CTBS Processing Techniques 5 — Questions and Answers
Question 1: Which of the following processing steps is specifically aimed at prion (TSE) risk reduction in neural tissue allografts?
- Standard gamma irradiation at 25 kGy
- Sodium hydroxide (NaOH) treatment combined with autoclaving at 134°C (Correct answer)
- Peracetic acid soaking for 60 minutes
- Ethylene oxide gas sterilization
Correct answer: Sodium hydroxide (NaOH) treatment combined with autoclaving at 134°C
Prions are highly resistant to standard sterilization; NaOH treatment (1N, 1 hour) combined with autoclaving at 134°C for at least 18 minutes is recommended by WHO for prion inactivation.
Question 2: In a tissue bank clean room, what is the distinction between 'controlled environment' and 'critical zone'?
- Controlled environment requires ISO 5; critical zone requires ISO 7
- Controlled environment is the overall clean room space; critical zone is where tissue is directly exposed to the environment (Correct answer)
- Critical zone uses HEPA filtration; controlled environment uses UV sterilization only
- Controlled environment is monitored monthly; critical zone is monitored annually
Correct answer: Controlled environment is the overall clean room space; critical zone is where tissue is directly exposed to the environment
The controlled environment encompasses the entire clean room maintained at specified air quality standards, while the critical zone is the specific area of direct tissue exposure requiring the highest (ISO 5) air quality.
Question 3: What is the function of DMSO (dimethyl sulfoxide) when used in tissue cryopreservation?
- It acts as an antimicrobial agent to reduce bioburden before freezing
- It penetrates cell membranes to prevent intracellular ice crystal formation (Correct answer)
- It maintains physiological pH during the freeze-thaw cycle
- It crosslinks collagen fibers to increase mechanical strength after thawing
Correct answer: It penetrates cell membranes to prevent intracellular ice crystal formation
DMSO is a cryoprotectant that rapidly penetrates cell membranes and reduces intracellular ice crystal formation during freezing, thereby preserving cell membrane integrity and viability.
Question 4: Which in-process test is used to confirm the effectiveness of the decontamination step during bone allograft processing?
- Endotoxin (LAL) test on processed bone segments
- Microbiological cultures (aerobic, anaerobic, and fungal) from process samples (Correct answer)
- Residual moisture content measurement by Karl Fischer titration
- Scanning electron microscopy for surface contamination
Correct answer: Microbiological cultures (aerobic, anaerobic, and fungal) from process samples
Microbiological cultures testing for aerobic bacteria, anaerobic bacteria, and fungi from tissue samples taken after decontamination steps confirm the effectiveness of bioburden reduction.
Question 5: During the processing of pericardium allografts for cardiac surgery use, glutaraldehyde fixation is sometimes applied. What is the primary effect of this fixation?
- It sterilizes the tissue by alkylating nucleic acids of microorganisms
- It crosslinks collagen to reduce immunogenicity and improve durability, but eliminates cell viability (Correct answer)
- It preserves cell viability by stabilizing membrane lipids during storage
- It removes calcium deposits that would cause valve calcification after implantation
Correct answer: It crosslinks collagen to reduce immunogenicity and improve durability, but eliminates cell viability
Glutaraldehyde crosslinks collagen in pericardium, masking antigenic epitopes to reduce immune response and increasing structural durability, but the resulting tissue is acellular and not viable.
Question 6: What processing technique is used to produce 'cortical bone chips' or 'cancellous bone chips' from whole long bones?
- Lyophilization followed by milling under sterile conditions
- Mechanical sizing using sterile saws, mills, or grinders in a clean room environment (Correct answer)
- Enzymatic digestion to separate cortical from cancellous components
- Ultrasonic fragmentation in antibiotic solution bath
Correct answer: Mechanical sizing using sterile saws, mills, or grinders in a clean room environment
Mechanical processing using sterile power tools (oscillating saws, bone mills, grinders) in a controlled clean room environment is the standard technique to size whole bones into cortical or cancellous chips.
Question 7: Which regulatory document must accompany a tissue allograft from processing through distribution to maintain its full chain of custody?
- The donor's hospital discharge summary
- The tissue chain of identity/custody record linking donor to each processed unit (Correct answer)
- The clean room environmental monitoring logs for the processing date
- The tissue bank's CAP accreditation certificate
Correct answer: The tissue chain of identity/custody record linking donor to each processed unit
A chain of identity/custody record is required to maintain traceability linking the original donor to every processed allograft unit distributed, enabling recall if a safety concern arises.
CTBS Processing Techniques 5
Which of the following processing steps is specifically aimed at prion (TSE) risk reduction in neural tissue allografts?