Rheological Properties and Printability of Alginate Hydrogel Inks for Extrusion‐Based 3D Printing

Abstract

Extrusion‐based three‐dimensional (3D) printing has emerged as a powerful fabrication strategy in tissue engineering. However, achieving reliable printability and structural stability in hydrogel‐based systems remains a persistent challenge. Alginate‐based hydrogels are among the most widely investigated biomaterial inks for this purpose, due to their biocompatibility, biodegradability, and capacity for ionic crosslinking. This preliminary study investigated the influence of calcium chloride (CaCl 2 ) concentration on the rheological behavior, extrudability, and scaffold geometric fidelity of alginate hydrogel inks for extrusion‐based 3D printing. Formulations were prepared at three CaCl 2 concentrations (2.73, 3.33, and 3.91 mg/mL) and characterized by oscillatory rheology to determine storage modulus ( G ′), loss modulus ( G ″), yield stress, and complex viscosity. Gelation behavior was evaluated through inversion assays, and printability was assessed via extrusion tests, filament spreadability analysis, and scaffold geometric fidelity evaluation across multiple printed geometries. Among the formulations evaluated, the intermediate CaCl 2 concentration (3.33 mg/mL) yielded the most favorable rheological profile, exhibiting G ′ >  G ″ in the small‐amplitude oscillatory shear region and a yield stress compatible with continuous filament extrusion. Scaffold fidelity assessment revealed persistent structural limitations: including rounded pores, pore‐size variation, and partial layer collapse indicating that printability was improved relative to the other formulations but not fully resolved at this crosslinking level. These findings establish a rheological‐to‐printability framework for CaCl 2 ‐crosslinked alginate inks, identifying yield stress and G ′ dominance in the SAOS regime as predictive criteria for extrusion‐based printability, and provide a reproducible technical foundation for systematic formula optimization prior to biological validation and tissue engineering application.