Iohexol as a refractive index tuning agent for bioinks in high cell density bioprinting

Light-based 3D bioprinting has emerged as a transformative technology for fabrication of biomimetic tissues and artificial organs. High cell density (HCD) bioprinting aims to recapitulate the cellular density and interactions in native tissue, but faces significant challenges in achieving both high resolution and structural fidelity due to light scattering during the photopolymerization process. Refractive index (RI) tuning of the bioink mitigates light scattering to improve printing fidelity. In this study, we developed an iohexol (IHX)-based bioink for digital light processing (DLP) bioprinting. IHX effectively tuned the RI of the bioink to match cellular components to reduce light scattering while still maintaining printability. The bioink demonstrated excellent biocompatibility across multiple cell types, including epithelial, endothelial, parenchymal, and stem cells, while simultaneously supporting post-printing cellular viability, reorganization, and functionality. Using IHX-bioink, we fabricated tubular constructs with lumen diameters ranging from 400 μm to 1.1 mm and utilized strategies to minimize overpolymerization and ensure lumen fidelity. Our results underscore IHX-bioink as a promising biomaterial for scalable, RI-matching 3D bioprinting, enabling the creation of perfusable, HCD constructs for various applications in tissue engineering and regenerative medicine.