Shakers, rockers, and stirred tank bioreactors – advantages of each
We’ve previously written articles comparing single-use bioreactors to stainless steel or glass multi-use bioreactors. You can read about when to switch to single-use, the advantages of single-use in small-scale bioprocessing, and the environmental impacts of single- and multi-use bioreactors.
In this article, we compare the following mixing technologies: shaker, rocker, and stirred tank bioreactors. At Interphex 2021 we had the opportunity to speak with engineers from Kuhner Shaker about their new shaker bioreactors, MicroDigital Co. about their single-use Cel Bic rocker bioreactors, and Eppendorf about their stirred tank bioreactors.
Each of these bioreactor technologies can be used with single-use or reusable bioreactors, differing primarily in their method of aerating and mixing the culture to maximize oxygen transfer from the bioreactor environment into the growing cells.
Stirred tank bioreactors
Stirred tank bioreactors are the industry classic. They are generally cylindrical, contain at least one sparger to deliver gas into the culture medium, and utilize an impeller to mix the cell culture and break up/distribute the gas bubbles throughout the bioreactor.
These bioreactors may be either single-use or stainless steel. Single-use reactors range from about 15 mL to 2000 L, and reusable bioreactors may be as large as 50,000 L.
Stirred tank bioreactors are often used to scale a bioprocess from R&D to manufacturing scale. Because they are time tested and most commonly available, the math, physics, and biology of mass transfer is well known.
These known mixing principles make for highly efficient gas transfer in stirred tank bioreactors. They are also highly flexible across a wide range of operating conditions, meaning they can be used to culture sensitive mammalian cells at low shear stresses, or to grow certain fungi requiring extreme temperatures and high pressures.
While sparging allows for oxygen transfer through larger volumes and has a smaller footprint, it is not as efficient as oxygen transfer through the headspace. Another disadvantage is the shear stress introduced by the impellers, which must be minimized when stirring mammalian cultures. Impellers additionally introduce foam into bioreactors and must be treated with anti-foaming agents. Finally, the impellers and spargers in stainless steel bioreactors must be thoroughly cleaned to prevent contamination.
Rocker (or wave) bioreactors are also fairly common. They are generally large, plastic, single-use bags that lay flat on a gently rocking platform (<100 rpm). These bioreactors deliver oxygen into the cell culture through the headspace and mix the broth using the rocker platform.
Rocker bioreactors are most commonly used in laboratories. Since they are highly efficient but have a large footprint, they may also be used for small production volumes or to seed larger stirred tank bioreactors.
The large, flat, 2-dimensional rocker bioreactors have a very high surface-area-to-volume ratio for highly efficient oxygen mass transfer. They are also gentler than stirred tank bioreactors because they fully aerate the culture without the need for impellers. Finally, as rocker bioreactors do not use spargers or impellers and are most often single use, they are simple to clean and pose almost no risk of cross-contamination.
Large, flat rocker bioreactors do not scale well. They generally range from only 5 to 100 L, with their size limited by the rate of oxygen transfer through the headspace.
Shaker bioreactors sit on a platform that mixes by moving in a circular motion as simple as a 2D circle or as complex as a 3D figure eight. Like rocker bioreactors, they deliver gas entirely through the headspace.
The swirling motion moves the cell culture broth up onto the sides of the bioreactor, resulting in a very thin fluid layer adhering to the side of the vessel. This enables maximum oxygen transfer without the need for a large footprint. Mass transfer is entirely dependent on gas flow through the headspace, so shaker bioreactors scale well linearly.
This approach to mixing also mitigates shear stress, making it well suited for mammalian cell cultures.
While shaker bioreactors solve many of the issues associated with sparging and impelling, they are a much newer technology. The math of scale-up and oxygen mass transfer are much less well-known than for other bioreactor types.
What bioreactor type should I use?
Stirred tank bioreactors are proven to scale well, can be tightly controlled, and operate on known mass transfer principles. Rocker bioreactors have the most efficient mass transfer, but footprint rapidly becomes an issue during scale up. Shaker bioreactors are a newer technology, but one with the potential for high efficiency and yields, and linear scaling.
Depending on the production volumes needed and the scale-up plan, different types of bioreactors will likely be more or less advantageous during different development phases. Choosing bioreactors that are optimized for each development phase is a solid strategy. However, it may be viable to instead choose a bioreactor which is not well suited for a early phases but can easily scale from lab to manufacturing scale.