Internally-crosslinked alginate dialdehyde/alginate/gelatin-based hydrogels as bioinks for prospective cardiac tissue engineering applications

Cardiovascular diseases represent a global challenge due to heart-limited regenerative capabilities. 3D-bioprinted cell-laden constructs are a promising approach as cardiac patches or in vitro models. However, developing bioinks with optimal mechanical, rheological, and biological properties remains challenging. Although alginate (Alg)- based bioinks have been extensively explored, such hydrogels lack cell adhesion properties and degradability. Additionally, 3D Alg structures are usually obtained by microextrusion bioprinting, exploiting conventional external crosslinking methods, which introduce inhomogeneities and unpredictability in construct formation. This work exploits Alg internal ionic gelation mechanism to obtain homogeneous self-standing multilayered 3D-printed constructs without employing support baths or post-printing crosslinking treatments. Alg was blended with oxidized alginate (ADA) and gelatin (Gel) to achieve degradable and cell-adhesive hydrogels for cardiac tissue engineering. Firstly, ADA/Alg bioink composition was tailored to achieve cardiac tissue-like viscoelastic properties. Then, the amount of Gel in ADA/Alg hydrogels was optimized to support cell adhesion, producing shear thinning inks with tunable viscoelastic properties (storage modulus [G’]: 650–1300 Pa) and degradation profile (40–80% weight loss after 21 days in phosphate-buffered saline [PBS]) by varying Gel concentration. ADA/Alg/Gel hydrogels displayed shear thinning behavior, suitable for 3D bioprinting depending on the ink stabilization time, due to the gradual pH-triggered release of calcium ions over time. Adult human cardiac fibroblast (AHCF) and H9C2-laden ADA/Alg/Gel bioinks were successfully printed, producing scaffolds with high shape fidelity and good cell viability post-printing. Finally, the highest Gel content (25% [w/w]) supported cell adhesion after 24 h of incubation, displaying potential for cardiac tissue modeling. This research presents a comprehensive framework for advancing the design of bioink