news of the week
MAY 13, 2013 EDITED BY WILLIAM G. SCHULZ & NADER HEIDARI
HEAR, HEAR FOR
THE BIONIC EAR
TISSUE ENGINEERING: 3-D-printed
devices detect frequencies
beyond human perception
ONE GOAL of tissue engineering is to create de- vices that give humans abilities that they don’t naturally possess. For example, imagine being
able to detect sounds outside the normal range of human hearing. Human ears can typically pick up sounds
within the frequency range of 20 Hz to 20 kHz. At the
low end are the rumblings of engines; at the high end
are the shrill screeches of high-pitched whistles.
A new bionic ear, developed by a team of engineering researchers at Princeton University, can detect not
just those frequencies but others in the megahertz to
gigahertz range—the range of radio waves. The bionic
ear “hears” by detecting electromagnetic waves instead
of sound waves, although the signals it detects can be
converted into sounds audible to humans.
To develop the device, researchers had to integrate
sophisticated electronics—capable of transmitting signals to the auditory nerve—into engineered tissue that
looks and functions like an ear. The team, led by Michael C. McAlpine, an assistant professor of mechanical and aerospace engineering, used three-dimensional
printing to pattern the tissue (Nano Lett. 2013, DOI:
10.1021/nl4007744). Other researchers have previously
made molds for ears using 3-D printing, or they have
placed flexible electronics on top of bioengineered tissue. But McAlpine’s team is the first to have inserted
electronics directly into growing tissue layers during
the printing process.
“This research team is the first to combine these
individually demonstrated components into an integrated bionic construct,” says Jennifer A. Lewis, an engineering professor at Harvard University who was not
involved in the work.
“The ear is one of the simpler organs to make, in the
sense that the cartilage has no vasculature,” McAlpine
says. But at the same time, the outer ear’s complex
geometry is difficult to mimic with conventional tissue
engineering methods. So he and his coworkers adopt a
In typical tissue engineering methods, cells are seed-
ed on a scaffold. The cells excrete their o wn scaffold
as the tissue grows, and the original scaffold dissolves.
McAlpine’s team instead uses computer-aided design
to make a 3-D model of an ear, which they print using
a combination of biological, electronic, and structural
“inks.” The biological ink is a hydrogel matrix contain-
ing cartilage-forming cells, the electronic ink is silver
nanoparticles, and the structural ink is silicone.
McAlpine and coworkers exposed the 3-D printed
ears to left and right channels of stereo music. They
connected the cochlear electrodes to a digital oscil-
loscope, which allowed them to visualize the sounds.
They also attached the cochlear electrodes to speakers,
which allowed them to play back the output. After go-
ing through the entire system, the music was recogniz-
able as Beethoven’s “Für Elise.”
The ears detect radio waves and other electromag-
netic radiation, but McAlpine envisions 3-D-printing
other structures that detect acoustic signals directly.
The ears are a long way from being used in a person,
but “this work represents a first step,” Harvard’s Lewis
says. “An important next step is to extend this work by
printing more complex 3-D tissue with embedded vascular and conductive networks.”—CELIA ARNAUD
The bionic ear
with an electronic
To see bionic ears “listening” to Beethoven,
go to http://cenm.ag/ear.