Scientists from the University of Freiburg and 3D printer manufacturer Nanoscribe have utilized a two-photon-polymerization (2PP) system to fabricate glass silica microstructures with a resolution of just a few tenths of a micrometer.
Using their novel ‘Glassomer’ polymer-based resin, the team 3D printed objects with a surface roughness of 6 nanometers, much less than the 40-200 nanometers seen in many other glass parts. In the future, the scientists believe that their unique printing, debinding, and sintering process could be deployed to produce next-generation micro-optics with potential biomedical applications.
“This technology allows, for the very first time, to process glass using one of the most exciting 3D printing techniques,” said Bastian Rapp, a professor at the University of Freiburg. “With this, previously unachievable structural details and components with outstanding complexity will become readily accessible.”
The evolution of micro-glass optics
Silicate glass offers a high level of optical transparency and thermal and chemical resistance qualities that make it ideal for optics, microfluidics, and chemistry applications. However, when used within manufacturing processes such as grinding and polishing, it’s often only possible to create objects with simple geometries and micrometer-level precision.
Similarly, when produced using laser‐assisted etching techniques, silicate glass parts tend to have rough surfaces of 40–200 nm, requiring excessive post-processing before use. 2PP, on the other hand, uses two‐photon absorption, which confines the polymerizing voxel during printing, yielding higher resolution parts with smoother surfaces.
The technique is often utilized to fabricate plastic, ceramic, or metal objects, and although extensive glass 2PP R&D is being conducted, the process has not yet been perfected. Given the commercial biomedical potential of fully-optimized glass silicate parts, the Freiburg team, therefore, decided to team up with Nanoscribe to innovate a revised 3D printing process.
The scientists’ ‘Glassomer’ process
At the core of the researchers’ new method was their novel Glassomer silicate nanocomposite, which consisted of silica nanoparticles encased in a binder matrix. While the team had previously managed to use the material within an SLA process, they couldn’t use it to 2PP 3D print glass optics due to its low transparency level.
To combat this, the scientists increased their resin’s chemical crosslinking to provide it with greater curing speed. This not only aided its chemical stability but also gave it transparency of 91.6%. Leveraging their revised mixture and a Photonic Professional GT2 3D printer, the team then fabricated a series of prototype polymeric nanostructures.
Once printed, the samples were dunked in methanol to eliminate any non-polymerized material and heated at a temperature of 600°C to remove their polymeric binder. The resulting parts were then sintered into fused silica glass, and although these featured minor shrinkage, they could also be printed into highly-complex structures.
To demonstrate this, the team 3D printed three upright microlenses together, which had a surface roughness of 6.1 nm without the need for any post-processing. What’s more, the devices featured an average refractive index of 1.4585, giving them almost identical characteristics to those of commercial glass optics devices.
With further R&D and an application-specific parameter set, the team concluded that their novel approach could be deployed to create a new generation of ultra-smooth glass components with extensive photonics, life sciences, and biomedical engineering applications.
Advances in nano 3D printing
Nanoscribe is one of the early leaders in an emerging 2PP 3D printing market, that’s seeing companies compete to develop processes of creating increasingly complex microscopic parts.
Nanoscribe introduced its 2PP Quantum X 3D printer in June 2019, which is capable of producing refractive and diffractive micro-optics as small as 200 microns. At the time, the firm’s Co-founder Michael Thiel claimed that the machine offered users “unprecedented design freedom and ease-of-use.”
Similarly, 2PP specialist UpNano debuted its NanoOne 3D printer just last month. The company’s first commercial launch has already secured several orders across both industry and academia, reflecting the technology’s growing research applications.
2PP 3D printing has also found experimental applications, and a team based at the University of Grenoble have attempted to control their additive microstructures using magnetic fields. By embedding microbeads into a millennium falcon-shaped print, the scientists were effectively able to make it ‘fly.’
The researchers’ findings are detailed in their paper titled “Two‐Photon Polymerization of Nanocomposites for the Fabrication of Transparent Fused Silica Glass Microstructures.” The research was co-authored by Frederik Kotz, Alexander S. Quick, Patrick Risch, Tanja Martin, Tobias Hoose, Michael Thiel, Dorothea Helmer and Bastian E. Rapp.
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Featured image shows a side-on view of one of the team’s 3D printed fused silica glass lenses. Photo via Bastian Rapp.
