The technology of AM has been developing for more than 30 years, and its utilization in our era covers even house construction at the final, high-quality level. In recent years, 3D printing devices have become cheaper, more reliable, and easier to use, leading to rapid application development in various fields. Nowadays, additive manufacturing (AM) technology is verified in many production processes as a rapid prototyping tool, except for the production of glass 3D structures, in which processing remains a challenge.
The primary aim of the work was to introduce a new sustainable route for upcycling pharmaceutical glasses in a borosilicate system and to fabricate novel transparent and porous 3D glass structures. In the first step, glass precursor with particle size less than 80 μm was prepared from pharmaceutical glass waste by milling. The powdered glass was fed into an oxygen-methane (O₂/CH₄) torch (flame synthesis process), and solid glass microspheres (SGMs) were prepared. The spherical shape enabled the preparation of a high solid content suspension, up to 70 wt% of the SGMs in a photocurable resin.
The second step was the fabrication of various 3D structures by stereolithography (SLA) 3D printer (Original Prusa SL-1, Prusa Research a.s., Prague, Czech Republic) operating in the visible light range (405 nm). After burn-out of the organic binder and viscous flow sintering in the temperature range of 750 -1200°C with different heating and holding regimes, various scaffolds (porous and/or transparent) have been successfully prepared.

Acknowledgement
This paper is a part of the dissemination activities of the project FunGlass. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 739566. The authors also gratefully acknowledge the financial support from the Slovak Grant Agency of the Ministry of Education, Science, Research and Sport, VEGA 1/0456/20.