Medical Design Briefs - October 2022 - 11

A panoply of additives are integrated
into polymer formulations to assist in
the manufacturability of the resin systems.
The final part products need to
have some level of chemical resistance;
this is especially true for medical device
enclosures due to repeated exposure
to chemical disinfectants. Like disinfectant
manufacturers, raw material
manufacturers rely on various testing
methodologies to evaluate chemical
resistance of their materials. This testing
informs the raw material manufacturers
about their product's response
to chemical disinfectants used in the
healthcare space.
The companies that make medical
devices, or original equipment manufacturers
(OEMs), use thermoplastic
materials to enclose and protect their
devices, ensuring that they maintain full
functionality when exposed to the environmental
stresses seen in multiple use
cases, while continuing to meet the device's
design criteria and safety requirements,
as well as being aesthetically
pleasing, ergonomic, and cost-effective.
Because these devices are frequently
cleaned with chemical disinfectants,
the polymer resins sourced need to be
chemically resistant or compatible with
a significant number of chemical disinfectants
and solutions. Plastic materials
incompatible with common chemical
disinfectants can weaken, craze, crack,
embrittle, exhibit leaching, and eventually
lead to substantial enclosure
breakdown. OEMs rely on material performance
data to make well-informed
decisions on enclosure materials. The
greater the similarity in chemical resistance
data across material specifications,
the easier it is for OEMs to compare data
and choose enclosure materials that best
suit the end user's needs. Medical device
failure in the field has substantial adverse
impacts to end users, reduces hospital efficiencies,
and increases patient risk.
Selecting Chemically Resistant
Materials
How does one select chemically resistant
enclosure materials for medical devices?
How are the materials tested for resistance
to chemical disinfectants? Luckily,
chemical resistance is not a new concept;
there are a variety of ASTM and ISO material
testing standards that guide material
testing. Common testing standards are
ASTM D 543, D 638, and D 6110. These
Medical Design Briefs, October 2022
Carefully load standard flex bars to a constant strain jig. Choose the jig strain level based on your actual application.
(Credit: Eastman)
Apply nonwoven coupon material saturated with the desired chemical solution onto testing samples on the
strain jig. (Credit: Eastman)
standards are used across industries to
guide material conditioning, exposure,
and mechanical testing of materials.
Standards generally afford the experimenter
some latitude in experimental
design, often written to provide a
broad framework in which to conduct
the experiment. However, this broad
www.medicaldesignbriefs.com
framework can cause a lack of uniformity
in conditioning, exposure, testing,
and pass/fail criteria. Pass/fail criteria
are often aligned to the experimenter's
own needs and expectations, further
confounding data generated. This often
occurs in chemical resistance testing/environmental
stress crack testing,
11

http://www.medicaldesignbriefs.com

Medical Design Briefs - October 2022

Table of Contents for the Digital Edition of Medical Design Briefs - October 2022