1、Designation: F 2079 02Standard Test Method forMeasuring Intrinsic Elastic Recoil of Balloon-ExpandableStents1This standard is issued under the fixed designation F 2079; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. 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 The purpose of this test method is to quantify thepercentage by which the diameter of a stent decreases from itsexpande
3、d diameter while still on the delivery balloon to itsrelaxed diameter after deflating the balloon. This test method isappropriate for stents manufactured from a material that isplastically deformed when the stents diameter is increasedfrom its predeployed size to its postdeployed size by mechani-cal
4、 means. This test method may be performed in air at roomtemperature unless there is a known temperature dependence ofthe material, in which case, the temperature at which the test isconducted shall be stated in the report.1.2 This standard does not purport to address all of thesafety concerns, if an
5、y, 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. Terminology2.1 Definitions:2.1.1 labeled diameter, nthe nominal deployed size of astent as
6、 indicated on its manufacturers label.2.1.2 stent recoil, nthe amount, expressed as a percentage,by which the diameter of a stent changes from the expandeddiameter measured with the stent on the inflated deliveryballoon to the final value measured after deflating the balloon.3. Summary of Test Metho
7、d3.1 A sample device representative of product that will bemarketed is either premounted or mounted on the deliveryballoon at the time of use. The delivery balloon is inflated tothe nominal expansion pressure indicated for the labeled stent.The outer diameter of the stent is measured in two approxi-
8、mately orthogonal rotational positions while the stent is still onthe inflated delivery balloon. The balloon is deflated and theouter diameter of the stent is remeasured in the same positionsat approximately the same location.4. Significance and Use4.1 Minimal stent recoil is a desirable feature of
9、a stentbecause it minimizes the maximum diameter to which a stentmust be expanded to achieve its final relaxed diameter. A stenthaving a high recoil must be expanded to a greater diameter toachieve its final relaxed diameter than a stent having lowrecoil. Practically, excessive expansion of the vess
10、el into whichthe stent is to be implanted may cause tissue damage resultingin a poor immediate result or poor long-term outcome. Stentrecoil is affected by intrinsic properties of the material used toconstruct the stent and the specific geometric design of thestent; therefore, measuring stent recoil
11、 is an essential part ofevaluating the design.5. Apparatus5.1 A means to inflate with noncompressible fluid, typicallywater, the delivery balloon on which the stent is mounted. Themeans used must be capable of achieving the pressure requiredto maintain the expanded diameter of the stent until it can
12、 bemeasured and may include a device to monitor pressure.5.2 A means to measure the outer diameter of the stentwithout deforming the stent. Typically, a calibrated opticalsystem, which does not require contact with the stent, is used.The resolution of the measurement system shall be 0.01 mm orbetter
13、. The accuracy of the system shall be 2 % of reading orbetter.6. Sampling, Test Specimens, and Test Units6.1 Unless otherwise justified, all samples selected fortesting should be taken from fully processed, clinical qualityproduct. It is not required that these devices undergo terminalsterilization.
