Processing and Properties of Chitosan Inks for 3D Printing of Hydrogel Microstructures

The ability to precisely control the properties of natural polymers and fabricate three-dimensional (3D) structures is critical for biomedical applications. In this work, we report the printing of complex 3D structures made of soft polysaccharide (chitosan) inks directly in air and at room temperature. We perform a comprehensive characterization of the 3D printing process by analyzing the effect of ink properties (i.e., rheological properties and solvent evaporation) and process-related printing parameters (i.e., nozzle diameter, robot velocity, and applied pressure). The effects of the neutralization step on the hydrogel formation and their mechanical properties are also investigated. Solvent evaporation tests show that the chitosan ink prepared using an acidic mixture contains residual acids after printing, helping reducing shrink-induced shape deformation. A processing map presents the appropriate ranges of process-related parameters for different structures including filaments, 30-layer scaffolds, starfish, leaf, and spider shapes, showing the versatility of the fabrication approaches. After neutralization, 3D scaffolds still maintain their shape while neutralized filaments show high tensile properties such as a maximum tensile strength of ∼97 MPa in the dry state and high strain at break ∼360% in the wet state. Our fabrication approach provides guidelines to optimize the design and fabrication of aqueous-based inks and opens a new door for fabricating complex structures from natural polymers and achieving tunable material properties for biomedical applications such as tissue engineering and drug delivery.