3D Printing of dECM Hydrogels for in vitro Cardiac Tissue Modelling

Congenital heart diseases are a leading cause of paediatric morbidity and mortality worldwide, and ventricular septal defects (VSDs) are among the most common, accounting for 20–30% of all cases. The "Swiss Cheese" VSD, defined by four or more muscular defects across the interventricular septum, remains the most challenging subtype, with outcomes still marked by high rates of residual shunting, ventricular dysfunction and complete heart block. To address these challenges, this thesis aims to develop and characterise a printable hydrogel system as a first step towards the biofabrication of in vitro models of complex cardiac defects. Decellularized extracellular matrix (dECM)-based hydrogels were selected as the scaffold material owing to their capacity to recreate tissue-specific microenvironments. Cardiac dECM was obtained by decellularization and pepsin solubilisation of native porcine myocardium. Different washing regimes were compared, and cellular clearance was assessed histologically, while collagen and sulphated glycosaminoglycan contents were quantified biochemically to evaluate retention of the structural components of the matrix. The solubilised dECM was reconstituted into thermally gelled precursors and photocrosslinked with Ac-β-CD and LAP, the system intended for the fabrication of the final constructs, while a concentration series of the Ru/SPS system was characterised in parallel as a reference. The resulting hydrogels were assessed by swelling and degradation studies, uniaxial and cyclic compression testing and oscillatory rheology, and their cytocompatibility was evaluated with normal human dermal fibroblasts seeded on the surface and encapsulated within the gels, in order to identify the concentration range compatible with cell-laden processing. The optimised formulations were then processed by extrusion-based 3D printing. Shape fidelity and printing parameters were first assessed on grid constructs, after which constructs reproducing the geometry of a mono-defect septum were fabricated by direct deposition and by embedded printing in a support bath, comparing the support required by the two crosslinking systems. Overall, this work establishes a comprehensive material and processing framework for the biofabrication of structurally defined cardiac tissue constructs. The developed platform provides a foundation for the future development of physiologically relevant in vitro models of congenital cardiac defects and for the investigation into biomaterial-assisted defect closure and cardiac tissue regeneration.