cell stripper final Interview Questions and Answers

1. What is a cell stripper?

   • Answer: A cell stripper is a tool or process used to remove cells from a substrate, such as a cell culture flask or a microplate, without damaging the underlying surface. This is crucial in various biological research and manufacturing processes.

2. What are the different types of cell strippers?

   • Answer: Common types include enzymatic solutions (like trypsin or collagenase), chelating agents (like EDTA), and mechanical methods (like scraping or using a cell lifter). The choice depends on the cell type and substrate.

3. Describe the mechanism of action of trypsin as a cell stripper.

   • Answer: Trypsin is a protease that cleaves proteins, including those involved in cell-to-cell adhesion and cell-to-substrate adhesion. This breaks down the extracellular matrix and allows cells to detach.

4. What are the advantages and disadvantages of using trypsin?

   • Answer: Advantages: Effective for many cell types. Disadvantages: Can damage cells if used improperly or for too long, requires inactivation (e.g., with serum), can be expensive.

5. How does EDTA work as a cell stripper?

   • Answer: EDTA chelates divalent cations like calcium and magnesium, which are essential for cell adhesion. By removing these ions, EDTA weakens cell-to-substrate and cell-to-cell interactions, facilitating detachment.

6. What are the advantages and disadvantages of using EDTA?

   • Answer: Advantages: Generally less damaging to cells than trypsin. Disadvantages: May be less effective for some cell types, can be slower than trypsin.

7. When would you choose a mechanical method over an enzymatic method for cell stripping?

   • Answer: Mechanical methods are preferred when enzymatic methods are ineffective or when rapid detachment is needed and cell viability is less critical (e.g., for some types of analysis). However, they risk damaging the cells or the underlying substrate.

8. Explain the process of cell passaging. How does cell stripping play a role?

   • Answer: Cell passaging involves transferring cells from a confluent culture to a new culture vessel to maintain cell growth and prevent overcrowding. Cell stripping is the crucial first step, detaching cells from the original vessel before they can be resuspended and seeded into a new vessel.

9. How do you determine the optimal concentration and incubation time for a cell stripper?

   • Answer: This depends on the specific cell type and the stripper used. It's usually determined experimentally by testing different concentrations and incubation times to find the combination that yields efficient detachment with minimal cell damage. Microscopic observation is crucial.

10. What are the signs of over-treatment with a cell stripper?

    • Answer: Signs include significant cell death (rounded, detached cells with compromised membranes), cell clumping, and reduced cell viability after passaging.

11. How do you inactivate trypsin after cell stripping? Why is this important?

    • Answer: Trypsin is typically inactivated by adding serum (containing trypsin inhibitors) or a trypsin inhibitor solution. This is crucial to prevent further cell damage as trypsin remains active until neutralized.

12. What safety precautions should be taken when working with cell strippers?

    • Answer: Always wear appropriate personal protective equipment (PPE), including gloves and eye protection. Work in a biological safety cabinet when dealing with potentially hazardous agents. Proper disposal of waste is also crucial.

13. How do you assess cell viability after cell stripping?

    • Answer: Cell viability can be assessed using various methods, including trypan blue exclusion assay (a simple and common method), MTT assay, or flow cytometry.

14. What are some factors that can affect the efficiency of cell stripping?

    • Answer: Factors include cell type, cell density, age of the culture, the type and concentration of the cell stripper, incubation time, temperature, and the condition of the culture vessel.

15. Describe a time you encountered a problem during cell stripping and how you solved it.

    • Answer: *(This requires a personalized answer based on the interviewee's experience. A good answer would describe a specific problem, the troubleshooting steps taken, and the successful solution.)*

16. What are some alternative methods for cell detachment besides enzymatic and mechanical methods?

    • Answer: Some less common methods include using other proteases, using detergents (carefully, as they can be more damaging), or using specialized cell-dissociation reagents.

17. How would you troubleshoot poor cell detachment after using trypsin?

    • Answer: Possible causes include insufficient trypsin concentration, too short of an incubation time, cells being too loosely attached, or the presence of serum in the media. Troubleshooting steps would include increasing the concentration, extending the incubation time, and making sure the media is serum-free before treatment.

18. What is the importance of maintaining sterility during cell stripping?

    • Answer: Maintaining sterility is essential to prevent contamination of the cell culture, which can lead to inaccurate experimental results, cell death, and potential safety hazards.

19. How would you document your cell stripping procedure?

    • Answer: Detailed documentation should include the date, cell type, cell passage number, type and concentration of cell stripper used, incubation time and temperature, observations during the procedure (e.g., cell morphology before and after detachment), cell viability assessment, and any troubleshooting steps taken.

