Planar and Homeotropic Liquid Crystal Alignment on 3D-Nanoprinted Layers and Microstructures.

Precise control of liquid crystal (LC) alignment is essential for most LC-based applications and is typically achieved using alignment layers that induce molecular orientation through surface topography or chemical interactions. Although two-photon polymerization (2PP)-based direct laser writing (DLW) has previously been explored for fabricating such layers, existing studies have largely focused on flat surfaces designed for patterned planar alignment, where LC orientation is governed by surface topography. Consequently, one of the key advantages of this technique, which is the fabrication of arbitrary three-dimensional geometries with nanoscale precision, has remained largely unexplored for LC alignment. In this work, we investigate 2PP-based DLW as a versatile fabrication platform for engineering LC alignment through the combined use of surface topography, material chemistry, and three-dimensional geometry. We first demonstrate patterned planar-homeotropic alignment on a single substrate by integrating topographical and chemical alignment mechanisms. The alignment concept is then extended beyond flat surfaces to three-dimensional microstructures, including inclined prism-like geometries, capillaries, and fully 3D-printed cells in which both alignment layers and spacers are fabricated in a single process. This approach enables controlled twisted nematic configurations without the need for postassembly substrate alignment. Furthermore, we show that arbitrary 3D-nanoprinted microstructures can be chemically functionalized with conventional alignment agents, providing additional means of tailoring LC orientation. By combining the tunable optical properties of liquid crystals with the ability of 3D nanoprinting to fabricate arbitrary three-dimensional architectures, this approach may enable the future development of microstructures that serve specific functions while simultaneously acting as alignment components.