3D Printable κ-carrageenan-Based Granular Hydrogels Reinforced with Sugar-Mediated Metal Ion Coordination

The ocean covers a much larger surface area than land, where plants have long been used for food and construction. Similarly, the ocean provides abundant bioactive substances that can be extracted from marine organisms like algae. From the latter, κ-carrageenan, a polysaccharide, known for its emulsifying and stabilizing properties, is extracted and commonly used in food and beauty products [1] [2]. Its abundance, resemblance to natural glycosaminoglycans, and biocompatibility have recently made it a promising alternative to animal gelatin for tissue engineering applications. However, its intrinsic thermorheological properties pose challenges for continuous processing methods, such as direct ink writing (DIW)-based 3D printing.<br/>Here, I will introduce a κ-carrageenan-based formulation that can be direct ink written at room temperature. This is achieved by formulating κ-carrageenan as microgels that when jammed have rheological properties ideal for DIW. These microgels can be connected with a covalently crosslinked second network, resulting in double network granular hydrogels (DNGH) after they have been imparted the final shape [3]. The stiffness and strength of the DNGHs can be enhanced even more through the addition of metal ions and glucose. The reinforced κ-carrageenan-based gels reach Young’s moduli up to 0.9 MPa under tension and stiffnesses up to 1.1 MPa under compression. The metal ion/glucose reinforcement increases the work of fracture up to 1.1 MJ*m^-3, 50 times higher than that of unmodified κ-carrageenan DNGHs. We harness the rheological properties of the polysaccharide-based ink to 3D print cm-sized free standing and load-bearing structures at room temperature. Our κ-carrageenan-based granular gels show great potential for implant and tissue engineering and food applications, for instance as encouraging alternative to animal gelatin.<br/><br/>[1] X. Lin, J. Wang, X. Wu, Y. Luo, Y. Wang, and Y. Zhao, “Marine-Derived Hydrogels for Biomedical Applications,” <i>Advanced Functional Materials</i>, vol. 33, no. 6, p. 2211323, 2023, doi: 10.1002/adfm.202211323.<br/>[2] M. Beaumont <i>et al.</i>, “Hydrogel-Forming Algae Polysaccharides: From Seaweed to Biomedical Applications,” <i>Biomacromolecules</i>, vol. 22, no. 3, pp. 1027–1052, Mar. 2021, doi: 10.1021/acs.biomac.0c01406.<br/>[3] M. Hirsch, A. Charlet, and E. Amstad, “3D Printing of Strong and Tough Double Network Granular Hydrogels,” <i>Advanced Functional Materials</i>, vol. 31, no. 5, p. 2005929, 2021, doi: https://doi.org/10.1002/adfm.202005929.