2.6. Fabrication of Liver-on-a-chip
The dual extruder Flashforge 3D printer was used to fabricate the PLA-based LOC platform. The chip platform was designed using Solidworks (Dassault) (Figure 1). To print the LOC platform, PLA was loaded into the thermosensitive extruder and printing was performed at a nozzle temperature of 220°C. A core/shell liver 3D in-vitro model was developed using a pneumatic in-house-developed extrusion bioprinter. A polymeric formulation of collagen–alginate composite bioink was used for the encapsulation of HepG2 cells. The composite bioink was prepared by uniformly mixing equal volumetric ratios of collagen (15 mg/mL) and alginate (40 mg/mL). Cell printing of the core/shell liver in-vitro model was performed using a coaxial nozzle connected to two syringes of the bioprinter. HepG2 (2 × 106 cells/mL)-encapsulated collagen–alginate bioink was loaded in the syringe connected to the outer nozzle, whereas the syringe containing 3% gelatin bioink was connected to the inner nozzle. By using a printing code and optimized printing parameters (speed: 200 mm/min, outer pressure: 55 MPa, inner pressure: 55 MPa), the hydrogel was extruded into a lumen-based structure with HepG2-based collagen–alginate bioink on the outer region and gelatin bioink on the core region. The printed structure was crosslinked with CaCl2.