Single shot of sound can create 3D objects

The world of 3D design and printing has come a long way, especially in the last few years. It seems there are limitless possibilities when it comes to creating objects in three dimensions, from houses and schools to skin, and even pizza. And now researchers are taking the process one stage further, by utilising sound as a means to create objects in 3D.

By using multiple acoustic holograms, the research team are able to generate pressure fields from which solid particles, gel beads and biological cells can be printed.

Traditional 3D printing builds an object one layer at a time, but by using sound waves scientists are able to “assemble microparticles into a three-dimensional object within a single shot using shaped ultrasound,” comments Kai Melde, Postdoctoral Researcher and first author of the study.

Peer Fischer, Professor from Heidelberg University further comments: “This can be very useful for bioprinting. The cells used there are particularly sensitive to the environment during the process.”

It’s oh so quiet

Sound waves can create a powerful force, but high-frequency ultrasound is inaudible to the human ear. The wavelengths can be a millimetre into the microscopic realm, which is used to manipulate very small building blocks, such as biological cells.

Previously the teams were able to show how to form ultrasound using acoustic holograms – 3D-printed plates, which are made to encode a specific sound field.

They were able to demonstrate that those sound fields could be used to manipulate materials into two-dimensional patterns. Spurred by this finding, the teams wanted to take things further.

Freely floating particles

The team can capture particles and cells freely floating in water and assemble them into 3D shapes. They are able to utilise a number of materials such as glass, hydrogel beads and biological cells.

“The crucial idea was to use multiple acoustic holograms together and form a combined field that can catch the particles,” comments Heiner Kremer, who wrote the algorithm to optimise the hologram fields, adding: “The digitisation of an entire 3D object into ultrasound hologram fields is computationally very demanding and required us to come up with a new computation routine”.

Because ultrasound is gentle, it can be usedfor biological cells that need to travel deep into tissue, and it is now possible to remotely manipulate and push cells without harm.