ASTM F2477-07(2013)
(Test Method)Standard Test Methods for in vitro Pulsatile Durability Testing of Vascular Stents
Standard Test Methods for <emph type="bdit">in vitro</emph> Pulsatile Durability Testing of Vascular Stents
ABSTRACT
This test method covers the procedure for determining the durability of ballon-expandable and self- expanding metal or alloy vascular stents. Tests are performed by exposing specimens to physiologically relevant diametric distention levels using hydrodynamic pulsatile loading. Specimens should have been deployed into a mock or elastically simulated vessel prior to testing. The test methods are valid for determining stent failure due to typical cyclic blood vessel diametric distention and include physiological pressure tests and diameter control tests. These do not address other modes of failure such as dynamic bending, torsion, extension, crushing, or abrasion. Test apparatus include a pressure measurement system, dimensional measurement devices, a cycle counting system, and a temperature control system.
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.
1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.8 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.
1.9 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.
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Designation: F2477 − 07 (Reapproved 2013)
Standard Test Methods for
in vitro Pulsatile Durability Testing of Vascular Stents
This standard is issued under the fixed designation F2477; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.9 General Caveat—This document contains guidance for
testing as is currently carried out in most laboratories. Other
1.1 These test methods cover the determination of the
testing techniques may prove to be more effective and are
durability of a vascular stent by exposing it to physiologically
encouraged. Whichever technique is used, it is incumbent upon
relevantdiametricdistensionlevelsbymeansofhydrodynamic
the tester to justify the use of the particular technique,
pulsatile loading. This testing occurs on a stent test specimen
instrument, and protocol. This includes the choice of and
that has been deployed into a mock (elastically simulated)
proper calibration of all measuring devices. Deviations from
vessel.Thetypicaldurationofthistestis10yearsofequivalent
any of the suggestions in this document may be appropriate but
use (at 72 beats per minute), or at least 380 million cycles.
may require the same level of comprehensive justification that
1.2 Thesetestmethodsareapplicabletoballoon-expandable
the techniques described herein will require.
and self-expanding stents fabricated from metals and metal
alloys. It does not specifically address any attributes unique to
2. Referenced Documents
coated stents, polymeric stents, or biodegradable stents, al-
2.1 Other Documents:
though the application of this test method to those products is
ISO 7198: 1998(e), 8.10, Determination of Dynamic Com-
not precluded.
pliance
1.3 These test methods do not include recommendations for
FDA Guidance Document 1545, Non-Clinical Tests and
endovascular grafts (“stent-grafts”) or other conduit products
Recommended Labeling for Intravascular Stents and As-
commonly used to treat aneurismal disease or peripheral vessel
sociated Delivery Systems, (issued January 13, 2005)
trauma or to provide vascular access, although some informa-
tion included herein may be applicable to those devices.
3. Terminology
1.4 These test methods are valid for determining stent
3.1 Definitions of Terms Specific to This Standard:
failure due to typical cyclic blood vessel diametric distension.
3.1.1 cardiac cycle, n—defined as one cycle between dia-
These test methods do not address other modes of failure such
stolic and systolic pressures.
as dynamic bending, torsion, extension, crushing, or abrasion.
3.1.2 compliance, n—the change in inner diameter of a
1.5 These test methods do not address test conditions for
vessel due to cyclic pressure changes. Compliance, if
curved mock vessels.
calculated, shall be expressed as a percentage of the diameter
change per 100 mm Hg and defined per ISO 7198, 8.10.5:
1.6 These test methods do not address test conditions for
overlapping stents.
~Dp2 2 Dp1! 310
%Compliance/100 mm Hg 5 (1)
Dp1 p2 2 p1
1.7 The values stated in SI units are to be regarded as ~ ~ !!
standard. No other units of measurement are included in this
where:
standard.
Dp1 = inner diameter at the pressure of p1,
1.8 This standard does not purport to address all of the
Dp2 = inner diameter at the pressure of p2,
safety concerns, if any, associated with its use. It is the
p1 = lower pressure value (diastolic), in mm Hg, and
responsibility of the user of this standard to establish appro-
p2 = higher pressure value (systolic), in mm Hg.
priate safety and health practices and determine the applica-
3.1.3 diametric strain, n—a change in mock artery diameter
bility of regulatory limitations prior to use.
divided by the initial diameter. This term does not relate to the
These test methods are under the jurisdiction of ASTM Committee F04 on
Medical and Surgical Materials and Devices and is the direct responsibility of Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
Subcommittee F04.30 on Cardiovascular Standards. 4th Floor, New York, NY 10036, http://www.ansi.org.
