Current 3D-printing techniques for fabricating glass involve time-consuming processes that require high temperatures and considerable resources to complete. In a new approach, a research team at the Georgia Institute of Technology (Georgia Tech) used deep ultraviolet (DUV) light, instead of extremely high temperatures, to 3D-print glass microstructures. The micron-size, silica glass structures resulting from the team’s printing technique could be used in optics, microfluidics, medical devices, and other applications. Researchers used this raw material to create 3D-printed glass structures no bigger than the width of a human hair. The researchers employed a light-sensitive resin based on a widely used soft polymer called PDMS (sample at left). The sample on the right is glass created using DUV light to convert the the photoresin to hardened, inorganic glass. Courtesy of Candler Hobbs. The researchers used a photosensitive polydimethylsiloxane (PDMS) resin as the ink for their 3D structures. They shaped the PDMS resin into microstructures using two-photon polymerization (2PP), a high-precision 3D-printing technique. They converted the 2PP-printed PDMS microstructures into silica glass using a DUV lamp in an ozone environment. The team confirmed the conversion of the PDMS structures into silica glass through a series of chemical characterization techniques. The printed silica glass was found to be highly transparent with a smooth surface comparable to commercial fused silica glass. The maximum processing temperature used to print the glass was around 220 °C, and the process took less than 5 hours. The researchers fabricated various complex 3D glass microstructures using their technique, including a proof-of-concept, 150- × 150-μm, silica glass lens that could be used for medical devices such as endoscopes. They also created a 3D glass microfluidic channel with low surface roughness and a diameter of around 30 μm. Glass chips for microfluidics could offer advantages over chips made of polymer materials, the researchers said, because glass would be resistant to corrosion from chemicals or body fluids. Ph.D. student Mingzhe Li (left) and postdoctoral scholar Liang Yue led development of a process creating 3D-printed glass microstructures using light-sensitive resin based on a widely used soft polymer called PDMS. Courtesy of Candler Hobbs. The low-temperature, 3D-printing technique also could be used to fabricate microelectronics with glass structures, according to researcher Mingzhe Li. “We can print in situ, directly into microelectronics,” he said. “Semiconductor materials used in microelectronics cannot withstand very high temperatures. If we want to print directly on a board, we have to do it at a low temperature, and 200 °C can definitely do this job.” Existing methods for 3D-printing glass can take more than 12 hours, or even days, to complete, and require large amounts of energy, with temperatures exceeding 1100 °C. The new technique, which is the first photochemistry-based approach to fabricating 3D silica glass microstructures using DUV-ozone treatment, could offer numerous advantages over the current methods. With the new technique, the conversion to transparent silica glass is performed at moderate temperatures of 220 °C, much lower than conventional sintering temperatures. The conversion process is fast and takes less than 5 hours to complete for microscale structures. Unlike conventional approaches that use an intentionally decelerated heat treatment protocol, the Georgia Tech team’s approach does not require additional shrinkage-controlling steps to keep the microstructure intact during conversion. A 3D-printed, glass microfluidic channel, shown hollow and filled with liquid. Courtesy of the Georgia Institute of Technology. This fast, low-temperature process for printing silica microstructures is energy-efficient. Also, the photoresin used for the technique is based on a widely used polymer and does not contain any silica nanoparticles, which protects the process from the dispersion-, viscosity-, and optical-related issues associated with conventional methods. The technique does not require extra polymer material to be added, which also saves resources. Currently, the low-temperature 3D-printing approach can be used to create glass structures that are 200 to 300 μm in size. The team has begun work on scaling up the glass structures so they can be printed at the millimeter scale. “This is one of the exploratory examples showing that it is possible to fabricate ceramics at mild conditions, because silica is a kind of ceramic,” said professor H. Jerry Qi, who led the research. “It is a very challenging problem.” Qi said that advancements in 3D printing technology and an interest in ceramics pushed the researchers to think about new approaches to their fabrication. “We have a team that includes people from chemistry and materials science, engaged in a data-driven approach to push the boundary and see if we can produce more ceramics with this approach,” Qi said. “We really want to do the cutting-edge — things nobody has done before in the space of low-temperature conversion of polymers to ceramics within additive manufacturing.” The research was published in Science Advances (www.science.org/doi/10.1126/sciadv.adi2958).
