Several investigators have demonstrated that freshly harvested hepatocytes self-assemble into three-dimensional, compacted, freely suspended aggregates known as spheroids (1 –3 ). These aggregates have smooth, undulating surfaces and average approx 120 �m in diameter. Hepatocyte spheroids exhibit enhanced liver-specific activities and prolonged viability, compared to cells maintained as a monolayer (4 ,5 ). Extensive cell–cell contacts, tight junctions, and microvilli-lined channels that resemble bile canaliculi have been observed between hepatocytes in spheroids (6 ,7 ). Thus, these cells appear to mimic the morphology and ultrastructure of an in vivo liver lobule. Reorganization of hepatocytes into these three-dimensional structures is hypothesized to contribute to their enhanced liver-specific functions. Because of their enhanced function and tissue-like ultrastructure, hepatocyte spheroids show great promise for use in tissue-engineering applications and drug metabolism studies.
