1、Designation: F2942 13Standard Guide forin vitro Axial, Bending, and Torsional Durability Testing ofVascular Stents1This standard is issued under the fixed designation F2942; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide includes three separate cyclic deformationdurability guides related to vascular stents: bending, axial,
3、andtorsional.1.2 This guide does not address flat plate, local crushdurability, or multi-mode testing.1.3 This guide applies to balloon-expandable and self-expanding stents fabricated from metals and metal alloys. Itdoes not specifically address any attributes unique to coatedstents (i.e., stent wit
4、h a surface layer of an additionalmaterial(s), monolithically polymeric stents, or absorbablestents, although the application of this standard to thoseproducts is not precluded.1.4 This guide is applicable to testing of stent(s) (or arepresentative portion of a stent). While durability testing ofcou
5、pon samples (e.g., a scaled-up portion of the stent structure)can provide useful information, it is not within the scope of thisguide.1.5 This guide applies to endovascular grafts (“stent-grafts”) and other conduit products commonly used to treataneurismal disease, peripheral vessel trauma, or to pr
6、ovidevascular access. The information provided herein does notaddress all issues related to testing of these devices.1.6 This guide applies to in vitro modeling of stent durabil-ity from non-radial arterial motions. Such motions may arisefrom musculoskeletal activities, including walking andbreathin
7、g, and cardiac motion. ASTM F2477 addresses pulsa-tile (i.e., radial) durability of vascular stents.1.7 This guide does not provide the in vivo physiologicdeformation conditions for a vascular stent. It is incumbentupon the user of the standard to develop and justify theseboundary conditions (e.g.,
8、literature review, in vivo studies,cadaver studies, or modeling of stent vessel interaction) inthese durability bench tests. Additional conditions that may beconsidered include vessel calcification, vessel taper, eccentriclesions, loading excursions (e.g., exercise), and vessel remod-eling.1.8 This
9、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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2
10、.1 ASTM Standards:2F2477 Test Methods forin vitro Pulsatile Durability Testingof Vascular Stents2.2 Other Documents:ASTM STP 588 Manual on Statistical Planning andAnalysis, R.E. Little, 1975ISO 25539 Cardiovascular ImplantsEndovascular Device-sPart 2: Vascular StentsFDA Guidance Document #1545 “Non-
11、Clinical EngineeringTests and Recommended Labeling for Intravascular StentsandAssociated Delivery Systems” (IssuedApril 18, 2010)3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 axial, adjcompression or tension of a stent and/ormock vessel along its longitudinal axis.3.1.2 bend
12、ing, adjdeformation on the longitudinal axis ofa stent and/or mock vessel to achieve a specified stent radius ofcurvature.3.1.3 fracture, nthe complete separation of a stent struc-tural feature.3.1.4 mock vessel, na simulated vessel typically manufac-tured from an elastomeric material.3.1.5 radius o
13、f curvature, nthe inner, outer or centerlinebend radius of a stent.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.30 on Cardiovascular Standards.Current edition approved Aug. 15, 2013.
