How Researchers Used Salt To Give Masks An Edge Against Pathogens

December 19, 2020 by Donald Papp 32 Comments

Masks are proven tools against airborne diseases, but pathogens — like the COVID-19 virus — can collect in a mask and survive which complicates handling and disposal. [Ilaria Rubino], a researcher at the University of Alberta, recently received an award for her work showing how treating a mask’s main filtration layer with a solution of mostly salt and water (plus a surfactant to help the wetting process) can help a mask inactivate pathogens on contact, thereby making masks potentially re-usable. Such masks are usually intended as single-use, and in clinical settings used masks are handled and disposed of as biohazard waste, because they can contain active pathogens. This salt treatment gives a mask a kind of self-cleaning ability.

Analysis showing homogenous salt coating (red and green) on the surface of fibers. NaCl is shown here, but other salts work as well.

How exactly does salt help? The very fine salt coating deposited on the fibers of a mask’s filtration layer first dissolves on contact with airborne pathogens, then undergoes evaporation-induced recrystallization. Pathogens caught in the filter are therefore exposed to an increasingly-high concentration saline solution and are then physically damaged. There is a bit of a trick to getting the salt deposited evenly on the polypropylene filter fibers, since the synthetic fibers are naturally hydrophobic, but a wetting process takes care of that.

The salt coating on the fibers is very fine, doesn’t affect breathability of the mask, and has been shown to be effective even in harsh environments. The research paper states that “salt coatings retained the pathogen inactivation capability at harsh environmental conditions (37 °C and a relative humidity of 70%, 80% and 90%).”

Again, the salt treatment doesn’t affect the mask’s ability to filter pathogens, but it does inactivate trapped pathogens, giving masks a kind of self-cleaning ability. Interested in the nuts and bolts of how researchers created the salt-treated filters? The Methods section of the paper linked at the head of this post (as well as the Methods section in this earlier paper on the same topic) has all the ingredients, part numbers, and measurements. While you’re at it, maybe brush up on commercially-available masks and what’s inside them.

Hybrid Respirator Uses Repurposed Filters

December 5, 2020 by Lewin Day 15 Comments

With the coronavirus raging worldwide, 2020 has seen major shortages of personal protective equipment impact healthcare workers and individuals alike. This has led many to improvise their own solutions. One of the more complete offerings we’ve seen is this hybrid respirator build from [Ben Howard].

[Ben’s] build goes above and beyond the usual craft project masks. It uses a laser-cut chipboard frame to fit three HEPA filters, originally designed for the Roomba robotic vacuum cleaner. Two are used for exhalation, while one is used for inhalation. A small blower fan is installed with the intake filter, to provide mild positive pressure when breathing in. The assembly is wrapped up in fabric, using layers of spandex, fleece, and ripstop nylon to provide the best possible seal against the wearer’s face.

It’s a build that should appeal to those who want to breathe cleaner air and also protect others from exhaled particles that can spread respiratory viruses. We’ve seen all kind of masks hit the scene this year; the graphene-impregnated variety is one of the more interesting designs. Still, one can hope that future years lead to less reliance on such measures!

Put That New Resin Printer To Work Making PCBs

October 9, 2020 by Dan Maloney 33 Comments

With all the cool and useful parts you can whip up (relatively) quickly on a 3D printer, it’s a shame you can’t just print a PCB. Sure, ordering a PCB is quick, easy, and cheap, but being able to print one-offs would peg the needle on the instant gratification meter.

[Peter Liwyj] may just have come up with a method to do exactly that. His Instructables post goes into great detail about his method, which uses an Elegoo Mars resin printer and a couple of neat tricks. First, a properly cleaned board is placed copper-side down onto a blob of SLA resin sitting on the print bed. He tricks the printer into thinking the platform is all the way down for the first layer by interrupting the photosensor used to detect home. He lets the printer go through one layer of an STL file that contains his design, which polymerizes a thin layer of plastic onto the copper. The excess resin is wiped gently away and the board goes straight into a ferric chloride etching bath. The video below shows the whole process.

As simple as it sounds, it looks like it works really well. And [Peter] didn’t just stumble onto this method; he approached it systematically and found what works best. His tips incude using electrical tape as a spacer to lift the copper off the print surface slightly, cleaning the board with Scotchbrite rather than sandpaper, and not curing the resin after printing. His toolchain is a bit uncoventional — he used SketchUp to create the traces and exported the STL. But there are ways to convert Gerbers to STLs, so your favorite EDA package can probably fit in to the process too.

Don’t have a resin printer? Don’t worry — FDM printers can work too.

