Is Printing with Sound the Wave of the Future?

It's hard to print with stuff like liquid metals and living cells using traditional inkjet-style machines, but new tech that uses sound waves may make it easier. Learn how it works in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works pay brain Stuff.
I'm Lauren Vogelbaum, and I'm here today to tell you
that Harvard University has announced that its researchers have developed
a way to print objects using sound as the delivery system,
called acoustophoretic printing. The method, according to their press release quote,
could enable the manufacture of many new biopharmaceuticals, cosmetics, and food,

(00:26):
and expand the possibilities of optical and conductive materials. Let's
unpack all that printing with liquid such as ink has
become a way of life thanks to the ink jet
printing process. But what if instead of ink, you wanted
to print living cells or other biological materials. What if
you wanted to print liquid metal with ink jets. The
ability of a printer to pull a substance out of

(00:48):
a nozzle grinds to a halt as that substance becomes thicker.
But now the team of scientists at Harvard has announced
significant progress in the creation of sound fields that can
pull viscous substances, much as liquid metal or living cells
from the nozzle of a printer. It begins with gravity.
Simple gravity is what causes liquid to drip. How fast

(01:09):
or how often it drips depends on its viscosity, that's,
its thickness and its resistance to shearing and tensile stresses. Water,
for example, is far less viscous than coin syrup. Coin
syrup is far less viscous than honey. The more viscous
that a fluid is, the longer it takes for gravity
to produce a droplet. Printing systems, such as in chip printing,

(01:30):
typically use a droplet method of transferring a liquid material
like ink onto a medium like paper. The more viscous
a material is, however, the more difficult it is to
manipulate for printing. Daniel Feresti, a research associate in material
science and mechanical engineering at Harvard, said, our goal was
to take viscosity out of the picture by developing a

(01:51):
printing system that is independent from the material properties of
the fluid. And this is where sound comes in. Foresti
and his fellow researchers and experimenting with the pressures of
sound waves on liquids. In order to give gravity a boost,
They built a sub wavelength acoustic resonator. It's designed to
produce tightly controlled acoustic fields that effectively increase the relative

(02:13):
gravity at the printing nozzle. According to the release, the
researchers have been able to generate pulling forces one times
the gravitational forces that a printer nozzle would normally experience
here on Earth. That amount of force also happens to
be more than four times the gravity that a printer
nozzle would experience on the Sun. At that point, the
size of the droplet is determined by the amplitude of

(02:33):
the sound wave. The higher the amplitude, the smaller the drop. First,
he said, the idea is to generate an acoustic field
that literally detaches tiny droplets from the nozzle, a much
like picking apples from a tree. A wide range of
materials have been used to test this new printing method,
including honey stem cell inks, biopolymers, optical resins, and liquid metals.

(02:56):
Doctor Jennifer Lewis, a professor of biologically inspired engineer RING
at Harvard, stated, our technology should have immediate impact on
the pharmaceutical industry. However, we believe that this will become
an important platform for multiple industries. Today's episode was written
by Jared W. Alexander and produced by Tyler Clang. To

(03:18):
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