Communications of the ACM
Researcher explores Earwax's Potential as Robotic Filter
Researchers found the properties of earwax are extremely consistent across different mammals.
While most of us consider earwax to simply be an unappealing substance, Alexis Noel, a doctoral student in David Hu's laboratory at the Georgia Institute of Technology, sees its innovative potential as a high-tech filter for use in robotics and other fields.
Noel attributes her inspiration for studying earwax to an event during a diving vacation. Her boyfriend had gotten water trapped in his ear, and nothing seemed to be able to get it out. Eventually, he had to go to a doctor, who found that the water was actually being held in place by his earwax.
"A couple years later I was reminiscing and thought: why would it block the water like that? And it just started this snowball effect of me and David [Hu] just asking questions about earwax and how it works," says Noel. They realized that this strange bodily fluid could potentially be a template for developing adhesives for applied usage in technology. But first, its complex behavior must be understood.
She and undergraduate researcher Zac Zachow began investigating earwax by collecting samples from several animals: pigs, sheep, rabbits, and dogs. What they have found is fascinating. First, the properties of earwax are extremely consistent across these different mammals, which have a variety of ear shapes and sizes. The thickness, the way it flows, and even the appearance is highly similar. This indicates that those properties of earwax seem to be a solution that works well across species.
They also examined the ear canal shapes of different animals and motions of the jaw to see how these factors affect the flow of the earwax and lead to it falling out of the ear. It turns out that earwax is a non-Newtonian, shear-thinning fluid, which means that when it is left alone, it is very thick and sticky (earwax is as viscous as molasses), but when a force is applied to it, it flows more quickly. As a result, although earwax is used within the ear for a long time, pressure and motion of the jaw will eventually force it out.
In the ear, earwax is excellent at filtering air. In the same way that Noel's boyfriend's earwax trapped the water, earwax traps other particles, catching them in a "web" of small hairs coated with sticky wax and protecting the inner ear from debris and bacteria. Noel and Zachrow have also found that as earwax accumulates dust, it becomes crumbly "like adding too much flour to dough when making bread," Noel explains. This allows the dusty wax to separate and fall out of the ear, making room for newer, cleaner wax to continue its work within the ear.
It is these filtering properties that have piqued Noel's interest for practical applications. One potential is to create some sort of biomimetic earwax adhesive surface that can be used in a ventilation system for robotics or for other kinds of machinery.
"Obviously you're not going to have earwax sitting on a Mars rover to protect it from dust," laughs Noel. "We are still trying to understand what is earwax and how does it work the way it works. And once we really understand that we can start applying it [to new technology]."
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