CTBS Tissue Processing & Preservation 5 — Questions and Answers
Question 1: What is the functional difference between 'fresh' and 'fresh-frozen' allograft bone regarding osteoinductivity?
- Fresh bone has no osteoinductive capacity; fresh-frozen does
- Fresh bone retains more viable cells and growth factors; fresh-frozen loses some bioactivity but retains structural properties (Correct answer)
- Fresh-frozen bone is more osteoinductive due to ice crystal disruption releasing BMPs
- There is no clinically significant difference
Correct answer: Fresh bone retains more viable cells and growth factors; fresh-frozen loses some bioactivity but retains structural properties
Fresh bone retains living osteoblasts and higher concentrations of growth factors, while freezing partially denatures proteins and kills cells though structural integrity is largely preserved.
Question 2: A processing technician inadvertently leaves a skin allograft at 4°C for 72 hours in nutrient media. Which microorganism is of GREATEST concern regarding overgrowth during this period?
- Staphylococcus aureus
- Pseudomonas aeruginosa (Correct answer)
- Candida albicans
- Clostridium perfringens
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa is a psychrotolerant gram-negative bacterium that can proliferate at refrigerator temperatures, posing the greatest risk during prolonged cold storage.
Question 3: Which statement BEST describes the role of sucrose in cardiac valve cryopreservation media?
- It serves as the primary intracellular cryoprotectant
- It acts as an extracellular impermeant to reduce osmotic cell swelling (Correct answer)
- It provides a carbon source for cell metabolism during storage
- It increases the glass transition temperature of the solution
Correct answer: It acts as an extracellular impermeant to reduce osmotic cell swelling
Sucrose is a large molecule that does not cross cell membranes; it raises extracellular osmolality to counteract osmotic swelling caused by cryoprotectant-induced cell shrinkage.
Question 4: Which processing step is UNIQUE to the preparation of demineralized bone matrix (DBM) compared to standard cortical bone processing?
- Antibiotic soaking
- Acid demineralization (typically in 0.5N HCl) (Correct answer)
- Gamma irradiation
- Lyophilization
Correct answer: Acid demineralization (typically in 0.5N HCl)
DBM production requires an acid demineralization step (commonly 0.5N HCl) to dissolve the mineral hydroxyapatite and expose the collagen and growth factor matrix.
Question 5: In tissue banking, what is the significance of the 'D-value' (decimal reduction value) when validating a sterilization process?
- The dose of radiation required to achieve sterility assurance level of 10⁻⁶
- The time or dose required to reduce the microbial population by 90% (one log) (Correct answer)
- The minimum concentration of EO gas needed for sterilization
- The temperature differential required between two processing steps
Correct answer: The time or dose required to reduce the microbial population by 90% (one log)
The D-value represents the time or dose needed to kill 90% of a test organism population under defined conditions, forming the basis for sterilization cycle validation.
Question 6: What AATB requirement governs the handling of tissues when the monitored storage temperature is found to have exceeded its validated range?
- The tissue must be immediately discarded
- A documented deviation investigation must be performed and the tissue quarantined pending review (Correct answer)
- The tissue can be released if it passes microbiological testing
- The tissue must be re-processed with additional sterilization
Correct answer: A documented deviation investigation must be performed and the tissue quarantined pending review
AATB standards require a formal deviation investigation and quarantine; the tissue disposition is determined by the outcome of the investigation, not automatic discard or release.
Question 7: Which structural feature of cortical bone makes it more resistant to cryoprotectant penetration compared to cancellous bone?
- Higher collagen content
- Dense, low-porosity Haversian system with minimal interconnected channels (Correct answer)
- Greater mineral density preventing diffusion
- Presence of periosteum blocking diffusion
Correct answer: Dense, low-porosity Haversian system with minimal interconnected channels
Cortical bone's dense Haversian system with small, poorly interconnected channels severely limits the diffusion of cryoprotectant solutions into the tissue interior.
CTBS Tissue Processing & Preservation 5
What is the functional difference between 'fresh' and 'fresh-frozen' allograft bone regarding osteoinductivity?