The Critical Importance of Viscoelastic Parameters (G′, G′′, tanδ) in the Formulation of Chitosan Hydrogel Bioinks for Additive Manufacturing

The development of bioinks for the additive manufacturing of biomaterials, particularly in 3D bioprinting, is a field that fundamentally depends on materials engineering to accurately mimic the extracellular matrix (ECM) and the properties of native tissues. This report addresses the critical importance of viscoelastic rheological parameters—namely, the storage modulus (G′), the loss modulus (G′′), and the loss tangent (tanδ)-in the formulation of chitosan hydrogel-based bioinks. Chitosan, a natural modified polymer with high biocompatibility, faces challenges due to its intrinsically weak mechanical properties. The characterization and adjustment of these viscoelastic parameters are key to overcoming this limitation, allowing the bioink to exhibit the shear-thinning behavior necessary for extrusion and, simultaneously, maintain high shape fidelity after deposition. The report details how the balance between elastic and viscous behaviors, characterized as a "weak gel," is the ideal state for a successful extrusion bioprinting process, and describe the fitting in rheological models, such as the 3-element Generalized Maxwell Model and power-law analysis.