Every day, we use filters. They keep damaging particles from entering our motors, carcinogens from entering our air or lungs, and unsafe matter out of our drinking water. In your kitchen they keep the coffee grounds from entering your coffee. In the summer they keep mosquitoes and other bugs on the outside while letting cool air in.
We’re so accustomed to them keeping small irritants out of our food, water, air and nearby environment that we hardly even think about how they work. Indeed, it’s difficult to imagine a filter working any other way.
But try to imagine a screen of some sort that lets large pieces of matter through but waylays all the tiniest particles, even the air. That’s what a team of mechanical engineers at Penn State University has done, re-imagining what we thought we knew about filters.
“We started thinking about four years ago how conventional filtration allows small particles to pass through and large ones are retained. [We]wondered, ‘Can we do the opposite?” Birgitt Boschitsch, the team leader, told The Daily Beast.
“We feel this unique kind of filtration could open up a number of different applications.”
The group’s innovative liquid membrane is a lot like the soapy bubble wands of your youth. Did you ever dip a small wand with a circle end into a store-bought container of soapy water and blow air through them to create bubbles? That watery film is a membrane, and that’s how the bubbles are made. They capture the air, while the membrane reforms, repairing itself as the bubble drifts off.
Indeed, the researchers’ preliminary studies literally used simple soap film before developing the biochemical prototype for their membrane. The team said that the ultimate inspiration for the project were the biological processes of endo- and phago-cytosis, the process where by which substances are subsumed or ingested by cells, such as when a white blood cells subsumes a pathogen.
Traditional filters create apertures for the smallest matter to escape. If the matter is too big it simply can’t pass through. A square peg will not pass through a round aperture.
A membrane, unlike a typical screen or filter, is as solid as the surface of the water. There are no holes; poke your finger in a lake, and it surrounds you whole. Now imagine covering your hand with soap and sticking it into the water. When you pull your hand out of the water, the soap stays behind. Penn State’s membrane works a little like that.
Think about how a rock can skip across the top of the water. The surface tension keeps it from penetrating. Now imagine that tension working in reverse. So while big things can easily puncture the surface, smaller ones don’t easily dent it. In physical terms the membrane lets those things with higher kinetic energy (bigger, larger, faster moving things) and stops those with lower kinetic energy (parasites and microbacteria riding on the surface of an object, for example).
You know how the surface of the water closes behind your finger when you move, or how if you’re blowing bubbles on that aforementioned bubble wand, when one bubble goes through, the film reforms? This is known as self-healing, and is a potentially important feature of the Penn State filter in keeping microorganisms out.
Because of this, the group reasoned that the filter could have a promising future in medicine. In unsanitary circumstances, medical tools could conceivably by sterilized by passing through a membrane. Open wounds and surgical entry points could be covered with the membrane, preventing infection while the doctor’s hands move through and do their work.
“Instead of having to keep a whole room clean you can just keep the wound clean and allow medical devices through while preventing dust or germs,” Boschitsch said.
One surprising use of the membrane is wiping out the stink of solid waste. This goes beyond your bathroom or mobile home. Boschitsch noted that Bill Gates has been developing smell-cancelling odors, arguing that poor sanitation costs India over $55 billion annually.
“Over a billion people in the world don’t have access to toilets. “There are a lot of factors but one of them is foul odors,” Boschitsch says. “Sequestering foul odors in water-less toilets is something our lab group is interested in, in general, as well as a lot of other toilet-related technologies.”
For now, the group continues to perfect their membrane for different situations. It’s liquid-based, so new chemical additives are easily added to amplify different aspects or features depending on the requirements of the application.
“If we wanted to use this membrane for a very long lasting applications we have to optimize the composition for longevity. If we’re looking at medical applications… that would mean tailoring it to be antibacterial or something like that,” Boschitsch says.
Ultimately, the group hopes to expand the technology to places in need.
“I really care about making technologies that help people and it’s fun to see a new concept put to use in the real world,” she says. “We have a concept and a solution. Now it’s about finding the people with the right problem and connecting with them.”