The liver is the main metabolic organ in the body; it plays important roles such as protein synthesis and drug metabolism. Hence, hepatocytes have often been used for research involving pharmacokinetics and toxicity assays. The conventional method involves culturing the hepatocytes as a monolayer. However, this results in the loss of the tissue-like organization of the hepatocytes and the rapid deterioration of liver-specific functions. In contrast, cultured hepatocyte spheroids (spherical multicellular aggregates) can maintain a high level of liver function in vitro, which is attributable to their resemblance to tissues in terms of the presence of abundant cytoplasmic organelles and close cell-cell contact. Therefore, the spheroid culture system has been advocated as a useful technique to replace monolayer culture. Numerous reports have suggested that the hepatocyte spheroids can be cultured using various methods such as rotation culture and non-adhesion culture. We have also developed a microchiptechnique that can generate uniform hepatocyte spheroids in a regularly arrangement. However, the expression of hepatocyte functions in vitro is limited, even in the spheroid culture system.
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