Cell Culture Systems
Petri dish and T-flask
Typically, adherent cells are grown as monolayers in static cell culture systems such as Petri dishes and T -flasks. T-flasks vary in size and can provide a surface area from 25 cm2 to 225 cm2 for cell culture. They are generally used for subculture, generation of seed material for small-scale and large-scale productions. In the case that a larger surface area is needed, more t-flasks are usually used. Scaling out using T-flasks however, is labor intensive and takes up more incubator space.
Multi-tray systems, also known as cell factories or cell stacks, have been developed for cell culture systems that require surface area up to 25,400 cm2. They provide cells with a large multi-level surface area for adherence and growth with trays stacked one above the other.
While a cell factory is capable of overcoming the limitations of T-flasks in terms of scaling out, it is essentially still a large T-flask with multiple layers. Hence, it remains a traditional static system with no agitation, aeration or movement of media. There are also concerns with regards to possible differences in the gaseous exchange between the middle unit and top or bottom unit s. Significant differences could lead to variability in yield and quality of cells.
Roller bottles have been widely used for applications of biotechnology, particularly in the development of vaccines. Unlike static systems, roller bottles allow agitation of the media and prevent formation of gradient that can adversely affect the cells. They can also provide a larger surface area than the standard T-flasks and are much easier to use than cell factories but require an additional device that would facilitate rotation of roller bottles.
Automation is recommended when a large number of roller bottles have to be utilized. Though automated roller bottle systems can potentially provide surface area of more than 350,000 cm2, the process tends to be labor intensive as number of roller bottles needed increases.
Microcarriers are particles to which adherent cells can attach and grow suspended in a stirred tank bioreactor. Compared to the mentioned static systems, microcarriers can significantly provide surface area for large-scale production. However, some issues such as shear stress and uneven oxygen distribution, that often arise when using microcarriers, can significantly affect the quality and yield of cells. For more information on the limitations of microcarriers, click here.
Stirred Tank Bioreactor
The stirred tank bioreactor is capable of supporting the growth of suspension cells and adherent cells attached to microcarriers suspended in the culture medium. For research and development purposes, small stirred-tank bioreactors whose vessels are made of heat-resistant silicate borate glass are usually used. On the other hand, stainless steel models are used large scale production. Due to agitation, however, the use stirred tank bioreactors generates shear stress which is harmful to the cells.
The wave bioreactor makes use of rocking movement to agitate the cells. It can provide good nutrient distribution, efficient oxygen transfer, and low shear stress. The main disadvantage though of the wave bioreactor is its limited scalability.
Fixed Bed / Packed Bed Bioreactor
Packed bed bioreactors offer large surface area and can produce high cell densities (0.5-2 x 108 c/ml carrier). The main drawbacks of the system though, include limited scalability due to concentration of gradients over the fixed bed and generation of a nutrient/oxygen/CO2 gradient over the height of the fixed bed resulting to a non-homogeneous environment
What VacciXcell Offers
VacciXcell offers a product line of bioreactors developed to solve problems such as limited scalability, low yield, and poor quality encountered in using traditional culture systems. For those starting out in the research and development, the CelCradle™ is an ideal bioreactor system that is capable of processing adherent cell culture. Operating under the tide motion principle, the cells residing in the matrix vessel are alternately exposed to aeration and nutrition via the gentle oscillation of the culture medium. It has the advantage of producing high cell density, has no oxygen limitation, and being cost-effective. On the other hand, the TideCell® is a pilot and production scale bioreactor that works under the tide motion principle as well. It is linearly scalable up to 5000L and the only packed bed bioreactor that can be placed inside a cGMP isolator.
For start-up biopharmaceutical companies that want to determine which cell line-to -bioreactor combination will have the best yield, VacciXcell™ Hybrid Bioreactor is a more practical bioreactor due to its dual features as it is costly to try different bioreactors for different types of cells used in cell culture. It is capable of supporting both the growth of suspension and adherent cells and performing fermentation.
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