Sep 4, 2018 | By Thomas
Researchers from Harvard University’s John A Paulsen School of Engineering and Applied Sciences (SEAS) have developed a new 3D printing technique that uses sound waves to generate droplets from liquids with an unprecedented range of composition and viscosity. According to researchers, this technique enables myriad materials to be 3D printed in a drop-on-demand manner and could be used to synthesize biopharmaceuticals and cosmetics, as well as optical and conductive materials.
CREDIT: Daniele Foresti, Jennifer A. Lewis, Harvard University
Currently, microcapsules used for drug delivery are made using inkjet 3D printer. Inkjet 3D printing utilizes fluid liquid droplets to form solids, however it's only suitable for liquids that are roughly 10 times more viscous than water, according to the researchers. Yet many fluids of interest to researchers are far more viscous. For example, the biopolymer and cell-laden inks used in biopharmaceuticals and bioprinting are at least 100 times more viscous than water. Some sugar-based biopolymers could be as viscous as honey, which is 25,000 times more viscous than water.
The viscosity of these fluids also changes dramatically with temperature and composition, makes it even more difficult to optimize printing parameters to control droplet sizes.
The SEAS research team has therefore developed a 3D printing system that is independent from the material properties of the fluid. They built a system using acoustic waves to assist gravity in forming drops of controlled size from viscous fluids.
In a paper in Science Advances, the Harvard team, led by Prof Jennifer Lewis, who is also affiliated to the Wyss Institute for Biologically Inspired Engineering and the School of Arts and Sciences, describe how they designed and built a subwavelength acoustic resonator capable of generating a confined acoustic fields which causes a pulling force more than 100 times stronger the normal gravitation forces at the tip of the printer nozzle.
By controlling the target position, the ejected droplets can be carefully deposited and patterned anywhere. In this example, honey drops are patterned on a glass substrate. CREDIT: Daniele Foresti, Jennifer A. Lewis, Harvard University
"The idea is to generate an acoustic field that literally detaches tiny droplets from the nozzle, much like picking apples from a tree," said Daniele Foresti, first author of the paper, the Branco Weiss Fellow and Research Associate in Materials Science and Mechanical Engineering at SEAS and the Wyss Institute.
The researchers tested the process on a wide range of materials, including honey, stem-cell inks, biopolymers, optical resins and liquid metals. The controllable force pulls each droplet off of the nozzle when it reaches a specific size, ranging from a maximum value that exceeds 800 μm to less than 65 μm, and ejects it towards the printing target. The researchers found that The higher the amplitude of the sound waves, the smaller the droplet size, irrespective of the viscosity of the fluid. Importantly, sound waves don't travel through the droplet, making the method safe to use even with sensitive biological cargo, such as living cells or proteins.
To eject droplets, acoustophoretic printing utilizes airborne ultrasounds - virtually material independent. Even liquid metal can be easily printed! This particular liquid metal forms a solid shell when in contact with the atmosphere, and this particular property makes it easy to pile drops one on top of another. (Image courtesy of Daniele Foresti, Jennifer A. Lewis, Harvard University.)
"Our technology should have an immediate impact on the pharmaceutical industry," said Lewis. "However, we believe that this will become an important platform for multiple industries."
Posted in 3D Printing Technology
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