20. What is the difference between primary cells and cell lines, and how might this affect cell stripping?

    • Answer: Primary cells are directly isolated from tissues and have a limited lifespan. Cell lines are immortalized cells capable of continuous growth. Primary cells are often more sensitive and require gentler stripping methods than established cell lines.

21. Explain the concept of cell density and its relevance to cell stripping.

    • Answer: Cell density refers to the number of cells per unit area. High cell density might require longer incubation times or higher concentrations of the cell stripper. Very low cell densities could make it difficult to harvest enough cells efficiently.

22. How does the surface of the culture vessel affect cell stripping?

    • Answer: Different culture vessel surfaces (e.g., tissue culture-treated plastic, collagen-coated surfaces) can affect cell adhesion. Cells adhering strongly to a surface might require more aggressive cell stripping methods.

23. What are some common problems encountered during cell stripping, and how can they be prevented?

    • Answer: Common problems include cell damage, incomplete detachment, contamination, and poor cell recovery. Prevention strategies include using the appropriate cell stripper, optimizing concentration and incubation time, maintaining sterility, and using gentle handling techniques.

24. Discuss the importance of proper training and adherence to standard operating procedures (SOPs) in cell stripping.

    • Answer: Proper training ensures the safe and efficient execution of the procedure, minimizing the risk of errors and contamination. Adherence to SOPs ensures consistency and reproducibility of results.

25. What are some ethical considerations related to the use of cell strippers and cell culture techniques?

    • Answer: Ethical considerations include the humane treatment of animals if animal cells are used, responsible handling of biohazardous materials, and proper waste disposal to protect the environment.

26. Describe your experience with different types of cell lines and their specific requirements for cell stripping.

    • Answer: *(This requires a personalized answer based on the interviewee's experience.)*

27. What is your understanding of Good Cell Culture Practices (GCCP)?

    • Answer: GCCP is a set of guidelines designed to ensure the quality and reliability of cell culture experiments. It encompasses aspects like sterility, accurate record-keeping, and proper handling of cells and reagents.

28. How would you troubleshoot cell clumping after cell stripping?

    • Answer: Cell clumping can be caused by over-treatment with the stripper, leading to cell damage and aggregation. It could also be due to the cell type. Troubleshooting involves reducing the concentration or incubation time of the stripper, gentler pipetting techniques, and potentially using a cell strainer to separate clumps.

29. How would you handle a situation where the cell stripper is ineffective?

    • Answer: I would first check the concentration and incubation time, making sure they are appropriate for the cell type. If the problem persists, I would try a different cell stripper (e.g., switching from trypsin to EDTA) or a different detachment method. I would also check the condition of the culture (e.g., cell density, media quality). Finally, I would document all steps and seek advice from a senior colleague or supervisor if necessary.

30. What is your experience with automated cell stripping systems?

    • Answer: *(This requires a personalized answer based on the interviewee's experience.)*

31. How do you ensure the reproducibility of your cell stripping procedure?

    • Answer: Reproducibility is ensured by using standardized protocols, detailed documentation, consistent reagent preparation, calibrated equipment, and careful adherence to SOPs. Regular quality control measures help in identifying variations and making necessary adjustments.

32. Describe your experience with cryopreservation of cells and its relationship to cell stripping.

    • Answer: *(This requires a personalized answer based on the interviewee's experience.)*

33. How would you manage a situation where you suspect contamination of a cell culture after cell stripping?

    • Answer: I would immediately isolate the contaminated culture and perform a thorough investigation to identify the source of contamination. I would then discard the contaminated culture properly according to lab protocols and take steps to prevent further contamination, including thorough decontamination of equipment and workspaces.

34. What are the downstream applications of cells after successful cell stripping?

    • Answer: Successfully stripped cells can be used for various applications, including cell-based assays, drug screening, cell transplantation, gene therapy, and regenerative medicine.

35. What are the key performance indicators (KPIs) for evaluating the effectiveness of a cell stripping procedure?

    • Answer: KPIs include cell viability after detachment, the percentage of cells detached, the time taken for detachment, and the absence of significant cell damage or clumping.

36. How does cell stripping contribute to the overall success of a cell culture experiment?

    • Answer: Efficient and gentle cell stripping is critical for ensuring high cell viability and enabling successful passaging, preventing contamination, and allowing accurate and reliable results in downstream applications.

37. What are your career goals, and how does this position align with them?

    • Answer: *(This requires a personalized answer based on the interviewee's career aspirations.)*

38. Why are you interested in this specific position?

    • Answer: *(This requires a personalized answer based on the interviewee's reasons for applying.)*

39. What are your salary expectations?

    • Answer: *(This requires a personalized answer based on the interviewee's research and expectations.)*

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