Max Planck and Heidelberg researchers explore touchless 3D printing using acoustic holograms 

Researchers at the Max Planck Institute for Medical Research and Heidelberg University have been investigating the “touchless 3D printing” concept to improve precision and 3D printing speed.

The new study is published in the journal of Advanced Sciences. Multiple acoustic holograms are used in the study to make pressure fields that can be used to 3D print solid particles, gel beads, and even living cells. By doing this, the researchers hope to open up new possibilities in fields like biomedicine, where being able to make very precise and complex structures could be very useful. 

Concept to form compact acoustic 3D pressure images. Image via Max Planck Institute for Medical Research.
Concept to form compact acoustic 3D pressure images. Image via Max Planck Institute for Medical Research.

Creating 3D shapes with ultrasound holograms

The study’s lead author, Kai Melde, highlights the potential of ultrasound-based 3D printing technology for assembling biological cells, as it is gentle and non-toxic to cells. Additionally, the non-contact remote assembly feature helps maintain sterility, which can keep cells healthy. 

The research introduces a novel method of creating precise 3D shapes through the use of multiple “acoustic holograms,” which resemble sound blueprints. The team was able to test the method by putting together tiny particles and cells into specific shapes faster than with traditional 3D printing. This technology can be used with a variety of materials and may have medical applications, such as drug delivery and tissue engineering.

Melde said that making 3D shapes with sound waves requires complex algorithms and multiple holographic fields that interact with each other. However, this presents a computational challenge as the memory requirements increase with the third dimension, and the wavefield needs to be computed for the entire volume. Heiner Kremer, a member of the team who wrote the necessary computer programs, says that digitizing a 3D object into ultrasound hologram fields takes a lot of computing power, so a new way to do computations had to be made. To overcome this challenge, the researchers used GPU acceleration and Google’s TensorFlow software

Despite the technology’s limitations, such as being constrained by the power of sound waves and requiring materials that can resist gravity, the new 3D printing method represents a “promising step forward” in the field of sound wave-based 3D fabrication.

3D printed shapes. Image via Max Planck Institute for Medical Research.
3D printed shapes. Image via Max Planck Institute for Medical Research.

Were ultrasound technologies used in 3D printing before?

Researchers at Universiti Teknikal Malaysia Melaka (UTeM) created a 3D printer that can create more resilient parts from recycled ABS. Engineers were able to make recycled ABS stronger by attaching two piezoelectric transducers to a standard gantry Fused Filament Fabrication (FFF) 3D printer. After granulating used ABS and extruding it into a 1.75 mm filament, the UTeM study started 3D printing samples with a prototype FFF machine that was fitted with a piezoelectric transducer to make it more stable through ultrasound vibration. Even though the first models made with a nozzle temperature of 230°C had surface flaws, the engineers found that raising this parameter to 270°C and slowing down the print speed fixed these problems. Researchers also found that making parts vibrate at 20 kHz with ultrasound “significantly improved recycled layer adhesion.”

Concordia University scientists introduced a novel direct sound printing (DSP) approach that employs ultrasound waves to produce intricate and precise objects. Their study, which is detailed in a published paper, explains how the method employs sound waves to generate sonochemical reactions in tiny cavities. This leads to the creation of intricately designed geometries that cannot be accomplished using current methods.

“Ultrasonic frequencies are already being used in destructive procedures like laser ablation of tissues and tumors,” said Muthukumaran Packirisamy, a professor in Concordia’s Department of Mechanical, Industrial, and Aerospace Engineering. “We wanted to use them to create something.”

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Featured image shows concept to form compact acoustic 3D pressure images. Image via Max Planck Institute for Medical Research.