(4c) Printing 3D Structures with Controlled Chiral Self-Assembly

The emergence of three-dimensional (3D) printing has advanced the fabrication of on-demand architectures for various applications, from functional devices to organs. However, 3D printing is limited to feature size and lacks the nanoscale design of the constituents vital for functional devices. Herein, we combine the "bottom-up" approach with a "top-down" fabrication strategy to program the nanoscale chiral self-assembly of cellulose-based materials in the printed objects. The chiral or helical arrangement, in which layers of nanoparticles/fibers are slightly twisted by a fixed angle relative to the neighboring layers, is known as the origin of the superior fracture resistance of the mineralized chitin in the "smasher-type" mantis shrimp's dactyl club and the vivid metallic colors in beetles. We design our inks based on cellulose nanocrystals and ether variants of cellulose to built-in nanoscale chiral self-assembly with controlled helical pitch length. The flow-induced alignment intrinsic to the printing process is exploited to direct hierarchical chiral self-assembly in the printed constructs. By tuning the ink formulation, its rheological properties, and printing parameters, we have been able to print architectures with uniformly organized built-in chiral nanostructure. Our biomimetic approach will open the path to developing materials with new optical (dynamic color and photonic properties) and mechanical (toughness, strength) properties, naturally emerging from their nanostructure and transferred into the larger scale printed architectures, expanding 3D printing material technologies well beyond what has been conceived and attempted so far, into a new generation of composite and metamaterials and process design.