As COVID-19 continues to spread worldwide, Stevens researchers are imagining the next generation of face protection.
The protection in current N95 masks — industrial-grade respirators that filter out 95% of particles larger than 0.3 microns — consists of a non-woven membrane constructed of polypropylene fibers. Particles are trapped as they migrate through the dense network of fibers; electrostatic charges can also be added to further attract particles to the mask.
A process known as melt blowing is used worldwide to manufacture the membrane layers in N95 masks. During this process, polypropylene is molten in an extruder, shaped into fine strands and then stretched into even thinner fibers by the flow of hot air.
However, this process presents a challenging bottleneck worldwide for firms attempting to scale up production of the masks.
"The machines to manufacture them are difficult and time-intensive to build, mainly due to the exacting standards required of them," explains Stevens researcher and interim Vice Provost for Research, Innovation & Entrepreneurship Dilhan Kalyon.
But now there may be a solution.
To assist in the COVID-19 response, Kalyon's team is working to develop new nanofibrous membrane meshes in Stevens labs that could prove more effective at protecting against viral particle transmission as well as a technology to fabricate the membrane meshes.
"It would be desirable to build the membrane cores of the respirators from multiple contiguous layers of different porosity, pore size, surface charge and concentrations of different antiviral nanoparticles," notes Kalyon, who had already been working on aspects of high-grade filtration since 2007.
"That's what we are trying to accomplish."
New processes, new materials
Kalyon notes that the novel, so-called twin-screw extrusion and electrospinning process developed at Stevens has already been demonstrated to be highly effective in projects and applications including tissue engineering scaffolds, implants and catalytic meshes for the fabrication of polymeric meshes with multiple layers.
"In addition to producing smaller fiber sizes offering better potential filtration, multiple antiviral materials can be incorporated into different layers of the membrane meshes in the new process," he notes
In one experimental prototype produced by the Stevens team, tiny nanoparticles of silver, gold, platinum and palladium were deposited on nanotubes as small as 20 to 30 nanometers wide. These were then incorporated into larger (yet still very small) hollow polymeric nanofibers that are still only 200 nanometers wide each, creating a material of interwoven meshes.
"The ordering of the nanotube and nanoparticle-containing layers with different types of nanoparticles was designed to provide multiple successive functionalities, says Kalyon, meaning masks developed with the material could be used for a wide variety of industrial and medical purposes.
The team is currently applying for patent protection for the process.