1、Designation: F3067 14Guide forRadial Loading of Balloon Expandable and Self ExpandingVascular Stents1This standard is issued under the fixed designation F3067; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. 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 document provides guidance for developing invitro test methods for measuring the radial strength or collapsepressure of ball
3、oon-expandable vascular stents and chronicoutward force of self-expanding vascular stents.1.2 This guide is applicable to balloon-expandable andself-expanding stents of tubular geometry. It covers both stentand stent grafts. It does not cover bifurcated stents. It does notcover stents with non-circu
4、lar cross-sections or tapered stents.1.3 UnitsThe values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard.1.4 This guide does not recommend any specific test methodor apparatus for measuring the radial strength, collapsepressure, or chronic
5、 outward force. Instead, this guide providesexamples of test methodologies and equipment that could beused and recommends the format for presenting test results.1.5 This guide covers only in vitro bench testing methods.In vivo behavior might be different.1.6 This standard does not purport to address
6、 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 Documents2.1 ASTM Standards:E4 Practices for F
7、orce Verification of Testing MachinesE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsF2079 Test Method for Measuring Intrinsic Elastic Recoil ofBalloon-Expandable StentsF2081 Guide for Characterization and Presentation of theDimensional Attributes of Vascular StentsF2477 Tes
8、t Methods for in vitro Pulsatile Durability Testingof Vascular Stents3. Terminology3.1 Definitions (alphabetically listed):3.2 balloon-expandable stenta stent that is expanded atthe treatment site by a balloon catheter. The stent material isplastically deformed by the balloon expansion such that the
9、stent remains expanded after deflation of the balloon.3.3 chronic outward forcethe minimum continued open-ing force of a self-expanding stent acting on the vessel wall ata specified diameter. The range of chronic outward force isdefined by the unloading curve at the maximum and minimumindicated use
10、diameters. Additional loading force consider-ations for self-expanding stents are evaluated as load excur-sions and described in Appendix X2. Chronic outward force isnot defined for balloon-expandable stents.3.4 collapse pressurethe uniform radial load during test-ing with a hydraulic or pneumatic a
11、pparatus in which aballoon-expandable stent undergoes buckling over a specificregion or the entire stent length.3.5 loada normalized, scalar value of force applied by thestent to the vessel and, at equilibrium, the vessel upon the stent.Load should be normalized by length (newton or millinewtonper m
12、illimeter length) or by area (pascal or kilopascal).3.6 loading linefor balloon-expandable stents, the linederived from the substantially linear portion of the radialloading curve during initial compression. The term is notdefined for balloon-expandable stents tested using collapsepressure apparatus
13、.3.7 radial forceoutput of radial loading that equals theradial pressure times the stent cylindrical area. The relationshipbetween radial force (FR) and radial pressure (P) is given in theequation:P 5FRAwhere:P = radial pressure,FR= radial force, and1This test method is under the jurisdiction of AST
14、M Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.30 on Cardiovascular Standards.Current edition approved Oct. 15, 2014. Published March 2015. DOI: 10.1520/F306714.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Co
15、nshohocken, PA 19428-2959. United States1A = instantaneous stent cylindrical area:A 5 DLwhere:D = instantaneous stent expanded outer diameter, andL = Lofor length change less than 10 % and L = L(D) forlength change greater than 10 %. L:L0is the expandedstent length for balloon-expandable stents and
16、uncon-strained length for self-expanding stents. L(D)istheinstantaneous length of the stent as a function of thecurrent instantaneous diameter. L(D) may be eitherexperimentally determined or computationally derived.3.8 radial loadinga mechanical loading mode in whichthe load is directed perpendicula
17、r to the longitudinal axis of acylinder and applied to the outer cylindrical surface of thestent. The load is applied to the entire outer surface or to atleast three areas that are equally distributed around the outercircumference and extend over the entire cylinder length. Loadmight be expressed as
18、 radial force or radial pressure.3.9 radial loading curvethe graph of radial loading outputon the y-axis versus diametric deformation of a stent on thex-axis.3.10 radial pressurethe area normalized output of radialloading equaling the average pressure applied to the stent bythe loading fixture in th
