Hooked spines of cats’ tongue a mechanical gem

Cats, depending on your point of view, are cute or aloof, predatory or lazy. What’s indisputable is that they are well-honed little machines.

Take their ability to flip over while falling, which makes them appear to violate the rules of physics. Or their way of balancing gravity and inertia to keep their whiskers and chins dry while lapping up beverages, unlike their sloppy canine housemates. Cats’ ears can move in multiple directions, and they can hear at two octaves higher than people. Their paws are perfectly moistened to keep their movement quiet, helping them stalk prey.

Now researchers at Georgia Tech have unmasked yet another example of cats’ efficient anatomy: Their rough pink tongues are actually hairbrushes far better at detangling — and much easier to clean — than the hair tools for humans that are available at your local drugstore. This is no small detail for cats, who can spend half of their awake hours grooming, and not just out of vanity. Those licks remove fleas and dirt, spread body oils and improve circulation.

Despite common wisdom, the tongue that carries this out is not like sandpaper at all, according to the researchers, who created a 3D-printed cat tongue model to prove their point. Cat tongues are covered in tiny, backward-facing spines that are shaped like claws and made of keratin, the same material fingernails are made of. In a “single grooming sweep,” the researchers wrote, a cat tongue moves in four directions, helping the tongue essentially act as a flexible comb that adapts to the knots it encounters.

“When the tongue glides over fur, the hooks are able to lock onto tangles and snags,” said lead author Alexis Noel, a Ph.D. candidate in mechanical engineering who presented her research at a physics conference this month. “As the snags pull on the hook, the hook rotates, slowly teasing the knot apart. Much like claws, the front of the spine is curved and hook-like. So when it encounters a tangle, it is able to maintain contact, unlike a standard hairbrush bristle, which would bend and let the tangle slide off the top.”

And as shown by the 3D-printed cat tongue — made at a scale 400 times the size of an actual cat tongue — the flexible spines lie flat when they’re not in lick mode, enabling collected fur to slide right off (and be swallowed and balled in the gut for handy hacking on the carpet at a later date). Most hairbrushes, in contrast, have spines that stick straight out and gather hair in a yucky mat that requires effort to extract.

Noel, who describes her focus of study as “adhesion with soft, squishy materials,” said she first became intrigued by the cat tongue while watching her family cat, 3-year-old Murphy, lick a blanket and promptly get stuck. He soon freed himself by pushing his tongue into the blanket, which Noel now knows means he was unhooking his tongue spines from the blanket loops.

If you’ve made it this far, you may be wondering why cat grooming mechanics matter. There are two big reasons: First, it might add insight to the field of soft robotics, which, among other things, is about making robots that can move through small spaces for search-and-rescue missions or surgeries. Second, it might help make a better brush that, Noel said, could herald improvements in cleaning work, from a janitor shampooing a carpet to a nurse tending a wound.

Even better? It could bring a cat-tongue-style brush to a hair salon near you. Noel and colleagues are applying to patent their 3D tongue, and they’re planning to talk about possible uses with professionals in various fields — including the beauty industry.