Conventional 3D printing methods often require multiple steps, high temperatures, or mechanical forces that can damage sensitive materials such as biological cells. German scientists have developed a novel technique that uses sound waves to create pressure fields that manipulate solid particles, gel beads, and cells into desired shapes, all in a single step.
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In this article, we'll explore how this innovative method, which employs multiple acoustic holograms, works and examine its potential applications and limitations.
What are Acoustic Holograms, and How do They Work?
Acoustic holograms are devices that can shape sound waves into complex patterns. They are made of 3D-printed plates that have a specific pattern of holes or bumps.
The principle of acoustic holograms is to encode the phase of a desired sound wavefront on a 3D-printed surface profile. The mechanism of action is that when a plane sound wave hits the 3D-printed plate, it is modulated by the pattern of holes or bumps on the plate, which changes its phase and amplitude according to a pre-designed algorithm. The resulting sound wave then forms a complex shape that can manipulate objects in 3D space.
The Use of Multiple Acoustic Holograms for 3D Printing
Acoustic holography itself dates back to the mid-1960s. It was only in 2016 that a study published in the Nature journal by a team of scientists from the Max Planck Institute for Intelligent Systems, the University of Stuttgart, and the University of Erlangen-Nuremberg presented a novel method for designing acoustic holograms that can generate complex 3D pressure fields using an iterative algorithm.
They used a device called a sound printer that consists of four plates with holes arranged in a specific pattern. Each plate acts as an acoustic hologram that shapes the sound waves emitted by a speaker behind it. They created a 3D pressure field that can trap and move particles in mid-air by combining the sound waves from different plates.
The researchers successfully printed various shapes, including letters, rings, and pyramids, using polystyrene beads, gelatin beads, and yeast cells. They were able to print multiple objects at once and change their shape dynamically by switching between different plates. The scientists suggested that their technology could have potential applications in bioprinting, microfluidics, and soft robotics.
Recently, the same research group took the research further in an exciting article published in the Science Advances Journal on the use of 3D holographic ultrasound fields to assemble matter using acoustic forces. Acoustic waves had been known to exert forces on matter, but with the precise shaping of ultrasound fields in 3D, the researchers found they could control the force landscape and potentially assemble particulates into whole 3D objects in one shot.
They demonstrated the generation of compact holographic ultrasound fields and showed the one-step assembly of matter using acoustic forces. They combined multiple holographic fields to drive the contactless assembly of solid microparticles, hydrogel beads, and biological cells inside standard labware. The structures were then fixed via gelation of the surrounding medium.
On the Max Planck Institute for Medical Research website, the first author of the study, Kai Melde, explained that the key concept was to utilize multiple acoustic holograms simultaneously to create a collective field capable of capturing particles. Meanwhile, Heiner Kremer, who developed the algorithm for optimizing the hologram fields, noted that digitizing an entire 3D object into ultrasound hologram fields was a computationally intensive task that necessitated the creation of a novel computation routine.
This new technology shows great promise for rapid prototyping, particularly in biofabrication, where conventional methods can be slow and potentially damaging to biological cells. Importantly, this approach handles matter with positive acoustic contrast and does not require opposing waves, supporting surfaces, or scaffolds, which sets it apart from previous work in this field.
Why Use Multiple Acoustic Holograms for 3D Printing and Its Advantages Over Other Methods
Using multiple acoustic holograms to manipulate objects has several advantages over other methods like optical tweezers or magnetic fields. This technology is particularly advantageous for biofabrication because it does not apply mechanical or chemical stress on biological cells, which can damage them. Acoustic holograms can form complex shapes and manipulate different types of materials, and multiple objects can be manipulated simultaneously.
Additionally, they have higher resolution and speed for 3D manipulation and are gentler and safer for biological cells.
Applications of Multiple Acoustic Holograms in 3D Printing
The potential applications of 3D holographic ultrasound fields in tissue engineering and additive manufacturing are significant, and the ability to assemble cells into complex 3D structures could be transformative in this field.
This technology could potentially allow for the creation of complex tissues, such as organs, which could then be used for transplantation or drug testing. In additive manufacturing, 3D holographic ultrasound fields could revolutionize the way products are made by allowing for the rapid assembly of components without the need for complicated machinery or assembly lines.
Limitations of Using Multiple Acoustic Holograms in 3D Printing
The study does not mention any limitations explicitly, but possible challenges include accuracy and resolution depending on hologram plate quality and design, efficiency being affected by plate movement and alignment, limited range of printable materials based on acoustic properties, and requiring additional steps for stability and durability. These limitations may also apply to other acoustic-based 3D printing methods.
Multiple acoustic holograms for 3D printing are a promising technology for the creation of complex 3D structures in a single step.
The technology uses multiple acoustic holograms to generate pressure fields that can manipulate solid particles, gel beads, and even cells into desired shapes. The lack of mechanical or chemical stress on biological cells is a significant advantage of this technology, and its potential applications in bioprinting, microfluidics, and soft robotics are significant.
Possible limitations such as accuracy, resolution, efficiency, and range of printable materials based on acoustic properties must be considered. Nevertheless, the use of 3D holographic ultrasound fields has the potential to transform the fields of tissue engineering and additive manufacturing.
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References and Further Reading
Baily, S. (2022). The Untapped Potential of 3D Printing in Advanced Materials [Online]. AZoM.com. URL https://www.azom.com/article.aspx?ArticleID=21825 (accessed 2.3.23).
Enuh, B.M. (2023). How Can We 3D Print Hydrogel Electronics? [Online]. AZoM.com. URL https://www.azom.com/article.aspx?ArticleID=22364 (accessed 2.24.23).
Marzo, A., Drinkwater, B.W. (2019). Holographic acoustic tweezers. Proceedings of the National Academy of Sciences U.S.A. 116, 84–89. https://doi.org/10.1073/pnas.1813047115
Max Planck Institute for Medical Research (2023). Creating 3D objects with sound [Online]. Max Planck Institute for Medical Research. URL https://www.mr.mpg.de/14580718/3dprintingwithsound (accessed 2.24.23).
Melde, K., Kremer, H., Shi, M., Seneca, S., Frey, C., Platzman, I., Degel, C., Schmitt, D., Schölkopf, B., Fischer, P. (2023). Compact holographic sound fields enable rapid one-step assembly of matter in 3D. Science Advances 9, eadf6182. https://doi.org/10.1126/sciadv.adf6182
Melde, K., Mark, A.G., Qiu, T., Fischer, P. (2016). Holograms for acoustics. Nature 537, 518–522. https://doi.org/10.1038/nature19755
ScienceDaily (2023). Creating 3D objects with sound: Scientists assemble matter in 3D using sound waves for 3D printing [Online]. ScienceDaily.com. URL https://www.sciencedaily.com/releases/2023/02/230213120734.htm (accessed 2.24.23).
Trevelyan, O. (2022). Creating Molecules Using 3D Printing [Online]. Azolifesciences.com. URL https://www.azolifesciences.com/article/Creating-Molecules-Using-3D-Printing.aspx (accessed 2.24.23).
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