Most water filters work by a sieve principle, in which waterborne particles that are too large to pass through a filtration membrane's pores end up collecting on its surface. The problem is, such filters ultimately get clogged with trapped particles. The manta ray, however, has developed a work-around that could be applied to human technology.

Although manta rays may be big and weird-looking, they're harmless to humans. They feed entirely on plankton and microcrustaceans which they filter out of seawater.

It was already known that filter-feeding fish generally do so by gulping water into their mouths, then forcing it out through their gills. On its way out, the water passes through closely-spaced rows of hook-lined appendages known as gill rakers – plankton too large to pass through the gaps between the hooks get trapped, and are subsequently swallowed.

Scientists from Oregon State University, however, recently noticed that manta rays have uniquely modified gill rakers which take the form of long, parallel arrays of leaf-like lobes (see the photo below). As expelled water flows through them, it forms into swirling eddies which cause plankton to ricochet off the lobes and back into the mouth cavity.

Essentially, the modified rakers form a filter that repels particles instead of trapping them. Not only does this mean that the system is very resistant to clogging and can operate at high flow rates, but it also allows the animals to retain prey that's much smaller than the gaps in the rakers.

"We are currently looking at whether we can adapt this mechanism for engineered systems," says assistant professor Jim Strother, co-author of a paper on the study. "For example, one future direction is exploring whether this can be applied to wastewater treatment in order to address the emerging threat from microplastics pollution."

The paper was published this Thursday in the journal Science Advances.

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