While traditional 3D printers work by depositing layers of material, tomographic volumetric additive manufacturing (TVAM) involves shining laser light at a rotating vial of resin until it hardens where accumulated energy exceeds a certain threshold. An advantage of TVAM is that it can produce objects in a matter of seconds , compared to around 10 minutes for layer-based 3D printing. But a disadvantage is that it is very inefficient, because only around 1% of the encoded light reaches the resin to produce the desired shape.
Researchers from EPFL's Laboratory of Applied Photonic Devices , led by Professor Christophe Moser, and from the SDU Centre for Photonics Engineering, led by Professor Jesper Glückstad, have reported a TVAM method in Nature Communications that significantly reduces the amount of energy required to fabricate objects, while simultaneously boosting resolution. The technique involves projecting a three-dimensional hologram of a shape onto the spinning vial of resin. Unlike traditional TVAM, which encodes information in the amplitude (height) of projected light waves, the holographic method takes advantage of their phase, or position.
This small change has a big impact. "All pixel inputs are contributing to the holographic image in all planes, which gives us more light efficiency as well as better spatial resolution in the final 3D object, as the projected patterns can be controlled in the projection depth," Moser summarizes.
In the recently published work, the team printed complex 3D objects such as miniature boats, spheres, cylinders, and art pieces in under 60 seconds with exceptional accuracy, using 25 times less optical power than previous studies.
Mimicking complex biological structures
The holograms are generated using a technique called HoloTile, which was invented by Professor Glückstad. HoloTile involves superimposing multiple holograms of a desired projection pattern, and eliminates random light interference called speckle noise that would otherwise create grainy images. Although holographic volumetric additive manufacturing has been reported previously, the joint EPFL-SDU team's approach is the first to yield such high-fidelity 3D-printed objects, largely thanks to the use of HoloTile.
EPFL student and lead author Maria Isabel Alvarez-Castaño explains that another unique aspect of the holographic approach is that the hologram beams can be made 'self-healing', meaning they can spread through a resin without being thrown off course by small particles. This self-healing property is essential for 3D printing with bio-resins and hydrogels that are loaded with cells, making the method ideally suited for biomedical applications.
"We are interested in using our approach to build 3D complex shapes of biological structures, allowing us to bio-print, for example, life-scale models of tissues or organs," says Alvarez-Castaño.
Going forward, the team aims to improve the efficiency of their method another twofold. Moser says that with some computational enhancements, the ultimate goal is to use holographic volumetric additive manufacturing to fabricate objects by simply projecting a hologram onto a resin, without needing to rotate it. This could further simplify volumetric additive manufacturing and increase the potential for high-volume, energy-efficient fabrication processes. He adds that the fact that the holograms can be coded using standard commercial equipment adds to the practicality of the approach.
"The holographic addition to TVAM technology sets the stage for the next generation of efficient, precise, and rapid volumetric additive manufacturing systems," he summarizes.
