Development of Capacitance Tools: At‐Line Method for Assessing Biomass of Mammalian Cell Culture and Fixed Cell Calibration Standard

: Capacitance is used to monitor "biomass" in cell culture and fermentation processes. The present work explores various ways to support good manufacturing practices (GMP) use and create robust methods that can assure proper performance of capacitance equipment. An at-line capacitance measurement method is particularly valuable as it can be used to correct or confirm online measurements from bioreactors. To obtain consistent predictions of online capacitance, the at-line method requires appropriate control of culture temperature, vessel geometry, mixing, and timing. The at-line method yields values that differ systematically from online values, but the variation is ≤11% for two cell lines tested. A cell line-specific conversion factor addresses the difference and enables accurate predictions of online capacitance values. In addition to the at-line method, verification of equipment performance is further enabled by using formaldehyde-treated cell standards. The cell-derived standards create a stabilized system for studying capacitance and recapitulate the performance of metabolically active cell culture. The formaldehyde-treated cells, however, require a much greater conversion factor to predict online outputs. The stabilized system proves useful for evaluation and calibration of capacitance measuring systems. The at-line method and stabilized cell-derived suspensions support use of capacitance for process control in large scale mammalian cell culture.