Biomedical subjects

R Pörtner

Publications and source records attributed to R Pörtner.

9 recordsLinked to original sources

PubMed2003

Improvement of a mammalian cell culture process by adaptive, model-based dialysis fed-batch cultivation and suppression of apoptosis.

Both conventional and genetic engineering techniques can significantly improve the performance of animal cell cultures for the large-scale production of pharmaceutical products. In this paper, the effect of such techniques on cell yield and antibody production of two NS0 cell lines is presented. On the one hand, the effect of fed-batch cultivation using dialysis is compared to cultivation without dialysis. Maximum cell density could be increased by a factor of approximately 5-7 by dialysis fed-batch cultivation. On the other hand, suppression of apoptosis in the NS0 cell line 6A1 bcl-2 resulted in a prolonged growth phase and a higher viability and maximum cell density in fed-batch cultivation in contrast to the control cell line 6A1 (100)3. These factors resulted in more product formation (by a factor of approximately 2). Finally, the adaptive model-based OLFO controller, developed as a general tool for cell culture fed-batch processes, was able to control the fed-batch and dialysis fed-batch cultivations of both cell lines.

Adaptation, Physiological↗

PubMed1999

Experimental and theoretical considerations on oxygen supply for animal cell growth in fixed-bed reactors.

The supply of oxygen is a crucial parameter when cultivating animal cells in fixed-bed reactors because of the reaction-diffusion limitation within the porous carriers. To reduce limitation and increase productivity, the dissolved oxygen concentration was raised to above air saturation (hyperoxia) in long-term experiments using hybridoma cultures. This resulted in a threefold increase of the steady-state antibody production at high dilution rates compared to air saturated medium. A reaction-diffusion model was developed as a tool to describe the oxygen distribution in fixed-bed systems. The model corresponded well to the experimental data. It was also used to study the influence of several parameters on the performance of the fixed-bed system, such as the carrier size, the dissolved oxygen concentration, or the superficial flow velocity. By adapting the model it was shown that reaction-diffusion limitation is generally not a problem for other substrates such as glucose or glutamine.

Animals↗

PubMed1998

Dialysis cultures.

Dialysis techniques are discussed as a means for effective removal of low-molecular-mass components from fermentation broth to reach high cell density. Reactor systems and process strategies, the relevant properties of membranes and examples for high-density fermentation with dialysis, and problems related to scale-up are addressed. The dialysis technique has turned out to be very efficient and reliable for obtaining high cell densities. As in dialysis processes the membranes are not perfused, membrane clogging is not a problem as it is for micro- and ultrafiltration. By applying a "nutrient-split" feeding strategy, the loss of nutrients can be avoided and the medium is used very efficiently. The potential of dialysis cultures is demonstrated on the laboratory scale in a membrane dialysis reactor with an integrated membrane and in reactor systems with an external dialysis loop. In dialysis cultures with different microorganisms (Staphylococci, Escherichia coli, extremophilic microorganisms, Lactobacilli) the cell densities achieved were up to 30 times higher than those of other fermentation methods. The technique enables high cell densities to be attained without time-consuming medium optimization. For animal cell cultures the concept of a fixed bed coupled with dialysis proved to be very effective.

Animals↗

PubMed1996

Modelling hybridoma cell growth and metabolism--a comparison of selected models and data.

Unstructured models for cell growth (cell specific growth and death rate) and metabolism (cell specific substrate uptake and metabolite production rates) of hybridoma cell lines were compared with special respect to significance, analytical error and range of validity. The diversity of the unstructured models cited reveals their mostly descriptive character compared to structured models. Bearing in mind this limited knowledge, empirical models can still serve as a valuable tool for process design. For understanding of the cell metabolism itself they might have been overemphasized in the past. For proper model design, care has to be taken to cover the whole range of process conditions. In particular if a process is to be run at very low substrate and high metabolite concentrations, chemostat cultures which have mostly been used for the model formulations, are not sufficient and have to be completed by, for example, fed-batch cultures.

Ammonia↗

PubMed1995

Performance of a membrane-dialysis bioreactor with a radial-flow fixed bed for the cultivation of a hybridoma cell line.

A bioreactor system for the continuous cultivation of animal cells with a high potential for scale-up is presented. This reactor system consists of radial-flow fixed-bed units coupled with a dialysis module The dialysis membrane enables the supply of low-molecular-weight nutrients and removal of toxic metabolites, while high-molecular-weight nutrients and products (e.g., monoclonal antibodies) are retained and accumulated. This concept was investigated on the laboratory scale in a bioreactor with an integrated dialysis membrane. The efficiency of the reactor system and the reproducibility of the cell activity (hybridoma cells) under certain process conditions could be demonstrated in fermentations up to 77 days. Based on model calculations, an optimized fermentation strategy was formulated and experimentally confirmed. Compared to chemostat cultures with suspended cells, a ten-times higher mAb concentration (383 mg1(-1)) could be obtained. The highest volumetric specific mAb production rate determined was 6.1 mg mAb (1 fixed bed)-1h-1.