Current edition approved March 1, 2013. Published March 2013. Originally Available from Food and Drug Administration (FDA), 5600 Fishers Ln.,
approved in 2006. Last previous edition approved in 2007 as F2477 – 07. DOI: Rockville, MD 20857, http://www.fda.gov. This document available at http://
10.1520/F2477-07R13. 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 − 07 (2013)
mechanical strain seen in the stent material. The diametric theODofthemockvesselandarelationshipisdeterminedand
strain can be identified as: justified for the ratio of the stent OD versus measured mock
vessel OD.
Dp2 2 Dp1
~ !
diametric strain 5 (2)
Dp1
5. Specimen Size, Configuration, and Preparation
that is,
5.1 Unless otherwise justified, all samples selected for
testing shall be taken from fully processed, implant quality
maxID 2 minID
~ !
product.Sterilizationshouldberequiredunlessitcanbeshown
diametric strain 5
minID
not to influence the fatigue/durability test results.
3.1.4 distension, n—the change in diameters; such as the
5.2 Thenumberofspecimenstestedforeachstentgeometry
inner diameter (ID) of a vessel due to a pressure change. The
should be sufficient to support any claims to be made based on
term “diametric distension” is meant to represent the change in
the test results. Fatigue/durability shall be evaluated for the
inner diameter of a blood vessel during each pulse of blood
worst case labeled diameter, and a rationale shall be provided
circulation.As an example, the change in diameter between the
stating why the particular labeled diameter is considered worst
diastolic and systolic pressure for each pulse of blood circula-
case.
tion.
5.3 Mock Vessels:
3.1.5 hydrodynamic loading, n—causing a change in the
5.3.1 The choice of inside diameter of the mock vessel is
inner diameter (ID) of a mock vessel by injecting a volume of
critically important to the effectiveness of any durability test to
fluid into the confined test volume.
be carried out. The mean non-stented mock vessel ID over a
3.1.6 mock vessel, n—a simulated vessel typically manufac-
cardiac cycle shall be consistent with the worst case stent OD,
turedfromanelastomericmaterial.Themockvesselismadeto
for the stent being tested, over the full test duration.
approximate the ID and diametric distention of a native vessel
5.3.2 See Annex A1 and Annex A2 for specific require-
at physiological pressures (see A1.2.2 and A2.4.2)orat
ments.
non-physiological pressures (see A2.4.4).
5.4 The sample size, in combination with other tests, animal
3.1.7 native vessel, n—defined as a natural healthy blood
and clinical tests, analysis (such as FEA (Finite Element
vessel.
Analysis), and/or comparisons to predicate devices shall be
3.1.8 strain control, n—a term to describe control of dia- sufficient to enable demonstration of an adequate justified
metric distention, relative to an initial diameter of the mock
reliability. In these test methods, one stent shall be considered
vessel, not to be confused with controlling the strain in the
one sample. The reliability justification may reference addi-
stent material.
tional testing and/or analysis used to establish stent durability.
3.1.9 vascular stent, n—a synthetic tubular structure that is
6. General Apparatus Requirements
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.
4. Summary of Test Methods
6.2 Pressure Measurement System—Pressure transducers
should be chosen that allow for the accurate evaluation of the
4.1 These test methods cover fatigue/durability testing of
pressures within the tubes at the frequency of the test. See
vascular stents that are subjected to hydrodynamic loading that
Annex A1 and Annex A2 for method specific requirements.
simulates the loading and/or change in diameter that the stent
The pressure measuring system must be calibrated and justi-
will experience in vivo. The stent shall be deployed into mock
fied.
vessels that can be used to produce a cyclic diameter change of
the stent. This document details two test methods that are
6.3 Dimensional Measurement Devices, such as linear vari-
currently used.
able displacement transducers, lasers, and high-speed cameras
4.1.1 Physiological Pressure Test Method—This test
must be calibrated and justified.
method (provided in Annex A1) requires the use of mock
6.4 Cycle Counting System—The apparatus shall include a
vessels that possess similar diametric compliance properties to
cycle counting system for measuring the number of load cycles
native vessels at physiological pressure and rate of pulsation as
applied to the stent/mock artery combination.
well as at higher testing frequencies.
6.5 Temperature Control System—The apparatus shall in-
4.1.2 Diameter Control Test Method—(Sometimes called a
clude a calibrated temperature control and measurement sys-
strain control test method.) This test method (provided in
tem to provide the testing temperature for stents being tested.
