"Acoustic holograms" quickly assemble objects from particles or cells

“Acoustic holograms” quickly assemble objects from particles or cells

Scientists have created “acoustic holograms” that can assemble matter into 3D objects, using only sound. The technique works with different types of particles and even living cells, enabling a new kind of fast, non-contact 3D printing.

Sound exists as pressure waves moving through a medium, such as air or water. These waves can exert pressure on the surfaces they hit, although this force is so small that we usually only notice it on our eardrums. But scientists have experimented with manipulating high-frequency ultrasound to levitate small objectscreate complex soundscapesor add a sense of touching visible holograms.

For the new study, scientists from Max Planck and the University of Heidelberg investigated a new use for ultrasound – moving tiny building blocks in precise ways to put 3D objects together. They used specially designed 3D printed plates 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 a bit like an invisible mold – when this ultrasonic hologram is applied to particles suspended in liquid, pressure waves are applied at different strengths in different areas, until the particles coalesce into the 3D shape desired precision. In tests, the team was able to create shapes such as a dove, a number 8 and a propeller, using materials like glass beads, hydrogel and even biological cells.

There are a few potential benefits to the technique. It can be faster and more efficient because it works in one step, rather than conventional 3D printing which builds an object layer by layer. And because the particles don’t need to be physically touched, they’re kinder to biological cells, which could make them perfect for creating tissues and organs.

“This can be very useful for bioprinting,” said study author Peer Fischer. “The cells used there are particularly sensitive to the environment during the process.”

The team says future work could explore ways to improve the technique, including using more hologram plates, higher ultrasound frequencies and different materials.

The research was published in the journal Scientists progress.

Source: Max Planck Institute

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