Extracellular matrix-mimetic ink for 3D printing and minimally invasive delivery of shape-memory constructs

Direct injection of hydrogels loaded with therapeutics holds great promise for tissue regeneration; however, injectable hydrogels typically fill defect spaces without spatiotemporal control, which is critical for regenerating certain tissues. Conversely, 3D printing enables the fabrication of patterned hydrogel constructs but often requires invasive surgical implantation. Here, we present a novel strategy for the non-invasive delivery of 3D-printed constructs. Specifically, we developed gallic acid-modified hyaluronic acid (HA) that was crosslinked for the first time using potassium iodide (KI) as a catalyst, without the need for an initiator or light exposure. This also enabled protein conjugation with gelatin and collagen to obtain an extracellular matrix (ECM)-mimetic ink for 3D printing. We determined the distinct pKa values of the phenolic hydroxy groups of gallol-modified HA, which were utilized to achieve 3D printing at acidic pH, followed by efficient solution-free covalent crosslinking using ammonia gas to ensure complete crosslinking. This approach enabled efficient printing through fine nozzles (G32) and produced robust structures. The printed scaffolds were subsequently loaded into a larger needle and injected, demonstrating shape-memory properties by retaining their geometry post-injection. Furthermore, the scaffolds supported stem cell coating, where the stemness and differentiation of stem cells could be modulated by hydrogel composition and culture conditions, including chondrogenic differentiation towards cartilage-like constructs using TGF-β3. This strategy offers a versatile platform for developing HA-based hydrogels capable of protein conjugation, 3D printing, cell or biomolecule coating, and minimally invasive implantation while maintaining structural fidelity.