Iohexol as a Refractive Index Tuning Agent for Bioinks in High Cell Density Bioprinting

This study introduces an iohexol-based refractive-index-matching bioink for digital light processing (DLP) bioprinting at high cell density (HCD). By tuning the optical properties of a GelMA hydrogel with Iohexol (IHX), the authors minimized light scattering during polymerization and enabled high-fidelity fabrication of perfusable micro- and milli-scale tissue constructs. The IHX-bioink preserved excellent biocompatibility for epithelial, endothelial, parenchymal, and stem cells, and supported lumen formation with HCD > 50 million cells mL⁻¹. This refractive-index-tuned strategy reduced overpolymerization artifacts and produced tubular constructs with lumen diameters as small as 400 µm and lengths up to 9 mm, demonstrating record-level printing resolution at HCD while maintaining cellular viability and structural integrity.