The University of Illinois has been at the forefront of COVID-19 research and innovation. This research further highlights the effectiveness of multi-institutional collaboration at the nexus of engineering and healthcare. The research team consisted of Kenneth Long, a medical student at the University of Illinois College of Medicine at Urbana (UICOM), bioengineering’s Ian Berg and alumna Elizabeth Woodburn who, along with Valerie Chen, are medical students at the Carle Illinois College of Medicine (CIMED) and Dr. William Scott, a clinical associate professor at CIMED and the head of Occupational and Environmental Medicine and Employee Health at the Carle Foundation Hospital.

The idea and design process started in mid-march when the medical students had to stay home from clinical rotations. Woodburn was making homemade masks early in the pandemic when she reached out to Long to discuss how to assess the filtration characteristics of different materials. The team completed the experiments in April and May with funding from CIMED and experimental space through Dr. Blair Rowitz, the associate dean for clinical affairs at CIMED. 

 "Creating a sense of community and open dialogue between institutional partners, including UICOM, CI MED, and the bioengineering department that fosters such relationships enabled us to co-innovate with expertise from our various backgrounds," said Long. "The commitment of each of those partners to support such collaborations was quick, definitive, and efficient—precisely what was needed to rapidly respond amidst an evolving pandemic."