Medical Design Briefs - December 2021 - 18

Biomedical QC Testing
Fig. 1 - Flexural Testing of coronary stent.
determined, as well as its shape memory,
which is evaluated by loading and
unloading in a cyclic test per ASTM
F2516 (see Figure 1).
After the material is tested and the
stent is produced, the stent must be evaluated
to ensure that it meets the required
expectations. Stents must pass through
curvatures in the vascular system in order
to reach their intended destination.
Therefore, their flexibility must be evaluated
per ASTM F2606, which subjects
them to a three-point bend test to generate
a force-displacement curve for both
unload and unloading. Manufacturers
are also interested in quantifying the frictional
forces of the stent to simulate the
action of the product being pushed
through a patient's body. This type of test
is often referred to as tortuosity testing.
Another critical property is the radial
force that a stent or graft imparts onto
the arterial wall. Evaluating the radial
strength of a stent graft, e.g., radial stiffness,
chronic outward forces during
expansion and compression, and reactive
force helps to ensure the efficacy
and reliability of the medical device
when implanted in vivo.
Finally, the stent is subjected to millions
of fatigue loading cycles as part of the
product durability and validation testing.
ASTM F2477 involves placing complete
devices into mock arteries and subjecting
them to 400 million cycles of internal
pressure pulsation (10 years of human
heartbeats), forcing them to radially
expand and contract in each cycle. This
test can reproduce the minimum and
maximum diameters that a stent would
see in vivo under worst-case conditions.
Other medical devices such as
syringes, pacemakers, and implants also
require their own unique testing profile
depending on the materials being used
and the device's end-use application.
Manufacturers must have a thorough
understanding of the different testing
requirements in order to ensure that
their products meet expectations, and a
well-optimized lab will invest in testing
equipment that allows them to efficiently
perform all relevant tests.
Ensuring the Quality of Your
Results
After the initial challenge of understanding
the various testing requirements
for each of their products, the
most critical concern in global medical
device QC laboratories is resolving
inconsistencies in their test results.
Mechanical testing results must be
repeatable and reliable between individual
testing systems, whether those systems
are located in the same lab or in different
labs, or when a comparison is
being made between multiple suppliers
or customers. Quality assurance depends
on the ability of testing systems to provide
accurate results.
Fig. 2 - A software package should include electronic signatures and approvals, file revision history,
and automated, secure audit trail requirements associated with FDA 21 CFR Part 11, ISO 17025,
and other relevant standards and regulations.
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ToC
Furthermore, as many industries ex -
pand R&D and manufacturing operations
into different parts of the world,
data comparisons have become increasingly
more important and complex.
Sources of test errors can be categorized
into six distinct categories: method, measurement,
operator, material, machine,
and environment. Within these major
categories are subcategory sources of
error that must be specifically addressed

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Medical Design Briefs - December 2021

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