A newly discovered cell type could transform how plastic surgeries are performed—from facial reconstructions to nose jobs.

Cartilage transplants are central to many procedures, being used to fix cleft palates, correct missing or misshapen ears, or to repair damage to someone’s larynx caused by cancer. They’re also common in elective nose augmentations.

But the results aren’t always stellar. Surgeons often resort to transferring cartilage from the rib, which is stiff, or using silicone implants, with neither material matching the real thing. Implanted tissues are not flexible in the same way as those they’re implanted into, and don’t become part of the natively occurring tissue. “They often do not integrate, and they move around,” says Maksim Plikus, a cell biologist at UC Irvine. “The nose gets crooked and needs another revision.”

However a newly defined tissue that lurks within flexible parts of animals’ bodies could change this. Dubbed lipocartilage, it was noticed by Plikus and his team for the first time while studying mouse ears over a decade ago. The cells staring back at Plikus through the microscope were distinctly fattier than the cells that usually forge cartilage, known as chondrocytes. Perhaps they were fat cells, known as “adipocytes,” he thought.

“They’re big. They’re filled with lipids. They look like a pearl—whitish, and iridescent under the microscope. That’s an adipocyte,” Plikus recalls thinking—until a pang of dissonance struck him. The tissue may resemble fat, but fat cells don’t belong in cartilage. “If somebody starts calling a cat a dog, they’re absolutely wrong. It’s a completely different species,” Plikus says. “Well, this is like a completely different species of cell. To call it an adipocyte is fundamentally wrong.”

Over the next decade, his team subjected the mysterious cells to a gauntlet of high-tech biological profiles akin to personality tests. They proved that this bouncy connective tissue is neither typical chondrocyte nor adipocyte, according to results published today in Science.

Plikus calls them lipochondrocytes, or LCs. The cells appear to simultaneously provide structure (like cartilage) and natural squishiness (like fat). They appear in many mammals, including humans, and the unique structure they provide gives reconstructive surgeons a clearer understanding of what materials make up our faces. Plikus believes this new tissue discovery sets the stage for better cartilage transplants—and so better plastic surgery. “The field is really desperate for new ways of making safe, biocompatible human cartilages that are living tissues, not some synthetic silicone implant,” he says.

Depending on how you count, your body hosts about 400 types of cells that make up dozens of different types of tissue, from skin to salivary glands. Skeletal tissues, like cartilage, are among the simplest, but this new study proves that they’re no less enigmatic. “It goes to show we still don’t understand it very well,” says Justine Lee, a plastic and reconstructive surgeon and researcher with UCLA who was not involved in the study. “We’re still finding cool new things. It’s something that could potentially result in future implants that are soft, pliable.”

So how could this new cell elude scientists and doctors for so long? In a way, it didn’t. Plikus and his graduate student scoured centuries of scientific papers for any lost trace of fatty cartilage. They found a clue in a German book from 1854 by Franz Leydig, a contemporary of Charles Darwin. “Anything and everything that he could stick under the microscope, he did,” Plikus says. Leydig’s book described fat-like cells in a sample of cartilage from rat ears. But 19th-century tools couldn’t expand beyond that observation, and, realizing that a more accurate census of skeletal tissue might be valuable for medicine, Plikus resolved to crack the case.

His team began their investigation by looking at the cartilage that’s sandwiched between thin layers of mouse ear skin. A green dye that preferentially stains fatty molecules revealed a network of squishy blobs. They isolated these lipid-filled cells and analyzed their contents. All of your cells contain the same library of genes, but those genes aren’t always activated. Which genes did these cells express? What proteins slush around inside? That data revealed that lipochondrocytes actually look very different, molecularly, from fat cells.

They next questioned how lipochondrocytes behave. Fat cells have an unmistakable function in the body: storing energy. When your body stores up energy, cellular stores of lipids swell; when your body burns fat, the cells shrink. Lipochondrocytes, it turned out, do no such thing. The researchers studied ears of mice put on high-fat versus calorie-restricted diets. Despite rapidly gaining or losing weight, the lipochondrocytes in the ears didn’t change.

“That immediately suggested they must have a completely different role that has nothing to do with metabolism,” Plikus says. “It has to be structural.”

Lipochondrocytes are like balloons filled with vegetable oil. They’re soft and amorphous but still resist compression. This contributes meaningfully to the structural properties of cartilage. Based on data from rodents, the tensile strength, resilience, and stiffness of cartilage increased 77 to 360 percent when comparing cartilage tissue with and without lipochondrocytes—suggesting that these cells make cartilage more pliable.

And the structural gifts appear to benefit all sorts of species. In the outer ear of Pallas’ long-tongued bat, for example, lipocartilage underlies a series of ruffles that scientists believe attunes them to precise wavelengths of sound.

The team have discovered lipochondrocytes in human fetal cartilage, as well. And Lee says this discovery seems to finally explain something that reconstructive surgeons commonly observe: “Cartilage always has a little bit of slipperiness to it,” she says, especially in young children. “You can feel it, you can see it. It’s very obvious.”

The new findings suggest that lipochondrocytes fine-tune the biomechanics of some of our cartilage. A rigid scaffold of cartilage proteins without lipids is more durable and is used for building weight-bearing joints in your neck, back, and—yes, you got it—the ribs, one of the traditional sources of cartilage for implants. “But when it comes to more intricate things that actually need to be pliable, bouncy, elastic—ears, nose tip, the larynx,” Plikus says, that’s where the lipocartilage shines.

For procedures that involve modifying these parts of the body, Plikus one day envisions growing lipocartilage organoids in a dish and 3D-printing them in any desired shape. Lee, though, urges caution: “Despite 30 or 40 years of study, we’re not very good at making complex tissues,” she says.

Though an operation like that is far off, the study suggests it’s feasible to grow lipochondrocytes from embryonic stem cells and isolate them safely for a transplant. Lee figures that regulators wouldn’t green-light using embryonic cells to grow tissue for a non-life-threatening condition, but says she’d be more optimistic if the researchers can grow transplantable tissue from patient-derived adult cells. (Plikus says a new patent application he has filed covers using stem cells from adult tissue.)

Lipochondrocytes update our understanding of how cartilage should look and feel—and why. “When we’re trying to build, say, the nose, sometimes we could use the [lipid-filled cells] for a little bit of padding.” Lee says. Lipocartilage could one day fill that void as a growable, transplantable tissue—or it could inspire better biomimicking materials. “It could be both,” she says. “It’s exciting to think about. Maybe that’s one thing that we’ve been missing.”