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Monitoring Viable Cell Density for
Improved Bioreactor Control

inserted into the bioreactor with in-situ sterilizable standard 12mm and 25 mm diameter probes to fit any bioreactor port. The probes design and materials are ideal for working in a cGMP environment as the wetted material conform to FDA requirements (PEEK, 316L stainless steel).
The BIOMASS SYSTEM is ideal for monitoring animal cell in suspension (including clumping cell lines) or attached to microcarriers, it is also routinely used for yeast or bacteria batch and fed-batch processes with high biomass concentration up to Cell culture and fermentations are used to produce
pharmaceutical products or other molecules of interest. To achieve maximum efficiency or quality assessment during the synthesis of targeted products, on-line information 200g/l dry weight. It includes a unique triple frequency about the active metabolic cell concentration is of crucial measurement that results in insentivity to cell size variations importance. Although the biomass is the catalyst of the bio- production and its concentration is a key parameter in the reaction, the bioreactors are still commonly monitored with only usual pH, CELL CULTURE OPTIMIZATION
temperature, and dissolved oxygen sensors. In fact the optical DURING PROCESS DEVELOPMENT
techniques that have been proposed to monitor the biomass suffer Figure 1 demonstrates how the on-line Permittivity signal can from a number of disadvantages such as sensitivity to cell debris be used to monitor viable cell density during a 2 L CHO batch and other media components or loss of linearity.
culture. The BIOMASS SYSTEM (fitted with a 12 mm diameter From its 20 years of experience in capacitive metrology, sensor) Permittivity is providing a linear correlation with viable FOGALE nanotech has introduced the direct capacitance cell count over the complete timecourse of the culture. In measurements into a robust, precise and reliable system. addition, it is obvious from figure 2 that changes in cell metabolism can be monitored by means of the Permittivity MEASUREMENT PRINCIPLE
measurement. The first drop in Permittivity corresponds to a The use of capacitance for on-line process monitoring is very metabolic shift where glutamine becomes a limiting nutrient; attractive and selective by only taking into account the viable the oxygen uptake rate also decrease significantly. Alanine is cells : under the influence of an electric field between two accumulating until glutamine is depleted and is subsequently electrodes, only cells with intact plasma membranes are consumed. The second drop is correlated to the exhaustion of polarized and behave as tiny capacitors. The resulting alanine and glucose that marks the beginning of the death capacitance (medium Permittivity) can be measured by a phase. The same patterns are obtained from a larger scale second electrode pair and is accurately and linearly correlated culture with a 25 mm diameter sensor.
with viable biomass concentration. Dead cells with broken By providing real time signals, the BIOMASS SYSTEM is a membranes do not contribute to the signal.
useful tool for cell culture process monitoring and control and process optimization.
Geoffrey Esteban is product manager at FOGALE nanotech, Park
From the Permittivity measurement technique FOGALE Kennedy - Bât A3, 285 rue Gilles Roberval, CS 32028, 30915 Nîmes nanotech has recently launched the new generation of on-line Cedex 2, France; 33-466-620555, fax 33-466-627160;; biomass monitoring tools. The patented BIOMASS SYSTEM is an affordable sensor for viable cell density monitoring, it is directly Figure 2: Permittivity, volumetric O2 uptake rate, and main nutrient
Figure 1: Permittivity, viable and total cell counts during a CHO 2 L
concentrations during a CHO 2 L batch culture (Data courtesy of F. batch culture (Data courtesy of F. Hoffmann-La Roche Ltd. 2004) BioProcess International



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