Direct Cryo-Writing by 3D Printing of Aligned Cellulose Nanocrystal-based Aerogels Inspired by the Plant Cell Wal

Direct Cryo Writing (DCW) is an extrusion 3D printing technology that combines traditional directional freeze casting and the spatial fidelity of 3D printing. Bio-based aerogels inspired by the plant cell wall were printed on a cold stage which is monitored by a thermal camera, resulted in directional growth of the ice crystals throughout the printing process. DCW overcomes the need of fixation by chemical crosslinking or photo-polymerization, due to rapid conversion of the fluid ink into a frozen solid. By controlling the front speed of ice crystals growth, 3D objects can be printed, having internally aligned structures. Following freez-drying, the resulting object is converted into an aerogel.

The DCW method is demonstrated using water-based bio-inks composed of cellulose nanocrystals (CNCs) and xyloglucan (XG), both of which are important components of the plant cell wall. Detailed morphological examination coupled with studies of ice growth and crystallite formation indicate a change in the pore structure of the aerogels from organized and tubular to disordered and flakey with increasing XG content. The XG-CNC aerogel structures are related to the plant cell wall structure of various wood species, and may be useful as wood mimics for model studies and more importantly, to create wood-like structures by Additive Manufacturing (AM) technologies using only renewable wood-based materials.