New Reusable Silicone Masks with N95 Filtration Rate Could Help COVID-19 Frontliners: Study
Sat, April 17, 2021

New Reusable Silicone Masks with N95 Filtration Rate Could Help COVID-19 Frontliners: Study


As the COVID-19 pandemic continues, the demand for face masks increases due to quarantine protocols. To help with the shortage, a team of engineers developed a reusable, silicone rubber version that could be sterilized and worn multiple times.

The prototype silicone rubber face mask was developed by engineers at Brigham and Women's Hospital, and the Massachusetts Institute of Technology (MIT), a private research university in the US. The reusable face mask could be sterilized and used several times. On top of that, the mask featured a filtration efficiency rate of 95% against tiny particles, similar to N95 respirators. They published their findings in the British Medical Journal (BMJ) Open.

New Reusable Face Mask on Par with N95

During the first month of the COVID-19 outbreaks across many cities, hundreds of thousands of people became worried about being infected. This resulted in the panic-buying of certain medical supplies, such as face masks, alcohol, and disinfectants. While those three examples are needed by clinics and hospitals, face masks are crucial for healthcare workers. Without face masks, they are likely to catch the virus and get sick. Healthcare workers infected with COVID-19 could not attend to patients until they recover. The situation would effectively weaken the healthcare sector.

At MIT, engineers had an idea to address two major issues in the use of face masks in the healthcare setting. They created a prototype reusable face mask to address the shortage in the supply and the growing problem in medical waste. Since surgical masks could not be used after a specific period, they have to be thrown away. And in a single day, healthcare workers would dispose lots of surgical masks. So, their prototype was designed to filter tiny particles in the air and could be sterilized for reuse.

"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. We also wanted to maximize the reusability of the system, and we wanted systems that could be sterilized in many different ways," said Giovanni Traverso, the senior author of the study and assistant professor of mechanical engineering at MIT.

In the study, the filtration efficiency of the prototype was based on N95 respirators, composed of polypropylene fibers that filter out SARS-CoV-2, other viruses, and tiny particles in the air. However, these devices would be thrown away just like surgical masks after use. The ideal setting of its application would be switching to a new N95 respirator. Yet the pandemic forced doctors, nurses, and other medical practitioners to use the respirators for extended periods – a result of the shortage.



Some hospitals had to conserve their supplies. As such, they started sterilizing N95 with hydrogen peroxide vapor. The vapor could be applied on a respirator for up to 20 times before the device is ultimately considered unfit for use. Although the creative method helped those hospitals, other hospitals could not implement the same due to budget concerns. Specialized equipment would be required to properly sterilize N95. Moreover, the mask treated with the vapor was never recommended to be worn for more than 24 hours.

Due to the expensive and less efficient nature of hydrogen peroxide vapor in sustaining N95 respirators, the engineers developed a reusable mask made of silicon rubber, a material typically used in silicon baking sheets. The material was selected because of durability and convenience in molding, compared to other materials. The design of the prototype in this study was inspired by the 3M 1860 style N95 respirators.

To provide a high filtration efficiency rate, engineers molded the prototype mask with dedicated space for N95 filters. The mask could be designed with one or two holes for the filters, which are replaceable. Instead of throwing away the whole mask, the wearer simply needs to change the filters after using the mask for a certain period. Before replacing new filters, the mask could be sterilized to eliminate microbes. This design aimed to produce substantially less amount of medical waste, compared to standard N95 respirators.

Several sterilization methods were tested on the prototype mask. They sterilized the masks in an autoclave or steam sterilizer, in an oven, in a bleach solution, and in isopropyl alcohol. All of those methods left the masks undamaged, indicating the feasibility of the design in real-world settings.

And finally, engineers tested the greatest factor in wearing masks: the fit. They recruited 20 healthcare workers from the emergency department and oncology clinic at Brigham and Women's Hospital. Each participant was instructed to perform the standard N95 fit test from the Occupational Safety and Health Administration. The test included performing a series of movements while the mask was worn. This could show if the device would stay in its place as the person moves.

During the test, a nebulizer sugar solution had been sprayed inside the test room. The solution would determine if the mask's fit was flawed. If the participants could smell or taste the solution, then the fit was improper. Results from the participants gave the prototype mask high ratings for fit and breathability. All of them passed the test as well, showing no one smelled or tasted the solution. In terms of preference, only a few expressed either a preference between N95 and the prototype or to the new silicone mask.



Face Masks and COVID-19

Before the pandemic began, a study published in BMJ Open back in 2015 showed how crucial surgical masks are in the healthcare setting. The authors tested the filtration efficiency rates between surgical and cloth masks. The focus had been the infection outcomes of healthcare workers who wore cloth masks while in hospitals. The penetration chance of particles on cloth masks was nearly 97%, compared to the 44% penetration rate on surgical masks. Thus, the authors warned the World Health Organization not to recommend cloth masks in the healthcare setting.

But in the average setting, people could use cloth masks to put a barrier between their faces and particles in the air. Even though cloth masks are less effective than N95 and surgical masks, they would still provide some level of protection than wearing nothing at all. And because COVID-19 may be airborne, the use of face masks could save lives and hospitals. Right now, the critical care capacity of hospitals around the world is vulnerable to being overrun by patients.

Statista, a German portal for statistics, showed that face masks could significantly reduce the risk of contracting COVID-19. The potential risk of someone wearing a mask or respirator could be 3.1%, lower than 17.4% from not wearing one. If the person wears eye protection, their risk from wearing such an item alone would be 5.5%, lower than 16% from not wearing one.

The engineers are now busy with the second version of the silicone mask. The upcoming version is expected to be more comfortable and durable than the first one. They also plan to test its filtration rate against viruses.