Medical Design Briefs - June 2021 - 11

Tensile Strain (%)
-1
1
2
3
4
5
6
7
-1
-1
1
2
3
4
5
6
7
0.5 % strain
-1
1
2
3
4
5
6
7
0 123456789 10
Tensile Strain (%)
1.5 % strain
Strain
0.5%
1.5%
1.0%
11
12
13
1.0 % strain
-101234 5 6789 10
Tensile Strain (%)
Material A - Chemical agent ESCR for (x) hour
Tensile property retention (%)
Modulus Strength Elongation at Yield Elongation at Break
Crazing
No
No
No
Property Retention
Compatibility Legend
80-90%
>90%
<80%
-1012345 67
Tensile Strain (%)
Fig. 3 - Scenario to evaluate mechanical response of material upon strained exposure to a chemical
agent. Compatibility assessment showing the stress-strain curves at variable strains (0.5 percent,
1.0 percent, and 1.5 percent) for duration and environment of exposure. The curves in different colors
denote stress strain behavior for five test specimens tested from the same sample/product.
Strain (%)
0.5%
1.0%
1.5%
Modulus
Strength
Elongation at Yield
Elongation at Break
Crazing
No
No
No
Table 1a. Tensile property retention for CYROLITE® Med 2 after exposure to IPA/water (70 percent)
for 5 hours at strain rates of 0.5, 1.0, and 1.5 percent. Property retention: >90% (green), 80-
90% (yellow), <80% (red).
Strain (%)
0.5%
1.0%
1.5%
Modulus Strength
Elongation at Yield
Elongation at Break
Crazing
No
No
No
Table 1b. Tensile property retention for CYROLITE® Med 2 after intralipid for 24 hours at strain rates
of 0.5, 1.0, and 1.5 percent. Property retention: >90% (green), 80-90% (yellow), <80% (red).
Color
als. Relevance needs to be established
on the chemical exposure method with
guidelines laid out for the dimensions of
the patch, frequency of chemical agent
reapplication, the setup in a controlled
environment, and duration of exposure
- all with respect to the chemical agent
tested. Lack of a standardized methodology
leads to inconsistency in data comparisons
between resin manufacturers.
Evaluation of Test Results and
Tensile Property Retention. The goal is
to gauge representative behavior of the
polymer under investigation. Property
retention can be expressed in terms of
one or a combination of tensile modulus,
strength, elongation at yield, and
break elongation characteristics. Un -
doubtedly, all of these present a unique
piece of information about the mechanical
characteristics of the material to the
medical device manufacturer.
A unanimous parameter(s) (modulus,
strength, elongation at yield, and break
elongation) should be published for ranking
the compatibility matrix against chemicals
tested in line with the geared application.
Tensile strength and elongation at
yield present closer relevance to materials
deformation behavior under mechanical
loads in use.7 Elongation at break measures
the materials failure stress but often
is misleading and shows the most scatter
across the tested pool of tensile bars as
shown in Figure 4. In addition, visual
observations linked to onset and development
of crazing or stress whitening of
material during exposure should be
recorded (see Tables 1a and 1b). Figure 4
and Tables 1a and 1b present the twofold
scenario expressing ESCR output.
Case Study: Environmental Stress
Crack Resistance (ESCR)
Performance Testing
Mild Crazing
Severe Crazing
1
2
3
4
No attack
Slight attack
Moderate attack
Severe attack
Broke on strain jig
Fig. 4 - Compatibility assessment to include visual evaluation across the test specimens and proposed
ranking system.
Medical Design Briefs, June 2021
Cov
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ToC
For CYROLITE Med 2, ASTM type 1
tensile bars molded from the material
were annealed for 4 hours at 64 °C. The
test bars were preconditioned for at least
>40h, at 23 ± 2 °C, 50 ± 5% relative humidity
prior to strain exposure (ASTM-D
618). Note: ESCR Upon Exposure to (70
percent) IPA/Water (ASTM D543-14)
and Mechanical Property Changes
(ASTM D638, Section 12).
The tensile bars were mounted on
control strain jigs at 0.5, 1.0, and 1.5 percent
respectively (see Figure3). A wet
patch saturated in 70 percent IPA was
applied every 30 minutes for 5 hours.
Tensile testing per ASTM D638 was performed
on all specimens (5 replicates)
11
Tensile Stress (kpsi)
Tensile Stress (kpsi)
Tensile Stress (kpsi)
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Medical Design Briefs - June 2021

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