This is the world’s smallest 3D-printed wineglass, Swedish scientists claim

The world’s smallest 3D-printed wineglass (left) and an optical resonator for fiber optic telecommunication
Enlarge / The world’s smallest 3D-printed wineglass in silica glass (left) and an optical resonator for fiber optic telecommunication, photographed with scanning electron microscopy. The glass rim is less than the width of one human hair.

KTH Royal Institute of Technology

A team of Swedish researchers has developed a new 3D-printing method for silica glasses that simplifies an energy-intensive, complex process. As a proof of concept, they 3D-printed the world’s smallest wineglass (made of actual glass) with a rim smaller than the width of one human hair, as well as an optical resonator for fiber optic telecommunications systems—one of several potential applications for 3D-printed silica glass components. In a recent article in Nature Communications, they described their new technique.

“The backbone of the Internet is based on optical fibers made of glass,” said co-author Kristinn Gylfason of the KTH Royal Institute of Technology in Stockholm. In these systems, filters and couplers of all types are required. Our technique can 3D print them. This opens many new possibilities.”

According to the authors of the study, silica glass (also known as amorphous silicone dioxide) remains incredibly difficult to 3D print, especially at the microscale. Several methods are being used to overcome this challenge, such as stereolithography and direct ink writing. Even then, they have only been successful in achieving feature sizes that are on the order tens or hundreds of micrometers. However, one study published in 2021 showed nanoscale resolution.

All of these processes use silica-nanoparticles in different organic mixtures. The printed structures, therefore, are composites containing many organic materials. They lack the desirable properties of silica glasses (i.e. chemical and thermal stability, hardness, transparency at a range of wavelengths). It requires an extra sintering step at high temperatures of around 1,200° Celsius (2,192° F) for several hours to remove the organic residues and achieve those properties. The energy-intensive additional step severely limits possible applications because only substrates that can tolerate such high temperatures are allowed to be used. Some approaches require 3D printed structures to be assembled into a finished form. This is difficult at the micrometer level.

Gylfason created a 3D printing technique that uses silica to print glass. et all. Hydrogen silsesquioxane, an inorganic substance similar to silica, can be patterned using electron beams and ion lasers. The method is able to achieve a high level of precision because it doesn’t rely on organic molecules as photoinitiators, binders or other materials that remain on the surface like stereolithography. The method relies upon the direct crosslinking of inorganic HSQ.

Three steps make up the main process. They first drop-cast the HSQ in organic solvents onto a substrate. After the HSQ dries they trace the 3D shape with a laser beam focused at sub-picoseconds. The HSQ that has not been exposed is then dissolved using a potassium hydroxide. Raman spectroscopy revealed all the features of silica in the microstructures.

But there were also traces remaining hydrogen and carbon. For applications requiring a more pure silica glass, the residual organics can be removed by annealing the structures at 900° Celsius (1,652° F)—an extra step, granted, but at a much lower temperature than the usual extra sintering step. The spectrum of the structures then matched a commercially available fused silica substrate. Although annealing 3D microstructures may cause them shrink or distort the authors found the maximum shrinkage of their silica glasses structures to be around 6 percent. This compares to between 16 and 56 percent in the case of glass objects made by stereolithography and using direct ink.

They also created a proof-of concept tiny wine glass, an optical resonator and a KTH logo. The authors believe their method can be used to create customized lenses for micro-robots and medical devices. Coating 3D printed microstructures in nanodiamonds (or ferrous nanoparticles) could allow for further customization of properties, such as hybrid quantum photonics incorporation or magnetically removing motion control.

“The concerns when integrating 3D printing methods are usually different for different applications,” said co-author Po-Han Huang, a graduate student at KTH. “Even though optimization of our method is still required for different applications, we believe our method presents an important and necessary breakthrough for 3D glass printing to be used in practical scenarios.”

Nature Communications, 2023. 10.1038/s41467-023-38996-3  (About DOIs).