The key to the large-scale industrialization and commercialization of animal cell culture technology in biopharmaceuticals lies in the selection and design of suitable bioreactors. Since mammalian cells are very different from microbial fermentation, traditional microbial fermenters are obviously not suitable for large-scale culture of animal cells. First of all, it must satisfy the ability to provide sufficient oxygen for cell growth and product synthesis by cells under low shear and good mixing conditions.

1.Classification of common bioreactors

At present, bioreactors for animal cell culture mainly include: rotary flask cultures, plastic bag proliferators, packed bed reactors, multilayer plate reactors, tubular screw reactors, and fluidized bed reactors. reactor, fluidized bed reactor, hollow fiber reactor, membrane reactor, stirred reactor, air-lift reactor, etc.;

According to their different ways of culturing cells, these reactions can be divided into the following three categories:

Suspension culture: such as stirred reactors, hollow fiber reactors
adherent cultures: e.g. stirred reactors (microcarriers/paper sheets), hollow fiber reactors;
embedded cultures: e.g. fluidized bed reactors, cured bed reactors;

2. Introduction to common bioreactors

1. Stirred bioreactor

This is the most classic and earliest adopted type of bioreactor. This type of reactor is similar to the traditional microbial bioreactor, with different stirrers and aeration methods for the characteristics of animal cell culture. The action of the stirrer makes the cells and nutrients uniformly distributed in the culture medium, so that the nutrients are fully utilized by the cells and the gas-liquid contact surface is increased, which is conducive to the transfer of oxygen.

The common ones are: cage-type aeration stirrer, double-layer cage-type aeration stirrer, paddle stirrer and so on.

2.Aerostatic bioreactor

The basic principle of aerostatic bioreactor is that the gas mixture enters into the central deflector of the reactor from the bottom ejector tube, which makes the density of the liquid on the side of the central deflector lower than that on the outside area thus circulation is formed. It is structurally much the same as the stirred type, with the distinctive feature of using a gas stream instead of stainless steel blades for stirring, thus generating relatively mild shear forces and less cell damage.

Commonly used: internal circulation type, external circulation type, internal and external circulation type.
3. Fixed-bed bioreactor

The carrier is fixed in the bioreactor, and the cells are adhered to the carrier, and the nutrient solution circulates to supply nutrients needed for the growth of the cells in three dimensions, and it can effectively protect the cells from being damaged by the shear force of stirring and collision, and it can also retain the cells in the bed. It can effectively protect the cells from damage by shear force caused by stirring and collision, and can also retain the cells in the bed, which is especially suitable for continuous perfusion culture, and is conducive to later purification and separation.

4.Hollow fiber bioreactor

The principle is to simulate the three-dimensional state of the cell growth in vivo, the use of thousands of hollow fibers within the reactor longitudinal arrangement, to provide the cells with approximate physiological conditions of the growth of the micro-environment of the in vitro growth of the cells, so that the cells grow continuously. Hollow fiber is a fine tubular structure, the wall of the tube is a very thin semi-permeable membrane, rich in capillaries, the culture of the fiber tube filled with oxygen serum-free culture fluid, the outer wall of the tube for the cells to adhere to the growth of nutrients through the semi-permeable membrane from the tube permeate out for cell growth; the cell's metabolic wastes can also be seeped through the semi-permeable membrane into the tube, to avoid the toxic effects of excessive metabolites on the cells, the advantages of the following are:

• occupies less space;
• high cell yield, cell density of up to 109 orders of magnitude;
• lower cost of production }
• Structural tightness without leakage, able to withstand steam sterilization, harmless and corrosion-resistant material production, the inner wall and pipeline valves smooth and no dead ends;
• Have a good gas-liquid contact and solid-liquid mixing, mass and heat transfer;
• Ensure that the quality and yield of the bioreactor 115}}Save energy consumption as much as possible under the premise of guaranteeing quality and output;
• Reduce foam generation and shear force;
• Reliable parameter detection and instrumentation control; {
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• Safe and stable control system;
• Solid-liquid mixing and heat transfer;
• Solid-liquid mixing and heat transfer. 127}} control system is safe and stable, with traceable records;

2, the principle of scaling up of bioreactors is:

a new biotechnology product from the laboratory to the The development process of industrial production will encounter the problem of amplification of the bioreactor step by step, about 10 to 100 times per level. The amplification of bioreactors seems to be only a volume or scale enlargement problem, but in fact it is not so simple. Although many methods have been proposed for reactor amplification, none of them is universally applicable. At present, it can only be semi-theoretical and semi-empirical, that is, to seize a small number of key parameters or phenomena in the reaction process for amplification, such as:
① Oxygen transfer
Oxygen transfer problems in the bioreactor, the rate of oxygen transfer to meet the rate of cellular uptake of oxygen, and to make the reactor in the dissolved oxygen concentration CL should be maintained at a certain level. concentration CL is to be maintained at a certain level. That is to say, in the steady state situation, the following relationship exists between oxygen supply and oxygen demand: KLa(C*-CL)=r
Here, KLa is the oxygen transfer coefficient; C* is the concentration of dissolved oxygen equivalent to the partial pressure of oxygen in the gas phase, CL is the concentration of dissolved oxygen in the culture solution, and r is the oxygen uptake rate. Thus, the factors affecting oxygen delivery in general are the KLa and C*-CL values.
To increase the C*-CL, there is nothing more than increasing the C* value or decreasing the CL value. The measures to increase C* are two ways to appropriately increase the operating pressure in the reactor and to increase the partial pressure of oxygen in the gas phase. In practice, the reactor maintains a certain positive pressure to prevent the invasion of atmospheric stray bacteria from shaft seals, valves, etc. However, while increasing the tank pressure, the CO2 produced by the fermentation metabolism will be more dissolved in the culture fluid and unfavorable to the fermentation. As for the CL value, it is generally not allowed to reduce it excessively, because there is a critical oxygen concentration in cell growth, below which cell respiration will be inhibited.
The factors affecting KLa can be broadly categorized into three areas: first, the structure of the reactor, including the ratio of relative geometrical dimensions; second, the operating conditions, such as the amount of stirring power or circulating pump power input, the amount of aeration, etc.; and, third, the physicochemical properties of the culture or fermentation broth such as the rheological properties, especially its viscosity or display viscosity, surface tension, diffusion coefficient, cell morphology, degree of foaming, etc.
② Heat transfer
Heat transfer in bioreactors During cell culture and fermentation, heat release and absorption are common. This is because during the culture or fermentation process cells metabolize with substances from the surrounding environment, i.e., heterogeneity (catabolism) and assimilation (synthesis) occur, while heterogeneity generally releases energy and assimilation absorbs energy. At the same time, the emission of exhaust gases and the heat exchange between the tank and the outside world can lead to changes in heat transfer.