3D Printable κ-Carrageenan-Based Granular Hydrogels

κ-carrageenan, an algae-extracted polysaccharide known for its emulsifying properties, is widely used in food and beauty products. Because of its abundance in nature, similarity to natural glycosaminoglycans, and biocompatibility, it is a promising alternative to animal gelatin for tissue engineering. Key to the more widespread use of κ-carrageenan for biomedical applications is its processability, which is hampered by its temperature-dependent rheological properties. Here, a κ-carrageenan-based ink is introduced that can be 3D printed at room temperature through direct ink writing (DIW). This is achieved by formulating κ-carrageenan as microgels that are covalently crosslinked through a second network, resulting in double network granular hydrogels (DNGHs). These DNGHs can be stiffened to reach stiffnesses up to 0.9 MPa under tension and 1.1 MPa under compression through the addition of metal ions and glucose. The metal/glucose reinforcement also increases the work of fracture up to 1.1 MJ m⁻³, exceeding that of unmodified κ-carrageenan DNGHs 50-fold. The potential of the ink by room temperature 3D printing cm-sized free-standing load-bearing structures is demonstrated. This ink is envisaged to be a well-suited algae-derived alternative for the animal-based gelatin for tissue engineering and in food applications for example as soft confectionery products.