Glycosaminoglycan-mimetic Gelatin-Methacrylate/κ-Carrageenan bioink: A synergistic approach for enhanced printability, osteogenesis, and apatite mineralization in bone constructs

Engineering bioinks that integrate printability, mechanical stability, and osteoconductivity remains a significant challenge for generating mineralizing bone tissue models. While numerous gelatin methacrylate (GelMA)-based bioinks have been developed, comprehensive demonstration of cell-mediated, apatite-like mineral formation within bioprinted constructs remains limited. Here, we present a synergistic gelatin-methacrylate/κ-carrageenan (GelMA/κCGN) composite hydrogel that couples printability with mineralization potential. Incorporation of κCGN increases pre-gel viscoelasticity, improves shear-thinning, and maintains rapid photocrosslinking of GelMA, enabling uniform filament extrusion, multilayer stacking, and high shape fidelity. The composite hydrogels display reinforced compressive properties and improved structural stability compared to GelMA. Human mesenchymal stem cells (hMSCs) embedded in these constructs remain viable and exhibit a strong osteogenic programme. Histological staining demonstrates abundant collagen matrix deposition, accompanied by calcium accumulation. Localized SEM-EDS compositional analysis of discrete domains reveals calcium‑phosphorus co-localization and Ca/P ratios consistent with early-stage, calcium-deficient apatite-like phases, supporting cell-mediated matrix mineralization within the 3D hydrogel microenvironment. Bioprinted constructs retain these characteristics, supporting homogeneous cell distribution, sustained osteogenic differentiation, and robust matrix deposition. Collectively, these findings demonstrate that engineered GelMA/κCGN composite hydrogels, integrating optimized rheological performance with biologically driven, apatite-like mineralization, offer a promising platform for bone tissue engineering and advanced in vitro models.