A strange combination of tissue and electronics could help us repair — or someday even replace — human ears. Researchers led by Michael McAlpine, an assistant engineering professor at Princeton, have created a prototype artificial ear from an antenna and 3D printed cells. McAlpine has worked for years on making electronics that could be integrated with the human body: in 2011, his team built a graphene tattoo that could be stuck on a tooth to detect bacteria. In this project, though, he wanted something more: an organ with electronics embedded inside it.

To make the ear, McAlpine started with a 3D printer. While it's possible to reconstruct an ear with cartilage grafts or cultured tissue, printing it allowed researchers to closely duplicate the shape of an ear while building in an antenna. The team used a hydrogel seeded with calf cells for the structure, adding layers of silver nanoparticles that formed a coil antenna. Those cells could then turn into cartilage, as seen above. The end of the antenna connects to a system meant to simulate the cochlea, which lets us sense sounds.

Cultured cells share space with silver nanoparticles

In tests, the ear could pick up radio waves, and a "complementary" left and right pair could listen in stereo; future versions could pick up acoustic audio with different sensors. For now, though, it remains a lab prototype. McAlpine says that it could theoretically be attached to human nerve endings, like some hearing aids, but doing so would require much more testing. His research on the subject has been accepted for publication in Nano Letters.

McAlpine's ultimate hope is to help push forward advances in "bionic" organs, which would seamlessly combine sensors or other electronics with the human body. "Previously, researchers have suggested some strategies to tailor the electronics so that this merger is less awkward. That typically happens between a 2D sheet of electronics and a surface of the tissue," he says. "However, our work suggests a new approach — to build and grow the biology up with the electronics synergistically and in a 3D interwoven format."