In terms of a bioreactor, this means maintaining pH, temperature, ensuring sufficient gas supply and, depending on how the instrument has been configured, adding nutrients for successful maintenance of growth. Tony Allman. Given the abundance of functions that a bioreactor must perform, you might be wondering how it can do it all.
What components does it need? How do you know what the conditions in the bioreactor currently are and how you can you correct them? And finally, just for perspective: how do you take the data captured during a batch bioprocess, display them in a meaningful way, and then save and evaluate them while keeping them organized? The most important process parameters and the mechanisms for regulating them are covered below:. The culture in a bioreactor needs to be mixed thoroughly at all times.
If the nutrients in the bioreactor are not dispersed well enough, conditions in certain parts of the bioreactor will deviate significantly from the ideal. The pH could be too acidic, for example, or the supply of nutrients might be insufficient. Deviations like these not only reduce the efficiency of the planned bioprocess, but can also promote genetic modifications.
Temperature distribution is an additional concern. Without uniform stirring, the microorganisms or cell cultures along the edge of the vessel will literally be boiled, while those in the middle get cold feet. If you have ever heated soup in the microwave and then eaten it with great anticipation without stirring it, you will know what we mean.
Adjusting stirring speeds for cultivating either microorganisms, plant cells, animal cells or insect cells is very important, as these react differently to shear stress, i. Depending on the cell line, cell cultures can have a much more intense response to overly vigorous stirring, i.
Microorganisms and cell cultures alike have enzymes that work best within certain temperature and pH ranges. If conditions fall outside of these ranges, the desired bioprocess will proceed much more slowly, because growth and metabolic performance are highly dependent on these enzymes, i.
In the worst case scenario, unfavorable environmental conditions may even destroy them. Therefore, a platinum resistance sensor known as a Pt sensor is used in the bioreactor to determine the temperature.
If working at temperatures near or below room temperature, you will need an active cooling system such as a recirculating chiller. For most bioprocesses, the temperature should remain constant during the entire cultivation. For some products, however, such as penicillin or recombinant proteins i.
Measuring and controlling pH is a very important aspect of bioprocesses, as changes in the pH can significantly alter growth conditions — usually with major consequences. Culture media commonly include buffers, i. Because an acid dripping into the culture medium can damage many cell lines, scientists often carefully enrich the gas mixture used in the cell culture with CO2 rather than adding a liquid acid. The gas then dissolves in the culture medium, allowing the carbon dioxide to influence the pH in combination with a buffer.
For measuring pH during the bioprocess, each bioreactor is equipped with a pH sensor known as a combination electrode for pH. The concentration of the acid and base must be skilfully selected for this to work — if it is too high, the drops of concentrated acid or base may damage the microorganisms and cell cultures before they are distributed in the bioreactor.
If, on the other hand, the concentration is too low, operators will have to add more acid or base, unnecessarily diluting the culture medium. During a bioprocess, microorganisms usually consume a wide array of nutrients. The basic composition of a nutrient medium usually consists of water, a usable energy source for the organism e.
Depending on the organism, other compounds are necessary that cannot be synthesized by yourself vitamins, essential amino acids, etc. Depending on the bioprocess strategy these nutrients are either all made available at the beginning of a bioprocess batch bioprocess or added over time such as in a fed-batch or in a continuous process.
Schematic illustration of the correlations between living cell concentration, dissolved oxygen, and the limiting carbon source in batch operation. In the initial lag phase, the living cell count only increases slowly, which leads to a moderate but steady uptake of the carbon source. Oxygen consumption increases during the exponential growth phase until it exceeds possible oxygen input. Biopharmaceutical companies are reducing the time it takes for their products to reach the clinic by adopting platform processes.
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The addition of nutrients feeds throughout the process prevents the depletion of nutrients and provides additional cell growth.
This can extend the process duration, resulting in a higher cell density capabilities and higher product yield. A fed-batch process is the most common process, as it is one of the simplest and can have better results than a batch process.
There are different strategies for a fed-batch culture: high cell-density, constantly-fed-batch and exponential-fed-batch. High cell density is achieved by adding a high concentration feed in order to not dilute the cells.
Constantly-fed-batch involves simply adding a constant stream of feed throughout the process. Finally, exponential-fed-batch involves matching the feed rate with the feed consumption rate, so as the cells grow exponentially the feed rate is increased exponentially. Perfusion involves removing unwanted compounds, such as lactic acid, allowing the process to last longer than fed-batch. It involves recycling some of the media and utilizing tangential flow filters to remove unwanted compounds.
The pump and filter used in perfusion is very important as to not destroy the cells or clog up the filter, and to help maintain sterility. Diaphragm or peristaltic pumps can be used in conjunction with a tangential flow filter TFF. For single-use technologies, alternating tangential flow ATF is a common perfusion method paired with a single-use bioreactor. Because of this waste flow of media out of the bioreactor there is a constant fresh feed of media into the bioreactor to maintain volume.
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