February 21, 2013

When a child is born with the congenital deformity known as microtia, they have an underdeveloped external ear – also known as the pinna. Even though their inner ear may be normal, the lack of the external structure can affect their hearing, plus it looks unusual. Normally, a replacement pinna is made from a foam-like material (or sometimes even cartilage from the rib cage) and implanted under the skin, although these don’t always look particularly natural. Now, scientists from Cornell University have developed a more realistic pinna grown from biological material, using a 3D printer.
The study was led by associate professor of biomedical engineering Lawrence Bonassar, and associate professor of plastic surgery Dr. Jason Spector. Their research team started by creating a 3D digital model of a five year-old girl’s fully-developed external ear, then using a 3D printer to build a mold based on that model.

Collagen harvested from rat tails was combined with cartilage cells gathered from cows’ ears to form a hydrogel, which was then injected into the mold. The collagen served as a scaffolding, upon which the cartilage cells could settle and grow.
“It takes half a day to design the mold, a day or so to print it, 30 minutes to inject the gel, and we can remove the ear 15 minutes later,” said Bonassar. “We trim the ear and then let it culture for several days in nourishing cell culture media before it is implanted.” After three months of being implanted under the back skin of lab rats, newly-grown cartilage had largely replaced the collagen in the ears.