19、e radial direction toward the stentcylindrical axis.3.11 radial resistive loadthe peak load during a compres-sion excursion of a self-expanding stent. The excursion mightbe a single event or a cycle. A typical example is pulsatilecycling of an implanted self-expanding stent (refer to Appen-dix X2).3
20、.12 radial strengtha specific load on the radial loadingcurve that corresponds with a specific and clinically (practi-cally) relevant amount of inward plastic deformation from theunloaded state. The term is defined only for balloon-expandable stents tested whose sole mechanism of expansion isby a ba
21、lloon.Additionally, the term applies only to stents testedusing a segmented head or sling type apparatus and not usinga hydraulic or pneumatic pressure apparatus.3.13 self-expanding stenta stent that expands without theapplication of external forces or pressure, to a size and shapethat is close to t
22、he desired final size and shape, when releasedfrom the delivery system.3.14 stent lengthunstressed length of the stent after de-ployment. If the stent has marker bands on non-radial force-producing components, the length is measured from the ends ofthe radial force producing sections. The measured l
23、ength ofmounted or expanded stents should be measured by non-contacting instruments (profile projection, laser micrometer,and so forth) with a resolution of 0.1 mm or better (see GuideF2081).3.15 stent grafttransluminally placed tubular vascularprosthesis, with one or more integral stent components
24、toprovide fixation or radial support, or both, residing partially orcompletely within a vascular conduit to form an internal bypassor shunt between sections of the vascular system.3.16 unloading linefor balloon-expandable stents, the linederived from the substantially linear portion of the radialunl
25、oading curve. The term does not apply for balloon-expandable stents tested using collapse pressure apparatus.3.17 vascular patencya measure of the extent to which thevessel is open (unrestricted). Typically reported as a percent ofthe reference (unrestricted, adjacent) vessel diameter or cross-secti
26、onal area.3.18 vascular stenta tubular synthetic structure that isimplanted in the native or grafted vasculature and that isintended to provide mechanical radial support to enhancevessel patency. For the purpose of this guide, a stent might bemetallic or non-metallic. It might be durable or absorbab
27、le.3.19 zero compression diameterthe diameter referencepoint required for the testing apparatus to fully engage the stentouter surface. Stent compression is calculated in comparison tothis diameter.4. Significance and Use4.1 Upon deployment, at the site of the vascular stenosis,the stent establishes
28、 the patency of the lumen until vascularremodeling occurs. The radial load acting upon the stent isimparted by vessel and lesion stretch. Additionally, the vesselmight be affected by excursions due to pulsation (systolic anddiastolic variation), muscle-skeletal interactions due to patientmovement, a
29、s well as external sources (e.g., patient is struck inthe neck during a car accident). The excursions vary inmagnitude and type based on the location of the vessel.4.2 In order to maintain vessel patency, the stent has towithstand the forces acting on it without experiencing exces-sive deformation,
30、migration, or sustained collapse; therefore, itis required that the stent possess adequate resistance to theseloads.4.3 Depending on the type of device and the clinicalconcern, the resistance to these loads can be presented throughmultiple test outputs: radial strength, collapse pressure, orchronic
31、outward force.4.4 The guidelines presented here can be used in thedevelopment of test methods to determine the radial loadingproperties of stents. This guide provides examples of differenttest apparatus (equipment and tooling), radial loading curves,and calculations. Although the apparatus and metho
32、ds pre-sented can be used as a reasonable simulation of actual clinicaluse, they have not been demonstrated to predict the actual invivo clinical performance of any stent.5. Summary of Guide5.1 As defined, radial loading is applied uniformly over theentire stent surface at a minimum of three evenly
33、distributedcircumferential locations over the full length of the stent.Testing in which a portion of the stent extends outside apertureis not specifically discussed within the guide because it doesnot result in uniform radial loading since a portion of the stentoutside the aperture might also contri
34、bute to the load. Further,the direction of loading is radially inward as shown in Fig. 1.The uniform radial loading is applied to at least three areas thatF3067 142are equally spaced around the outer circumference and extendover the entire cylinder length.5.2 Some stents are designed to have signifi
