2.7. Culture condition of Liver-on-a-chip
After the fabrication process, a hepatocyte culture medium was added to the LOC platform. The LOC was incubated at 37°C for 24 h to allow the dissolution of sacrificial bioink (3% gelatin) from the core region of the bioprinted construct. The LOC setup was then transferred onto a rocker cultured at 37°C in a humidified 5% CO2atmosphere. The free movement of the medium through the hollow lumen of the 3D model simulating a perfusion-based liver in-vitro model was driven by gravity-induced force. The flow rate (Q) of the medium was calculated using Eqs. (1) and (2):
ΔP = ρ gΔh, (1)
Q = ΔPπ R4/8μ L, (2)
where ΔP, ρ, g, and Δh denote the pressure, fluid density, gravity constant, and height difference (L × sin [10°]), respectively. ΔP, R, μ , and L denote the pressure drop, hydraulic radius of the channel, dynamic fluid viscosity (0.78 × 10−3 Pa·s), and length of the channel (20 mm), respectively. The lumen-based 3D liver microphysiological system had a flow rate of 25 µl/min. Every two days, the culture-related media were replaced.