1、Designation: F2129 17Standard 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 ofo
2、riginal 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 ofsma
3、ll, 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, supportsegme
4、nts 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 t
5、he 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 var
6、iety 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 sta
7、ndard 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 Documents2.1
8、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 Conventions Applicable
9、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 PotentiodynamicPolarization Measurements for Local
10、ized 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 referenceelectrode (see Te
11、rminology 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) direction as defined in
12、Practice G3.The potential scan is continued until a predetermined potentialor 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 unti
13、l the specimen repassivatesor the potential reaches a preset value.1This 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 edition approved Jan. 1, 2017. Pub
14、lished March 2017. Originallyapproved in 2001. Last previous edition approved in 2015 as F2129 15. DOI:10.1520/F2129-17.2For 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
15、 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 international standard was developed in
16、 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) Committee.13.1.3 scan rate, nthe rate
17、 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 pitting corrosion is associatedwit
18、h 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 reaches a minimum during the fo
19、rward 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 the forward scan at a value
20、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 susceptibility increases with increasi
21、ng 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.Typically, the scan is reversed w
22、hen 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,alternatively, until the rest pote
23、ntialstabilizes 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 approximately two decades grea
24、ter 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) versus the potential in mV
25、 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 determine the generalcorrosion beh
26、avior 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 selection process of a material
27、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 of holding devices can be use
28、d.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 in artificial physiological
29、 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. Apparatus6.1 Potentiostat, calibrated
30、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 condition of aspecimen simu
31、lating 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 and reference electrode, suc
32、h 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 electrodesmay be used in accor
33、dance 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-effective than plati-num cylin
34、ders 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 counterelectrode, and to prevent changes in pH during testing.Furthermore, the cell needs to be appropriately sealed to avoidoxygen access and
35、 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.F2129 1726.7 Water Bath, or other heating appliance capable ofmaintaining the test solution temperature at 37 6 1C (seeX1.5).6.8 Purge Gas Delivery S
36、ystem, 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 suspended from a clampingdevice. Fo
37、r 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 based on the length of wire or c
38、oil 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 justbelow the interface. If specim
39、ens 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 connection to thespecimen ho
40、lder 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 shall be used for this testmethod
41、 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 distilled or deionized conformin
42、gto 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 of two simulated bile solution
43、s 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 physiological solutions.8.1.3 The pH of
44、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 sufficiently buffered.Several pH contr
45、olling 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-quality product.Cosmetic reject
46、s 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 specimens used for design paramet
47、er 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 that the portion exposed toth
48、e 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 specimendur
49、ing 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 accumulation of corrosionproducts that may affect further corrosion. At a minimum,transfer 500 mL of electrolyte to a clean polarization cell.Measure and record the pH of the solution before and aftereach test.10.3 Place the auxiliary electrodes, salt bridge probe,thermometer, and gas purge diffuser in the test chamber andbring the temperature
