Medical Design Briefs - October 2022 - 12

Chemical Resistance of Thermoplastics
ical device design and manufacturing
space. Further convoluting test results
are exposure times; the experimenter is
free to choose the intervals for plastic exposure
to chemical disinfectant. These
differences in strain amounts and exposure
periods make data comparisons
across medical device plastics difficult.
OEMs are often at a loss on how best to
evaluate one material against another
when selecting for chemical resistance.
A consensus on clearer conditioning,
exposure criteria, and pass/fail criteria
that all chemical disinfectant manufacturers
and plastic manufacturers follow
would help obviate this problem.
Tensile bar specimens placed on strain jig prior to application of saturated nonwoven strip (left). Exposure of strained
tensile bar test specimens to disinfectants via nonwoven strips (right). (Credit: PDI)
skewing results. Currently, no consistent
minimum testing standards are required
to validate that disinfectants are
compatible with surface materials used
for the design of medical devices.
A common source for testing inconsistency
comes when executing ASTM
D 543, Standard Practice for Evaluating
the Resistance of Plastics to Chemical
Reagents. This standard provides the
mathematical relationship between a
tensile bar's out fiber strain, the tensile
bar's thickness, and the radius of curvature
that the bar is deflected against.
This standard, in essence, helps the experimenter
define geometry of strain
jigs and affords the experimenter the
freedom to determine the level of strain.
Several different strain values, sometimes
inconsistently, are used as a result
of experimenter freedom. An unfortunate
result of this freedom is the plethora
of strains used across a multitude of
plastic materials throughout the medThe
Healthcare Surfaces Institute is the only organization focused on how
surfaces contribute to the spread of microbes that cause deadly infections.
Mission
To reduce preventable infections through the collaboration of industry, academia,
science, regulatory, and service sectors by interrupting the transmission of surface-related
pathogens in healthcare in support of the community and public health.
HSI's plan
Testing & Certification
* Develop test methods and minimum standards for testing surface materials to validate
their ability to be cleaned and disinfected without damage.
Surface Disinfection Compatibility
* Develop test methods that evaluate the damage caused by disinfectants and determine
when there is a risk to patients and healthcare workers
Surface Selection
* Provide surface material selection criteria so materials used for product design will
support infection prevention cleaning guidelines without causing damage.
For more information or to get involved,
visit www.healthcaresurfacesinstitute.org.
HSI is a 501c3 Charitable Non-Profit organization.
12
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Coming to Consensus
In the Spring of 2020, under the
aegis of the nonprofit organization
HealthCare Surfaces Institute (HSI),
engineers and scientists representing
different companies across the medical
device and healthcare space met to
work on the conditioning, exposure,
and testing of plastics used for medical
device enclosures. The participants
formed the Plastic Testing Standards
subcommittee for the Healthcare Surfaces
Institute
Surface
Material and
Product Certification program. Eastman,
Solvay, and Roehm each had participants
representing the thermoplastic
industry, with Zebra Technologies
representing original equipment manufacturers
and PDI as the chemical disinfectant
manufacturer representative.
Throughout 2020, participants met
once a week to discuss current testing
standards and to determine whether
the standards could be more clearly
defined, with the intent to facilitate
ease of data comparison. Initially, each
company provided feedback into their
conditioning, exposure, and testing
practices with accompanying justification.
The companies chose testing
methodology based on strong material
science practice, relevancy to equipment
manufacturer needs, end customer
use cases, and reasonable material
testing throughput.
All participating companies used or
referenced ASTM D 543, ASTM D 638,
and ASTM D 6110. Consensus was that
the standards are defining testing, such
as ASTM D638 Standard Test Methods
of the Tensile Properties of Plastics and
ASTM D 6110 - 04 Standard Test Method
for Determining the Charpy Impact
Medical Design Briefs, October 2022

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Medical Design Briefs - October 2022

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