ASTM F2477-06
(Test Method)Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents
Standard Test Methods for <bdit>in vitro</bdit> Pulsatile Durability Testing of Vascular Stents
SCOPE
1.1 These test methods cover the determination of the durability of a vascular stent by exposing it to physiologically relevant diametric distension levels by means of hydrodynamic pulsatile loading. This testing occurs on a stent test specimen that has been deployed into a mock (elastically simulated) vessel. The typical duration of this test is 10 years of equivalent use (at 72 beats per minute), or at least 380 million cycles.
1.2 These test methods are applicable to balloon-expandable and self-expanding stents fabricated from metals and metal alloys. It does not specifically address any attributes unique to coated stents, polymeric stents, or biodegradable stents, although the application of this test method to those products is not precluded.
1.3 These test methods do not include recommendations for endovascular grafts ("stent-grafts") or other conduit products commonly used to treat aneurismal disease or peripheral vessel trauma or to provide vascular access, although some information included herein may be applicable to those devices.
1.4 These test methods are valid for determining stent failure due to typical cyclic blood vessel diametric distension. These test methods do not address other modes of failure such as dynamic bending, torsion, extension, crushing, or abrasion.
1.5 These test methods do not address test conditions for curved mock vessels.
1.6 These test methods do not address test conditions for overlapping stents.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.7 General Caveat This document contains guidance for testing as is currently carried out in most laboratories. Other testing techniques may prove to be more effective and are encouraged. Whichever technique is used, it is incumbent upon the tester to justify the use of the particular technique, instrument, and protocol. This includes the choice of and proper calibration of all measuring devices. Deviations from any of the suggestions in this document may be appropriate but may require the same level of comprehensive justification that the techniques described herein will require.
General Information
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Standards Content (Sample)
Designation: F 2477 – 06
Standard Test Methods for
in vitro Pulsatile Durability Testing of Vascular Stents
This standard is issued under the fixed designation F 2477; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope instrument, and protocol. This includes the choice of and
proper calibration of all measuring devices. Deviations from
1.1 These test methods cover the determination of the
any of the suggestions in this document may be appropriate but
durability of a vascular stent by exposing it to physiologically
may require the same level of comprehensive justification that
relevantdiametricdistensionlevelsbymeansofhydrodynamic
the techniques described herein will require.
pulsatile loading. This testing occurs on a stent test specimen
that has been deployed into a mock (elastically simulated)
2. Referenced Documents
vessel.Thetypicaldurationofthistestis10yearsofequivalent
2.1 Other Documents:
use (at 72 beats per minute), or at least 380 million cycles.
ISO 7198: 1998(e), 8.10, Determination of Dynamic Com-
1.2 Thesetestmethodsareapplicabletoballoon-expandable
pliance
and self-expanding stents fabricated from metals and metal
FDA Guidance Document 1545, Non-Clinical Tests and
alloys. It does not specifically address any attributes unique to
Recommended Labeling for Intravascular Stents and As-
coated stents, polymeric stents, or biodegradable stents, al-
sociated Delivery Systems, (issued January 13, 2005)
though the application of this test method to those products is
not precluded.
3. Terminology
1.3 These test methods do not include recommendations for
3.1 Definitions of Terms Specific to This Standard:
endovascular grafts (“stent-grafts”) or other conduit products
3.1.1 cardiac cycle, n—defined as one cycle between dias-
commonly used to treat aneurismal disease or peripheral vessel
tolic and systolic pressures.
trauma or to provide vascular access, although some informa-
3.1.2 compliance, n—the change in inner diameter of a
tion included herein may be applicable to those devices.
vessel due to cyclic pressure changes. Compliance, if calcu-
1.4 These test methods are valid for determining stent
lated,shallbeexpressedasapercentageofthediameterchange
failure due to typical cyclic blood vessel diametric distension.
per 100 mm Hg and defined per ISO 7198, 8.10.5:
These test methods do not address other modes of failure such
as dynamic bending, torsion, extension, crushing, or abrasion.
~Dp2 2 Dp1! 3 10
%Compliance/100 mm Hg 5 (1)
1.5 These test methods do not address test conditions for Dp1 p2 2 p1
~ ~ !!
curved mock vessels.
where:
1.6 These test methods do not address test conditions for
Dp1 = inner diameter at the pressure of p1,
overlapping stents.
Dp2 = inner diameter at the pressure of p2,
1.7 This standard does not purport to address all of the
p1 = lower pressure value (diastolic), in mm Hg, and
safety concerns, if any, associated with its use. It is the
p2 = higher pressure value (systolic), in mm Hg.
responsibility of the user of this standard to establish appro-
3.1.3 diametric strain, n—a change in mock artery diameter
priate safety and health practices and determine the applica-
divided by the initial diameter. This term does not relate to the
bility of regulatory limitations prior to use.
mechanical strain seen in the stent material. The diametric
1.8 General Caveat—This document contains guidance for
strain can be identified as:
testing as is currently carried out in most laboratories. Other
~Dp2– Dp1!
testing techniques may prove to be more effective and are
diametric strain 5 (2)
Dp1
encouraged. Whichever technique is used, it is incumbent upon
the tester to justify the use of the particular technique,
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
These test methods are under the jurisdiction of ASTM Committee F04 on 4th Floor, New York, NY 10036.
