A novel bioreactor system developed for high-density cultures of suspended mammalian cells is described using a tangential-flow filtration device outside the culture vessel to separate viable cells from spent medium. The filtration device is based on thin porous microfiltration membranes with a pore size of 0.20-0.65 microns. Because cells have a diameter of about 10-20 microns, they cannot permeate these membranes with the spent medium. So, allowing a perfusion culture to be created using this system. In most membrane filtration systems, clogging of the membranes has made long-term operation difficult. In this system, however, high pressure is not applied directly to the membrane, thus minimizing clogging. Also, clogging of the membrane was prevented by washing the membrane surface once a day, and increasing the membrane surface area. With this system, FM-3A cells were cultured and maintained at a high density of 3.0 x 10(7) cells/ml for two weeks, and a continuous culture was supported for as long as 34 days.

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Ceramic pieces composed of 99.5% Al2O3, 3 to 6 mm long, were found to be a good matrix for growth of the human embryonic lung diploid fibroblast, IMR-90 cells. The tissue plasminogen activator (t-PA) was secreted in DME medium containing proteose peptone as a t-PA inducer. In addition, production of t-PA was enhanced by increasing extracellular CaCl2, from 3.6 to 5.4 mM. In order to eliminate negative feed-back control caused by t-PA produced and thus raise productivity, perfusion cultivation was performed using a ceramic-packed bed column, with a recirculating vessel. The recirculating vessel was used to mix fresh medium with spent medium, and to control dissolved oxygen concentrations in the extracellular environment by stirring. In continuous production using the packed bed column with 2 kg of ceramics (phi = H = 150 mm), increasing dilution rate to 0.5 day-1 could reduce product inhibition at 3-4 x 10(5) cells/ml. Cellular productivity of 560 IU/10(6) cells/day was obtained over 40 days and corresponded to the volumetric productivity of 183 IU/ml/day.