Even though type I collagen is a common collagen in the body, it didn’t make the cartilage cells produce more of their own type II collagen—so the cells are picky about what they respond to.

Putting whole collagen into the dish didn’t make the cartilage cells produce more cartilage protein—only the broken-down pieces did.

When cow cartilage cells are grown in a lab and given broken-down collagen, they make more of the key structural protein (type II collagen) that helps keep cartilage healthy—but whole, intact collagen doesn't do this.

Cartilage cells respond to broken-down collagen like a signal to rebuild, but ignore whole collagen—like they’re reading a message in the fragments.

After two days of being exposed to broken-down collagen, cow cartilage cells made more of the main cartilage protein—and scientists confirmed this using three different lab methods.

The cartilage cells seem to 'recognize' broken-down collagen and respond to it—other proteins don’t trigger the same reaction, hinting at a special biological sensor for collagen pieces.