Bioprinted high cell density liver model with improved hepatic metabolic functions.

In vitro liver tissue models are valuable for studying liver function, understanding liver diseases, and screening candidate drugs for toxicity and efficacy. While three-dimensional (3D) bioprinting shows promise in creating various types of functional tissues, current efforts to engineer a functional liver tissue face challenges in replicating native high cell density (HCD) and maintaining long-term cell viability. HCD is crucial for establishing the cell-cell interactions necessary to mimic the liver's metabolic and detoxification functions. However, HCD bioinks exacerbate light scattering in light-based 3D bioprinting. In this study, we incorporated iodixanol into our bioink formulation to minimize light scattering, enabling the fabrication of hepatic tissue constructs with an HCD of 8 × 107 cells/mL while maintaining high cell viability (∼80 %). The printed dense hepatic tissue constructs showed enhanced cell-cell interactions, as evidenced by increased expression of E-cadherin and ZO-1. Furthermore, these constructs promoted albumin secretion, urea production, and P450 metabolic activity. Additionally, HCD hepatic tissue inactivated the YAP/TAZ pathway via cell-cell interactions, preserving primary hepatocyte functions. Further screening revealed that hepatocytes in the dense model were more sensitive to drug treatments than those in a lower-density hepatic model, highlighting the importance of HCD in recapitulating the physiological drug responses. Overall, our approach represents a significant advancement in liver tissue engineering, providing a promising platform for the development of physiologically relevant in vitro liver models for drug screening and toxicity testing.