Content:
The choice of reactor depends on the concentration of production cells, ventilation volume and the degree of dispersion of the nutrients provided. Bioreactors can be divided into the following categories according to the type of ventilation and stirring system:
1. Mechanical stirring bioreactor
Mechanical stirring bioreactors have a large operating range, high mixing degree, wide adaptability, and are widely used in large-scale production. The shear force generated in the stirring tank is large, which can easily damage cells and directly affect cell growth and metabolism, especially the generation of secondary products. The higher the stirring speed, the greater the shear force generated, and the greater the damage to plant cells. For some cells that are sensitive to shear force, traditional mechanical stirring tanks are not suitable. For this reason, the stirring tank has been improved, including changing the stirring form, impeller structure and type, air distributor, etc., in an effort to reduce the shear force generated while meeting the requirements of oxygen supply and mixing.
2. Non-stirring bioreactor
Compared with traditional stirred reactors, non-stirring reactors generate less shear force and have a simple structure, so they are considered suitable for plant cell culture. Its main types include bubble reactors, airlift reactors and rotary drum reactors. By comparing the bioreactors for culturing perilla cells, it was found that the bubbling reactor is superior to the mechanical stirring reactor. However, due to the low oxygen utilization rate of the bubbling reactor, if a large ventilation volume is used, the shear force generated will damage the cells. Studies have shown that turbulent shear force is an important reason for inhibiting cell growth and damaging cells when large bubbles are sprayed. Larger bubbles or higher gas velocities lead to higher shear forces, which are harmful to plant cells. Airlift reactors are widely used in the research and production of plant cell culture. Through carrot cell culture research, it was found that by comparing the stirred tank, gas injection tank and airlift reactor with a vent, the highest cell concentration and the shortest doubling time can be obtained from the airlift tank. The airlift reactor is used for suspension culture or immobilized cell culture of a variety of plant cells, but its operating flexibility is small. At low gas velocities, especially when H/D is large and high-density culture, the mixing performance is poor. Excessive gas supply and excessive oxygen concentration will affect cell growth and the synthesis of secondary metabolites. Combining an airlift fermenter with slow stirring can make up for the weakness of poor mixing at low gas speeds. The use of segmented airlift pipes is also conducive to oxygen utilization and mixing.
Research on the use of rotary drum reactors for tobacco cell suspension culture found that compared with an airlift reactor with a ventilation pipe, the growth rate in the rotary drum reactor was higher under the same conditions, and its oxygen transfer and shear force damage to cells were better than those of the airlift reactor.
3. Photobioreactor
Many plant cell culture processes require illumination, and it is often considered to add an illumination system on the basis of ordinary reactors, but there are many problems in practice, such as the installation and protection of light sources, the transmission of light, and the influence of the illumination system on the reactor gas supply and mixing. Small-scale experiments often use external illumination. The reactor surface has a transparent lighting area, and the light source is fixed around the outside of the reactor. However, the setting of light-transmitting windows and the uniform reception of light by the internal culture are difficult to solve in large-scale production, so many people have studied reactors using internal light sources.