Bioreactors are used to culture cells or other organisms such as yeast or bacteria. There are many uses for bioreactors (also called fermentors), but in this article we'll focus on their uses in production of biopharmaceuticals such as monoclonal antibodies (mAbs), vaccines, and cell and gene therapies.
What is the purpose of a bioreactor?
Biopharmaceuticals synthesized by living cells are very complex. They differ from traditional pharmaceuticals, such as acetaminophen (paracetamol), which are small molecules and produced through chemical synthesis. In bioprocessing, if any of the process parameters in the bioreactor fall outside of the desired culture conditions, it could kill the cells or lead to a change in the product. Thus, bioreactors are designed to maintain conditions optimal for cellular growth and expression of the target molecule.
Fig 1. Bioreactors exist in a wide range of sizes and forms. This image shows a range of stirred-tank bioreactors with working volumes of 50-2000 L used for mammalian cell culture in process development and manufacturing.
Bioreactor principles
Bioreactors are used to grow cells in a specific environment. The bioreactor provides essential gassing, mixing, temperature control, fluid delivery, and other critical process parameters (CPPs). These CPPs support specific applications and may vary depending on the requirements of the process demands. CPPs increase the concentration of cells, the ratio of living cells (viable cell density) as well as sustain the environmental conditions required while the cells complete their cellular tasks (for example, secrete the desired proteins).
Oxygen transfer is a key CPP for mammalian cell culture. Learn about the 7 factors that affect oxygen transfer to cells.
The control of CPPs mentioned above, such as temperature, pH, and dissolved oxygen levels, use a combination of sensors and actuators to read the process-specific condition and to drive a signaled change. This process must be done accurately and repeatedly over time, as the types of cells used are complex and sensitive to environmental change. Optimizing and monitoring these processes can be challenging, and most bioreactor systems include automation to help address these complexities. Learn more about controlling the key processes of a bioreactor.
There are strict regulatory approval processes involved in biopharmaceutical production to ensure the process is controlled and validated to the product of interest. Typically, the process variables must be recorded, and any variance will mean the run does not pass regulatory controls. The cells used inside a bioreactor have a lifecycle. They have a lag phase, a growth phase, a stationary phase, and a death phase. In other words, they grow, secrete the desired proteins, and then die. The cells typically used are mammalian cells, such as Chinese hamster ovary cells (CHO). A typical run will last for approximately 10 to 14 days for fed-batch as an example.
How does a bioreactor work?
There are many different types of bioreactors, including stirred-tank, rocker, air lift, and fixed-bed. Stirred tank is the most widely used bioreactor design in bioprocessing. These range in size from 15 mL to >2000 L and can be used to scale up a process from lab to manufacturing scale. They are equipped with an impeller for homogenizing culture media and a sparger for delivering oxygen to the cells.
Rocker bioreactors, often offered as single-use systems, involve a bag on a moving platform and are usually used for small-scale production or for seeding into larger bioreactors.
Air-lift bioreactors are infrequently used in the biopharma industry. They rely on air bubbles to aerate and carry the media around the reactor for mixing at the same time. Fixed-bed bioreactors are used for adherent cells, involving specialist cells that can only grow when attached to a surface. Learn more about the different types of bioreactors.
What are the key components of a bioreactor?
Large-scale bioprocessing often uses stirred-tank bioreactors. These can be single-use, in which cells are cultured in a disposable container that's replaced for each new batch of cells, or they can be multi-use, in which a stainless steel tank is used for multiple batches of cells. Multi-use bioreactors can handle batch sizes up to 15 000 L, but the cleaning and validation requirements can be cumbersome. Single-use bioreactors, on the other hand, top out at around 2000 L, but they offer faster changeover between batches and can be used in parallel to increase production volume by scaling out (vs scaling up a single container). Learn more about the differences between single-use and stainless-steel bioreactors.
Key components of stirred-tank bioreactors include an impeller, sparger, probes, aseptic seals, baffles, feed lines, drain line, air vent, and a temperature control unit. How these are designed influences the performance of the bioreactor system. Read more about these components in detail in Parts of a stirred-tank bioreactor and their function.
How are bioreactors used in cell culture?