AnnexA2) requires the use of a diameter measurement system
and mock vessels to ensure that the desired minimum and
7. General Test Parameters
maximum stent diameters, or the equivalent change in stent
diameter and mean stent diameter, are being achieved at the 7.1 Temperature—The temperature shall be 37 6 2°C. If
test frequency. For conditions where a direct measurement of other temperatures are to be used, a rationale shall be provided
the stent is not possible, measurements are typically made over stating why the particular temperature is considered worst case
F2477 − 07 (2013)
or equivalent. The unit is to be stable over the intended period deviations on the significance of the test results shall be
of the test and maintained within the established parameters. reported.All real, artifact, and anomalous observations shall be
reported, including a justification for considering negative
7.2 Actual temperatures and precisions shall be documented
findings as artifacts or discounting their clinical significance.
by the user with accompanying justifications.
8.2 Test reports should include:
7.3 Solutions—The test solution shall be phosphate buffered
8.2.1 Test parameters and acceptance criteria:
saline (PBS) or equivalent unless testing in a different envi-
8.2.1.1 Test parameters (such as):
ronment (such as in distilled water or in air) can be justified.
(1) Mock vessel dimensions.
Rationale for use of a different environment shall be provided.
(2) Fluid temperature.
7.4 Physiological Pressure—The pressure change in the
(3) Fluid pressure range and variability, or desired change
intended blood vessel. A suggested range for coronary stent
in stented vessel diameter.
pulsatile fatigue evaluation is 80 to 160 mm Hg.
8.2.1.2 Acceptance criteria (such as):
(1) Minimum level of pulsatile distention to define accep-
NOTE 1—Selection of the systolic and diastolic pressures should be
based on the patient population for which the stent is indicated. tance.
(2) Maximum number of failures to define acceptance.
7.5 Physiological Pulse Rate—Forthepurposesofthesetest
(3) Minimum number of cycles required to define accep-
methods, determined to be 1.2 Hz or 72 beats per minute.
tance.
7.6 Biological growth can inhibit post-test evaluation of the
8.2.2 Test specimen information:
stent surface characteristics. Use of a biological growth inhibi-
8.2.2.1 Number of test specimens.
tor (such as algaecides or chemical agents) may be used unless
8.2.2.2 Size (diameter, length, or other relevant dimensions)
such use would negatively impact the test by unintended
of all test specimens.
degradation of the stent or the test set-up.
8.2.2.3 Rationale for the number of test specimens and sizes
7.7 The ID of the non-stented mock vessel is to be empiri-
used.
cally verified on the test instrument after the mock vessel(s)
8.2.2.4 Whether the specimens are representative of the
have been mounted in their initial test position.
finished product.
8.2.2.5 Sterilization parameters and number of sterilization
7.8 Vessel Degradation—Mock vessels made of materials
cycles applied to the test specimens.
that may degrade with exposure to environmental factors (such
8.2.2.6 Traceability information.
as UV light) shall be protected from such exposure.
8.2.3 Materials used:
7.9 Stent Deployment—The stent shall be deployed in the
8.2.3.1 Test equipment.
mockvesselinsuchamannerastominimizeendeffectswhere
8.2.3.2 Mock vessels.
the vessel is connected to the test article and at a sufficient
8.2.3.3 Test fluid/solutions.
distance from other stents that may be deployed in the same
8.2.3.4 Measurement devices.
vessel (see X2.5).
8.2.4 Test protocol, including all justifications and ratio-
7.10 Test Frequency—See AnnexA1 and AnnexA2 for test nales required by these test methods.
specific details.
8.2.5 Protocol deviations.
8.2.6 Raw data.
7.11 Test Validation—The investigator shall demonstrate
8.2.7 Test results.
that the stent to be tested maintains contact with the ID of the
8.2.8 Data analysis
vessel to be used in the durability test throughout the cycle,
8.2.9 Fracture reporting:
when evaluated with the same pressures and frequencies to be
8.2.9.1 Report any fractures that occur during the test.
used in the durability test. This is not required for every
8.2.9.2 Fracture information should include number of
sample. This and any justifications shall be documented in the
cycles to failure, number and locations of all fractures along
test report. Rationale: The functionality of a test method used
the length of the stent, type of fracture such as transverse or
to test a stent inside a vessel depends on the stent remaining in
spiral, with or without dislocation, and any root cause analysis
contact with the ID of the vessel throughout the distension
performed to determine the reason for the fracture.
cycle of that vessel.
8.2.10 Conclusions.
7.12 Acceptance Criteria—A detailed test protocol shall be
written that describes all procedures unique to th
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