Engineers design a reusable, silicone rubber face mask

Researchers at MIT and Brigham and Women's Hospital (BWH) have designed a new face mask that could stop viral particles as effectively as N95 masks. Unlike N95 masks, the new masks are designed to be easily sterilized and used many times.

As the number of new COVID-19 cases in the United States continues to rise, there is still an urgent need for N95 masks for health care workers and others. The new mask is made of durable silicone rubber and can be manufactured using injection molding. The mask includes an N95 filter but requires less N95 material than a traditional N95 mask.

“One of the key things we recognized early on was that in order to help meet the demand, we needed to really restrict ourselves to methods that could scale,” says Giovanni Traverso, an MIT assistant professor of mechanical engineering and a gastroenterologist at BWH. “We also wanted to maximize the reusability of the system, and we wanted systems that could be sterilized in many ways.”

The team is now working on a second version of the mask based on feedback from health care workers and is working to establish a company to support scaled-up production and seek approval from the FDA and the National Institute for Occupational Safety and Health (NIOSH).

Easy sterilization

The N95 masks that health care workers wear to protect against exposure to SARS-CoV-2 and other viruses are made from polypropylene fibers designed to filter out tiny viral particles. Ideally, a health care worker would switch to a new mask each time they see a different patient, but mask shortages have forced doctors and nurses to wear them for longer than they are meant to be worn.

In recent months, many hospitals have begun sterilizing N95 masks with hydrogen peroxide vapor, which can be used up to 20x on a single mask. However, this process requires specialized equipment that is not available everywhere, and even with this process, a mask can only be worn for one day.

The MIT/BWH team set out to design a mask that could be safely sterilized and reused multiple times. They decide on silicone rubber – used in silicone baking sheets and other products – due to its durability. Liquid silicone rubber can be easily molded into any shape using injection molding, a highly automated process that generates products rapidly.

The masks are based on the shape of the 3M 1860 style of N95 masks used at BWH. Most of the mask is made of silicone rubber, and there is also space for one or two N95 filters. Those filters can be replaced after every use while the rest of the mask can be sterilized and reused.

“With this design, the filters can be popped in and then thrown away after use, and you're throwing away a lot less material than an N95 mask,” Wentworth says.

The researchers tested several different sterilization methods on the silicone masks, including running them through an autoclave (steam sterilizer), putting them in an oven, and soaking them in bleach and in isopropyl alcohol. They found that after sterilization, the silicone material was undamaged.

Fit test

To test the comfort and fit of the masks, the researchers recruited health care workers from the emergency department and oncology clinic at BWH. They had each of the subjects perform the standard fit test required by the Occupational Safety and Health Administration (OSHA) for N95 masks. During this test, the subject puts the mask on and then performs a series of movements to see if the mask stays in place. A nebulized sugar solution is sprayed in the room, and if the subject can taste or smell it, it means the mask is not properly fitted.

All of the subjects passed the fit test and reported that they were able to successfully insert and remove the N95 filter. When asked their preference between the new mask, a typical N95 mask, and a standard surgical mask, most either said they had no preference or preferred the new silicone mask. They also gave the new mask high ratings for fit and breathability.

The researchers are now working on a second version of the mask, which they hope to make more comfortable and durable. They also plan to do additional lab tests measuring the mask's ability to filter viral particles.