Medical and Surgical Materials and Devices and is the direct responsibility of Available from Food and Drug Administration (FDA), 5600 Fishers Ln.,
Subcommittee F04.30 on Cardiovascular Standards. Rockville, MD 20857, http://www.fda.gov. This document available at http://
Current edition approved Nov. 1, 2006. Published December 2006. www.fda.gov/cdrh/ode/guidance/1545.pdf.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2477–06
that is,
product.Sterilizationshouldberequiredunlessitcanbeshown
not to influence the fatigue/durability test results.
~max ID – min ID!
diametric strain 5
min ID 5.2 Thenumberofspecimenstestedforeachstentgeometry
should be sufficient to support any claims to be made based on
3.1.4 distension, n—the change in diameters; such as the
the test results. Fatigue/durability shall be evaluated for the
inner diameter (ID) of a vessel due to a pressure change. The
worst case labeled diameter, and a rationale shall be provided
term “diametric distension” is meant to represent the change in
stating why the particular labeled diameter is considered worst
inner diameter of a blood vessel during each pulse of blood
case.
circulation.As an example, the change in diameter between the
5.3 Mock Vessels:
diastolic and systolic pressure for each pulse of blood circula-
5.3.1 The choice of inside diameter of the mock vessel is
tion.
critically important to the effectiveness of any durability test to
3.1.5 hydrodynamic loading, n—causing a change in the
be carried out. The mean non-stented mock vessel ID over a
inner diameter (ID) of a mock vessel by injecting a volume of
cardiac cycle shall be consistent with the worst case stent OD,
fluid into the confined test volume.
for the stent being tested, over the full test duration.
3.1.6 mock vessel, n—a simulated vessel typically manufac-
5.3.2 See Annex A1 and Annex A2 for specific require-
turedfromanelastomericmaterial.Themockvesselismadeto
ments.
approximate the ID and diametric distention of a native vessel
5.4 The sample size, in combination with other tests, animal
at physiological pressures (see A1.2.2 and A2.4.2)orat
and clinical tests, analysis (such as FEA (Finite Element
non-physiological pressures (see A2.4.4).
Analysis), and/or comparisons to predicate devices shall be
3.1.7 native vessel, n—defined as a natural healthy blood
sufficient to enable demonstration of an adequate justified
vessel.
reliability. In these test methods, one stent shall be considered
3.1.8 strain control, n—a term to describe control of dia-
one sample. The reliability justification may reference addi-
metric distention, relative to an initial diameter of the mock
tional testing and/or analysis used to establish stent durability.
vessel, not to be confused with controlling the strain in the
stent material.
6. General Apparatus Requirements
3.1.9 vascular stent, n—a synthetic tubular structure that is
implanted in the native or grafted vasculature and is intended 6.1 For test methods requiring precision measurement and
to provide mechanical radial support to enhance vessel patency control of pressure, dimensions, or cycle counts, verification of
over the intended design life of the device. A stent is metallic the dynamic performance of these systems shall be performed
and not covered by synthetic textile or tissue graft material. and documented with justification of the means used.
6.2 Pressure Measurement System—Pressure transducers
4. Summary of Test Methods
should be chosen that allow for the accurate evaluation of the
pressures within the tubes at the frequency of the test. See
4.1 These test methods cover fatigue/durability testing of
Annex A1 and Annex A2 for method specific requirements.
vascular stents that are subjected to hydrodynamic loading that
The pressure measuring system must be calibrated and justi-
simulates the loading and/or change in diameter that the stent
fied.
will experience in vivo. The stent shall be deployed into mock
6.3 Dimensional Measurement Devices, such as linear vari-
vessels that can be used to produce a cyclic diameter change of
able displacement transducers, lasers, and high-speed cameras
the stent. This document details two test methods that are
must be calibrated and justified.
currently used.
6.4 Cycle Counting System—The apparatus shall include a
4.1.1 Physiological Pressure Test Method—This test
cycle counting system for measuring the number of load cycles
method (provided in Annex A1) requires the use of mock
applied to the stent/mock artery combination.
vessels that possess similar diametric compliance properties to
6.5 Temperature Control System—The apparatus shall in-
native vessels at physiological pressure and rate of pulsation as
clude a calibrated temperature control and measurement sys-
well as at higher testing frequencies.
tem to provide the testing temperature for stents being tested.
