3D-Printable Granular Hydrogel Composed of Hyaluronic Acid-Chitosan Hybrid Polyelectrolyte Complex Microgels

When it comes to 3D printing of hydrogels, optimizing rheological properties is crucial to ensure (i) a smooth flow of the ink through the nozzle during printing and (ii) structural integrity postprinting. Granular hydrogels offer excellent printability due to their intrinsic yield-stress properties; however, they typically lack postprinting integrity in aqueous environments. To address this limitation, a novel approach is proposed to integrate the yield-stress behavior of granular hydrogels with polyelectrolyte complexes, which exhibit tunable mechanical properties and structural integrity in aqueous media. In this approach, hybrid microgels composed of chemically co-cross-linked hyaluronic acid-chitosan polyelectrolytes are prepared in a high-salt medium to shield electrostatic interactions and then jammed to form a printable granular hydrogel. By reducing the salt concentration below the critical threshold for electrostatic association, intra- and interparticle electrostatic interactions are activated, causing both the microgels and the granular hydrogel to shrink. This process yields a hydrogel with tunable stiffness, packing density, and dimensions. Overall, this strategy paves the way for the design of 3D hydrogel constructs with dynamic properties.