(a) Micro cell culture analog (μCCA) device containing fat, lung, liver, and other tissue chambers. Reprinted with permission from Viravaidya et al., Biotechnol. Prog. 20, 316 (2004). Copyright 2004 John Wiley and Sons. (b) Microfluidic chip for zebrafish embryo with a concentration gradient generator. Reprinted with permission from Biomicrofluidics 5, 1 (2011). Copyright 2011 AIP Publishing LLC. (c) 3D Hepatox chip design with a concentration gradient generator. Reprinted with permission from Toh et al., Lab Chip 9, 2026 (2009). Copyright 2009 The Royal Society of Chemistry.