3D printing can be a slow process, constructing objects one line or one layer at a time. Researchers in Heidelberg and Tübingen have discovered how to form a 3D object from smaller building blocks in one step. Using sound waves.
The results of the study have been published in the journal Science Advances.
The technology uses multiple acoustic holograms to generate pressure fields that can be used to print solid particles, gel spheres and even biological cells.
“We have layered microparticles into a three-dimensional object in a single production run using ultrasonic waves,” says first author Kai Melde. “This can be very useful for bioprinting. The cells used for this are particularly sensitive during the process,” adds Professor Peer Fischer.
Sound waves exert forces on matter. High-frequency ultrasound, which is inaudible to the human ear, can affect the microscopic realm at sub-millimeter wavelengths.
In previous studies, Fischer and colleagues showed how to shape ultrasound using acoustic holograms – 3D printed plates made to encode a specific sound field. Those sound fields can be used to combine materials into two-dimensional patterns. Now the team has captured particles and cells floating freely in the water and assembled them into three-dimensional shapes. In addition, the new method works with different materials, including glass or hydrogel beads and biological cells.
Melde says that “the crucial idea was to use several 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 calculation routine”.
The scientists believe their technology is a promising platform for the formation of 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 tissue. In this way, it can be used to manipulate and push cells from a distance without damage.
