"Acoustic Holograms" Offer One-Shot 3D Printing in Mediums Up To and Including Biological Cells
Theoretically printable within living tissue, these tiny objects are assembled at the focal point of ultrasonic sound waves.
Researchers at the Max Planck Institute for Medical Research and Heidelberg University have used "acoustic holograms" to 3D print tiny objects with sound — and claim the technology could find a use in biomedical engineering.
"We were able to assemble microparticles into a three-dimensional object within a single shot using shaped ultrasound," first author Kai Melde explains of the work, in which silica gel beads were used as the "printing" medium. The secret to the team's success: an "overlooked configuration" of structured sound fields, in which multiple beams come together to focus in the shape of the desired object — aligning the beads and allowing them to be assembled into a solid object.
The team's printing system is one-shot — meaning that, rather the building up layer-by-layer as with traditional additive 3D printing, the object is created in an instant. The process of actually printing the objects is driven by "acoustic holograms," plates printed using more traditional 3D-printing techniques and which encode a specific sound field for assembly.
The technique is applicable to other materials, too, so long as they can be mixed with water. In testing, the team was able to assemble objects from glass beads and biological cells as well as silica gel beads. The only drawback: the computational complexity. "The digitization of an entire 3D object into ultrasound hologram fields is computationally very demanding," admits co-author Heiner Kremer, "and required us to come up with a new computation routine."
"This can be very useful for bioprinting," claims Peer Fischer, Heidelberg University professor and corresponding author of the work, of the potential applications for the sound-based 3D printing system, thanks to its ability to work within living tissue. "The cells used there are particularly sensitive to the environment during the process," making the low-impact ultrasound an appealing method of manipulating cells.
The team's work has been published under open-access terms in the journal Science Advances.