Introduction

The original concept of artificial liver support was based on the removal of toxic substances from the systemic circulation in acute liver failure (ALF). A large number of potentially toxic substances have been identified which are either produced in the gut, released from the necrotic liver or result from failure of metabolism in the damaged liver, and these substances lead to coma and the development of multiorgan failure. The early systems were based on adsorbents or dialysis membranes to remove substances directly from blood [1]. Substances such as ammonia, aromatic amino acids and related molecules, fatty acids, mercaptans, bile acids and bilirubin were used as biomarkers to assess the effects of a device on the patient. This type of device only replaced the excretory function of the failed liver and there was thus considerable interest in the development of devices which incorporated biological function, i.e. liver cells with the capability of replacing deficient metabolic and synthetic function. It should be emphasized that it is still not clear what exact missing function is required to promote recovery in the patient. Stimulation of liver regeneration is often suggested to be most important, but progression of the complications of liver failure is often more life threatening, particularly if a raised intracranial pressure develops due to brain oedema. Much effort has been made to develop bioartificial liver support systems to replace all functions of the liver.