The researchers from Massachusetts worked with a plastic surgeon to create the 3D mould.
It was filled with cow collagen while the team grew enough cartilage cells inside rats to replace the collagen in the mould.
Wires were then added to help maintain the shape of the ears.
Once the cartilage in the mould had fused and set, researchers put the ear through various stress tests to analyse its flexibility. A layer of skin was also applied to make the ear look more lifelike.