Hepatocyte Aggregate Culture Technique for Bioreactors in Hybrid Liver Support Systems

Utilizing a modified culture technique for hepatocytes, a high performance suspension culture is possible in which hepatocytes spontaneously form cell aggregates. The aggregates of 20-100 cells have been histologically confirmed to hold a three-dimensional structure, they show a long-term external metabolism and a survival time comparable with standard adhesion cultures. This technique has several advantages in the construction of large scale bioreactors for hybrid liver support systems.

Comparison of Hollow Fibre Membranes for Hepatocyte Immobilisation in Bioreactors

Various hollow fibre membranes of polyamide, cellulose and polypropylene were investigated as potential substrata for hepatocyte immobilisation in bioreactors for hybrid liver support systems. Membranes were subjected to a cytocompatibility test in which the attachment and morphology of primary hepatocytes were evaluated. The effect of coating with collagen and fibronectin was also studied. Adequate cell immobilisation was possible on polypropylene and polyamide membranes even without coating. The flattening process of the cells was dependent on the material and the coating. The incorporation of porous polypropylene and polyamide hollow fibres in hybrid liver cell bioreactors and their specific permeability properties could also offer means for cell oxygenation, metabolite distribution and immuno-isolation purposes.

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.

Polymeric membranes for hybrid liver support devices: the effect of membrane surface wettability on hepatocyte viability and functions

Extracorporeal therapies based on membrane hybrid liver support devices using primary hepatocytes are an interesting approach to the treatment of acute hepatic failure. In such devices, semipermeable polymeric membranes are effectively used as immunoselective barriers between a patient's blood and the xenocytes in order to prevent the immune rejection of the graft. The membranes may act also as the substratum for cell adhesion, thus favouring the viability and functions of anchorage-dependent cells such as the hepatocytes. Membrane cytocompatibility is expected to depend on the surface properties of the polymer, such as its morphology and its physico-chemical properties. In this paper, we report our investigation on the effect of the surface wettability of membranes on hepatocyte viability and functions. Polypropylene microporous membranes were modified to increase their surface wettability and were used as substrata for rat hepatocyte adhesion culture. Isolated hepatocytes were also cultured on collagen as a reference substratum. Hepatocyte viability generally improved as the cells were cultured on more wettable membranes. In agreement with the viability data, the increasing wettability of the membrane surface also improved some metabolic functions.

Hepatocyte culture between woven capillary networks: a microscopy study

A multi-compartment capillary membrane culture model with independently perfused three-dimensionally woven capillaries was developed for immobilization of hepatocytes in bioreactors. This enables spatial restructuring of cells and enhanced mass transfer performance with more efficient oxygenation and metabolite exchange. Seeding density defines cell behaviour in this model. With low densities cells attach to the membranes and flatten. Increasing density leads to spontaneous formation of aggregates which are immobilized between the capillaries.