Acoustic waves exert forces when they interact with matter. Precisely shaping ultrasonic fields in 3D allows control over the forcescape and should allow particles to fall into place to form full 3D objects in “potentially at once”.

This holds promise for rapid prototyping, particularly biofabrication, as conventional methods are typically slow and exert mechanical or chemical stress on biological cells.

Scientists from the Max Planck Institute for Medical Research and the University of Heidelberg have created compact holographic ultrasonic fields and demonstrated the one-step assembly of matter using acoustic forces. They have devised a new technology to assemble matter in 3D.

To figure this out, scientists used multiple acoustic holograms to generate pressure fields that allowed them to print solid particles, gel beads, and even biological cells. Their results showed how you can form a 3D object from smaller building blocks in one step.

Kai Melde, a postdoc in the group and first author of the study, said: “We were able to assemble microparticles into a three-dimensional object within a single image using shaped ultrasound.”

Peer Fischer, professor at the University of Heidelberg, said: “This can be very useful for bioprinting. The cells used there are particularly sensitive to the environment during the process.”

Previous studies have demonstrated the formation of ultrasound using acoustic holograms – 3D printed plates, which are made to encode a specific sound field. These sound fields can be used to assemble materials into two-dimensional patterns. Based on this, the scientists came up with a manufacturing concept.

In this new study, scientists take this concept a step further. They collect suspended particles and cells in the water and assemble them into three-dimensional shapes. In addition, the new technique is applicable to many materials, including biological cells, hydrogel or glass beads, and other materials.

First author Kai Melde says: “The crucial idea was to use multiple acoustic holograms together and form a combined field that can capture the particles.”

Heiner Kremer, who wrote the algorithm to optimize the hologram fields, adds: “The digitization of a full 3D object in ultrasonic hologram fields is computationally very demanding and required us to come up with a new computational routine.”

Scientists noted, “The technology is a promising platform for shaping cell cultures and tissues in 3D. The advantage of ultrasound is that it is gentle on the use of biological cells and can penetrate deep into the tissue. In this way, it can be used to manipulate and push cells from a distance without harming them.”

Magazine reference:

  1. Kai Melde, Heiner Kremer, Minghui Shi, Senne Seneca, Christoph Frey, Ilia Platzman, Christian Degel, Daniel Schmitt, Bernhard Schölkopf, Peer Fischer. Compact holographic sound fields enable rapid one-step assembly of matter in 3D. Scientific Progress, 2023; 9 (6) DOI: 10.1126/sciadv.adf6182