Abstract
The fabrication of large-scale, functional tissue constructs remains one of the most significant challenges in regenerative medicine due to the inherent diffusion limits of oxygen and nutrients, which typically restrict viable tissue thickness to approximately 200 micrometers. This study presents a comprehensive approach to overcoming these limitations through multimaterial bioprinting, integrating hierarchical vascular networks within centimeter-scale tissue analogs. Utilizing a custom-engineered quad-extrusion system, we successfully deposited a combination of cell-laden gelatin methacryloyl (GelMA), sacrificial Pluronic F-127, and structural polycaprolactone (PCL) to create mechanically robust constructs with internal lumen structures. Our methodology focused on the optimization of bioink rheology and crosslinking kinetics to ensure structural fidelity while maintaining high cell viability. Results indicated that the integration of a branched vascular network significantly enhanced the metabolic activity and survival of human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) within the construct core compared to non-vascularized controls. Over a 28-day culture period, we observed the formation of a confluent endothelial lining within the printed channels, confirmed by CD31 expression and dextran perfusion assays. The mechanical properties of the multimaterial constructs were tailored to mimic native soft tissues, providing a stable environment for cellular maturation. These findings demonstrate that multimaterial bioprinting can effectively bridge the gap between bench-top micro-tissues and clinically relevant organ-scale constructs, offering a viable pathway for the engineering of complex organs such as the liver or heart.