The operation of bioreactors is influenced by different cultivation parameters, which can significantly affect their cultivation results.
１. The influence of rotational speed on bioreactor cultivation
At present, more and more products are being produced on a large scale using bioreactors in the field of biology. Different cells require different rotational speeds for cultivation in bioreactors.
As a commonly used operating parameter, the stirring speed can not only affect the mixing of the liquid phase and the transfer rate of material energy, but also bring about fluid shear and micro carrier collision
Lu Minghua et al. [2] used a BC-7L bioreactor to culture suspended BHK-21 cells and concluded that at a speed of 40 r/min, more cells were observed to deposit at the bottom of the reactor.
When the rotation speed was increased to 70 r/min, there were no deposited cells at the bottom of the reactor, but more clustered cells were observed during sampling.
Therefore, by further increasing the rotation speed to 100 r/min, the clustering of cells was resolved and the cells grew well. The optimal stirring speed is 100r/min.
The rotational speed of the reactor is controlled according to the different types of cells and cultivation methods, and the operating speed of the reactor is determined by its requirements. Different rotational speeds have different effects on the results of cell culture.
２. The influence of temperature on bioreactor cultivation
The typical temperature for cell culture is 35-37 ℃, with the optimal temperature being 37 ℃ and controlled within ± 0.25 ℃.
During the cultivation process of mammalian cells, lowering the cultivation temperature can slow down the growth and metabolism of the cells, but the cell viability can be better maintained.
Yi Xiaoping et al. studied the effect of temperature on the growth of recombinant BHK cells, and the results showed that compared to 37 ℃, increasing or decreasing the temperature would reduce the growth rate and density of cells, and decreasing the temperature would prolong the lag period of cell growth.
However, the tolerance of cultured cells to low temperature is stronger than that to high temperature.
During the parameter adjustment process of the reactor, it is necessary to prevent the temperature from jumping too high, especially in animal cell culture systems, which often use low-speed stirring, resulting in poor mixing and low transmission efficiency.
Especially since there is always a temperature gradient from the outer wall of the tank to the inside of the cultivation system, strict requirements are placed on temperature monitoring and control.
３. The influence of pH value on bioreactor cultivation
The control of pH value is very important for animal cell culture, as pH can affect the adhesion, growth, survival and other functions of animal cells. The pH range of animal cells is generally between 6.8 and 7.4, and pH values below 6.8 or above 7.4 can have adverse effects on the cells.
Yuan Jianqin et al. set six different pH values (6.4, 6.8, 7.2, 7.4, 7.6, 7.8) to observe the growth of chicken embryo fibroblasts. The results showed that the growth of chicken embryo fibroblasts was good and stable within the range of 7.4 to 7.6.
Lu Minghua et al. used a BC-7L bioreactor to culture suspended BHK-21 cells and verified that pH changes within a certain small range did not have a significant impact on cell growth, but if the changes were large, it would slow down cell growth and result in poor condition.
The experimental results showed that cell growth was optimal at pH 7.4.
４. The impact of dissolved oxygen on bioreactor cultivation
The dissolved oxygen in the bioreactor is achieved by introducing a mixture of oxygen and air into the culture medium through a bubble distributor, and the structural form of the bubble distributor largely determines the state of dissolved oxygen in the bioreactor.
The dissolved oxygen control subsystem is divided into two major systems: surface and deep aeration. The deep ventilation system uses a microbubble generator to provide dissolved oxygen.
The bubbles are small and uniform, and the dissolved oxygen transfer effect is good. By optimizing the design with the stirring blade, the mass and heat transfer efficiency is greatly increased.
Surface ventilation can quickly inject fresh air into the reactor and the surface, increasing the oxygen transfer coefficient of the surface liquid.
How to maintain a certain dissolved oxygen (DO) concentration without damaging cells is a key factor in large-scale animal cell culture.
Cells cannot survive under hypoxic conditions, and low dissolved oxygen can affect cell metabolism, thereby affecting cell growth; When dissolved oxygen is too high, it not only has a toxic effect on cells, inhibits cell growth, but also increases production costs.
Cells have different oxygen requirements at different stages of growth, and the logarithmic growth stage cells have particularly strong oxygen consumption capacity. The dissolved oxygen concentration in the general large-scale cultivation process is controlled at an air saturation of 20% to 60%.
Adjusting the ratio of air, oxygen, and nitrogen in the gas supply, or increasing the stirring speed, can maintain a certain dissolved oxygen concentration.
Source: Lu Meilin, Ayimuguli, Qiao Zilin, Ma Qi Analysis of the current status of commonly used parameters for animal cell bioreactor culture [J]. Gansu Animal Husbandry and Veterinary Medicine, 2018, 48 (10): 29-31. [1] Zhu Qinghu, Chen Hong, Qin Hongli, et al The main operating modes of animal cell culture reactors [J]. Livestock and Veterinary Science and Technology Information, 2010, (10): 7-9. [2] Lu Minghua, Liu Junsheng, Liu Yanting, et al Research on Suspension Culture Parameters of BHK-21 Cell Bioreactor [J]. Chinese Journal of Animal Health, 2015, 17 (12): 69-70. [3] Li You, Zhou Hang, Li Jincai, et al Development and application of mammalian cell perfusion culture technology [J]. Chinese Journal of Pharmaceutical Biotechnology, 2015, 10 (3): 267-270. [4] Yi Xiaoping, Sun Xiangming, Zhang Yuanxing The effect of temperature on the growth, metabolism, and vWF protein expression of recombinant BHK cells [J]. Journal of East China University of Science and Technology (Natural Science Edition), 2007, 33 (1): 28-32. [5] Yuan Jianqin, Gao Binzhan, Zheng Mingxue The effect of different pH values on the culture of chicken embryo fibroblasts [J]. Culture and Feed, 2010, (9): 1-5. [6] Xiao Shang, Deng Chongfei, Ke Jun, et al. The effect of pH on the growth, monoclonal antibody expression, and quality of recombinant CHO cells [J]. Biotechnology Bulletin, 2015, 31 (12): 256-261
