1、Designation: F2129 17bStandard Test Method forConducting Cyclic Potentiodynamic PolarizationMeasurements to Determine the Corrosion Susceptibility ofSmall Implant Devices1This standard is issued under the fixed designation F2129; the number immediately following the designation indicates the year of
2、original adoption or, in the case of revision, the year 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 test method assesses the corrosion susceptibility ofsm
3、all, metallic, implant medical devices, or componentsthereof, using cyclic (forward and reverse) potentiodynamicpolarization. Examples of device types that may be evaluatedby this test method include, but are not limited to, vascularstents, ureteral stents (Specification F1828), filters, supportsegm
4、ents of endovascular grafts, cardiac occluders, aneurysmor ligation clips, staples, and so forth.1.2 This test method is used to assess a device in its finalform and finish, as it would be implanted. These small devicesshould be tested in their entirety. The upper limit on device sizeis dictated by
5、the electrical current delivery capability of thetest apparatus (see Section 6). It is assumed that test methods,such as Reference Test Method G5 and Test Method G61 havebeen used for material screening.1.3 Because of the variety of configurations and sizes ofimplants, this test method provides a va
6、riety of specimenholder configurations.1.4 This test method is intended for use on implantabledevices made from metals with a relatively high resistance tocorrosion.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This st
7、andard 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.1.7 This international sta
8、ndard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2.
9、Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodF1828 Specification for Ureteral StentsG3 Practice for
10、 Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G61 Test Method for Conducting Cyclic PotentiodynamicPolarizatio
11、n Measurements for Localized Corrosion Sus-ceptibility of Iron-, Nickel-, or Cobalt-Based Alloys3. Terminology3.1 Definitions:3.1.1 potentiostat, nan instrument for automatically main-taining an electrode in an electrolyte at a constant potential orcontrolled potentials with respect to a suitable re
12、ferenceelectrode (see Terminology G15).3.1.2 potentiodynamic cyclic polarization (forward and re-verse polarization), na technique in which the potential ofthe test specimen is controlled and the corrosion currentmeasured by a potentiostat. The potential is scanned in thepositive or noble (forward)
13、direction as defined in Practice G3.The potential scan is continued until a predetermined potential1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current ed
14、ition approved Dec. 1, 2017. Published January 2018. Originallyapproved in 2001. Last previous edition approved in 2017 as F2129 17a. DOI:10.1520/F2129-17B.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST
15、MStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis int
16、ernational standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) C
17、ommittee.1or current density is reached. Typically, the scan is run until thetranspassive region is reached, and the specimen no longerdemonstrates passivity, as defined in Practice G3. The potentialscan direction is then reversed until the specimen repassivatesor the potential reaches a preset valu
18、e.3.1.3 scan rate, nthe rate at which the controlling voltageis changed.3.2 Symbols:3.2.1 Eb= Breakdown or Critical Pitting Potentialtheleast noble potential at which pitting or crevice corrosion orboth will initiate and propagate as defined in Terminology G15.An increase in the resistance to pittin
19、g corrosion is associatedwith an increase in Eb.3.2.2 Er= Rest Potentialthe potential of the workingelectrode relative to the reference electrode measured undervirtual open-circuit conditions (working electrode is not polar-ized).3.2.3 Ezc= Zero Current Potentialthe potential at whichthe current rea
20、ches a minimum during the forward scan.3.2.4 Ef= Final Potentiala preset potential at which thescan is stopped.3.2.5 Ei= Initial Potentialthe potential at which thepotentiostat begins the controlled potentiodynamic scan.3.2.6 Ep= Protection Potentialthe potential at which thereverse scan intersects
