Development of a hybrid liver support system.

Hybrid liver systems are being developed as temporary extracorporeal liver support therapy. The overview given here emphasizes the development of both hepatocyte culture models for bioreactors and of systems for clinical therapy. In vitro studies demonstrate long term external metabolic function in isolated primary hepatocytes within bioreactors. These systems are capable of supporting essential liver functions. Animal experiments verify the possibility of upscaling bioreactors for clinical treatment. However, since there is no reliable animal model for investigating the treatment of acute liver failure, the promising results obtained from these studies have limited relevance to human beings. The small number of clinical studies performed thus far are not sufficient to enable any conclusions concerning improvements in the therapy of acute liver failure. Although important progress has been made in the development of these systems, multiple hepatocyte culture models and bioreactor constructions are being discussed in the literature, indicating competition in this field of medical research. For the use of hepatocytes and sinusoidal endothelial cells in coculture, a bioreactor has been designed. The construction is based on capillaries for hepatocyte aggregate immobilization. Four separate capillary membrane systems, each permitting a different function, are woven in order to create a three-dimensional network. Cells are perfused via independent capillary membrane compartments. Decentralized oxygen supply and carbon dioxide removal with low gradients is possible. The parallel use of identical units enables easy upscaling. Initial studies on the use of discarded organs that are unsuitable for transplantation as a source for primary human liver cells seem to be promising.