Scientists have created “acoustic holograms” that can assemble matter into 3D objects, using just sound. The technique works with various types of particles and even living cells, allowing for a new kind of 3D printing that’s fast and contact-free.
Sound exists as pressure waves moving through a medium, like air or water. Those waves can exert pressure onto surfaces that they strike, although that force is so tiny that we usually only notice it working on our eardrums. But scientists have been experimenting with manipulating high-frequency ultrasound to levitate small objects, create complex soundscapes, or add a sense of touch to visible holograms.
For the new study, scientists at Max Planck and the Heidelberg University investigated a new use for ultrasound – moving tiny building blocks in precise ways to assemble 3D objects. They used 3D-printed plates that were specially designed to produce a certain sound field. Combining several of these plates with different designs can create an acoustic hologram in a specific 3D shape.
It works kind of like an invisible mold – when this ultrasound hologram is applied to particles suspended in liquid, the pressure waves are applied at different strengths in different areas, until the particles coalesce into the precise 3D shape desired. In tests, the team was able to create shapes such as a dove, a figure 8 and a helix, using materials like glass beads, hydrogel and even biological cells.
There are a few potential advantages to the technique. It can be faster and more efficient, since it works in a single step, rather than conventional 3D printing that builds up an object layer by layer. And because the particles don’t need to be physically touched, it’s gentler on biological cells, which could make it perfect for creating tissues and organs.
“This can be very useful for bioprinting,” said Peer Fischer, an author of the study. “The cells used there are particularly sensitive to the environment during the process.”
The team says that future work could explore ways to improve the technique, including using more hologram plates, higher frequencies of ultrasound, and different materials.
The research was published in the journal Science Advances.
Source: Max Planck Institute