Rheology and Printability of Hydroxyapatite/Sodium Alginate Bioinks Added with Bovine or Fish Collagen Peptides

The high biocompatibility and the key role of collagen in bone extracellular matrix make it useful for tissue engineering. However, the high demand, costs, and challenges of extracting good-quality collagen have led to the use of collagen derivatives and search for non-human alternatives. This study investigates fish and bovine collagen peptides (Collf and Collb, respectively) as sustainable sources for 3D-printed bone scaffolds by developing and characterizing peptide-incorporated alginate/hydroxyapatite-based bioinks. The chemical analysis revealed structural similarities between the peptides, while rheological tests showed a slightly higher viscosity of Collf-based inks, which improved shape fidelity during the printing process. Upon oscillating rheological tests, both the Collf and Collb-based ink formulations demonstrated a solid-like behavior at frequencies higher than 0.4 Hz, which is crucial for maintaining the printed structure integrity during extrusion. Although Collb-based inks exhibited better pore printability, Collf-based inks achieved superior resolution and geometry retention. Macro-porous structures printed from both inks showed good accuracy, with minimal shrinkage attributed to hydroxyapatite. Both the produced inks had a high gel fraction and swelling behavior, with Collb-based outperforming Collf-based inks. Finally, both ink formulations resulted to be cytocompatibile with human dermal fibroblasts. These findings position Collf- and Collb-based inks as promising alternatives for bone tissue scaffolds, offering a sustainable balance between performance and structural stability in 3D printing applications.