Newswise – Versatile and ubiquitous, glass is increasingly found in specialty applications such as fiber optics, consumer electronics and microfluidics for lab-on-a-chip devices. However, traditional glassmaking techniques can be expensive and slow, and 3D printing glass often results in rough textures, making them unsuitable for smooth lenses.
Using a new laser-based volumetric additive manufacturing (VAM) approach – an emerging technology in near-instantaneous 3D printing – researchers from Lawrence Livermore National Laboratory and the University of California, Berkeley have demonstrated the ability to 3D printing microscopic objects in silica glass, part of an effort to produce delicate layerless optics that can be built in seconds or minutes. The results are published in the latest edition of the journal Science.
Nicknamed “the Replicator” after the fictional “Star Trek” device that can instantly fabricate almost any object, the computed axial lithography (CAL) technology developed by LLNL and UC Berkeley is inspired by methods of computed tomography (CT) imaging. CAL works by calculating projections from many angles through a digital model of a target object, optimizing these projections by calculation, and then delivering them into a rotating volume of photoresist using a digital light projector . Over time, the projected light patterns reconstruct or accumulate a 3D light dose distribution in the material, hardening the object to points exceeding a light threshold as the resin vat rotates. The fully formed object materializes in seconds – much faster than traditional layer-by-layer 3D printing techniques – and then the vat is emptied to retrieve the part.
Combining a new micro-scale VAM technique called micro-CAL, which uses a laser instead of an LED source, with a nanocomposite glass resin developed by the German company Glassomer and the University of Fribourg, researchers from the UC Berkeley reported the production of complex and robust microstructured glass objects with a surface roughness of only six nanometers with features down to a minimum of 50 microns.
Hayden Taylor, associate professor of mechanical engineering at UC Berkeley, principal investigator of the project, said the micro-CAL process, which produces a higher dose of light and hardens 3D objects faster and at higher resolution, combined with the characterized nanocomposite resins at LLNL proved to be a “perfect match for each other”, creating “striking results in the strength of the printed objects”.
“Glass objects tend to break more easily when they contain more flaws or cracks or have a rough surface,” Taylor said. “CAL’s ability to make objects with smoother surfaces than other 3D printing processes is therefore a big potential advantage.”
The team compared the fracture toughness of micro-CAL glass to objects of the same size made by a more conventional layer-based printing process, and found that the fracture loads of CAL-printed structures were higher. tightly clustered, which means researchers could have had more confidence in the breaking load of a CAL printed component compared to conventional techniques.
LLNL co-author Caitlyn Krikorian Cook, group leader and polymer engineer in the lab’s Materials Engineering Division, characterized the kinetics of nanocomposite resin curing with exposure to light. Printing higher viscosity resins is difficult, if not impossible, with current traditional LLNL stereolithography systems, Cook said, adding that the advantage of VAM for micro-optics is that it can produce extremely smooth without layering artifacts, allowing faster printing without additional add-ons. post-processing time.
“You can imagine trying to create these small micro-optics and complex microarchitectures using standard manufacturing techniques; it’s really not possible,” Cook said. “And being able to print it out of the box without having to do any polishing techniques saves a lot of time. If you can eliminate the polishing steps after forming the optic – with low roughness – you can print a part ready to use.
Cook performed on the spot characterization of the resin with a spectrometer to measure the thresholding response of an inhibitory modifier in the photopolymerization kinetics of the material. The modifier, combined with the precision of the VAM laser method, was the “secret sauce” for printing high resolution optics at the microscopic scale.
“By creating a thresholding response, we’re able to dramatically improve resolution,” Cook said. “We take advantage of the similar thresholding response reported in our previous work, except that we implement it in a different class of photopolymer chemistry. We are beginning to better understand the kinetics required for volumetric manufacturing.
Over the past few years, the LLNL/UC Berkeley VAM collaboration has experimented with different resins and materials to create complex objects. The latest breakthrough stems from a study with UC Berkeley to discover new classes of versatile materials that could expand the range of material chemistries and properties achievable through the VAM method.
Cook and the UC Berkeley researchers said VAM patterned glass could impact solid glass devices with microscopic characteristics, produce optical components with more geometric freedom and at higher speeds and could potentially enable new functions or products at a lower cost.
Real-world applications could include micro-optics in high-grade cameras, consumer electronics, biomedical imaging, chemical sensors, virtual reality headsets, advanced microscopes, and microfluidics with challenging 3D geometries such as “lab-on-a-chip” applications, where microscopic channels are needed for medical diagnosis, basic science studies, nanomaterial manufacturing and drug screening. Additionally, the benign properties of glass lend themselves well to biomaterials, or where there is high temperature or chemical resistance, Cook added.
The Berkeley/LLNL team is also looking at applications in bioprinting, such as fabricating “lung”-like organs or structures using a combination of VAM and projection micro-stereolithography.
At LLNL, Cook said she and her team will further adjust the VAM resolution and doses required for a varying range of print resolutions and speeds. Cook continues to support material characterization and development, and Dominique Porcincula and Rebecca Walton, members of his Functional Architected Materials Engineering group, currently have a VAM feasibility study to advance VAM glass printing efforts for higher optics. large.
“The challenge with printing glass is that the larger the part, the greater the shrinkage stresses when going from a green state to burning the binder between the silica particles to a brown part to fuse the particles together into a fully dense glass part. Cracking issues typically occur in larger prints due to these shrinkage stresses,” Cook said. “Our teams at LLNL develop custom formulations to produce larger and glass printed parts that will not crack during the debinding and sintering processes.”
LLNL’s latest work was funded by the Laboratory-Led Research and Development (LDRD) program.
Co-authors on the Science the article included lead author Joseph Toombs and Chi Chung Li from UC Berkeley, Manuel Luitz and Sophie Jenne from the University of Freiburg in Germany, and Bastian Rapp and Frederik Kotz-Helmer from Glassomer and the University of Freiburg.