1、Designation: F 2477 07Standard Test Methods forin vitro Pulsatile Durability Testing of Vascular Stents1This standard is issued under the fixed designation F 2477; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of thedurability of a vascular stent by exposing it to physiologicallyrelevant di
3、ametric distension levels by means of hydrodynamicpulsatile loading. This testing occurs on a stent test specimenthat has been deployed into a mock (elastically simulated)vessel. The typical duration of this test is 10 years of equivalentuse (at 72 beats per minute), or at least 380 million cycles.1
4、.2 These test methods are applicable to balloon-expandableand self-expanding stents fabricated from metals and metalalloys. It does not specifically address any attributes unique tocoated stents, polymeric stents, or biodegradable stents, al-though the application of this test method to those produc
5、ts isnot precluded.1.3 These test methods do not include recommendations forendovascular grafts (“stent-grafts”) or other conduit productscommonly used to treat aneurismal disease or peripheral vesseltrauma or to provide vascular access, although some informa-tion included herein may be applicable t
6、o those devices.1.4 These test methods are valid for determining stentfailure due to typical cyclic blood vessel diametric distension.These test methods do not address other modes of failure suchas dynamic bending, torsion, extension, crushing, or abrasion.1.5 These test methods do not address test
7、conditions forcurved mock vessels.1.6 These test methods do not address test conditions foroverlapping stents.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet
8、y and health practices and determine the applica-bility of regulatory limitations prior to use.1.8 General CaveatThis document contains guidance fortesting as is currently carried out in most laboratories. Othertesting techniques may prove to be more effective and areencouraged. Whichever technique
9、is used, it is incumbent uponthe tester to justify the use of the particular technique,instrument, and protocol. This includes the choice of andproper calibration of all measuring devices. Deviations fromany of the suggestions in this document may be appropriate butmay require the same level of comp
10、rehensive justification thatthe techniques described herein will require.2. Referenced Documents2.1 Other Documents:ISO 7198: 1998(e), 8.10, Determination of Dynamic Com-pliance2FDA Guidance Document 1545, Non-Clinical Tests andRecommended Labeling for Intravascular Stents and As-sociated Delivery S
11、ystems, (issued January 13, 2005)33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 cardiac cycle, ndefined as one cycle between dias-tolic and systolic pressures.3.1.2 compliance, nthe change in inner diameter of avessel due to cyclic pressure changes. Compliance, if calcu-late
12、d, shall be expressed as a percentage of the diameter changeper 100 mm Hg and defined per ISO 7198, 8.10.5:%Compliance/100 mm Hg 5Dp2 2 Dp1! 3 104Dp1p2 2 p1!(1)where:Dp1 = inner diameter at the pressure of p1,Dp2 = inner diameter at the pressure of p2,p1 = lower pressure value (diastolic), in mm Hg,
13、 andp2 = higher pressure value (systolic), in mm Hg.3.1.3 diametric strain, na change in mock artery diameterdivided by the initial diameter. This term does not relate to themechanical strain seen in the stent material. The diametricstrain can be identified as:diametric strain 5Dp2Dp1!Dp1(2)that is,
14、diametric strain 5max ID min ID!min ID1These test methods are under the jurisdiction of ASTM Committee F04 onMedical and Surgical Materials and Devices and is the direct responsibility ofSubcommittee F04.30 on Cardiovascular Standards.Current edition approved April 1, 2007. Published May 2007. Origi
15、nallyapproved in 2006. Last previous edition approved in 2006 as F 2477 06.2Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.3Available from Food and Drug Administration (FDA), 5600 Fishers Ln.,Rockville, MD 20857, http:/ww
16、w.fda.gov. This document available at http:/www.fda.gov/cdrh/ode/guidance/1545.pdf.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4 distension, nthe change in diameters; such as theinner diameter (ID) of a vessel due to a pressu
17、re change. Theterm “diametric distension” is meant to represent the change ininner diameter of a blood vessel during each pulse of bloodcirculation.As an example, the change in diameter between thediastolic and systolic pressure for each pulse of blood circula-tion.3.1.5 hydrodynamic loading, ncausi
