Esmaeili Mohsen, Norouzi Sepideh, George Kyle, Rezvan Gelareh, Taheri-Qazvini Nader, Sadati Monirosadat
Department of Chemical Engineering, University of South Carolina, Columbia, SC, 29208, USA.
Biomedical Engineering Program, University of South Carolina, Columbia, SC, 29208, USA.
Small. 2023 May;19(19):e2206847. doi: 10.1002/smll.202206847. Epub 2023 Feb 2.
Architected materials with nano/microscale orders can provide superior mechanical properties; however, reproducing such levels of ordering in complex structures has remained challenging. Inspired by Bouligand structures in nature, here, 3D printing of complex geometries with guided long-order radially twisted chiral hierarchy, using cellulose nanocrystals (CNC)-based inks is presented. Detailed rheological measurements, in situ flow analysis, polarized optical microscopy (POM), and director field analysis are employed to evaluate the chiral assembly over the printing process. It is demonstrated that shear flow forces inside the 3D printer's nozzle orient individual CNC particles forming a pseudo-nematic phase that relaxes to uniformly aligned concentric chiral nematic structures after the flow cessation. Acrylamide, a photo-curable monomer, is incorporated to arrest the concentric chiral arrangements within the printed filaments. The time series POM snapshots show that adding the photo-curable monomer at the optimized concentrations does not interfere with chiral self-assemblies and instead increases the chiral relaxation rate. Due to the liquid-like nature of the as-printed inks, optimized Carbopol microgels are used to support printed filaments before photo-polymerization. By paving the path towards developing bio-inspired materials with nanoscale hierarchies in larger-scale printed constructs, this biomimetic approach expands 3D printing materials beyond what has been realized so far.
具有纳米/微米级有序结构的材料可提供卓越的机械性能；然而，在复杂结构中重现这种有序程度仍具有挑战性。受自然界布利冈结构的启发，本文展示了使用基于纤维素纳米晶体（CNC）的油墨对具有引导长程径向扭曲手性层级结构的复杂几何形状进行3D打印。采用详细的流变学测量、原位流动分析、偏光显微镜（POM）和指向矢场分析来评估打印过程中的手性组装。结果表明，3D打印机喷嘴内的剪切流力使单个CNC颗粒取向，形成伪向列相，在流动停止后松弛为均匀排列的同心手性向列结构。引入光固化单体丙烯酰胺以固定打印细丝内的同心手性排列。时间序列POM快照显示，以优化浓度添加光固化单体不会干扰手性自组装，反而会提高手性松弛速率。由于打印油墨具有类似液体的性质，在光聚合之前，使用优化的卡波姆微凝胶来支撑打印细丝。通过为在更大规模的打印结构中开发具有纳米级层级结构的仿生材料铺平道路，这种仿生方法扩展了3D打印材料的范围，超越了目前已实现的水平。
