OOC and tumor modeling with multi-material bioprinting. (A) Schematic illustration of the 3D bioprinting technology for the OOC applications. (B) Digital image showing a bioprinted liver chip. (C) Various configurations of cells and biomaterials within the printed chips. Reproduced under the terms of the CC-BY Creative Commons Attribution 3.0 International license (https://creativecommons.org/licenses/by/3.0).[250] Copyright 2016, Royal Society of Chemistry. (D) Schematics showing precisely controlled multiple-cell patterning in microfluidic chips by inkjet printing and the detection of drug metabolism and diffusion. Reproduced with permission.[252]. Copyright 2016, Royal Society of Chemistry. (E) Multi-vat-photopolymerization bioprinting of hydrogel-based hepatic construct. (F) Gene expression profiles and albumin and urea secretion levels of HPCs from 2D, 3D single-cellular, and 3D multi-cellular cell cultures. Reproduced with permission.[51]. Copyright 2016, The Authors, published by National Academy of Sciences. (G) A 3D-bioprinted in vitro tumor model mimicking metastatic dissemination. (H) Plots and micrographs of the population of disseminated A549 lung cancer cells detected in the collection chamber versus time. Reproduced with permission.[268] Copyright 2019, Wiley-VCH.