21、the forward scan at a value that is lessnoble than Eb. Epcannot be determined if there is nobreakdown. Whereas, pitting will occur on a pit-free surfaceabove Eb, it will occur only in the range of potentials betweenEpand Ebif the surface is already pitted. The severity ofcrevice corrosion susceptibi
22、lity increases with increasing hys-teresis of the polarization curve, the difference between EbandEp.3.2.7 Ev= Vertex Potentiala preset potential, at which thescan direction is reversed.3.2.8 it= Threshold Current Density (mA/cm2)a presetcurrent density, at which the scan direction is reversed.Typic
23、ally, the scan is reversed when a current density twodecades higher than the current density at the breakdownpotential (Eb) is reached.4. Summary of Test Method4.1 The device is placed in an appropriate deaerated simu-lated physiological solution, and the rest potential (Er)isrecorded for1hor,altern
24、atively, until the rest potentialstabilizes to a rate of change less than 3 mV/min. Thepotentiodynamic scan is then started at Erand scanned in thepositive or noble (forward) direction. The scan is reversed aftereither the vertex potential (Ev) is reached or the current densityhas reached a value ap
25、proximately two decades greater than thecurrent density measured at the breakdown potential. Thereverse scan is stopped after the current has become less thanthat in the forward direction or the potential reaches Er. Thedata is plotted with the current density in mA/cm2on the x axis(logarithmic axis
26、) versus the potential in mV on the y axis(linear axis).5. Significance and Use5.1 Corrosion of implantable medical devices can havedeleterious effects on the device performance or may result inthe release of corrosion products with harmful biologicalconsequences; therefore it is important to determ
27、ine the generalcorrosion behavior as well as the susceptibility of the devicesto localized corrosion.5.2 The forming and finishing steps used to create animplantable device may have significant effects on the corro-sion resistance of the material out of which the device isfabricated. During the sele
28、ction process of a material for use asan implantable device, testing the corrosion resistance of thematerial is an essential step; however, it does not necessarilyprovide critical data regarding device performance.5.3 To accommodate the wide variety of device shapes andsizes encountered, a variety o
29、f holding devices can be used.5.4 Note that the method is intentionally designed to reachconditions that are sufficiently severe to cause breakdown anddeterioration of the medical devices and that these conditionsmay not necessarily be encountered in vivo. The results of thiscorrosion test conducted
30、 in artificial physiological electrolytescan provide useful data for comparison of different devicematerials, designs, or manufacturing processes. However, notethat this test method does not take into account the effects ofcells, proteins, and so forth on the corrosion behavior in vivo.6. Apparatus6
31、.1 Potentiostat, calibrated in accordance with ReferenceTest Method G5.6.2 Working Electrode, to be used as the test specimen, asdescribed in Section 9. Its configuration and holder will dependon the type of specimen being tested, as described in Section 7.In all cases, the metallurgical and surface
32、 condition of aspecimen simulating a device must be in the same condition asthe device.6.3 Reference ElectrodeA saturated calomel electrode(SCE), as described in Reference Test Method G5, shall beused as a reference electrode.6.4 Salt Bridge, such as a Luggin probe, shall be usedbetween the working
33、and reference electrode, such as the typeshown in Reference Test Method G5.6.5 Auxiliary Electrodes:6.5.1 Two platinum auxiliary electrodes may be preparedfrom high-purity rod stock. The surfaces may be platinized, asper Reference Test Method G5.6.5.2 Alternatively, high-purity graphite auxiliary el
34、ectrodesmay be used in accordance with Reference Test Method G5.Care should be taken to ensure that they do not get contami-nated during a test.6.5.3 The auxiliary electrode surface area should be at leastfour times greater than the sample surface area. Use ofwire-mesh platinum might be more cost-ef
35、fective than plati-num cylinders when testing larger specimens or whole devices.6.6 Suitable Polarization Cell, with a sufficient volume toallow the solution to cover the sample and the counterF2129 17b2electrode, and to prevent changes in pH during testing.Furthermore, the cell needs to be appropri
