Cell Culture FAQ

Information applicable to use of Pall single-use bioreactors in cell culture applications.


How do I estimate cell density in the iCELLis® 500 Bioreactor?

Generally, there are three ways to estimate the cell density in the iCELLis 500 Bioreactor.


  1. Biomass probe: cell density may be correlated to the normalized capacitance measured by the biomass probe, provided that this correlation has been established experimentally during process development. Capacitance measurement is dependent not only on cell density but also on cell diameter, media composition and other process parameters. Therefore, we recommend establishing the correlation specifically per process and per process step.

  2. Metabolites concentration: the cell density may also be correlated to the concentration of certain metabolites (e.g., glucose), provided that this correlation has been established experimentally during process development.

  3. For high cell densities, cell density value may also be correlated to the oxygen consumption, provided that this correlation has been established experimentally during process development. The oxygen consumption of a cell culture can be estimated by calculating the difference of dissolved oxygen (DO) measured by the probe in the media before it passes through the fixed-bed versus the probe in the media after it passes through the fixed-bed.
Can I put my iCELLis® Nano Bioreactor on the bench, and not in the biosafety laminar flow cabinet?

Yes, the iCELLis® Nano Bioreactor is a closed system and can be run outside a sterile environment.

What is the accuracy range of dissolved oxygen (DO) and pH probes used with the iCELLis® 500 Bioreactor?

As stated in the validation guide USTR 3393, in case of a one-point calibration in the range from 6.5 to 8.5, an accuracy of ± 0.1 is guaranteed for the pH sensor after gamma irradiation and with product calibration. For the DO sensor, an accuracy of ± 3.5% between 15 and 75% and of ± 7% between 75% and 150% after one-point calibration is provided after gamma irradiation and with product calibration.


What is the lowest seeding density I can use with the iCELLis® Bioreactors?

Seeding densities as low as 500 cells/cm2 may be used in iCELLis bioreactors. However, the use of very low seeding densities may result in a prolonged lag phase.


As a first approximation, it is generally accepted that:

  • Seeding densities ranging from 15,000 to 30,000 cells/cm2 can be used with no impact on lag phase.
  • Seeding density can be reduced to 5,000 cells/cm2 without noticeable impact on the lag phase for most (but not all) processes.
  • Reducing the seeding density below 3000 cells/cm2 is likely to impact the lag phase.


We recommend that end users evaluate the impact of cell seeding density on cell growth kinetics and process productivity in the iCELLis Nano bioreactor for their specific process.


For additional information, refer to the iCELLis product datasheet.

What grade/quality of gas is required for the iCELLis® Bioreactor?

As noted in the operating manual USD 3277b, the compressed gas provided should be a clean, dry, analytical grade source of each compressed gas (O2, CO2, air and optionally N2) regulated between 2 bar (29 psi) and 6 bar (87 psi). Gases from local compressors or generators must be filtered and dried.  This is required to prevent failure in the mass flow controllers and hardware.


What is the maximum cell density I can reach in the iCELLis® Bioreactors?

Generally, cell densities are highly process-dependent. Some cell lines (e.g., HEK293; Vero) may reach up to 800,000 cells/cm2 in iCELLis bioreactors. Wang et al. (2015, Large-scale Clinical-grade Retroviral Vector Production in a Fixed-Bed Bioreactor) reached 1,180,000 cells/cm² after 11 days of growing 294Vec.


However, for the majority of bioprocesses, very high cell densities negatively impact productivity. Furthermore, high cell densities are always achieved at the expense of a high media consumption, which may negatively impact process economics.


We recommend that users evaluate the actual impact of cell density on productivity as part of their individual process optimization.

What monitoring possibilities are available with iCELLis® Nano Bioreactor?

The iCELLis Nano Bioreactor features inline continuous monitoring of cell culture temperature, pH, dissolved oxygen (DO), and cell capacitance for estimating cell density. Aseptic sampling of supernatant through a needless swab-able valve is featured for offline monitoring of metabolites, pH verification and titer follow-up. Sampling of carriers (within reason without limitation) from the top of the fixed bed is featured for offline counting of nuclei to follow-up on cell density.


What are the advantages of using a perfusion process with the iCELLis® Bioreactor?

The iCELLis technology allows for setting-up perfusion processes. The significance of the advantage is of course process dependent. Perfusion allows for better media-management during growth phase (i.e., lower consumption or stable metabolite levels), as well as continuous harvest during production phase when the product is extracellular. This may greatly increase titers when the product is unstable at cell culture temperatures or sensitive to impeller caused shear.

Can I recover cells from iCELLis® Bioreactor carriers by trypsinization?

The iCELLis technology was not designed for the production and recovery of viable cells, but rather of drug substances produced by the cells.


Depending on process circumstances (including factors such as cell type and media composition), it may be possible to recover a small portion of live cells – for example, for cell characterization. For more information on how to perform such trials, contact us (link) to request support. 

What do I need to do to ensure even cell distribution with iCELLis® Bioreactor?

The most important factor to consider for an even distribution of cells is the quality of the biological material - i.e., a good single-cell suspension inoculum. Clusters of cells present on the inoculum will create patches of cells in certain areas of the fixed bed, causing an uneven cell distribution. Secondly, the process parameters during inoculation will impact the distribution. Our applications team can work with users to provide recommended settings for each process.  Contact us to request support


Can I use the iCELLis® Nano Bioreactor in GMP production?

Yes, the iCELLis Nano has been used in GMP production by some of our customers. The software delivered with the iCELLis Nano Bioreactor System is compatible with 21 CFR Part 11 requirements. Following the guidance of our Instructions for use,  USD328 (mPathLink)., the system can be implemented in a GMP environment.


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