Lecture 6.docx - Lecture 6 Bioreactor Monitoring and Control Measurement of cell culture parameters On-line measurements using in-situ sensors o

Lecture 6.docx - Lecture 6 Bioreactor Monitoring and...

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Lecture 6: Bioreactor Monitoring and Control Measurement of cell culture parameters - On-line measurements using in-situ sensors o Temperature, pH, Dissolved oxygen (DO), dissolved CO2 - Disposable sensors - Measurement of gas flow rates - Off gas analysis - On-line measurements of metabolite and product concentration Real-time monitoring of cellular activities - Growth, metabolic, and production rates - Oxygen consumption rate Monitoring or estimating cell density - Cell density probes - Estimates based on metabolic rates Process Control - Principles of process control - On-off (bang–bang) control - feedback control - PID control On-Line Bioreactor Monitoring and Control Overlay air in the headspace to minimize CO2 + O2 accumulation - Air, CO2, N2, and O2 are added at the same time based on the computer - Mass flow controllers are digital and can be controlled by the computer Agitator (RPM) is set by the control system On-Line Bioreactor Monitoring and Control Five Components - Probes/Sensors - measurement - Meters/Amplifiers gives you pH, temp, etc - Mass Flow Meters (MFCs) for Gas - Pumps for Liquids connected to the system - Controller Unit o Has I/O interface o In amps or mvolts Measurement of Temperature, pH, Dissolved Oxygen, Dissolved CO2 - Temperature in bioreactors is measured using Resistance Temperature Detectors (RTDs). The change in resistance due to temperature change is measured o Basically a wire and the tip of the wire has a resistance, the resistance changes by the temperature - pH, dissolved oxygen, and dissolved CO2: o Sensors (probes) are available for off-line and on-line measurements o On-line measurements in bioreactors require sterilizable probes
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Measurement of pH - Calibration using pH buffers (pH 7.0 first, then either pH 4.0 or 10.0 buffer) - Temperature compensation - Maintenance and care during storage - check the response time of the electrode - Sterilization may change the calibration, typically one-point recalibration is performed after sterilization - Uses a glass probe - pH buffer goes bad, has to change them or youll be in trouble for calibration Measurement of Dissolved Oxygen (DO) - Two types of sensors, Galvanic and Polarographic (more common) - Calibration of DO probes (100% in air at 1 atm, electronic zero, and/or use of N2) o Calibrated in air, 100% means 100% air saturation - Polarization of the electrode (2-8 hrs) is needed - Voltage is constant (-0.7 V), current is proportional to DO - Temperature and pressure can change the calibration - Maintenance: Membrane and electrolyte change - Sterilization may change the calibration, typically one-point recalibration is performed after sterilization DO Probe Reading and Dissolved Oxygen Concentration - DO probes are calibrated in air to read 100% air saturation (air is 21% oxygen) o if DO probe is exposed to 100% oxygen, it will read 476% air saturation o A reading of 50% saturation is equivalent to 10.5% oxygen - Concentration of oxygen in mmol o 100% air saturation at 37oC and at 1 atm ~ 0.2 mM (depends on solution) o Temperature and pressure should be included in the calibration of DO probe o
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