18、ng a change in theinner diameter (ID) of a mock vessel by injecting a volume offluid into the confined test volume.3.1.6 mock vessel, na simulated vessel typically manufac-tured from an elastomeric material. The mock vessel is made toapproximate the ID and diametric distention of a native vesselat p
19、hysiological pressures (see A1.2.2 and A2.4.2)oratnon-physiological pressures (see A2.4.4).3.1.7 native vessel, ndefined as a natural healthy bloodvessel.3.1.8 strain control, na term to describe control of dia-metric distention, relative to an initial diameter of the mockvessel, not to be confused
20、with controlling the strain in thestent material.3.1.9 vascular stent, na synthetic tubular structure that isimplanted in the native or grafted vasculature and is intendedto provide mechanical radial support to enhance vessel patencyover the intended design life of the device. A stent is metallicand
21、 not covered by synthetic textile or tissue graft material.4. Summary of Test Methods4.1 These test methods cover fatigue/durability testing ofvascular stents that are subjected to hydrodynamic loading thatsimulates the loading and/or change in diameter that the stentwill experience in vivo. The ste
22、nt shall be deployed into mockvessels that can be used to produce a cyclic diameter change ofthe stent. This document details two test methods that arecurrently used.4.1.1 Physiological Pressure Test MethodThis testmethod (provided in Annex A1) requires the use of mockvessels that possess similar di
23、ametric compliance properties tonative vessels at physiological pressure and rate of pulsation aswell as at higher testing frequencies.4.1.2 Diameter Control Test Method(Sometimes called astrain control test method.) This test method (provided inAnnex A2) requires the use of a diameter measurement s
24、ystemand mock vessels to ensure that the desired minimum andmaximum stent diameters, or the equivalent change in stentdiameter and mean stent diameter, are being achieved at thetest frequency. For conditions where a direct measurement ofthe stent is not possible, measurements are typically made over
25、the OD of the mock vessel and a relationship is determined andjustified for the ratio of the stent OD versus measured mockvessel OD.5. Specimen Size, Configuration, and Preparation5.1 Unless otherwise justified, all samples selected fortesting shall be taken from fully processed, implant qualityprod
26、uct. Sterilization should be required unless it can be shownnot to influence the fatigue/durability test results.5.2 The number of specimens tested for each stent geometryshould be sufficient to support any claims to be made based onthe test results. Fatigue/durability shall be evaluated for thewors
27、t case labeled diameter, and a rationale shall be providedstating why the particular labeled diameter is considered worstcase.5.3 Mock Vessels:5.3.1 The choice of inside diameter of the mock vessel iscritically important to the effectiveness of any durability test tobe carried out. The mean non-sten
28、ted mock vessel ID over acardiac cycle shall be consistent with the worst case stent OD,for the stent being tested, over the full test duration.5.3.2 See Annex A1 and Annex A2 for specific require-ments.5.4 The sample size, in combination with other tests, animaland clinical tests, analysis (such as
29、 FEA (Finite ElementAnalysis), and/or comparisons to predicate devices shall besufficient to enable demonstration of an adequate justifiedreliability. In these test methods, one stent shall be consideredone sample. The reliability justification may reference addi-tional testing and/or analysis used
30、to establish stent durability.6. General Apparatus Requirements6.1 For test methods requiring precision measurement andcontrol of pressure, dimensions, or cycle counts, verification ofthe dynamic performance of these systems shall be performedand documented with justification of the means used.6.2 P
31、ressure Measurement SystemPressure transducersshould be chosen that allow for the accurate evaluation of thepressures within the tubes at the frequency of the test. SeeAnnex A1 and Annex A2 for method specific requirements.The pressure measuring system must be calibrated and justi-fied.6.3 Dimension
32、al Measurement Devices, such as linear vari-able displacement transducers, lasers, and high-speed camerasmust be calibrated and justified.6.4 Cycle Counting SystemThe apparatus shall include acycle counting system for measuring the number of load cyclesapplied to the stent/mock artery combination.6.
