The pursuit of a bioartificial liver is well documented in the literature. Early techniques of artificial liver support that have undergone clinical testing included simple exchange transfusions, extracorporeal xenogeneic or allogeneic liver perfusion, cross-circulation, hemodialysis, charcoal hemoperfusion, and plasmapheresis with plasma exchange. These techniques failed because they were unable to adequately support those hepatic functions essential for survival and because they lacked a back-up therapy, such as liver transplantation, for irreversible forms of liver disease. The concept evolved that hepatic functions essential for survival would be best performed by hepatocytes in an apparatus that allowed sustained or repetitive application. The best results have been achieved with bioartificial liver technologies that employ hepatocytes as implantable systems or extracorporeal devices. Implantable bioartificial liver systems include hepatocytes that have been on coated microcarrier beads, within microencapsulated gel droplets, within biodegradable polymeric substrates, or as spheroid hepatocyte aggregates. Extracorporeal systems include hepatocytes in suspension, on flat plates, and in hollow fiber bioreactors. Several extracorporeal systems have undergone extensive animal testing and are entering the early stages of human clinical trials. Randomized trials are needed to establish the value of bioartificial liver support in the treatment of patients with acute hepatic failure or as a bridge to liver transplantation.
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