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A Graphene Mouth Screen

September 14, 2020 by Brian McEvoy 32 Comments

We are all intimate with face coverings to slow the spread of the coronavirus. Some are reusable, and some become waste after one use. [Dr. Ye Ruquan] and a research team from City University of Hong Kong, CityU, are developing an inexpensive reusable mask with outstanding antibacterial properties, and, get this, the graphene it contains will generate a tiny current when moistened by human breath. There isn’t enough power to charge your phone or anything, but that voltage drops as the masks get dirty, so it can help determine when it needs cleaning. The video after the break shows the voltage test, and it reminds us of those batteries.

All the remarkable qualities of this mask come from laser-induced graphene. The lab is producing LIG by lasering polyimide film with a commercial CO2 infrared model. In a speed test, the process can convert 100cm² in ninety seconds, so the masks can be made more cheaply than an N95 version with that melt-blown layer that is none too good for the earth. Testing the antibacterial properties against activated carbon fiber and blown masks showed approximately 80% of the bacteria is inert after 8 hours compared to the others in the single digits. If you put them in the sun for 10 minutes, blown fabric goes to over 85%, but the graphene is 99.998%, which means that one bacteria in 50K survives. The exact mechanism isn’t known, but [Dr. Ye] thinks it may have something to do with graphene’s sharp edges and hydrophobic quality. A couple of coronavirus species were also affected, and the species that causes COVID-19 will be tested this year.

An overly damp mask is nothing to sneeze at, so keep yourself in check and keep yourself fabulous.

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Pocket-sized Device Sniffs Out Damp Masks

September 6, 2020 by Tom Nardi 13 Comments

The realities of wearing a mask when you go out, from forgetting the thing in the car to dealing with fogged up glasses, have certainly taken some getting used to for most of us. But not every issue is immediately obvious. For example, experts say that as a mask gets damp from exhalation or perspiration it becomes less effective. Which is precisely why [Rick Pannen] has designed the Mask Moisture Meter.

As deep as we are into the Microcontroller Era, we really appreciate the simplicity of this design. It’s just a 555 timer, a buzzer, some LEDs, and a handful of passive components to get them all talking to each other. There’s no firmware or programming required; just put a fresh battery in the holder and away you go. The traces of the PCB serve as a moisture detector, so when the board is pushed against something wet enough, the red LED and buzzer will go off to warn the user.

Now admittedly, there’s a point where you certainly won’t need an electronic gizmo to tell you a mask is wet. But as [Rick] demonstrates in the video after the break, the circuit is sensitive enough to indicate when there’s moisture in the material that might not be immediately obvious to the eye.

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Fog-Free Mask Hack Solves Mask Versus Glasses Conundrum With Superb Seal

September 2, 2020 by Brian McEvoy 35 Comments

If you have worn a mask and glasses together for more than a quarter of a second, you are probably annoyed that we don’t have a magical solution for foggy lenses. Moisture-laden air is also a good indicator of where unfiltered air is escaping. Most masks have some flexible metal across the nose bridge that is supposed to seal the top, but it is woefully inadequate. The Badger Seal by [David Rothamer] and [Scott Sanders] from the University of Wisconsin-Madison College of Engineering is free to copy during the COVID-19 pandemic, even commercially. It works by running an elastic cord below the jaw and a formable wire over the nose to encourage contact all around both mouth and nose.

You can build your own in three ways. Each configuration is uniquely suited to a different situation. The first design is the easiest to make and should work for most people. The second is best for folks who need a better seal on the lower half of their face, like someone sporting a beard. It can also have ear loops, and that means your 3D printed ear savers have another use. The Madison campus of the University of Wisconsin also has fun with lock cracking and graphene experiments.
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Read My Lips, Under This No-Sew Mask

August 30, 2020 by Brian McEvoy 5 Comments

Humans continuously communicate with our bodies, and face masks cover one of the most expressive parts. For some, this is a muffler on strangers, but devastating for people who rely on lip-reading. Several masks exist that have a clear window for precisely this purpose, but they’re specialty and high-demand. [Erin St Blaine] over at Adafruit shows how she makes windowed masks with stuff you may already have in your house. Even if your sewing machine is locked up the local maker-space, you are in luck, because you don’t need a single stitch. For the thread-inclined, it is easy to tweak the recipe.

The part of the mask that touches your face is terry cloth, but any breathable cotton towel should work. There is a PDF in the instructions where you can print templates in four sizes. You will also find a cutout for the plastic window salvaged from your cold soft drink cup. A water bottle should work too. Flexible glue holds the fabric together, but to attach the ear-loops, we fall back on our old friend, the red Swingline. If you don’t have that color and brand, any stapler will do in a pinch. Don’t forget to add some defogger and keep smiling.

Wear your homemade mask proudly and fasten it well, but not too fast.

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