Bioprinting Vascularized Tissue Constructs

Abstract

Tissue engineering constructs thicker than 200 um require embedded vascular networks for oxygen and nutrient delivery, yet creating perfusable, hierarchical vasculature within bioprinted tissues remains the central unsolved challenge in the field. Without functional vascularisation, bioprinted constructs suffer core necrosis within 24-48 hours, limiting clinical translation to thin avascular tissues (cartilage, skin). This study developed and evaluated five bioprinting strategies for vascularised tissue fabrication -- sacrificial ink casting (Pluronic F127), coaxial core-shell printing, embedded printing in granular gel (FRESH), digital light processing (DLP) with photoablation, and a proposed multi-scale vascular bioprinting platform (MSVB) combining sacrificial macro-channel printing (>500 um), coaxial micro-vessel printing (100-500 um), and VEGF-loaded hydrogel microbeads for capillary sprouting (<100 um) -- for generating perfusable cardiac tissue patches (20 x 15 x 4 mm) from hiPSC-derived cardiomyocytes and endothelial cells. MSVB achieved the highest vascular density (142 +- 18 vessels/mm2 at 14 days), deepest viable tissue thickness (3.8 +- 0.2 mm vs 0.4 +- 0.1 mm for non-vascularised controls; p < 0.001), and best cardiac function (conduction velocity 18.4 +- 2.8 cm/s, contractile force 8.6 +- 1.4 mN/mm2). Perfusion through the hierarchical network maintained >90% cell viability throughout the 4 mm construct thickness at 14 days, compared to <20% viability beyond 200 um depth in non-perfused controls. Upon subcutaneous implantation in nude rats, MSVB constructs anastomosed with host vasculature within 5 days (confirmed by perfusion of injected FITC-dextran) and maintained viable, beating cardiac tissue at 28 days. These results establish multi-scale vascular bioprinting as a viable strategy for engineering clinically sized, functional cardiac tissue.