Animals↗

PubMed1994

Estimation of specific glucose uptake rates in cultures of hybridoma cells.

The specific glucose uptake rate of a hybridoma cell line was determined in batch and continuous suspension cultures. For high density cultivation a membrane dialysis reactor was used. The aim was to obtain data, which can be used for process design and control. A decrease of the specific glucose uptake rate was observed during the course of batch cultures, even when the specific growth rate remained constant. These results are valid for cell densities between 2 x 10(5) and 2 x 10(6) ml-1. At cell densities between 2 x 10(6) and 1.5 x 10(7) ml-1 during continuous cultivation the specific glucose uptake rate remained constant. A relationship between the specific glucose uptake rate and the cell number was found and formulated in a mathematical equation. Literature data for different hybridoma cell lines fit in this plot very well. Applying this relationship, a correct estimation of the course of the glucose concentration in batch and continuous cultivation is possible.

Animals↗

PubMed1994

High density cultivation of hybridoma in charged porous carriers.

A porous carrier whose surface is charged with polyethyleneimine (PEI) was evaluated for high-density cultivation of immobilized hybridoma cells. The carrier was used either in suspension or in fixed bed. For suspended carriers, the effect of carrier pore size, ion-exchange capacity (IEC), mixing intensity and inoculum concentration on the attachment and growth of HBs MAb-producing hybridoma cells in carrier CELLSNOW EX were studied. The carrier with 100 microns pore size was more efficient than that with 500 microns in supporting cell attachment. In addition, the amount of antibody which was detected by PHA (passive hemagglutination assay) was 4-times higher in 100 microns compared with 500 microns pore size. At low initial cell concentration, 2.8 x 10(5) ml-1, the attached cells did not grow in the first 7 d as indicated by a negligible glucose consumption. However, cell proliferation was observed at high inoculum, 9 x 10(5) ml-1. Hybridoma cells were expected to attach faster to EX with high IEC than with low IEC but results showed no significant difference. A different hybridoma cell line producing monoclonal antibody (MAb) against penicillin-G-amidase was successfully cultivated in an axial-flow fixed bed containing CELLSNOW carriers. The specific glucose uptake rate as an indicator for cell activity was 24-times higher compared with conventional chemostat cultures. The CELLSNOW carriers offers many advantages over other carriers.

Animals↗

PubMed1994

Effect of NH3 on the cell growth of a hybridoma cell line.

Ammonia often has been reported to inhibit cell growth. The aqueous ammonia equilibrium between the un-ionized from (NH3) and the ammonium ion (NH4+) depends on the pH of the solution. Extensive studies in batch and continuous cultivation by varying pH and total ammonia concentration were carried out to investigate whether a kinetic model describing growth inhibition by ammonia has to be based on the total ammonia concentration, or the concentration of NH3. A significant relationship between the specific growth rate and death rate, respectively, and the NH3 concentration, but not the total ammonia concentration, was detected. An adaptation of the cells to high ammonia levels was not observed. Based on these results a new kinetic model for ammonia mediated growth inhibition is suggested. For high density cultivation it is recommended to control the pH at the lower limit of the growth optimum to keep the NH3 level low.

Ammonia↗

PubMed1992

The membrane dialysis bioreactor with integrated radial-flow fixed bed--a new approach for continuous cultivation of animal cells.

A hybridoma cell was cultivated continuously in a membrane dialysis bioreactor with an integrated radial-flow fixed bed consisting of porous Siran carriers over a period of 6 weeks. Antibodies accumulated to an average of 100 mg l-1, approx. 10 times more than in fixed bed cultures without dialysis membrane. Serum costs could be reduced about 85% due to an appropriate feeding strategy. Siran carriers with 3-5 mm diameter showed an advantage compared to those with 1-2 mm diameter. For the 3-5 mm carrier the specific glucose uptake rate and the MAb production rate were constant, if the velocity was between 0.09 mm s-1 and 0.75 mm s-1. At higher velocities cells are washed out of the bed. Furthermore antibody consistency and cell stability were verified in long-term cultivations over a period of 96 days. From an estimation of the antibody concentration reachable with the reactor concept under optimal conditions a concentration 45 times higher compared to axial-flow fixed bed reactors and 11 times higher compared to stirred tank reactors can be expected.

Animals↗