A research team led by Mohsen Habibi from the University of California, Davis, has developed a method that enables 3D printing using acoustic holography. The process, known as Holographic Direct Sound Printing (HDSP), uses targeted ultrasonic waves to solidify polymer materials without contact. In the long term, the technology could enable processing within closed systems – such as the human body – without the need for surgical interventions.
At the heart of the process is an acoustic hologram that generates a defined sound pressure range. Instead of light, as is usual with optical holograms, an ultrasonic transducer placed in a water bath generates precise pressure zones in the polymer resin. These zones trigger so-called cavitation – microscopically small bubble formation that leads to a local chemical reaction and hardens the material. The shape of the sound field corresponds exactly to the object to be printed.
“With HDSP, I have a hologram that projects a holographic picture of a circle at a certain location,” he says. “That location is inside the build chamber that I filled with material, and it solidifies the picture I want to solidify.”
In contrast to established additive processes, HDSP does not build up an object layer by layer. Instead, the complete 2D projection of an object is generated all at once and transformed into a three-dimensional component.
Simple structures such as helices or geometric contours can currently be created in this way. “Bone, cartilage and similar biological tissues are not really complex in terms of geometry, so they could be projected with only one image,” Habibi says.
Even if clinical applications are still a long way off, the research shows that acoustically controlled printing processes are a realistic prospect for special application scenarios. The results were published in Nature Communications.
“When people read the 2022 paper in Nature Communications, they mentioned that direct sound printing was science fiction,” he says with a smile. “This is science over fiction.”
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