Fig. 1.

Modular construct design and fabrication. (a) Collagen with or without HepG2 cells is drawn into the lumen of a sterilized PE tube and incubated at 37°C for 30 min to allow gelation. The PE tubing containing the gel is fed through an automated tubing cutter and sectioned into 2-mm lengths, which are collected in a sterile centrifuge tube. Cell culture medium is added, and the tube is vortexed to release the collagen–cell modules from the lumen of the sectioned PE pieces. PE sections float, whereas collagen modules sink. The collagen cylinders with encapsulated HepG2 cells are subsequently seeded with HUVEC. Once complete coverage of the collagen surface with HUVEC has been achieved (typically 2–3 days), the cell-seeded cylinders are assembled into a larger structure (here a tube) to form the construct. Assembly of the modules creates a network of interconnected channels that permeate the construct. Medium or blood is perfused through this network to supply nutrients to the cells within the construct. (b) Light micrograph of a collagen–HepG2 module before HUVEC seeding. (c) Confocal microscopy image of vascular endothelial (VE)-cadherin-stained module indicating a confluent layer of HUVEC over the module surface at 7 days after seeding. (d) Modular construct in the flow circuit being perfused with PBS. (e) Confocal microscope image of a collagen–HepG2–HUVEC module retrieved from a construct after 7 days of medium perfusion with HepG2 cells labeled with Vybrant CFDA SE.