Cool—and/or creepy—news out of Japan, where researchers at the University of Tokyo and Kyoto University have created a human ear ... on the back of a rat. The researchers used stem cells that grew into ear cartilage, shaping the cells into an ear by putting them in "biological tubing," Discovery News reports. More specifically, they used "induced pluripotent stem cells," which the National Institutes of Health explains are "adult cells that have been genetically reprogrammed to an embryonic stem cell-like state." The ear-shaped cartilage was implanted under a rat's skin, where it was allowed to grow for two months; the tubing dissolved and a 2-inch-long ear was left behind.
The researchers believe this technology could be used to treat people who are born with no ears or with smaller-than-normal ears, Japan Today reports. It could also be used to repair ears disfigured in accidents, Discovery adds. In the case of a child born with a missing or misshapen ear, the researchers note that the ear they created is "living," and thus would develop and grow along with the child. A clinical trial involving humans is expected to start in five years. In 2013, researchers in Boston used sheep cells, bovine collagen, and an ear-shaped titanium wire frame to grow an ear on the back of another rat, Discovery notes. (These creatures can grow the heads and brains of other species.)