Because of its transparency as well as its stability in contact with heat or chemicals, glass is relevant for many high-tech applications. However, conventional processes for shaping glass are often tedious, energy-intensive and quickly reach their limits for small and complicated components. The Freiburg materials scientists Dr. Frederik Kotz-Helmer and Prof. Dr. Bastian E. Rapp, in cooperation with the University of California at Berkeley/USA, have developed a novel process that can be used to produce very small components from transparent glass quickly and precisely using micro 3D printing. Possible applications include components for sensors and microscopes, but also for lab-on-a-chip systems. The researchers were able to publish their results in the current issue of the renowned journal Science.
Glass powder in plastic binder
The new technology is based on so-called glassomer materials, which Kotz-Helmer and Rapp developed at the Institute of Microsystems Engineering (IMTEK) at the University of Freiburg.
“Glassomer materials consist of glass powder in a special plastic binder. This allows glass to be processed like plastic. In the end, the components consist of one hundred percent highly transparent quartz glass.”
- Dr. Frederik Kotz-Helmer
Component created in a single step
The Freiburg scientists have now combined Glassomer materials with a new 3D printing process developed by a research team led by Prof. Dr. Hayden Taylor from the University of California. Conventional 3D printers print their objects layer by layer — but in the new process, called Computed Axial Lithography (CAL), the component is created in a single step: A vessel containing liquid, light-sensitive material is exposed to two-dimensional light images of the object to be printed from many different angles. Where the images overlap and the amount of light absorbed thus locally exceeds a certain threshold, the material hardens abruptly — within a few minutes, the component is formed. The excess, still liquid material can be washed off.
Structures with the thickness of a hair
“The process also works in principle with these materials,” says Kotz-Helmer. For this purpose, the Freiburg scientists* developed a material made of glass powder and plastic that is both highly translucent and hardens quickly at a suitable threshold. “The devil was in the chemical details here,” says the materials scientist. Previously, moreover, the process had only been suitable for relatively coarse structures.
By combining the materials science expertise at the University of Freiburg and the project partner Glassomer GmbH — a Freiburg spin-off — as well as the further development of the system technology at the University of California, it has now been possible to combine and improve these technologies, says Kotz-Helmer: “For the first time, we were able to print glass with structures in the range of 50 micrometers in just a few minutes, which corresponds roughly to the thickness of a hair. In addition, the surfaces of the components are smoother than with conventional 3D printing processes.”
Glass as a substitute for vulnerable plastic
Kotz-Helmer sees potential applications for the innovative manufacturing process, for example, in micro-optical components of sensors, virtual reality headsets and modern microscopes: “The ability to produce such components at high speed and with great geometric freedom will enable new functions and more cost-effective products in the future.”
Microscopic fluid channels are also needed for so-called lab-on-a-chip systems for research and medical diagnostics. Until now, these have mostly been made of plastics, but they often cannot withstand high temperatures and aggressive chemicals. Thanks to the new process technology, complex channel systems can now be manufactured in glass, says Kotz-Helmer: “Thanks to the thermal and chemical stability of glass, many new fields of application are opening up, especially in the area of chemical on-a-chip synthesis.”
