Bioprocess Control
MATA KULIAH: PENGANTAR TEKNOLOGI BIOPROSES
Successful of bioprocessing depends on controlling key process variables:
1. Nutrient metabolite concentrations, 2. Growth factor compositions, and
3. Physiological parameters (e.g., temperature, pH, and oxygen)
Bioprocess Parameter
They affect cell growth, viability, and differentiation.
A fed-batch strategy is often considered most suitable for
tuning and optimizing cell metabolism. It is more efficient, which reduces metabolite accumulation in culture supernatant.
Nutrient metabolite concentrations
This play a crucial role in regulation of stem cell behavior.
So perfusion mode has been preferentially adopted for most stem cell bioprocesses because it ensures continuous renewal of nutrients and other factors as well as continuous removal of metabolic by-products.
Growth factor compositions
1. MSC differentiation is enhanced at lower temperatures (32 °C) than in 37 °C conditions (70), whereas high temperatures (39
°C) enhanced megakaryopoiesis in CD34-enriched cord blood cells (71).
2. High pH (7.60) enhanced differentiation and maturation of megakaryocyte progenitors (72), whereas lower values (7.1) increased their expansion capacity (73).
3. Oxygen is critical to hESC culture (18), and emerging evidence suggests that reducing its concentration to low levels (74, 75) can be beneficial for in vitro maintenance of pluripotent hESCs, supporting their self-renewal and reducing spontaneous differentiation while maintaining karyotypic integrity (76, 77) compared with normoxia conditions (20%). So a robust strategy has been developed for mass production of undifferentiated hESCs using pO2 –controlled bioreactors (61).
Physiological parameters (case study)
Bioprocess Parameter (all)
Optimization
For optimized process yields, control system performance is
critical to managing and documenting
perfusion, recirculation, and feeding of bioreactor cultures for an optimal growth environment and maximized cell viability.
This is particularly important for the dynamic environments created by differentiating stem cells.
Monitoring and controling
Process
Measure all of variable
Decide which variable relevant
Compare the measured value with the calculated(desired) one
Decide the action of result
Measurement of variable
2
Using sensor
2Manual analysis
1. Temperature 2. pH
3. Pressure (PO2, PCO2) 4. CO2, CCO2 (dissolved) 5. Biomass
6. Optical density 7. Redox potential 8. Thermodynamics
1. Cell mass concentration 2. Cell number concentration 3. Substrate
4. Product
5. Intermediet
Measurement of variable
Fig. 1. Common measurement and control of bioreactors as generally accepted as routine equipment
Measurement of variable
Taking
sample Insitu
measurement
The methods of direct growth measurement are cell optical
density, total cell
counters, coulter counter, cell dry weight, packed cell volume and optical detectors.
The indirect measurements of cell growth are based on cellular components, measurements of ATP, bioluminescence, substrate consumption and product formation, oxygen uptake
Basic control fasilities
Temperature control
pH control
Dissolved oxygen control Foaming
control Level
control
The vessel is jacketed for cooling and heating
Use base, acid or buffer
Rate of oxgygen supply Antifoam,
agitation Rate of
substrate (valve, flow meter)
Temperature
control Heat is generated in the fermenter by dissipation of power, resulting in an agitated system; heat is also generated by the exothermic biochemical reactions (related to the rate of cell growth).
Measuring temperature: using thermometers/
thermocouples/ thermistors/ platinum resistance thermometers/ miniature integrated circuit devices
Controlling: cooling by jacketed system with the principle of heat transfer; heat production is equal to the heat transfer by the jacketed system.
pH control
The pH has a major effect on cell growth and product formation by influencing the breakdown of substrates and transport of both substrate and product through the cell wall
Measurement of pH is based on the absolute standard of the electrochemical properties of the standard hydrogen electrode. Ag/AgCl electrode and KCl electrolyte saturated with AgCl2.
A constant potential is maintained at the inner surface of the glass membrane by filling the tube of the electrode with a buffered solution of accurately determined and stable composition, and with constant and accurate hydrogen ion activity.
Dissolved oxygen control
Method of DO measurement:
(1)The tubing method;
an inert gas flows through a coil of permeable silicon rubber tubing, oxygen diffuses from the broth then measured by an oxygen gas analyser
(3) electrochemical detectors (the most common)
types: galvanic and polarographic detectors
It use membranes to separate electrochemical cell components (2) Use of mass spectrometer probes;
priciple: the ability of the gas to diffuse across the surface membrane.
Exemple of sensoring scheme (PO2)
O2 changes
O2 react with H2O to release electron
(make a current)
Current was presented as “PO2”
by termistor
.P x
= PO since
PO higher the
is O M ore
O2
2
2 2
Foaming control
The problems caused by foam are the loss of broth, clogging of the exhaust gas system and possible contamination, a problem that is due to wetting of the gas filters.
Foam breaker: blades or disks operate on the centre of the shaft and generally mounted on the same agitator shaft.
Chemical anti-foams, based on silicon, prevent any foaming by reducing the interfacial tension of the broth. Use of chemical anti-foam may complicate the microbial fermentation process, and some may act as an inhibitor.
Measuring foam use foam detector
Foaming control
Level control
Rv = resistancce of
Level control is needed for continuous bioreactor.
This aimed to maintain its continuity and also prevent overflow that causes broth losses
When liquid reach the level detector (sensor), conductance changes and controller sent information to the inlet and effluent valve to adjust liquid level by consider this equation:
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