Figure 4.

Schematic representation of techniques used to vascularize 3D OoC models. These techniques can be divided into soft-lithography and 3D patterning approaches. (a) Membrane-based soft lithography technique in which a porous membrane is sandwiched between two microfluidic layers. (b) ECM-based soft lithography in which one or more channels are filled with ECM, embedded between the parenchymal and vascular channels. (c) Templating approaches in which a matrix is cast around the template. The template is subsequently removed, generating hollow channels, which can be seeded and perfused. (d) Layer-by-layer approach consisting of assembled modular layers. (e) Three-dimensional printing (bioprinting) in which vascular and cell inks are used to generate a 3D tissue with embedded, perfusable vascular channels.