14、 Cosmetic rejects or other nonclinical samples maybe used if the cause for rejection has been shown not to affectstent recoil.6.2 The number of specimens tested for each unique stentgeometry should be sufficient to meet sampling requirementsfor desired specification limits. In general, a minimum of
15、tenspecimens is recommended. If a single stent geometry isintended to be used for more than one labeled diameter, recoilshall be evaluated for test specimens expanded to the smallestand largest diameters intended for that geometry.6.3 Most stents are comprised of a repetitious continuous1This test m
16、ethod 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 May 10, 2002. Published July 2002. Originallypublished as F 2079 01. Last previous edition F
17、2079 01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.pattern or of repeating subunits. If stents are made longer byadditional repetition of the basic geometric pattern or byadding identical subunits, then recoil need be measured o
18、n onlya single length of each diameter stent. If, however, dimensionsof the substructure of the repeating pattern or of the subunits isaltered to change the length, then recoil must be measured foreach unique geometry.7. Procedure7.1 Corresponding paired outer diameter measurements,(that is, Diamete
19、rinflatedand Diameterfinal) shall be obtainedwith the stent in approximately the same rotational positionwith respect to the measurement system.7.2 The number of locations along the length of the stent atwhich recoil is measured should be determined by initialassessment of the stent geometry. Measur
20、ements should bemade at a single location near midlength unless otherwisewarranted by the stent design. For example, if the stent isspecifically designed to recoil less at the ends than in themiddle, recoil should be measured at both locations.7.3 Inflate the balloon to the nominal expansion pressur
21、eindicated on the stent labeling. To allow for full expansion ofthe stent, maintain the expansion pressure for 15 to 30 s beforetaking diameter measurements.7.4 Measure the outer diameter of the stent in two approxi-mately orthogonal rotational positions.7.5 Deflate the balloon.7.6 Measure the outer
22、 diameter of the stent at the samelocation(s) and in the same rotational positions with respect tothe measurement system as in 7.4. These measurements shouldbe taken no sooner than 10 s after deflating the balloon.8. Calculation8.1 Calculate the stent recoil for the location(s) measured in7.4 for ea
23、ch stent using the following equation:Stent Recoil %!5S1SDiameterfinalDiameterinflatedDD* 100 (1)where:Diameterinflated= outer diameter of stent while on inflateddelivery balloon andDiameterfinal= outer diameter of stent after deflatingdelivery balloon.8.2 Calculate the average and standard deviatio
24、n of stentrecoil for each location at which recoil is measured.9. Report9.1 Report the following information for each labeled diam-eter of each unique stent geometry:9.1.1 Labeled stent diameter, in millimetres.9.1.2 Labeled stent length.9.1.3 Number of samples measured.9.1.4 Diameterinflated(mean 6
25、 standard deviation, to thenearest 0.01 mm).9.1.5 Diameterfinal(mean 6 standard deviation, to the near-est 0.01 mm).9.1.6 Stent recoil average (mean 6 standard deviation, tothe nearest 0.5 %) for each location measured.9.1.7 Temperature at which test is performed.10. Precision and Bias10.1 Precision
26、The precision of this test method has notyet been established. An interlaboratory comparison to deter-mine the precision is being planned.10.2 BiasNo information can be presented on the bias ofthis test method because no material having an acceptablereference value is available.11. Keywords11.1 reco
27、il; stentAPPENDIXES(Nonmandatory Information)X1. RATIONALEX1.1 Balloon-expandable stents typically are deployed forpermanent implant by plastically deforming the material ofconstruction. Upon release of the balloon pressure, the diam-eter will decrease, the exact amount of which depends on themateri
28、al used to construct the stent and the specific design ofthe stent. For optimal clinical results, it is critical that the finaldeployed diameter be appropriate for the exact location ofdeployment. Moreover, a stent with excessive recoil must beinflated to a larger diameter to achieve the desired fin
29、aldiameter. This larger required initial inflation diameter maycause more damage to the vessel than would the lower inflationdiameter required for a stent with a lower recoil. The implant-ing physician must have guidance as to how much any givenstent design will recoil so that the balloon may be inf
30、lated tothe expanded diameter required to achieve the desired finaldiameter. This test method provides a standardized procedureto determine the recoil characteristics of stents so that consis-tent labeling can be written. Note that this test methodmeasures the intrinsic recoil of the stent and may n
31、ot predicthow the stent will perform when implanted in a vessel in whichstent recoil, stent stiffness, and vessel stiffness interact todetermine the final diameter.F 20792X2. REVISION HISTORYX2.1 This standard was originally approved in 2001. It wasrevised in 2002 to clarify terminology, measurement
32、 proce-dures, and reporting requirements.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and th
33、e riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision o
34、f this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should
35、make your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).F 20793
