Hans‐Jürgen Henzler

Particle Stress in Bioreactors

In many biological processes, e.g. the fermentation of cells and sensitive microorganisms or bioconversion with immobilised enzymes, low shear stress is of crucial importance for the optimal course of processes. Starting with the causes of particle stress, the following report discussed the hydrodynamic principles of the most frequently used model reactors and bioreactors, which are required for an approximate calculation of stress. The main part of the report describes the results of systematic investigations into the hydrodynamic stress on particles in stirred tanks, reactors with dominating boundary-layer flow, shake flasks, viscosimeters, bubble columns and gas-operated loop reactors. These results for model and biological particle systems permit fundamental conclusions on particle stress and the dimensions and selection of suitable bioreactors according to the criterion of particle stress.

Mass transfer resistance of sterile plugs in shaking bioreactors

One of the mass transfer resistances for the gas exchange of shaking flasks is the sterile plug. The gas exchange through the sterile plug is described by an extended model of Henzler and Schedel [Bioprocess Eng. 7 (1991) 123]. Based on this model, a new method was developed to obtain the mass transfer resistance of various sterile closures. It consists of measuring the water evaporation rate of the shaking flask and is therefore very easily applied. Sterile plugs made of cotton, wrapped paper, urethane foam and fibreglass and caps made out of aluminium and silicone have been examined. Instead of the oxygen transfer coefficient (k(O(2))), which is commonly found in the literature, the carbon dioxide diffusion coefficient (D(CO(2))) is used to describe the mass transfer resistance of the sterile plug. The investigation revealed that this resistance is mainly dependent on the neck geometry and to a lesser extent on the plug material and density. The gas exchange of aluminium-caps was not reproducible.

Avoiding viral contamination in biotechnological and pharmaceutical processes

produced from materials of animal or human origin, such as cultured cells, organs, medium components, or blood. Thus, the danger exists that manufactured biopharmaceutical products bear a risk of viral contamination. This has been shown by numerous epidemiological investigations, e.g., for classical serum hepatitis (hepatitis B virus, HBV) and for other infections by blood contamination. With the recent appearance of disease-causing human immunodeficiency virus (HIV) and hepatitis C virus (HCV) infections related to transfusions, the safety of pharmaceutical and biotechnological drugs with respect to viral contamination is now more important than ever. Targeted selection of the starting material, as well as screening procedures such as investigation for viral markers (e.g., antibodies), are not sufficient to guarantee the safety of the products and to exclude the possibility of viral transfer. There is a need for effective elimination/inactivation methods integrated into the production process or designed as additional barriers. Inactivation of viruses is achieved by the destruction of their lipid or protein covers, making them unrecognizable to the target cell, or by destroying the viral nucleic acid, and therefore the biological activity necessary for replication. Acute concern for virus transmission from biological products derived from natural sources has led to the development of various viral clearance methods.

The One Step Inoculation Concept: A New Seed-Train Expansion for Recombinant Mammalian Cell Lines

A new approach for the seed-train expansion process of recombinant mammalian cell lines using 50 or 100 mL cryo-bags that have been frozen at high cell density and are thawed directly into a newly designed inoculation bioreactor is presented. This dedicated inoculation reactor can be operated under pH, DO and temperature control and is seeded at an initial volume of 2 L.