Support-Enabled 3D Printing of Complex Anisotropic Hydrogel Structures Using Cellulose-Based Inks: Pathways Toward...

Three-dimensional (3D) printing of hydrogels has enabled new directions in biomedical engineering, soft material design, and biofabrication. However, unsupported hydrogel inks often collapse under their own weight or deform during printing, limiting achievable geometries. Herein, we present a reproducible, standardized support system combining a nanofibrillated cellulose/sodium alginate (NFC/ALG) structural ink with a cellulose-based sacrificial support ink composed of NFC, hydroxyethyl cellulose (HEC), and CaCl₂. The process operates in open air, in contrast to immersion-bath methods such as FRESH, and uses a dissolvable support that locally stabilizes and initiates cross-linking of deposited filaments without submersion. Detailed protocols are provided for ink preparation, cartridge loading, direct ink writing (DIW) parameters, postprinting cross-linking, and support dissolution. Quantitative validation using tubular models shows that unsupported tubes collapse before 50 mm height, whereas supported tubes remain upright and stable. Surface fidelity is substantially improved by reducing layer height from 840 to 420 μm, yielding watertight prints. Demonstrations of complex geometries, including an anatomical aorta, DNA double helix, and the benchmark 3D Benchy model, confirm the method's capability. Support dissolution in 30 mM CaCl₂ occurs over approximately 3 days, ensuring stability during cross-linking and handling. Compared with other sacrificial strategies, this approach is inexpensive, cellulose-based, and relies on mild ionic cross-linking compatible with future cell-laden systems. This work provides a robust and accessible hydrogel engineering protocol, supporting stable and high-fidelity DIW of complex anisotropic structures.