Adherent and suspension cell bioreactors
Adherent cell culture technologies such as the fixed-bed bioreactor system offer a large surface area for adherent cell cultivation in a closed and controlled environment. These can be adopted for various applications, and production of extracellular and intracellular viruses and proteins that are grown and produced by the cells attached to a surface.
Suspension bioreactors create a dynamic and controlled culture environment through agitating the fluid with the purpose of keeping the product in suspension. This may be achieved through a few different methods such as mechanical agitation, introduction of gas to keep the liquid turbulent, or by manipulation of the entire vessel.
Bioreactor applications in biotechnology
When considering the applications that use bioreactors, biotechnology is one of the main industries that employ this technology. For example, the growth of cells such as mammalian and insect cells can be performed in mechanically agitated bioreactors with or without microcarriers, rocking platform bioreactors, and rotatory bioreactors. These cells can then be used to produce a range of proteins, like antibodies and enzymes, along with viral vectors without having to remove the cells from the bioreactor. The use of bioreactors is not limited specifically to the biotech industry for therapeutic and medical use. For example, photobioreactors, which utilize a light source and airlift of gassing the solution, are used to culture organisms that use photosynthesis, such as algae and cyanobacteria. These organisms can be further refined into biofuel. Bioreactors, or fermenters, are also used to produce biofuels such as bioethanol from plant products such as corn and sugarcane.
And of course, bioreactors are not limited to biotechnology, we see them used by the food and beverage industry in milk processing and production of yeast and beer.
A brief history of bioreactors
Early in the 20th century, cell culture was fairly limited to small-scale tissue culture propagation techniques used for fundamental research. In parallel, large bioreactors were in use to produce economically valuable secondary metabolites by microbial fermentation. By the mid-1950s, huge vaccination campaigns were also implemented, bringing with them the development of industrial-scale cell culture bioreactors. Prior to this, primary cells were cultured for vaccine manufacture on a very small-scale using roller bottles.
Examples of the first cell culture bioreactors, such as plate propagators and packed beds, were made expressly for adherent cells. The first commercially viable suspension cell products – the interferon generated in Namalwa cells and the vaccination for the food-and-mouth disease – spurred the adaptation of homogenous bioreactor systems used for microbial growth, to meet the needs of the mechanically more delicate animal cells.
The development of numerous diverse bioreactors and culture systems suitable for suspension cell culture followed, with a focus on increasing the product yield per unit volume through improved nutrient supply and waste product removal. This was made possible by the emergence of the monoclonal antibody era in the 1970s. These specialized systems include fluidized bed reactors, hollow fiber bioreactors, and other compartmentalized bioreactors based on the perfusion of new media through the cell-containing compartment and the immobilization of cells.
The underlying concept was to create an environment that would enable the cells to continually generate the desired product at high levels while overcoming the two main drawbacks of cell cultivation – slow cell development and low final cell density. Many cell retention technologies for stirred tanks or airlift bioreactors were created concurrently, enabling continuous medium exchange in homogenous systems. In the 1980s, several protein therapies could be produced in mammalian cells thanks to recombinant DNA technology, which is the foundation of contemporary biotechnology. This unique potential also had an influence on the design and refinement of large-scale bioreactors for anchorage-dependent and suspension cells.
FAQs about bioreactors
What is a bioreactor in simple terms and how does it work?
A bioreactor is a tool or system used to grow cells in a controlled environment.
What is the purpose of a bioreactor?
Bioreactors are used to culture microbes or mammalian cells for research, biotechnology, biomanufacturing, or food and beverage production.
What are the key components of a bioreactor?
Key components of a stirred tank bioreactor include an impeller, sparger, probes, aseptic seals, baffles, feed lines, drain line, air vent, and a temperature control unit. Different types of bioreactors have different components depending on the application, cell type, and scale.
How is a bioreactor different from a fermenter?
Technically, these terms are interchangeable, but in practice their use often indicates the type of cells being cultivated. "Fermenter" is employed more often when used to cultivate bacteria, yeast, or fungi. "Bioreactor" often refers to systems for culturing mammalian cells.
Explore other articles in the series
What are the different types of bioreactors?
Parts of a stirred-tank bioreactor and their function