Question 1

What is the main difference between batch and continuous bioreactors?

Accepted Answer

Batch reactors are closed systems containing all components needed for cell culture, where nutrients are consumed and waste accumulates. Continuous stirred tank reactors are open systems where fresh nutrients flow in continuously and cells with waste flow out, enabling control of cell density through waste removal and nutrient replenishment.

Question 2

How do cells grow during batch reactor operation?

Accepted Answer

Batch cultures undergo four classic growth phases. Cells first enter lag phase, adapting slowly to their environment. They then enter log phase, dividing exponentially until nutrients deplete or toxic byproducts accumulate. Growth slows as cells reach stationary phase, providing an opportunity to harvest the product of interest from the culture.

Question 3

What parameters are controlled in bioreactors to optimize cell growth?

Accepted Answer

Multiple reactor parameters are controlled to maximize cell growth and density, including temperature, pressure, dissolved oxygen, and pH. Impellers maintain homogenous solutions and supply cells with sufficient nutrients and oxygen. Fermenter systems are equipped with probes to measure these conditions continuously, ensuring optimal growth environments.

Question 4

Why is sterilization important before using a bioreactor?

Accepted Answer

Sterilization, typically using steam in an autoclave, is essential to mitigate contamination before bioreactor use. All components are sterilized before assembly to eliminate microorganisms that could interfere with cell culture. This ensures a clean environment for reliable cell growth and product production.

Question 5

How does dilution rate affect cell density in continuous reactors?

Accepted Answer

In continuous stirred tank reactors, cell density at steady state depends on the dilution rate, calculated as feed and effluent rate divided by reactor volume. As the dilution rate approaches one, cell density decreases. This relationship allows operators to control final cell density by adjusting flow rates.

Question 6

What are practical applications of bioreactor technology in bioengineering?

Accepted Answer

Beer brewing uses batch reactors where yeast ferments malted barley, producing alcohol as a waste product. Specialized reactors enhance tissue engineering by improving cell viability through constant mixing and mechanical stimulation, promoting extracellular matrix production and directing cell growth and differentiation for tissue engineering and regenerative medicine applications.

Question 7

What are the advantages and limitations of batch versus continuous reactors?

Accepted Answer

Batch reactors are simple and cost-effective but have limited cell density. Continuous reactors achieve higher cell densities but risk aggregation at very high densities, reducing growth efficiency. Longer continuous fermentation periods increase contamination risk, requiring careful monitoring and maintenance to ensure product quality.

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