A two-inch human ear has been grown under the skin of a rat. University of Tokyo/Kyoto University

Back in the 90s, the world was disturbed by images that surfaced of a mouse with what looked like a human ear growing out of its back. They weren’t photoshopped, but the ear was actually made from cow cartilage – no human tissue was involved. Still, it didn’t take long for misinformation to spread like wildfire in the media and give people false hopes that the pioneering technique could soon allow people with disfigurements or birth defects to grow their own replacements.

Almost 20 years on, science has come a long way, and we might actually be close to a time where this is possible. Researchers in Japan have successfully grown an adult-sized “living” ear on the back of a rat using human stem cells. The ambitious group from the University of Tokyo and Kyoto University has also claimed to the media that human trials could begin in just five years.

If successful, the technique could represent a new way to help those born with anotia and microtia, where the external ear is either completely absent or malformed. Thought to affect up to five in every 10,000 live births in the U.S., treatment often involves reconstruction using cartilage from the patients’ ribs or a synthetic implant called Medpor, a less invasive option. While the former is technically living and therefore should be able to grow and heal with the child, up to five painful surgeries are needed to complete the graft, which can leave the patient with a deformity in their chest.

So although there are several options for affected individuals, evidently there is room for improvement. And while using live animals as growth platforms isn’t exactly an ideal solution, it would help reduce the suffering endured from graft surgeries. Human tissue is still required for this newly described research, but these days scientists can obtain stem cells from just a small sample of skin, so the procedure would be far less invasive.

Scientists from Princeton University are also bridging electronics with biomaterials to create "bionic ears." Frank Wojciechowski

After turning human cells into an embryonic stem cell-like state, basically erasing their identity and turning them into a blank slate, the Japanese team coaxed them into becoming specialized cells that form cartilage. These were then seeded into ear-shaped tubing that was implanted under the skin of a growing rat and left to grow. After roughly two months, the tube had dissolved and the team was left with a living ear made from human cells that, in theory, could be grafted onto patients with ear malformations or deformities resulting from injury, such as those wounded on the battlefield.

Similar work was conducted just a few years ago by a team in the U.S., but instead of using human stem cells, they took tissue from cows and sheep and grew it around an ear-shaped wire frame, which was also implanted into a rat. And it’s not just ears that scientists have set their sights on: Kidneys from aborted fetuses have also been grown in lab rodents, as well as a functioning thymus from mouse embryos.

Evidently there have been significant developments in the field of regenerative medicine, but among this progress are ethical issues that also need to be considered. For example, scientists recently announced that they are making progress in the creation of human-animal chimeras with organs that could be used for transplantation, quickly sparking a debate on whether such ethically questionable work should be allowed. 

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