CTBS Processing Techniques 3 — Questions and Answers
Question 1: Which factor most significantly affects the residual moisture content of a lyophilized bone allograft?
- The freezing rate during cryopreservation
- The duration and temperature of the secondary drying phase (Correct answer)
- The concentration of antibiotic solution used in decontamination
- The donor's age and bone density
Correct answer: The duration and temperature of the secondary drying phase
The secondary drying (desorption) phase of lyophilization, which removes bound water, has the greatest effect on final residual moisture content of the product.
Question 2: When processing soft tissue allografts (e.g., tendons, ligaments), what is the primary function of low-dose gamma irradiation (< 20 kGy)?
- To achieve terminal sterilization with a SAL of 10⁻⁶
- To reduce bioburden without significantly compromising mechanical properties (Correct answer)
- To activate osteoinductive growth factors in the tendon
- To crosslink collagen fibers and increase tensile strength
Correct answer: To reduce bioburden without significantly compromising mechanical properties
Low-dose gamma irradiation is used to reduce microbial bioburden while minimizing radiation-induced damage to the collagen structure and mechanical integrity of soft tissue allografts.
Question 3: What is the purpose of adding a radioprotectant such as ascorbic acid or mannitol during irradiation of soft tissue allografts?
- To enhance the lethality of radiation against resistant spores
- To scavenge free radicals generated by radiation and reduce collagen damage (Correct answer)
- To maintain the pH of the tissue during the irradiation process
- To prevent dehydration of the tissue during dry-ice irradiation
Correct answer: To scavenge free radicals generated by radiation and reduce collagen damage
Radioprotectants like ascorbic acid and mannitol are free radical scavengers that neutralize reactive oxygen species produced by radiation, thereby reducing radiation-induced collagen degradation.
Question 4: During aseptic tissue processing, which environmental classification is required for the critical zone where tissue is exposed?
- ISO Class 7 (Class 10,000)
- ISO Class 5 (Class 100) (Correct answer)
- ISO Class 8 (Class 100,000)
- ISO Class 6 (Class 1,000)
Correct answer: ISO Class 5 (Class 100)
ISO Class 5 (equivalent to Class 100) clean room conditions are required in the critical zone where tissue is directly exposed during aseptic processing to minimize particulate and microbial contamination.
Question 5: What processing step is used to remove lipids from bone allografts, and why is it performed?
- Defatting with organic solvents such as chloroform-methanol; improves handling and reduces inflammatory response (Correct answer)
- Lyophilization; removes lipid-soluble vitamins that could cause rejection
- Autoclaving; destroys lipid-enveloped viruses more effectively
- Antibiotic soaking; lipid-soluble antibiotics penetrate the marrow cavity
Correct answer: Defatting with organic solvents such as chloroform-methanol; improves handling and reduces inflammatory response
Defatting with organic solvents like chloroform-methanol removes bone marrow fat, which improves handling characteristics, reduces rancidity during storage, and decreases inflammatory response after implantation.
Question 6: Which validation study is required to demonstrate that a processing method effectively inactivates enveloped and non-enveloped viruses in tissue?
- Pyrogenicity testing using the rabbit pyrogen assay
- Viral clearance validation study using surrogate viruses (Correct answer)
- Endotoxin testing by limulus amebocyte lysate (LAL) assay
- Cytotoxicity testing using cell culture assays
Correct answer: Viral clearance validation study using surrogate viruses
Viral clearance validation studies use surrogate (model) viruses to demonstrate that the processing steps achieve adequate log reduction of both enveloped and non-enveloped viral contaminants.
Question 7: What is the recommended maximum residual moisture content for lyophilized bone allografts to ensure long-term stability at ambient temperatures?
- ≤ 8%
- ≤ 6% (Correct answer)
- ≤ 2%
- ≤ 12%
Correct answer: ≤ 6%
Lyophilized bone allografts should have a residual moisture content of ≤6% to prevent microbial growth and chemical degradation during ambient temperature storage.
CTBS Processing Techniques 3
Which factor most significantly affects the residual moisture content of a lyophilized bone allograft?