4.1.2 Diameter Control Test Method—(Sometimes called a
strain control test method.) This test method (provided in
7. General Test Parameters
AnnexA2) requires the use of a diameter measurement system
and mock vessels to ensure that the desired minimum and
7.1 Temperature—The temperature shall be 37 6 2°C. If
maximum stent diameters, or the equivalent change in stent
other temperatures are to be used, a rationale shall be provided
diameter and mean stent diameter, are being achieved at the
stating why the particular temperature is considered worst case
test frequency. For conditions where a direct measurement of
or equivalent. The unit is to be stable over the intended period
the stent is not possible, measurements are typically made over
of the test and maintained within the established parameters.
theODofthemockvesselandarelationshipisdeterminedand
7.2 Actual temperatures and precisions shall be documented
justified for the ratio of the vessel ID versus measured OD.
by the user with accompanying justifications.
7.3 Solutions—Thetestsolutionshallbephosphatebuffered
5. Specimen Size, Configuration, and Preparation
saline (PBS) or equivalent unless testing in a different envi-
5.1 Unless otherwise justified, all samples selected for ronment (such as in distilled water or in air) can be justified.
testing shall be taken from fully processed, implant quality Rationale for use of a different environment shall be provided.
F2477–06
7.4 Physiological Pressure—The pressure change in the 8.2.1 Test parameters and acceptance criteria:
intended blood vessel. A suggested range for coronary stent 8.2.1.1 Test parameters (such as):
pulsatile fatigue evaluation is 80 to 160 mm Hg. (1) Mock vessel dimensions.
(2) Fluid temperature.
NOTE 1—Selection of the systolic and diastolic pressures should be
(3) Fluid pressure range and variability, or desired change
based on the patient population for which the stent is indicated.
in stented vessel diameter.
7.5 Physiological Pulse Rate—For the purposes of these
8.2.1.2 Acceptance criteria (such as):
test methods, determined to be 1.2 Hz or 72 beats per minute.
(1) Minimum level of pulsatile distention to define accep-
7.6 Biological growth can inhibit post-test evaluation of the
tance.
stent surface characteristics. Use of a biological growth inhibi-
(2) Maximum number of failures to define acceptance.
tor (such as algaecides or chemical agents) may be used unless
(3) Minimum number of cycles required to define accep-
such use would negatively impact the test by unintended
tance.
degradation of the stent or the test set-up.
8.2.2 Test specimen information:
7.7 The ID of the non-stented mock vessel is to be empiri-
8.2.2.1 Number of test specimens.
cally verified on the test instrument after the mock vessel(s)
8.2.2.2 Size (diameter, length, or other relevant dimensions)
have been mounted in their initial test position.
of all test specimens.
7.8 Vessel Degradation—Mock vessels made of materials
8.2.2.3 Rationale for the number of test specimens and sizes
that may degrade with exposure to environmental factors (such
used.
as UV light) shall be protected from such exposure.
8.2.2.4 Whether the specimens are representative of the
7.9 Stent Deployment—The stent shall be deployed in the
finished product.
mockvesselinsuchamannerastominimizeendeffectswhere
8.2.2.5 Sterilization parameters and number of sterilization
the vessel is connected to the test article and at a sufficient
cycles applied to the test specimens.
distance from other stents that may be deployed in the same
8.2.2.6 Traceability information.
vessel (see X2.5).
8.2.3 Materials used:
7.10 Test Frequency—SeeAnnexA1 andAnnexA2 for test
8.2.3.1 Test equipment.
specific details.
8.2.3.2 Mock vessels.
7.11 Test Validation—The investigator shall demonstrate
8.2.3.3 Test fluid/solutions.
that the stent to be tested maintains contact with the ID of the
8.2.3.4 Measurement devices.
vessel to be used in the durability test throughout the cycle,
8.2.4 Test protocol, including all justifications and ration-
when evaluated with the same pressures and frequencies to be
ales required by these test methods.
used in the durability test. This is not required for every
8.2.5 Protocol deviations.
sample. This and any justifications shall be documented in the
8.2.6 Raw data.
test report. Rationale: The functionality of a test method used
8.2.7 Test results.
to test a stent inside a vessel depends on the stent remaining in
8.2.8 Data analysis
contact with the ID of the vessel throughout the distension
8.2.9 Fracture reporting:
cycle of that vessel.
8.2.9.1 Report any fractures that occur during the test.
7.12 Acceptance Criteria—A detailed test protocol shall be
8.2.9.2 Fracture information should include number of
written that describes all procedures unique to the stent being
cycles to failure, number and locations of all fractures along
evaluated. This protocol shall include any specific failure
the length of the stent, type of fracture such as transverse or
modes to be identified, and inspections to be performed to
spiral, with or without dislocation, and any root cause analysis
identify those failures in any acceptance/rejection criteria. (See
performed to determine the reason for the fracture.
Appendix for examples.)
8.2.10 Conclusions.
8. Test Report
9. Precision and Bias
8.1 The test report shall include a complete summary of the
9.1 Intralaboratory and interlaboratory reproducibility has
materials, methods, and results including any rationale for
not been systematically determined.
deviations from this procedure. The effects of any such
10. Keywords
deviations on the significance of the test results shall be
reported.All real, artifact, and anomalous observations shall be 10.1 durability test; endovascular cardiology; fatigue test;
reported, including a just
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