36、ately sealed to avoidoxygen access and include a secondary bubbler for the releaseof exhaust gas without the back diffusion of oxygen. The testcell must be able to hold a minimum of 500 ml.6.7 Water Bath, or other heating appliance capable ofmaintaining the test solution temperature at 37 6 1C (seeX
37、1.5).6.8 Purge Gas Delivery System, capable of delivering nitro-gen gas at 150 cm3/min.7. Specimen Holders7.1 There are a variety of holders that may be used in thistest method. Each is designed for a specific type or class ofdevice.7.2 Short wire or coil specimens:7.2.1 Specimens can be held suspen
38、ded from a clampingdevice. For example, the threaded end of a Reference TestMethod G5 holder can be used to hold two stainless steel nuts.The wire test specimen is clamped between these nuts and bentso as to enter the test solution.7.2.2 The surface area of the test specimen shall be calcu-lated bas
39、ed on the length of wire or coil immersed in the testsolution.7.2.3 This type of holder exposes the specimen to theair-liquid interface, which is subject to localized crevicecorrosion. Test specimens should be examined carefully aftertesting to ensure that there is no localized corrosion at or justb
40、elow the interface. If specimens show evidence of localizedcorrosion at the air-liquid interface, then the portion of thespecimen passing across this interface shall be sealed with animpervious coating.7.2.4 Alternatively, one may choose to coat the portion ofthe specimen out of the solution and the
41、 connection to thespecimen holder with a suitable coating. The surfaces out ofsolution will tend to have test solution condensed on them andthis may lead to undesirable results.7.3 One method for holding stents or cylindrical devices isshown in Appendix X3.8. Reagents8.1 Reagent grade chemicals shal
42、l be used for this testmethod when they are commercially available (for example,some components in bile solutions are not available in reagentgrade). Such reagents shall conform to the specifications of theCommittee on Analytical Reagents of the American ChemicalSociety.48.1.1 The water shall be dis
43、tilled or deionized conformingto the purity requirements of Specification D1193, Type IVreagent water.8.1.2 Unless otherwise specified, phosphate buffered saline(PBS) should be used as the standard test solution. A represen-tative PBS formulation is given in Appendix X2, along withthe formulations o
44、f two simulated bile solutions for testingimplantable medical devices intended for use in the biliarysystem, the formulations of two artificial urine solutions fortesting implantable indwelling materials intended for use in theurinary tract, and the compositions of two other commonlyused physiologic
45、al solutions.8.1.3 The pH of the electrolyte should be adjusted as neededbased on the nature of the solution (e.g., for PBS, adjust the pHto a value of 7.4 6 0.2 by the addition of NaH2PO4(acid) orNa2HPO4(base). When the electrolyte is deaerated, its pHmay change significantly if it is not sufficien
46、tly buffered.Several pH controlling methods are provided in Appendix X2.8.1.4 Nitrogen gas with a minimum purity of 99.99 %should be used for purging the test solution of oxygen.9. Test Specimen9.1 Unless otherwise justified, all samples selected fortesting should be taken from finished, clinical-qu
47、ality product.Cosmetic rejects or other nonclinical samples may be used ifthe cause for rejection does not affect the corrosion behavior ofthe device. Sterilization may be omitted if it can be demon-strated that prior sterilization has no effect on the corrosionbehavior of the device.9.1.1 Test spec
48、imens used for design parameter studies canbe prepared as detailed in Reference Test Method G5 forworking electrodes, with the requirement that the metallurgicaland surface conditions of the specimens are the same as theintended implantable medical device.10. Procedure10.1 Prepare the specimen such
49、that the portion exposed tothe test solution is in the same metallurgical and surfacecondition as the implantable form of the medical device beingstudied.10.1.1 Calculate the total surface area of the specimenexposed to the solution in order to determine the currentdensity (current per surface area) generated by the specimenduring the test.10.2 Prepare enough test solution to immerse the device andauxiliary electrodes and so to avoid any appreciable change inthe solution corrosivity during the test through exhaustion ofthe corrosive constituents or by accumul
