Researchers from Harvard University’s John A Paulsen School of Engineering and Applied Sciences (SEAS) in Massachusetts, have created an acoustophoretic 3D printing technique which uses sound waves to form drops of a wide range of viscous fluids into additively manufactured structures.
A myriad of inks
Inkjet 3D printing utilizes fluid liquid droplets of microliter-to-nanoliter volume to form solids; however, this process is limited to low viscosity inks that are approximately 10 to 100 times higher than the viscosity of water, according to the study. This rules out the 3D printing capabilities of vital biopolymer and cell-laden inks used within biopharmaceuticals and 3D bioprinting as well as sugar-based biopolymers, such as honey, which is 25,000 times more viscous than water.
In addition, studies have shown that the viscous fluid changes dramatically with temperature and composition, making it more difficult to optimize printing parameters to control droplet size.
To enable “myriad materials” experimentation, the SEAS research team built a subwavelength acoustic resonator capable of generating highly confined acoustic fields which can create pulling forces exceeding “100 times the normal gravitation forces (1G) at the tip of the printer nozzle – four times the gravitational force on the surface of the sun.”
Drip by drip
The researchers tested the acoustophoretic 3D printing process on a wide range of materials, including honey to stem-cell inks, a cell-laden collagen solution, a UV-curable optical adhesive, and liquid metals. The controllable force from the custom resonator pulls each droplet off of the “acoustophoretic printing head” with a specified radius from 800μm to less than 65μm nozzle, and ejects it toward the printing target.
The higher the amplitude of the sound waves, the smaller the droplet size, regardless of the liquid's viscosity, the researchers found.In addition, because sound waves cannot be transmitted through droplets, the researchers believe the method is safe for use with sensitive biological vectors such as living cells or proteins.
“Our technology should have immediate impact on the pharmaceutical industry,” said Jennifer Lewis, Senior Author of the paper and the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS. “But we believe this will become an important platform for multiple industries.”