14、 Published September 2013. DOI:10.1520/F2942-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright AST
15、M International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.6 specimen, narticle consisting of an implantable de-vice or a representative portion of an implantable device, thatis tested according to this guide.3.1.7 torsional, adjtwisting of a stent and/o
16、r mock vesselabout its longitudinal axis.4. Summary of Test Guides4.1 This guide covers in vitro durability testing of vascularstents using modes that represent those that might be observedin vivo such as bending, axial, or torsional deformation modes.Examples include, but are not limited to, the ax
17、ial and bendingdeformation that occurs in the superficial femoral artery duringthe walking gait, the bending that occurs in the renal arteryduring respiration, and the bending that occurs in the coronaryartery during the cardiac cycle. This guide provides details andguidance for separate tests for e
18、ach deformation mode: axial,bending, and torsional. This guide allows the direct fixation ofthe ends of the stent or indirect fixation inside a mock vessel.Direct fixation of the ends of the stent allows better control ofstent deformation; however, this can result in attachment-induced test artifact
19、.4.1.1 Axial Durability Test GuideThe purpose of this testis to subject the stent to a specified amount of cyclic axialdeformation. The stent is deployed into a mock vessel, unlessa justification is provided. This test guide is described in moredetail in Annex A1.4.1.2 Bending Durability Test GuideT
20、he purpose of thistest is to subject the stent to a specified amount of cyclicbending deformation. There are three suggested bendingguides presented in AnnexA2, AnnexA3, and AnnexA4, eachinvolving placement of the stent inside of a mock vessel:column buckling, bending on a mandrel, and bending in an
21、 arcwithout a mandrel. In order to avoid test artifacts, these testguides recommend placement of the stent inside a mock vessel(stent ends not fixed) with subsequent cyclic bending of themock vessel. When selecting the guide to conduct bendingdurability testing, consider the potential for the stent
22、designunder evaluation to be adversely affected by a particular guideand the ability of each test to simulate a particular clinicalcondition.4.1.3 Torsional Durability Test GuideThe purpose of thistest is to subject the stent to a specified amount of cyclictorsional deformation. This guide is descri
23、bed in more detail inAnnex A5.4.2 Each test may utilize either test-to-success (TTS) orthe fatigue-to-fracture (FTF) methodology.3The TTS meth-odology entails selection of a set of boundary conditionsconsidered physiologically relevant, selection of a sufficientnumber of specimens, and application o
24、f the appropriatenumber of cycles. The successful completion of the TTS isbased upon the number (if any) and type of stent strut fractures.The FTF methodology entails selection of the appropriatenumber of cycles considered runout (i.e., point to stop testinga specimen), selection of a sufficient num
25、ber of specimens, andcharacterization of the stent fatigue performance by applyingmultiple deformation levels (i.e., loading amplitude) and con-ducting periodic inspections of the stent during testing toobtain some test specimens with fractures and some without.For specimens that fracture, the numbe
26、r of cycles applied tocause fracture is obtained. The successful completion of a FTFtest is based upon a comparison of stent fatigue performance,at the various deformation levels, to the physiologically rel-evant deformation levels. Selection of deformation levels tocharacterize the fatigue behavior
27、 of the stent may use themethodology described in ASTM STP 588.5. Significance and Use5.1 It is important to consider the durability of stent designsin deformation modes that are intended to model in vivoconditions. The appropriate amplitude and number of cycles ineach of the modes has to be determi
28、ned independently for theparticular clinical use proposed for the stent. These tests do notreplicate all varieties and aspects of the deployment processand the in vivo mechanical environment so they cannot beproofs of durability. Instead, the tests provide evidence ofdurability. The durability tests
29、 can also provide a means ofassessing design, material or processing changes.5.1.1 This guide might be useful for development testing,specification acceptance testing, and regulatory submissiontesting and filings as it provides a basic assurance that the testsare designed, executed, and reported in
30、a suitable fashion.5.1.2 If the tests are conducted using a well-defined FTFmethodology, they can be useful in:5.1.2.1 Potential design improvement through identificationof better and worse geometries, materials, and manufacturingprocesses;5.1.2.2 Understanding product durability by estimating theef
31、fects of changes in geometry, materials, or manufacturingprocesses;5.1.2.3 Estimating the safety factor relative to the ampli-tudes and other factors in use conditions; and5.1.2.4 Validating finite element analysis (FEA) and fatiguelife models.5.1.3 As stated in the scope, this guide is not intended
32、 toprovide the in vivo physiologic deformation conditions that avascular stent can be subjected. Reliable clinical data charac-terizing cyclic vascular deformation may be lacking for someindications. The user should develop and justify the boundaryconditions (e.g., literature review, in vivo studies
