Geometric determinants of sinterless, low-temperature-processed 3D-nanoprinted glass.

Glass materials are essential for microsystems applications in fields ranging from optics and photonics to microfluidics and biomedicine, which has driven growing interest in additive manufacturing-or "three-dimensional (3D) printing"-to enable glass micro/nanotechnologies. Notably, the recent discovery that 3D-nanostructured fused silica glass components can be produced via "two-photon direct laser writing (DLW)" of hybrid organic-inorganic polyhedral oligomeric silsesquioxanes (POSS)-based resins holds unique promise, particularly due to the advantages of sinterless, low-temperature (i.e., 650 °C) post-processing. At present, however, it remains unknown how implementing such methodologies to 3D print larger glass microstructures (e.g., with ≥25-µm-thick features) affects critical material properties, such as the ultimate optical and mechanical characteristics. To address this knowledge gap, here we investigate DLW-printed feature size as a key determinant of the optical and mechanical properties of POSS-based fused silica glass microstructures. Experiments for DLW-printed microlenses reveal comparable optical transparency for initial thicknesses up to 40 µm, but increasing to 60 µm significantly reduces light transmission from 87.87 ± 1.18% to 63.57 ± 5.10%. Similarly, compressive loading studies for hollow glass cylindrical microstructures show consistent behavior for initial DLW-printed wall thicknesses up to 30 µm, but significant performance degradation beyond-e.g., Young's modulus decreasing from 251.6 ± 71.9 to 99.7 ± 63.9 MPa for the 30 to 40 µm cases, respectively. As an exemplar with relevance to biomedical microinjection applications, we harness this new knowledge to DLW-print POSS-based glass microneedle arrays (MNAs) and demonstrate their ability to penetrate into a medium not possible using standard polymer MNAs. In combination, this study establishes critical optical and mechanical benchmarks that underlie the utility of DLW 3D-printed POSS-based fused silica glass microstructures in emerging applications.