Bottom-Up Photonic Structuring through Flow-Directed 3D Printing of Liquid Crystalline Cellulose Inks

Hierarchical architectures in natural biomaterials, such as cellulose-, chitin-, or collagen-based helical assemblies, give rise to exceptional mechanical and optical properties. Inspired by these structures, we explore the use of structured materials in extrusion-based 3D printing to enable bottom-up design of macroscale constructs with embedded nanoscale order. This study focuses on photocurable, structurally colored hydroxypropyl cellulose (HPC)-based liquid crystalline inks. Using rheological and rheo-optical characterization, we investigate the structural dynamics under flow and post-flow conditions. Results show that shear rate during printing critically affects the chiral nematic ordering of the ink: low to intermediate shear promotes alignment and vivid structural color, while high shear induces elastic instabilities that disrupt photonic order. Finally, the curing kinetics are optimized to lock in the desired nanostructure, enabling precise control over optical functionality in 3D-printed materials.