23 February 2020

[Optics] – EPFL develops high-precision laser 3D printing method

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High-resolution tomographic printing - Codex International

Researchers at EPFL, Lausanne, Switzerland, have developed a new, high-precision method for 3D-printing small, soft objects. The process, which takes less than 30 seconds from start to finish, has potential applications in a wide range of fields, including 3D bioprinting.
The process starts with a translucent liquid polymer, from which the objects are formed. As the laser processes the shape, darker solid spots begin to form in the rotating vessel until, within 30 seconds, the finely-detailed finished product is formed.
This 3D-printing method, developed by researchers at EPFL’s Laboratory of Applied Photonics Devices (LAPD), can be used to make tiny objects with unprecedented precision and resolution – all in record time.
The team has published its findings in the journal Nature Communications.
Multiple applications
EPFL says the technology could have innovative applications in a wide range of fields, but its advantages over existing methods – the ability to print solid parts of different textures – make it ideally suited for medicine and biology. The process could be used, for instance, to make soft objects such as tissue, organs, hearing aids and mouthguards.
“Conventional laser 3D printing techniques, known as additive manufacturing, build parts layer by layer,” explained Damien Loterie, the CEO of Readily3D. “The problem is that soft objects made that way quickly fall apart.”
This process can also be used to make delicate cell-laden scaffolds, in which cells can develop in a pressure-free 3D environment. The researchers teamed up with a surgeon to test 3D-printed arteries made using the technique. “The trial results were extremely encouraging,” says Loterie.
Optically hardened

The new technique draws on the principles of tomography, a method often used in medical imaging to build a model of an object based on surface scans.
The printer works by sending a laser through the translucent gel – either a biological gel or liquid plastic, as required. “It’s all about the light,” explained Paul Delrot, Readily3D’s CTO. “The laser hardens the liquid through a process of polymerization. Depending on what we’re building, we use algorithms to calculate exactly where we need to aim the beams, from what angles, and at what dose.”
The system is currently capable of making 20mm-structures with a precision of 80µm, about the same as the diameter of a strand of hair. But as the team develops new devices, they should be able to build much bigger objects, potentially up to 150mm.
“The process could also be used to quickly build small silicone or acrylic parts that don’t need finishing after printing,” says Christophe Moser, who heads the LAPD. Interior design could be a potentially lucrative market for the new printer.
Nature Communications summary
The Nature Communications paper concludes, “In summary, we showed that both the étendue (spread) of the illumination system and the resin viscosity are critical parameters to produce high-resolution features with tomographic additive manufacturing (AM).
“We also demonstrate that the transparency in tomographic AM can be exploited to implement a feedback system to accurately control the photopolymerization kinetics. The 80 µm positive and 500 µm negative feature sizes achieved over centimeter-scale parts pave the way for ultrafast production of precise constructs such as functional tissue or organ models.”

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