1. The influence of rotation speed on bioreactor culture
At present, more and more products are produced on a large scale using bioreactors in the biological field. Different cells need different rotation speeds to be cultured in bioreactors. As a commonly used operating parameter, stirring speed can not only affect the mixing of the liquid phase and the transfer rate of material energy, but also cause fluid shear and microcarrier collision.
Lu Minghua et al. used BC-7L bioreactor to culture suspended BHK-21 cells and concluded that under 40r/min, more cells were observed to be deposited at the bottom of the reactor. When the rotation speed was increased to 70r/min, there were no deposited cells at the bottom of the reactor, but more cells were observed to be aggregated. Therefore, the rotation speed was further increased to 100r/min, and the cell agglomeration problem was solved, and the cells grew well. 100r/min is the optimal stirring speed.
The speed is different due to different cell types, culture methods, etc. The operating speed of the reactor is controlled by its needs. Different speeds produce different results for cell culture results.
2. Effect of temperature on bioreactor culture
The cell culture temperature is usually 35-37℃, the optimum temperature is 37℃, and it is controlled within ±0.25℃. During the culture process of mammalian cells, if the culture temperature is lowered, the cell growth and metabolism will slow down, but the cell viability can be better maintained .
Yi Xiaoping et al. studied the effect of temperature on the growth of recombinant BHK cells. The results showed that compared with 37℃, increasing or decreasing the temperature would reduce the cell growth rate and density, and decreasing the temperature would prolong the hysteresis period of cell growth. However, the tolerance of cultured cells to low temperature is stronger than that to high temperature. During the adjustment of reactor parameters, it is necessary to prevent the temperature from rising too high, especially because animal cell culture systems often use low-speed stirring, poor mixing, and low transmission efficiency. In particular, there is always a temperature gradient from the outer wall of the tank to the inside of the culture system, so strict requirements are placed on temperature monitoring and control.
3. Effect of pH value on bioreactor culture
The control of pH value is very important for animal cell culture. 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. pH values below 6.8 or above 7.4 will have an adverse effect on cells.
Yuan Jianqin et al. set 6 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 chicken embryo fibroblasts grew better and more stably in the range of 7.4 to 7.6.
Lu Minghua et al. used BC-7L bioreactor to culture suspended BHK-21 cells and verified that pH changes within a certain small range will not have a big impact on cell growth, but if the change is large, it will make the cells grow slowly and in poor condition. The experimental results show that when the pH is 7.4, the cell growth is best.
4. Effect of DO on bioreactor culture
The dissolved oxygen in the bioreactor is achieved by passing a mixture of oxygen and air into the culture medium through a bubble distributor. 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 ventilation. 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. In addition, the mass transfer and heat transfer effect are greatly increased by optimizing the design with the stirring blade. Surface ventilation can quickly inject fresh air into the reactor and the surface layer, increasing the surface liquid oxygen transfer coefficient.
How to maintain a certain dissolved oxygen (DO) concentration without damaging cells is a key factor in large-scale culture of animal cells. Cells cannot survive under hypoxic conditions. Too low dissolved oxygen will affect cell metabolism and thus cell growth; too high dissolved oxygen will not only have a toxic effect on cells, inhibit cell growth, but also increase production costs.
The oxygen demand of cells is different at different growth stages. The oxygen consumption capacity of cells in the logarithmic growth period is particularly strong. Generally, the dissolved oxygen concentration in large-scale culture processes is controlled at 20% to 60% of air saturation. A certain dissolved oxygen concentration can be maintained by adjusting the ratio of air, oxygen and nitrogen in the gas supply or increasing the stirring speed.