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e1
QUESTIONS
1. Overview of major terminal sterilization modalities:
a. What are the two dominant sterilization
modalities?
b. Why do so many device companies use them?
c. What are their major safety concerns?
2. Please provide brief descriptions of:
a. a gamma processing plant
b. how EO sterilization kills the germs on medical
devices.
4. Why does the biomaterial scientist need to be con-
cerned about material compatibility? Provide exam-
ples of materials that react, degrade, discolor or
cross-link during sterilization with EO and radiation
sterilization.
5. Terminal sterilization versus aseptic processing:
a. What is the difference between aseptic processing
and terminal sterilization?
b. Why is terminal sterilization preferred?
c. Why would one select aseptic processing?
ANSWERS
1. a. Radiation sterilization and ethylene oxide steril-
ization are the two dominant terminal steriliza-
tion modalities.
b. Medical device manufacturers use them exten-
sively because both have the capability to provide
robust microbial kill at reasonable costs for high
product volumes, while having minimal deleteri-
ous effects on device materials.
c. Radiation sterilization safety concerns arise since
the process uses doses that are orders of magni-
tude higher than a human lethal dose, so shielding
2. a. A 60Co gamma processing plant has three essen-
tial components:
i. shielding to keep the lethal radiation inside the
processing room away from the operators;
ii. double encapsulated radioactive isotope, with a
20-foot deep water storage pool with an eleva-
tor system to raise and lower the isotope; and
iii. a conveyor system and control system to bring
penetrating through the final sterile barrier pack-
aging of the device and inactivating microorgan-
isms through ionization and scission of the DNA
molecules.
3. a. A 100% EO processing plant has the following
components:
i. blast-limiting construction and appropriate
safeguards to avoid explosions and operator
exposure;
ii. a pre-conditioning area and an aeration area;
iii. EO process chambers into which product
is loaded. These chambers are equipped for
etrating through the breathable sterile barrier
packaging of the device along with water vapor,
and inactivating microorganisms through alkyla-
tion of their DNA.
4. Sometimes the biomaterial scientist has a polymer
that is suitable for a product, but the polymer cannot
tolerate any terminal sterilization process. In that case
it may not be possible to bring the product to market.
Alternatively, the product may need to be aseptically
processed which: (a) has less process control than
terminal sterilization and hence yields higher patient
risk; and (b) is more expensive than terminal steriliza-
tion, and hence reduces product profitability.
Examples of materials that may react with EO and
CHAPTER III.1.2
Sterilization of Implants and Devices
e2
known to have deleterious responses to a typi-
cal single EO sterilization. These materials may
be acceptable in certain applications, but must
be evaluated carefully after exposure to worse
case EO conditions, to ensure clinically accept-
able performance over the shelf-life and appli-
cation of the device.
• Bioabsorbable polymers may be difficult to
process with EO sterilization, in particular if
structural integrity is required. EO in combina-
Examples of materials that may react badly with
radiation sterilization:
• Polytetrafluoroethylene (PTFE), fluorinated eth-
ylene propylene (FEP), and polypropylene (PP)
exhibit chain scission and degradation to a sig-
nificant extent following radiation sterilization.
transition, may trap residual low energy elec-
trons which can cause yellow or brownish
discoloration.
• Bioabsorbable polymers, e.g., PLA and PLGA,
show significant molecular weight (MW)
reduction as a function of sterilization dose.
This may be manageable by utilizing a higher
initial MW in the product.
5. a. Aseptic processing of a product entails physical
removal of microbial contamination by filtering,
such contaminants.
b. It is predictive for any sterilization process, and
generally follows logarithmic microbial reductions
based on first order kinetics. It is much less expen-
sive and involves less patient risk than aseptic
processing.
