Harvard Researchers Create Revolutionary 3D Printer That Uses Sounds To Print With Liquids

The new technique enables printing with extremely viscous liquids, which couldn’t be used before.

A novel printing technique designed by engineers at the Harvard University in Massachusetts is revolutionizing 3D printing with liquids, reports Live Science.

Described in a study just published in the journal Science Advances, this brand-new technique goes by the name of acoustophoretic printing and allows scientists to print liquid droplets of incredible high viscosity — something deemed impossible until now.

According to the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), current methods of printing liquid droplets, such as inkjet printing, only work on substances that are 10 times more viscous than water at the most. This excludes a wide array of materials used in the food and pharmaceutical industries, which possess a substantially higher level of viscosity.

For instance, biopolymer and cell-laden solutions used in biopharmaceuticals and bioprinting are at least 100 times more viscous than water, notes SEAS. At the same time, some sugar-based biopolymers come close to the viscosity of honey, which is 25,000 times more viscous than water.

Yet these materials could be easily handled with the help of the new printing technique, which uses sound waves to generate a tremendous force at the printer’s nozzle and pull out liquid droplets of a specific size, regardless of the viscosity of the printing material.

“Our goal was to take viscosity out of the picture by developing a printing system that is independent from the material properties of the fluid,” study lead author Daniele Foresti said in a statement.

The new invention relies on a technique previously used to levitate liquids and works by creating a strong acoustic field around the tip of the printer’s nozzle. This field is generated by a subwavelength acoustic resonator and exerts an enormous pressure, accelerating the liquid droplets with more than 100 times Earth’s gravitational force at sea level — close to 1,000 meters per second squared, notes Live Science.

“That’s more than four times the gravitational force on the surface of the sun,” points out SEAS.

The incredible force produced by the sound waves controls the size of the liquid droplets that are about to be printed and fires them out of the nozzle only when they have reached certain dimensions.

Commenting on her team’s achievement, Foresti, who is a researcher at Harvard’s SEAS and the Wyss Institute for Biologically Inspired Engineering, offered a simple explanation of how the process works.

“The idea is to generate an acoustic field that literally detaches tiny droplets from the nozzle, much like picking apples from a tree.”

The method has been successfully tested on a variety of high-viscosity liquids, including honey, stem-cell inks, biopolymers, optical resins, and liquid metals, note the researchers.

“By harnessing acoustic forces, we have created a new technology that enables myriad materials to be printed in a drop-on-demand manner,” said study senior author Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS.

As SEAS officials stated in the news release, the team’s innovation “could finally enable the manufacturing of many new biopharmaceuticals, cosmetics, and food and expand the possibilities of optical and conductive materials.”

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