Randomly distributed spheroids or organoids enable 3-D establishment of homotypic cell-cell interactions surrounded by an extracellular matrix. The spheroids can be further cocultured with NPCs that facilitate heterotypic cell-cell interactions and allow the evaluation of outcomes resulting from drugs and other stimuli. Hepatic spheroids maintain major liver functions for several weeks and have proven to be compatible with multiple applications within the drug development pipeline.
These spheroids showed greater sensitivity in identifying known hepatotoxic drugs than did short-term primary human hepatocyte (PHH) monolayers. PHHs secreted liver proteins, such as albumin, transferrin, and fibrinogen, and showed cytochrome-P450 activities for 77-90 days when cultured on a nylon scaffold containing a mixture of liver NPCs and PHHs.
Nanopillar plates can be used to create induced pluripotent stem cell–derived human hepatocyte-like cell (iHep) spheroids; although these spheroids showed some potential for initial drug toxicity screening, they had lower overall sensitivity than conventional PHH monolayers, which suggests that further maturation of iHeps is likely required.
Potential limitations of randomly distributed spheroids include necrosis of cells in the center of larger spheroids and the requirement for expensive confocal microscopy for high-content imaging of entire spheroid cultures. To overcome the limitation of disorganized cell type interactions over time within the randomly distributed spheroids/organoids, bioprinted human liver organoids are designed to allow precise control of cell placement.