Hydrogel Viscoelasticity: Tissue Mechanics, Modulation Strategies, and Bioprinting

Three-dimensional (3D) bioprinting enables the fabrication of complex tissue constructs with precise spatial organization of cells and biomaterials. Hydrogels are widely used as bioinks due to their biocompatibility, high water content, porosity, and tunable mechanical properties. However, many conventional, permanently crosslinked hydrogels exhibit limited or poorly tunable time-dependent mechanical responses compared with native tissues, making it difficult to simultaneously satisfy printability, post-printing stability, and biological requirements. This review examines the viscoelastic mechanisms of natural tissues and key viscoelastic parameters across major tissue types. It also summarizes recent strategies for engineering hydrogel viscoelasticity through polymer composition, crosslinking networks, and microstructure design. Furthermore, we discuss how these strategies meet the requirements of force-driven, light-driven, and volumetric bioprinting. These developments provide a practical framework for designing next-generation viscoelastic bioinks and advancing functional tissue engineering.