Figure 2. Microengineered organs-on-chips.

(a) A microfluidic kidney epithelium model composed of a multi-layered microdevice that incorporates stacked layers of PDMS microchannels and a PDMS well separated by a porous polyester membrane. The 3D architecture of this microsystem provides physiologically relevant culture environments for polarized kidney epithelial cells, and enables precise control of fluid flows, selective exposure of the apical and basal sides of the cells to fluid shear, hormones, and chemical gradients, and collection of samples from both sides of the polarized tissue. (b) A microengineered liver-on-a-chip reconstitutes hepatic microarchitecture. The functional unit of this microsystem consists of a central liver cell culture chamber and a surrounding nutrient flow channel separated by microfabricated barrier structures patterned with a set of narrow (2 µm in width) microchannels that mimic the highly permeable endothelial barrier between hepatocytes and the liver sinusoid. This biomimetic device closely approximates transport of nutrients and waste products in the liver sinusoid and provides more favorable environments for the maintenance of primary liver cells in a differentiated state (scale bar, 50 µm). (c) Heterotypic interactions between tumor cells and endothelial cells are studied in a microfluidic device that permits co-culture of these cells in two separate microchannels connected via scaffold channels filled with 3D collagen gels (pink channels in the diagram). This microfluidic system is used to model the tumor microenvironment and gain better understanding of important disease processes such as angiogenesis and cancer cell invasion during cancer progression. Reproduced from [50], [55], [60, 61] with permission.