33、5 Temperature Control SystemThe apparatus shall in-clude a calibrated temperature control and measurement sys-tem to provide the testing temperature for stents being tested.7. General Test Parameters7.1 TemperatureThe temperature shall be 37 6 2C. Ifother temperatures are to be used, a rationale sha
34、ll be providedstating why the particular temperature is considered worst caseor equivalent. The unit is to be stable over the intended periodof the test and maintained within the established parameters.7.2 Actual temperatures and precisions shall be documentedby the user with accompanying justificat
35、ions.7.3 SolutionsThe test solution shall be phosphate bufferedsaline (PBS) or equivalent unless testing in a different envi-ronment (such as in distilled water or in air) can be justified.Rationale for use of a different environment shall be provided.7.4 Physiological PressureThe pressure change in
36、 theintended blood vessel. A suggested range for coronary stentpulsatile fatigue evaluation is 80 to 160 mm Hg.NOTE 1Selection of the systolic and diastolic pressures should bebased on the patient population for which the stent is indicated.F24770727.5 Physiological Pulse RateFor the purposes of the
37、setest methods, determined to be 1.2 Hz or 72 beats per minute.7.6 Biological growth can inhibit post-test evaluation of thestent surface characteristics. Use of a biological growth inhibi-tor (such as algaecides or chemical agents) may be used unlesssuch use would negatively impact the test by unin
38、tendeddegradation of the stent or the test set-up.7.7 The ID of the non-stented mock vessel is to be empiri-cally verified on the test instrument after the mock vessel(s)have been mounted in their initial test position.7.8 Vessel DegradationMock vessels made of materialsthat may degrade with exposur
39、e to environmental factors (suchas UV light) shall be protected from such exposure.7.9 Stent DeploymentThe stent shall be deployed in themock vessel in such a manner as to minimize end effects wherethe vessel is connected to the test article and at a sufficientdistance from other stents that may be
40、deployed in the samevessel (see X2.5).7.10 Test FrequencySee Annex A1 and Annex A2 for testspecific details.7.11 Test ValidationThe investigator shall demonstratethat the stent to be tested maintains contact with the ID of thevessel to be used in the durability test throughout the cycle,when evaluat
41、ed with the same pressures and frequencies to beused in the durability test. This is not required for everysample. This and any justifications shall be documented in thetest report. Rationale: The functionality of a test method usedto test a stent inside a vessel depends on the stent remaining incon
42、tact with the ID of the vessel throughout the distensioncycle of that vessel.7.12 Acceptance CriteriaA detailed test protocol shall bewritten that describes all procedures unique to the stent beingevaluated. This protocol shall include any specific failuremodes to be identified, and inspections to b
43、e performed toidentify those failures in any acceptance/rejection criteria. (SeeAppendix for examples.)8. Test Report8.1 The test report shall include a complete summary of thematerials, methods, and results including any rationale fordeviations from this procedure. The effects of any suchdeviations
44、 on the significance of the test results shall bereported.All real, artifact, and anomalous observations shall bereported, including a justification for considering negativefindings as artifacts or discounting their clinical significance.8.2 Test reports should include:8.2.1 Test parameters and acce
45、ptance criteria:8.2.1.1 Test parameters (such as):(1) Mock vessel dimensions.(2) Fluid temperature.(3) Fluid pressure range and variability, or desired changein stented vessel diameter.8.2.1.2 Acceptance criteria (such as):(1) Minimum level of pulsatile distention to define accep-tance.(2) Maximum n
46、umber of failures to define acceptance.(3) Minimum number of cycles required to define accep-tance.8.2.2 Test specimen information:8.2.2.1 Number of test specimens.8.2.2.2 Size (diameter, length, or other relevant dimensions)of all test specimens.8.2.2.3 Rationale for the number of test specimens an
47、d sizesused.8.2.2.4 Whether the specimens are representative of thefinished product.8.2.2.5 Sterilization parameters and number of sterilizationcycles applied to the test specimens.8.2.2.6 Traceability information.8.2.3 Materials used:8.2.3.1 Test equipment.8.2.3.2 Mock vessels.8.2.3.3 Test fluid/so
48、lutions.8.2.3.4 Measurement devices.8.2.4 Test protocol, including all justifications and ration-ales required by these test methods.8.2.5 Protocol deviations.8.2.6 Raw data.8.2.7 Test results.8.2.8 Data analysis8.2.9 Fracture reporting:8.2.9.1 Report any fractures that occur during the test.8.2.9.2
49、 Fracture information should include number ofcycles to failure, number and locations of all fractures alongthe length of the stent, type of fracture such as transverse orspiral, with or without dislocation, and any root cause analysisperformed to determine the reason for the fracture.8.2.10 Conclusions.9. Precision and Bias9.1 Intralaboratory and interlaboratory reproducibility hasnot been systematically determined.10. Keywords10.1 durability test; endovascular cardiology; fatigue test;interventional cardiology; intravascular device test; pressurec
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