The pandemic has seen a lot of changes, but one thing that's remained the same for the past two years is face mask technology: We're still using old designs.
Even the N95 respirators that use microscopic fibres and static electricity to trap viruses were invented in the 1970s.
Now a pair of novel prototypes are giving us a peek into how that might change, from masks that can diagnose the wearer with COVID or another illness, to ones that can detect leaks.
So how do they work and when will we be able to get our hands on them?
'Fitbit for the face'
The idea for a smart sensor that can automatically detect whether a face mask is properly fitted around the wearer's mouth occurred to Josiah Hester after speaking with Chicago clinicians dealing with the first wave of COVID, way back in March 2020.
"And they reached out and were like, 'How do I know if my mask is fitting if I'm on a 12-hour shift?'" Dr Hester said.
Last week, Dr Hester and his engineering colleagues at Northwestern University in Illinois unveiled what they'd come up with: a small electronic module packed with sensors that attaches to the inside of a standard medical-grade N95 mask.
Whether a mask is fitted properly can make all the difference to its ability to protect the wearer from viruses.
Medical staff usually undergo fit tests to ensure the masks they wear all day provide a proper seal, but it's a long procedure that can be quickly undone when a mask is inadvertently bumped.
Dr Hester's module, dubbed a "Fitbit for the face", uses motion sensors to detect when a mask has been bumped and then alerts the user.
Other sensors detect a drop in airflow resistance, which could also indicate a leak.
The design and construction process has been a long one, and at many points the researchers wondered if the pandemic would be over before their invention was ready.
"Unfortunately, the devices are still highly relevant," Dr Hester said.
After last week's unveiling, Dr Hester got back in touch with the Chicago clinician who had given him the idea for the device in March 2020.
"He was ecstatic," he said.
What would this cost and when will it be here?
The single prototype cost about $US180 ($250), Dr Hester said.
"You could probably divide that by 10 to 20 if you built thousands," he said.
The "FaceBit" is designed to be attached to a mask with magnets, so it can be detached and reused when the mask wears out.
Before it's rolled out en masse to hospitals, it still needs to undergo clinical trials.
"There'd have to be higher level intervention to realise the device in a hospital setting within a year," Dr Hester said.
That leaves open the possibility of the device launching as a commercial product (that is, not approved by hospital regulators, but still available for purchase) within that time frame, he said.
"I'm very hopeful," he said.
"Our team is trying to figure out the best way to push that forward. For now, at least, we're saying, 'Here, it's all open source.'"
"If clinical researchers like us want it, they can build it themselves."
How about a mask that can diagnose COVID?
It may seem hard to believe, but a laboratory at Harvard in the US has found a cheap way of putting a COVID test in an N95 mask.
Announced last year, the button-activated mask gives results within 90 minutes at levels of accuracy comparable to standard nucleic acid-based diagnostic tests like polymerase chain reactions (PCR).
And it costs about $US5 ($7), said Peter Nguyen, one of the Harvard scientists who developed the prototype.
"In essence, our technology miniaturises an entire laboratory onto a wearable garment," he said.
It could be worn daily, he says.
"After you wear it for about half an hour, you can start the test if you want it. But typically you would wear it all day.
"It would accumulate whatever you're breathing into it, then at the end of the day, right before you throw it away, you would press it.
"Come back within an hour, and you would get your result back.
"And then you throw it away."
How does it work?
The mask contains a biosensor that uses engineered genetic circuits to create sensors and detectors for a desired molecular target.
To make the sensor, the scientists relied on a technique that involves extracting and freeze-drying the molecular machinery that cells use to read and write genetic material.
Pressing a button on the mask releases a small amount of water into the sensor that reactivates the freeze-dried components so they can produce signals in response to the presence of a targeted molecule.
If the SARS-CoV-2 virus is present in the accumulated breath droplets on the inside of the mask's surface, the test will diagnose the wearer with COVID-19.
Dr Nguyen compares it to instant coffee.
The lab has found a way to take complicated reactions that would normally require laboratories, and then freeze-dry them into powder.
"So now instead of having a barista, making you coffee with fresh beans, you have instant coffee in a jar, right?
"It's super cheap, it sits there, and all you do is add water."
Could it be used for other viruses?
The researchers first applied this technology to diagnostics by integrating it into a tool to address the Zika virus outbreak in 2015.
When COVID appeared, Dr Nguyen and his colleagues began developing a SARS-CoV-2 biosensor.
Like with Dr Hester at Northwestern University, the idea came from speaking with doctors in the first wave of the pandemic.
"And the doctors that were talking to us were like, 'When flu season comes in the fall, it's going to be really bad, because we're not going to be able to triage anybody, we won't know it's flu or COVID.'"
Adapting the mask to detect flu would be easy, he said.
"It's literally just swapping out one component that tells the test, 'I want you to look for this particular piece of nucleic acid.'"
It can also be adapted for tuberculosis, an airborne infectious disease that damages the lungs.
"We've gotten a lot of interest from the TB community and researchers saying this would be perfect for countries where it's endemic."
When will it be available?
The researchers are still in talks with licensing the technology to a company that could produce the masks at scale, Dr Nguyen said.
"We're an academic lab, we don't have the means to actually take this on as a huge commercialisation project," he said.
Don't expect COVID-detecting masks to be in shops anytime soon.
And given the fact many people are still using reusable cloth masks rather than the more effective N95 versions, we may not yet be ready to upgrade.
"If I had to summarise the worldwide response to the pandemic, it would be messy," Dr Nguyen said.
While looking for a commercial partner, the Harvard lab is working on embedding biosensors in more kinds of wearables.
It may be possible to create protective equipment that responds to the presence of dangerous toxins, such as nerve gas, to protect the wearer, Dr Nguyen said.
"That would be the next step beyond sensing. Now you have sensing and protection. We are really viewing it almost as a second skin."
