Polyurethane membrane as an efficient immobilization carrier for high-density culture of rat hepatocytes in the fixed-bed reactor

A fixed-bed bioreactor with a polyurethane membrane (PUM) as a cell-support ing material was developed for high-density culture of rat hepatocytes. The PUM has a heterogeneous porous structure of micropores (pore size <100 mu m) and macropores (pore size >100 mu m) with a porosity of 90%. One importa nt feature of a PUM is that the macropores have finger-like structures and their diameters gradually decrease from the upper to the lower layer of the PUM. Most rat hepatocytes were readily immobilized in the micropores of PU M. Immobilized cell densities of 1-3 x 10(7) cells/cm(3) PUM were achieved within 5 min by natural downflow of cell suspension and their immobilizatio n efficiencies were more than 99%. Using a syringe pump, a cell density of 5 x 10(7) cells/cm(3) PUM was achieved with more than 96% immobilization ef ficiency. Perfusion cultures using this reactor were performed for 7 days w ithout cell leakage. The optimal cell density for albumin secretion was bet ween 2 x 10(7) and 3 x 10(7) cells/cm(3) PUM. Albumin secretion in the perf usion culture was maintained for a relatively long period of time when comp ared to that in the monolayer culture. The rate of albumin secretion in the perfusion culture was about 50% of that in monolayer culture. Hepatocytes immobilized in PUM were slightly aggregated, but they maintained spherical form individually even after 7 days of cultivation. The above results show that PUM is a promising cell-supporting material for efficient immobilizati on of high cell density of hepatocytes. (C) 2000 John Wiley & Sons, Inc.