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Medical Device Sterilisation : Key Essentials, Options And
Challenges
Selecting The
Sterilisation Method
After
selecting the Sterilisation method, be it gamma ray, EtO,
steam, e-beam, gas plasma sterilisation, etc. consider
following the pros and cons in 5 key areas:
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Efficacy:
Planning and testing has to be given for the effect of
irradiation on dosing, and developments are still
underway. For example, standard ethylene oxide (EtO) can
be damaging to the biologic, or active ingredient,
contained in a combination device.
-
Environmental Impact: Consider possibilities of side
effects i.e. Cobalt- 60 is used in gamma ray; ethylene
oxide, the chemicals have side effects varying greatly.
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Appearance:
Having a sterile appearance is essentially nonnegotiable
for medical devices. And, the reality is that several
processes can result in yellowing or browning effects on
certain polymers.
-
Materials:
There can be compatibility challenges; e.g. in studies,
gas plasma has caused corrosion in certain materials.
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Residual
Matter: One of the main disadvantages of EtO is the
potential for toxic residues to be left in products and
materials that have been sterilised. The three most common
toxic residues of importance are ethylene oxide and two of
its reaction products, ethylene chlorohydrin and ethylene
glycol.
Packaging And Sterilisation
Challenges
Medical device manufacturers
are sensitive to the fact that the package must be durable
enough to prevent damage of an expensive medical device
and be able to withstand the effects of sterilisation,
without degradation of the package. End users in a
hospital setting also like to see the product through a
clear rigid package before opening it.
Innovations in
products-especially biomaterials-require new approaches to
packaging and sterilisation. “The biggest challenge with
the packaging and sterilisation of biomaterials, such as
polymers and bio-cohesive, is that these products are
newer to the market so there is less knowledge about how
to handle these processes”. “How will the materials react
to the sterilisation process? Will their chemical
characteristics change? OEMs and outsourcing companies are
still learning about how to ensure their products will
still function the way they were intended to function.”
An ethylene oxide (EtO)
sterilised medical device must be sealed in a carefully
designed gas-permeable package that enables the EtO gas to
enter. This package must meet a variety of engineering,
regulatory, and marketing requirements. In use, a sterile
package is opened, the sterile device is dispensed, and
the opened package is then disposed into the hospital’s
waste stream. Sterile packaging is a cost driver at every
step in a product’s life cycle.
Effect Of Sterilisation On
Shelf Life
If the device design and
manufacturing processes are done adequately, there is a
high probability that the device will perform as desired
at the time it is manufactured. However, there are many
naturally occurring factors that can affect how long after
manufacturing the device will maintain the ability to
fully perform the intended function. Shelf life is the
term or period during which a commodity remains suitable
for the intended use. An expiration date is the
termination of shelf life, after which a percentage of the
commodity, e.g., medical devices, may no longer function
as intended. To determine if a particular device requires
a shelf life and assign an expiration date, there are a
number of different parameters that must be considered.
The device must be analysed to determine if it is
susceptible to degradation that would lead to functional
failure and the level of risk that the failure would
present. For some devices, e.g., tongue depressors, it is
not reasonable to assign a shelf life because of the small
likelihood of time-dependant product degradation and the
lack of serious consequences if it did fail to perform as
designed. For certain devices susceptible to degradation
that are intended to treat life-threatening conditions,
e.g. pacemakers, the failure rate should approach zero
within the labeled shelf life.
Stability Criteria And
Variables
The United States
Pharmacopoeia (USP) defines stability as “the extent to
which a product retains, within specified limits, and
throughout its period of storage and use, i.e., its shelf
life, the same properties and characteristics that it
possessed at the time of manufacture.” There is no one
exhaustive set of criteria that would apply equally to all
medical devices. The USP has included a list of following
five sets of criteria for acceptable levels of stability
for drug products :
1. chemical, 2. physical, 3.
microbiological, 4. therapeutic, 5. toxicological.
Although this set of criteria
applies specifically to the evaluation of drug product
stability, it is useful as a starting point in developing
a set of criteria to evaluate the stability of medical
devices.
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