CTBS Tissue Processing & Preservation 2 — Questions and Answers
Question 1: Which cryoprotectant is most commonly used for bone marrow and hematopoietic stem cell preservation?
- Glycerol
- Dimethyl sulfoxide (DMSO) (Correct answer)
- Propylene glycol
- Ethylene glycol
Correct answer: Dimethyl sulfoxide (DMSO)
DMSO is the standard cryoprotectant for hematopoietic stem cells due to its ability to rapidly penetrate cell membranes and prevent ice crystal formation.
Question 2: What is the purpose of the 'equilibration period' during cryoprotectant addition?
- To warm the tissue to room temperature
- To allow the cryoprotectant to penetrate tissue before freezing (Correct answer)
- To remove residual disinfectants
- To rehydrate the tissue after drying
Correct answer: To allow the cryoprotectant to penetrate tissue before freezing
The equilibration period allows the cryoprotectant to diffuse into cells so it can provide intracellular protection against ice crystal damage during freezing.
Question 3: Which sterilization method is contraindicated for tissues containing viable cells intended for transplant?
- Aseptic processing
- Gamma irradiation at 25 kGy (Correct answer)
- Low-dose gamma irradiation (<15 kGy)
- Antibiotic soaking
Correct answer: Gamma irradiation at 25 kGy
Gamma irradiation at 25 kGy is effective for terminal sterilization but destroys cellular viability, making it unsuitable for cell-based allografts.
Question 4: During freeze-drying (lyophilization), what is the PRIMARY mechanism of tissue preservation?
- Antimicrobial peptide activation
- Removal of free water to halt metabolic and microbial activity (Correct answer)
- Protein denaturation to prevent decomposition
- Osmotic cell shrinkage
Correct answer: Removal of free water to halt metabolic and microbial activity
Lyophilization preserves tissue by sublimating water under vacuum, leaving a dry matrix that resists microbial growth and enzymatic degradation.
Question 5: What is the recommended storage temperature for lyophilized (freeze-dried) bone allografts?
- -80°C
- -20°C
- 2–8°C (refrigerated)
- Room temperature (15–30°C) (Correct answer)
Correct answer: Room temperature (15–30°C)
Freeze-dried allografts have sufficiently low water activity that they can be stored at room temperature in sealed, moisture-proof packaging.
Question 6: A tissue bank is processing demineralized bone matrix (DBM). Which property is MOST directly affected by the demineralization process?
- Tensile strength
- Osteoinductive potential (Correct answer)
- Antimicrobial resistance
- Water content
Correct answer: Osteoinductive potential
Demineralization exposes bone morphogenetic proteins (BMPs) embedded in the bone matrix, significantly enhancing osteoinductive potential.
Question 7: Which parameter is MOST critical to monitor during controlled-rate freezing of cardiovascular tissue?
- pH of the media
- Cooling rate (°C/min) (Correct answer)
- Container fill volume
- Tissue donor age
Correct answer: Cooling rate (°C/min)
Cooling rate is the most critical parameter; too fast causes intracellular ice formation and too slow causes solution effects that damage cells.
CTBS Tissue Processing & Preservation 2
Which cryoprotectant is most commonly used for bone marrow and hematopoietic stem cell preservation?