Advantages of Hollow Fiber Cell Culture
A fundamentally different approach to cell culture is now available. Modeled after the mammalian circulatory system hollow fiber cell culture offers the most in-vivo like manner to grow cells in any laboratory.
Hollow fibers are small tube-like filters approximately 200 microns in diameter whose molecular weight cut-off can be between 5 kd and .1 µm. These fibers are sealed into a cartridge shell so that cell culture medium pumped through the end of the cartridge will flow through the inside of the fiber while the cells are grown on the outside of the fiber. These fibers then create a semi-permeable barrier of defined molecular weight cut-off (MWCO) between the compartment in which the cells are growing and the medium is flowing. Since the cells are attached to a porous support (the hollow fiber) rather than a non-porous plastic dish nutrients are delivered from the bottom layer of cells on upwards. Splitting of the cells is not required and cultures can be maintained for many months of continuous production. When the secreted protein is retained in the extra-capillary space it will accumulate to a concentration of up to 100 times higher than with conventional flask or roller bottle culture.
Hollow fibers also provide a tremendous amount of surface area in a small volume. Cells grow on and around the fibers at densities of greater than 1 x 108 per mL. Hollow fiber cell culture is the only means to culture cells at in vivo like cell densities. Cell culture at high densities has the following benefits:
- Reduces serum requirements and facilitates adaptation to serum- free medium, including CDM-HD
- Increases the concentration of secreted product by 10 to 100X
- Viral and parasitic infections proceed rapidly
FiberCell® Systems Hollow Fiber cell culture cartridges are the method of choice for the production of 10 mg to gram quantities of recombinant proteins and monoclonal antibodies and the culture of 109 to 1011 cells.
Protocols are available for monoclonal antibody production, recombinant protein production using CHO, 293 and other cell types, lymphocyte expansion, conditioned medium and endothelial cell culture under defined shear stress.
- Provides 10X the gross filtration rate of cellulosic hollow fibers.
- Improves cell viability.
- Eliminates dead spots with uniform fiber spacing and “wavy” fibers within the cartridge.
- Dialyzes waste and inhibitory cytokines away from cells.
- Stabilizes the pH of the cell culture medium.
- Enhances bio-safety with a closed system.
- Handles large cell numbers (up to 1011)
- Concentrates secreted proteins and antibodies in the small volume of the extra-capillary space.
- Provides flexible control options with unique micro-processor controlled pump assembly.
- Ensures long life of the cartridge and facilitates nutrient and waste exchange across the fiber with positive-pressure displacement pumping system.
Cartridge Selection Guide
A cartridge should be selected based on the intended application. FiberCell Systems offers three types of fibers: polysulfone, cellulosic, and PS+ fibers. We also offer three different molecular weight cut-offs (MWCO): 5 kd, 20 kd, and .1 micron.
The hydrophilic polysulfone fiber is specifically selected for good cell culture performance. Both the 5 kd MWCO and 20 kd MWCO fibers have ten times the gross filtration rate of the equivalent cellulosic fiber for rapid nutrient and waste exchange. This is seen as better cell growth and higher fidelity of protein production not seen in cellulosic fibers. Any cell type that will attach to plastic or grow in suspension culture should grow well in the polysulfone cartridge.
One unique feature of the FiberCell Systems hollow fiber bioreactor is that the fibers are cast with little “waves”, resulting in an even distribution of the fiber bundle within the cartridge shell. The FiberCell Systems hollow fiber bioreactors are the first bioreactors that are optimized for both adherent and suspension cells. The cellulosic fibers are generally not intended for use in cell culture, as their low gross filtration rate is not optimal for cell growth. They have specific applications for in vitro toxicology.
As a general rule the cartridge used will depend upon the size of the secreted product you wish to collect and the amount you wish to collect. FiberCell Systems cartridges are powerful cell culture tools and their small size can be misleading. The medium sized C2011 with a surface area of 3,000 cm2 and a volume of only 20 mL has been shown to out-produce a 10 liter bag type bioreactor by a significant degree. The larger cartridges should only be used when 500 mg or more of a recombinant protein is desired.
At FiberCell Systems, we define our molecular weight cut offs at the 50% retention mark as a convention. We also speak of the “useful retention” meaning the size of protein that will be retained by 90% or more. This depends upon the size, shape, post-translational modifications and stokes radius of the protein, not just the molecular weight. For the 5 Kd MWCO fiber we define the useful retention as 20 kd. It should be used for proteins in the range of 20 kd on up to about 140 kd. For larger proteins, the 20 kd MWCO fiber should be used. Since the gross filtration rate is so high there is no penalty (such as the requirement to feed the ECS) with using the 5 kd MWCO fiber though there may be a slight improvement in productivity when using the 20 kd fiber. Please see the recombinant protein section for more information.
For monoclonal antibody production the 20 kd MWCO fiber should be used to allow TGF beta to diffuse out while retaining the antibody within the small volume of the ECS. The scale-up option here is the C5011 which is optimized for hybridoma culture. Please see the monoclonal antibody section for more information.
The PS+ fiber has a unique chemistry that allows protein matrices, antibodies and cytokines to be bound to the surface of the fiber. This cartridge should be used for primary cell types where you wish to control the surface matrix that the cells interact with and also for the growth of endothelial cells on the inside of the fiber. The fiber must be coated with some matrix so this matrix should be taken into account when selecting this fiber.
Many other cell types have been cultured in the FiberCell Systems hollow fiber bioreactor system. FiberCellSystems can provide the benefits of a combined 20 years plus experience with working with these systems and would be happy to discuss your application.