For next generation photonics, sensing and imaging technologies, the ability to 3D print glass is critical to developing highly complex, freeform, or small-scale structures. Yet it has proven difficult to 3D print glass, which has a high melting point over 1400°C, while also retaining its unique chemical, mechanical and optical properties.
Recent advances have not only resulted in the successful 3D printing of glass, with properties and shape identical to that of commercial glass, but also in further developing specific 3D printing technologies to print glass structures at the scale and complexity never possible before—and with customizable optical properties. One of these is OptoGlass3D, a novel method of 3D printing glass developed by Glassomer GmbH and Nanoscribe GmbH, and led by Professor Bastian Rapp of the University of Freiburg and Head of NeptunLab.
The OptoGlass3D project is funded with a one-year €100,000 grant from ATTRACT, a collaborative initiative bringing together the research, industry and investment communities in Europe to develop the next-generation of sensing and imaging solutions, by streamlining breakthrough innovation, and using new, open innovation models at scale. ATTRACT is in turn funded by the EU Horizon 2020 program, and so far has provided grants to 170 projects focused in breakthrough innovation.
In 2017, researchers at Karlsruhe Institute of Technology (KIT) developed a sterelithography (SLA) method to 3D print glass, at high resolution, a few tens of micrometers, and possibly even 150-500 nanometers (just ten times the size of silica particles). By using a photocurable polymer infused with a glass nanopowder ink as the material, this method could 3D print at room temperature and produce objects with optical, surface, and compositional properties comparable to commercial fused silica glass. Their research, published in Nature, was led by Frederik Kotz and Bastian Rapp, who founded Glassomer GmbH in 2018 to produce and supply Glassomers, a novel range of materials that can be used by any off-the-shelf SLA 3D printer, as well as the “Liquid Glass” method to process 3D printed fused silica glass like polymer.
Soon, the company won the Formnext 2019 Start-Up Challenge, among a number of awards for its innovation in 3D printing glass. This liquid glass material, a nanocomposite containing amorphous silica material can be used to 3D print almost any kind of object in glass (with properties exactly as that of commercial fused silica glass) with feature resolution in the tens of micrometers and surface roughness within a few nanometers.
Explaining the relevance of these advances, Kotz, Chief Science Officer at Glassomer, said:
“Normally these things are done with polymers, but polymers lack the opacity and resistance to extreme temperatures and chemicals offered by high-purity glass. High opacity is important for optical data processing, as well as for high-powered lasers, which also require heat-resistant materials; while various industrial and scientific applications need materials that can cope with hazardous chemicals. People always wanted to use glass in these applications, but it was not always possible, because shaping with these high resolutions was not possible. Pure glass—silicon dioxide—melts at such high temperatures that it’s hard to create solid moulds for it, and lower-purity glass lacks the desired properties. These industrial uses also require much smaller and more intricate structures than other glass-shaping methods can achieve.”
The process is made up of two stages in which the composite is first 3D printed, then heated and sintered at 600°C and 1300°C respectively to leave a fully transparent, uniform, non-porous glass object.
In collaboration with Nanoscribe and Glassomer, the OptoGlass3D project will develop specific materials for 2PP technology and will then look to commercialize the material. As the project goal states:
“During this project the consortium will develop LiquidGlass formulations which can be structured via Nanoscribe’s 2PP process as well as the required process conditions, parameters and (potentially) instrumental adaptations. Based on the LiquidGlass process formulation, modifications will be developed which allow generating optical glasses with adjustable optical properties such as the index of refraction which will be made adjustable in a range of = 1.46 to = 1.50. Validation of the technology’s capability will be showcased by manufacturing of demonstrator samples addressing the potential of glass components for adjustable refractive and high-resolution diffractive optics.”
Early approaches to Glass 3D printing explored the use of glass powders in a sintering system. This continued to evolve and in 2015, Israel-based Micron3DP announced its high-temperature extrusion-based 3D printing system for glass. However these were limited due to issues in the porosity and uniformity of the glass structures. Due to a lack of a sizable market at the time, the company discontinued the product.
Following this, further advances were made in glass 3D printing by researchers at MIT, who developed an extrusion-based printer for molten glass: the G3DP, and the improved G3DP2, built for industrial production. Due to limited resolution in this 3D printed glass, it would not be suitable for high-tech applications that require high resolution and precise microstructures. Yet it did allow for the manufacture of complex, custom parts that could only be made using 3D printing, and these could be applied in aesthetic design and architecture, and such parts were on display at the Milan Design Week in 2017.
In 2017, at the Lawrence Livermore National Laboratory, a direct ink writing method was developed to print glass at room temperature, allowing for higher resolution parts with better optical uniformity. With this, it became possible to tailor the properties and composition of glass, allowing for example the printing of glass with difference refractive indices in a single flat optic. In 2019, research published in Optical Materials Express by researchers at the Universite Laval in Canada demonstrated a filament-based method to 3D print chalcogenide glass with complex geometries, which has tremendous scope in infrared sensor and imaging applications in defense and security, biomedicine, telecommunications and more. Advances such as these, including OptoGlass3D, have opened up a range of novel applications and possibilities with 3D printed glass, particularly in the next-generation of freeform optics, sensors, imaging and microfluidic devices.
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