Evaluation and applications of optical cell density probes in mammalian cell bioreactors

Abstract

On-line optical cell density probes were implemented to continuously monitor the cell densities in mammalian cell bioreactor and to achieve advanced bioreactor controls. We tested cell density probes from six manufacturers in high cell density bioreactors. When externally calibrated, Aquasant and Ingold backscattering probes produced the most linear probe responses (PR) versus cell density (CD), followed by the ASR and Cerex laser probes. Monitek and Wedgewood transmission probes had lower resolutions. All probes were tested in two murine hybridoma fermentations. Cell densities varied between 1 x 10(6) cells/mL to 20 x 10(6) cells/mL and the bioreactors were operated for 5 to 7 weeks. For our bioreactors, Aquasant, Ingold, ASR, Wedgewood, and Monitek probes gave satisfactory responses. Little fouling was observed with any probe at the end of 2 weeks. Fouling was a possibility after 3 weeks in one bioreactor but its effect can be easily corrected. Cell density control and specific perfusion control of bioreactors based on the Aquasant probe were achieved. Implementation of cell density probe based perfusion control, instead of "step perfusion adjustments" based on manual hemacytometer control, will result in smoother operation, healthier cultures, increased medium delivery efficiency, and reduced operational excursions.

Perfusion Processes

“…The OD probe measures the turbidity, which gives information about the interference of particles present in a fluid, in other words the total cell density given that these particles are only cells. Wu found that the prediction of the cell density by Aquasant probe was satisfying up to 20 Â 10 6 cells/mL when the culture had a high viability and a low level of cell debris but deviated otherwise (Wu et al 1995). Gorenflo mounted an OD detector in the acoustic settler and showed a linear correlation of the cell density with this signal up to 20 Â 10 6 cells/mL density (Gorenflo et al 2005a).…”

On-line Measurements and Control of Viable Cell Density in Cell Culture Manufacturing Processes using Radio-frequency Impedance

“…On-line optical sensors have been used in some cases to maintain the process (Merten et al 1987;Konstaninov et al 1992;Zho and Hu 1994;Wu et al 1995). In general, probe performance is acceptable for high viability culture but the light based probes do not distinguish between the viable and non-viable cells and these will also detect debris that can collect during the process.…”

“…Merten et al (1987) described an infra red sensor for determination of the cell number during continuous hybridoma fermentations but the range of cell densities tested and length of operation was limited. Laser turbidity probes have been used in batch culture (Konstantinov et al 1992;Zho and Hu 1994;Wu et al 1995) and the probe performance in general is acceptable for high viability cultures. The light based probes measure the total number of cells and during process operation upsets the optical measurements have been shown to deviate from the cell density determined by trypan blue exclusion (Wu et al 1995).…”

Specific heat flow rate: An on-line monitor and potential control variable of specific metabolic rate in animal cell culture that combines microcalorimetry with dielectric spectroscopy

“…While there are several off-line assays for biomass, the most basic (and time-consuming) being dry weight, it would be preferable to take advantage of the potential of heat flow rate measurements in real time by estimating biomass on-line. There are two comparable methods for this, optical density using laser light (Wu et al, 1995;Zhou and Hu, 1994) and dielectric spectroscopy (Harris et al, 1987). Because cell metabolism depends on viable biomass and in a declining metabolic condition the viability could reduce quickly, a direct measurement of viable cell mass would be ideal.…”