To build the bionic organ, the printer is guided by a computer model of an ear to which the team added the model of an internal electrode coil. Layer by layer, the machine alternates among three “inks”: a mix of bovine cartilage-forming cells suspended in a thick goo of hydrogel; silicone, to encase the cochlea-shaped electrodes; and a suspension of silver nanoparticles. The silver nanoparticles are packed tightly so that the cochlea-shaped coil can conduct electricity.
“It acts as a metal, but because they are nanoparticles, you can print them in a way that you couldn’t normally print a metal,” McAlpine says.
Printing takes about four hours. Then the ear is bathed in a nutrient-rich broth so that the cells can grow, produce collagen and other molecules, and replace their original surroundings with cartilage.
With its fully embedded coil, the bionic ear can detect and transmit radio signals—but not sound waves. McAlpine says that functionality could be added to future models by integrating piezoelectric materials, which convert mechanical energy into electrical energy.
One day these devices could help a person hear through the same mechanism used to connect cochlear implants, or perhaps provide a sixth sense of electromagnetic reception.