Sterilization of Cell Culture Media - Taking on the Challenges

Tuesday, July 28, 2020 by Filtration Team

Sterilization of Cell Culture Media - Taking on the Challenges_PROPOR SG Sterilizing Grade Filter Capsule_Parker Bioscience Filtration Cell culture media is a key component of upstream bioprocessing needed to encourage the growth and survival of cells. This is vital to achieving a viable cell density and, ultimately, the desired product titre. However, its filtration can be a challenge for biopharmaceutical manufacturers.

Cell culture media is a complex mixture and typically contains up to 60 ingredients. However, the exact composition will differ based on the media chosen for the specific application.

Media is usually supplied either as a powder, concentrate or working solution. If a powdered media is used, it must be mixed and sterilized on site prior to use.

Cell culture media can be categorized into several different formats based on its composition:

Serum

Serum is a nutritionally and protein-rich substance derived from animal blood. Serum containing media was once seen as essential for good cell growth and proliferation, however, the desire for animal component-free media due to concerns about contamination and regulation have led bioprocesses away from this media type.

Serum is also expensive and as it is a natural product, it is by nature uncharacterized and is prone to a high degree of variation.

Serum-free media

Serum-free media often contains proteins/protein hydrosolates and, while it is more characterized than serum-based media, it may still contain components derived from animal sources.

Animal-derived component-free media

Animal-derived component-free media offers an alternative to serum media. It uses non-animal derived proteins and hydrololates available from soy, yeast or other non-animal-based sources.

Protein-free media

Protein-free media allows greater chemical definition of the media's make up.

Chemically defined media

Chemically defined media aims to eliminate variation by using only fully defined components - these may be animal-derived or animal-free depending on the media.

Whichever media is used, a compromise must be found between safety, characterization and performance. Robust supplier quality assurance is needed to ensure traceability and the procurement of contamination-free media.

The media will ultimately be chosen to suit the process.

So, what is cell culture media composed of?

Depending on how characterized the media is, the concentrations of components and exact composition may vary lot-to-lot. Different medias will also have different compositions.

Sterilization of Cell Culture Media - Taking on the Challenges_Cell Culture Media Components and Functions_Parker Bioscience Filtration

The ingredients in cell culture media provide a rich nurturing environment for the cells biopharmaceutical manufacturers wish to propagate. Unfortunately, that kind of environment is a place in which bacteria or other unwanted microorganisms can flourish.

The role of filtration

Filtration is commonly used to protect cell culture media from contamination. If the powdered media is prepared on site, it will be prepared in a mixing vessel. Components such as water will be filtered to remove contamination prior to entering the vessel and any air and gas or venting will be protected using gas filters.

Prior to entering the bioreactor itself, the media will be filtered to ensure its sterility - and to, therefore, protect the bioreactor. This filtration may involve prefiltration as well as sterilizing-grade filtration or Mycoplasama removal filtration, depending on the process.

0.2 micron rated validated sterilizing-grade filtration is used to achieve sterility, or if Mycoplasma contamination is of concern. 0.1 micron rated filtration validated for Mycoplasma removal should be used. Depending of the process and media, prefiltration may also be required.

The correct design of this filtration system is crucial in optimizing the process. The design must take into account:

The required retention of the filters.
The sizing of the filters to ensure the required throughput can be met.
The flow rates the filters are capable of to ensure the process can be carried out within the available time.

The challenges of cell culture media filtration

A number of issues can arise in the cell culture media filtration process:

If the filters have not been sized correctly, this can result in a low flow rate - and, therefore long processing times.
Filters may foul or block prematurely. This can be due to a variation in raw ingredients, an excess bioburden in the process, or the filtration system being too small for the batch size.
If a process is at risk of Mycoplasma contamination, contamination may occur if a 0.1 micron Mycoplasma retentive filter isn't used.

However, these issues can be mitigated by optimizing the filtration system correctly.

Parker supports biopharmaceutical manufacturers in filtration system optimization through testing, process trials and validation as well as technical support for existing systems. We have an extensive range of filters designed for cell culture media filtration including PROPOR SG, our standard 0.2 micron sterilizing grade product, PROPOR HC, our high capacity sterilizing grade product for difficult to filter or variable medias and PROPOR MR 0.1 micron filter designed for use in processes where Mycoplasma contamination is a concern.

For more information on cell culture media filtration, view our recent webinar: Optimization of Cell Culture Media Filtration in Bioprocessing

What are your biggest challenges in sterilizing filtration media? Let us know in the comments below.

Sterilization of Cell Culture Media - Taking on the Challenges_David Heaney_Parker Bioscience Filtration This post was contributed by David Heaney, market development manager, Parker Bioscience Filtration, UK

Parker Bioscience Filtration specializes in automating and controlling bioprocesses. By integrating sensory and automation technology into a process, a manufacturer can control the fluid more effectively ensuring the quality of the final product. Visit www.parker.com/bioscience to find out more.