Capacitance has been used to monitor “biomass” in cell culture and fermentation processes. While it is generally accepted that capacitance measurements are related to viable cell mass, the molecular species responsible for carrying capacitive charge have not been identified. The absence of a mechanistic understanding precludes the ability to predict capacitive behavior across systems or methods. We show that culture samples obtained from bioreactors can be used to predict or confirm on-line capacitance values. The accuracy of our at-line monitoring method depends on proper control of vessel size, temperature, and mixing for the capacitance equipment; and timing is especially important due to the dynamic nature of the cultured cells. We compared the dynamic situation of viable cultured cells with a stabilized capacitance system comprised of formaldehyde-treated cells suspended in standard cell culture media. The stabilized cells are non-viable, but possess a comparable capacitance to viable cell cultures (at the same density of particulates per unit volume). Further, the stabilized system allowed confirmation of critical at-line parameters that had been identified using viable cell cultures. The formaldehyde-fixed cells are shown to function as calibration standards for testing various capacitance measuring equipment and/or methods. Finally, the combination of the at-line equipment and stabilized capacitive cells enabled studies to test the sensitivity of capacitance (rather than cellular responses) to system perturbations. Based on sensitivity to detergents, pH and temperature, the identity of the capacitive charge carriers appears consistent with molecules integral to cellular membranes. Capacitance signals are therefore subject to changes in membrane composition, but are not necessarily dependent on viability of the cell culture being assessed.

At-line investigation of capacitance for assessing biomass of mammalian cell culture

255th National Meeting (2018)

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