Listen Up


Princeton scientists used 3D printing to create a "bionic ear" made up of a coil antenna and cartilage. Image: Frank Wojciechowski

Michael McAlpine, assistant professor of mechanical and aerospace engineering at Princeton University, is a part of a group that added an ear to the bioengineering conversation—literally, through 3D printing.

“A lot of people are interested in 3D printing and yet so much of what they were printing were polymers and plastics,” he says. “As a material scientist I have a strong interest in functional materials, meaning biological and electronic materials.”

McAlpine had this rudimentary idea that they could adapt a 3D printer to print functional materials like biological and electronic materials and interweave them in three dimensions. “You find a way to feed electronic materials into a 3D printer and keep them functional,” he says. “When we merge them then you have something unique.”

Of course, he’ll admit the ear is also easier to print than many other parts of the body. “Some organs aren’t easy because many have vasculature, complicated with vessels that allow for blood flow and nutrient delivery,” he says. “The nice thing about the ear is as organs go, it’s not vasculature but a piece of cartilage with skin around it. And the nutrients are delivered but not by vessels.”

Another convenience is that the easiest electronic system to print, he says, would maybe be an antenna. “Two basic things but when we merged them together then you have a bionic ear,” he says.

Graduate student Manu Mannoor and professor Michael McAlpine inspect the bionic ear developed in their lab. Image: Frank Wojciechowski



3D Printing Cells

A challenge was the printer itself. “You can buy expensive 3D equipment for a few hundred thousand dollars but all you can really put through those printers are proprietary polymers that the company provides that extrude into plastic, but that’s no good because we wanted to use cells, nanoparticles, and functional materials,” he says. “You also would have to consider how the printer will jam. We had to build a printer from scratch that can handle these materials and then merge.

They had to consider the health of the cells as well. “We had all the components of a regular printer but we don’t apply heat because if we heat the cells then you’ll kill them,” he says. “We used an extruding process at room temperature. We needed to make sure we could print cells.”

The team also wanted to print the ear by itself and keep the nutrients near the cells, again, for their health. “We had to program the printer to print the shape of the ear and print the electronic coil and antenna,” says McAlpine. “We merged things together in the final printed ear.”

Making a Sound

They found the endproduct’s capabilities went well beyond what we can do. A normal ear hears between 20 hertz and 20 kilohertz, but this “bionic” ear can hear within that range and up to the gigahertz range, he says.

“The way a normal ear works is you have sound waves that are basically pressure waves that hit your ear and you have little hair cells that vibrate. And the vibration of hair cells sends a signal to the brain to tell it that you heard something,” says McAlpine. “Here it works differently because it doesn’t receive acoustic signals but receives electrical signals. With a bionic ear, it’s like communicating with a phone without having to go through the middle-man step of switching to acoustic transmission.”

McAlpine believes more 3D printing of this type would be done if the scientific community accepted it more.

“It’s actually very interesting because it’s not just the understanding of material science and biology but the ability to build an instrument,” he says. “It’s at the intersection of manufacturing, engineering, science and biology—it breaks a lot of barriers.”

Eric Butterman is an independent writer.

Learn more about nanoscale materials, methods, and devices at ASME 2015 4th Global Congress on NanoEngineering for Medicine and Biology

With a bionic ear, it’s like communicating with a phone without having to go through the middleman step of switching to acoustic transmission.

Prof. Michael McAlpine, Princeton University


March 2015

by Eric Butterman,