Fabrication of sub-micron pillars on curved surfaces using thermal nanoimprint lithography

Abstract

Studies have shown that pillars of specific dimensions and spatial arrangement can promote osteogenic differentiation of stem cells and kill bacteria that cause infections. Other studies have shown that surface curvature can also serve as a mechanical cue to modulate cell behavior. Therefore, the fabrication of pillars on curved surfaces would allow researchers to investigate the synergistic effect of pillars and curvature on cell behavior. In this project, a process was developed based on thermal nanoimprint lithography (TNL) and dry etching techniques for the fabrication of pillars into curved substrates made of hard materials. To this aim, a fused silica specimen containing sub-micron pillars was used as the master mold in a molding process to replicate the pillars as pits into a hybrid polydimethylsiloxane (PDMS) mold. The dimensions and morphology of the replicated patterns were assessed using a scanning electron microscope (SEM). Thereafter, TNL was employed to imprint the pits of the hybrid PDMS mold on the surface of the desired planar/ curved substrates. Finally, etching processes were employed to transfer the patterns into the bulk of the substrates. The process was first developed on planar fused silica substrates and then, on curved substrates. The interspace of the resultant pillars on the planar substrates was no more than 3% different than the interspace of the original pillars on the master mold. The diameter was also close to the values of the diameter of the original pillars (the maximum difference was 23%). The height of the pillars differed slightly (mo more than 16%) for the specific process conditions that were used. On the curved substrates, the interspace increased by 5% and 10%, and the diameter by 57% and 11%.