35、cantly differentmechanical properties along their length. In these cases, itmight be preferable to test specific regions of the device. Thismight require apparatus (equipment or tooling) or changes toaccommodate local application of loading (e.g., inserts, ma-chined gaps, or having the test article
36、extend past the edge ofthe fixture). In addition, the assessment of the loading iscomplicated because the loading of the tested region will beaffected by the portion of the stent which is not being tested.The treatment of these modifications and the normalization ofloading are not specifically cover
37、ed in this guide and should bementioned within the test report.5.3 Radial testing of stents will differ depending on the stenttype (balloon-expandable versus self-expanding) as well as theapparatus used (segmented head, sling, or hydraulic/pneumatic). The apparatus is selected based on clinical effe
38、cts(concerns) and limited by the stent type. For example, thehydraulic/pneumatic apparatus cannot typically be used fortesting of self-expanding stents from the sheath to the unloadeddiameter because the tubing is likely to flatten or rupture withinthe large test range. The following summary outline
39、s differentapparatus, based on stent type, and the associated clinicaleffects that can be evaluated (see Fig. 2).5.4 In order to distinguish between different stent types aswell as the apparatus used, separate test outputs are defined inorder to clarify, and limit, the comparisons between test resul
40、ts.For example, a distal ring (edge, local) collapse of a balloon-expandable stent as measured (collapse pressure) using ahydraulic/pneumatic test apparatus might not directly convertor correlate to the radial strength output of the same devicetested using a segmented head apparatus. Further, becaus
41、e theloading behavior of balloon-expandable and self-expandingstents are very different, the self-expanding stent test outputterminology is chronic outward force rather than radial strengthor collapse pressure. Different test output terms are utilized inorder to clarify the differences and limit com
42、parisons.5.5 The clinical effects listed in Fig. 2 are separate from thedevice effects. The device effects are directly observed stentevents, while the clinical effects are the anticipated concernsassociated with the event. The clinical concerns presented areexamples; other clinical concerns might b
43、e identified from thesame list of device effects.FIG. 1 Radial LoadingFIG. 2 Summary GuideF3067 1435.6 Since the test outputs of load are normalized (either bylength or area), it is important to realize that the interpretationof output has inherent limitations for stents that are designed tohave sig
44、nificantly stronger (more resistive) and weaker (lessresistive) portions. This is truer for the sling and segmentedhead apparatus than the hydraulic/pneumatic collapse pressureapparatus. The hydraulic/pneumatic tester can visually detect alocalized region of weakness that collapses during pressuriza
45、-tion.6. Apparatus6.1 The key element of radial testing is the selection, ordevelopment, of an apparatus (equipment and tooling) thatradially loads the stent.6.2 The type of radial loading, as described in Fig. 1,isatheoretical construct and each type of loading apparatus hassome degree of deviation
46、 from the perfectly distributed radialloading. There are multiple types of apparatuses that arecapable of applying a radial load to a cylindrical stent withadequate uniformity.6.3 This guide describes three specific types of apparatusthat might be considered for radial testing: segmented head,sling,
47、 and hydraulic (or pneumatic) chamber.6.4 This guide does not provide detailed descriptions orguidelines for test apparatus design; thus specific and uniqueinterpretations of the apparatus are expected by the testlaboratory or equipment developer. Additional tooling, notdescribed, might be valuable
48、in improving the test methodconsistency (precision and robustness) and accuracy.6.5 It is expected that other apparatus (i.e., significantdeviations from the equipment design concept) not describedwithin this standard might also be adequate to radially loadvascular stents. If another apparatus is ut
49、ilized, rationale tojustify the suitability of that apparatus should be provided. Forexample, a data correlation to test results from one of the testequipment listed in this guide might be used. It is expected thateach apparatus will have specific limitations or requirementswhen testing specific groups of specimens or testing specificranges of diameters. Test method development should map theuse and limitations of the equipment for test articles.6.6 It is recognized that the choice of test apparatus is likelyto influence the characteristic shape of the radial load