33、, cadaverstudies, or modeling of stent vessel interaction) for the chosendurability bench tests. Additional conditions that may beconsidered include vessel calcification, vessel taper, eccentriclesions, deformation excursions (e.g., exercise), and vesselremodeling.5.1.4 Test methods other than those
34、 provided in the annexesof this document might be appropriate, depending upon stentdesign. However, these methods are beyond the scope of thisguide.6. Specimen Size, Configuration, and Preparation6.1 Unless otherwise justified, all specimens selected fortesting should be taken from fully processed,
35、implant quality3Gong, X-Y, Chwirut, D. J., Mitchell, M. R., and Choules, B. D., Fatigue toFracture: An Informative, Fast, and Reliable Approach for Assessing MedicalImplant Durability, Journal ASTM International, Volume 6, Issue 7, July 2009.F2942 132product. Sterilization should be performed unless
36、 it can beshown not to influence the durability test results.NOTE 1Although sterilization may not directly affect the stent itself,it may affect the delivery system and, thus, the condition of theas-deployed stent.6.2 Prior to durability testing, specimens loaded in or ontheir delivery systems shoul
37、d be tracked through a modelrepresentative of the vasculature to simulate clinical delivery.6.3 To reduce the number of specimens to be tested,durability may be evaluated for the worst case justified devicesize/model. Alternatively, multiple sizes (length and/or diam-eter) at potentially multiple de
38、ployment diameters would needto be tested with an appropriate bracketing scheme (e.g., largestand smallest length and/or diameter or models).6.3.1 Stent LengthThe axial and torsional durability test-ing modes act to induce stent deformation normalized withlength (length change per length, and transv
39、erse angle changeper length, respectively). Thus, the fatigue resistance of a stentdesign with a repeating unit or cell design would also beindependent of length and any length may be tested. In caseswhere the stent design is length-dependent (e.g., non-repeatingunit cells), the length predicted or
40、expected to perform worstshould be justified (e.g., by finite element analysis or descrip-tion of stent design).NOTE 2Because of the nature of these test methods, it may not bepossible to test the longest stent length within a family of sizes, especiallyin the overlapped configuration. In such cases
41、, other means may need tobe implemented to justify the stent length tested or to allow extrapolationof test conclusions to the lengths not tested (e.g. justification based onfinite element analysis).6.3.2 Stent DiameterThe fatigue resistance of any specificstent design might be dependent upon the di
42、ameter. A rationalebased on finite element analysis or an explanation as to why theparticular diameter is predicted or expected to perform worstshould be provided. If different labeled diameter stents withina family have significantly different strut patterns, each uniquepattern should be considered
43、 separately.6.3.3 Deployment DiameterFor each labeled diameterstent tested, the test stent should be deployed to the “worst-case” deployed diameter per the instructions for use (IFU) (seesection 8.2 Mock Vessels). The diameter predicted or expectedto perform the worst should be justified by means su
44、ch as finiteelement analysis.6.3.4 Stent OverlappingWhen stents are expected to beoverlapped in clinical use, durability testing of overlappedstents should be performed.An overlap length representative ofclinical use should be selected. The relative position (rotationand overlap length) of the overl
45、apped stents should be selectedto ensure sufficiently challenging application of strain. Frettingand/or wear might lead to fracture of overlapped stents duringdurability testing. Thus, further analysis (e.g., scanning elec-tron microscopy (SEM) of the stents after durability testingmight be necessar
46、y to determine the failure mode.6.4 The number of specimens tested for each stent sizeand/or geometry should be sufficient to support any claimsmade based on the test results. The results of testing accordingto this guide in combination with other tests, animal andclinical tests, analysis (such as F
47、EA), and/or comparisons topredicate devices can be sufficient to enable demonstration ofan adequate durability. In this guide, one stent or a set of twooverlapped stents should be considered one specimen.7. General Apparatus Requirements7.1 The axial, bending and torsional dynamic displacementsof th
48、e test equipment should be verified at the selected testfrequencies. The dynamic stent deformation verification docu-mentation should include justification of the verification means(see section 8.6).7.2 Dimensional Measurement DevicesDevices such aslinear variable displacement transducers (LVDTs), l
49、asers, andhigh-speed cameras should be calibrated.7.3 Cycle Counting SystemThe apparatus should include acycle counting system for measuring the number of deforma-tion cycles applied to the stent. The cycle counting systemshould be verified at the test frequencies and the verificationshould be documented.7.4 Temperature Control SystemThe apparatus should in-clude a calibrated temperature control and measurement sys-tem to maintain the temperature of the stents being tested.8. General Test Parameters8.1 Completion of the durability test for stents deployedwit
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