1、Designation: F2129 17aF2129 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 th
2、e year oforiginal 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 susceptibi
3、lity of small, metallic, implant medical devices, or components thereof,using cyclic (forward and reverse) potentiodynamic polarization. Examples of device types that may be evaluated by this testmethod include, but are not limited to, vascular stents, ureteral stents (Specification F1828), filters,
4、 support segments ofendovascular grafts, cardiac occluders, aneurysm or ligation clips, staples, and so forth.1.2 This test method is used to assess a device in its final form and finish, as it would be implanted. These small devices shouldbe tested in their entirety. The upper limit on device size
5、is dictated by the electrical current delivery capability of the test apparatus(see Section 6). It is assumed that test methods, such as Reference Test Method G5 and Test Method G61 have been used formaterial screening.1.3 Because of the variety of configurations and sizes of implants, this test met
6、hod provides a variety of specimen holderconfigurations.1.4 This test method is intended for use on implantable devices made from metals with a relatively high resistance to corrosion.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this
7、 standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.7 Thi
8、s international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TB
9、T) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodF1828 Specification for Ureteral Ste
10、ntsG3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion TestingG5 Reference Test Method for Making Potentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)3G61 Test Method for Conducting Cyclic Potenti
11、odynamic Polarization Measurements for Localized Corrosion Susceptibility ofIron-, Nickel-, or Cobalt-Based Alloys3. Terminology3.1 Definitions:1 This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcomm
12、itteeF04.15 on Material Test Methods.Current edition approved Nov. 15, 2017Dec. 1, 2017. Published December 2017January 2018. Originally approved in 2001. Last previous edition approved in 2017 asF2129 17.F2129 17a. DOI: 10.1520/F2129-17A.10.1520/F2129-17B.2 For referencedASTM standards, visit theAS
13、TM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.This document is n
14、ot an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropria
15、te. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 potentiostat, nan instrument for automatically maintaining a
16、n electrode in an electrolyte at a constant potential orcontrolled potentials with respect to a suitable reference electrode (see Terminology G15).3.1.2 potentiodynamic cyclic polarization (forward and reverse polarization), na technique in which the potential of the testspecimen is controlled and t
17、he corrosion current measured by a potentiostat. The potential is scanned in the positive or noble(forward) direction as defined in Practice G3. The potential scan is continued until a predetermined potential or current density isreached. Typically, the scan is run until the transpassive region is r
18、eached, and the specimen no longer demonstrates passivity, asdefined in Practice G3. The potential scan direction is then reversed until the specimen repassivates or the potential reaches a presetvalue.3.1.3 scan rate, nthe rate at which the controlling voltage is changed.3.2 Symbols:3.2.1 Eb = Brea
19、kdown or Critical Pitting Potentialthe least noble potential at which pitting or crevice corrosion or both willinitiate and propagate as defined in Terminology G15. An increase in the resistance to pitting corrosion is associated with anincrease in Eb.3.2.2 Er = Rest Potentialthe potential of the wo
20、rking electrode relative to the reference electrode measured under virtualopen-circuit conditions (working electrode is not polarized).3.2.3 Ezc = Zero Current Potentialthe potential at which the current reaches a minimum during the forward scan.3.2.4 Ef = Final Potentiala preset potential at which
21、the scan is stopped.3.2.5 Ei = Initial Potentialthe potential at which the potentiostat begins the controlled potentiodynamic scan.3.2.6 Ep = Protection Potentialthe potential at which the reverse scan intersects the forward scan at a value that is less noblethan Eb.Ep cannot be determined if there
22、is no breakdown. Whereas, pitting will occur on a pit-free surface above Eb , it will occuronly in the range of potentials between Ep and Eb if the surface is already pitted. The severity of crevice corrosion susceptibilityincreases with increasing hysteresis of the polarization curve, the differenc
23、e between Eb and Ep.3.2.7 Ev = Vertex Potentiala preset potential, at which the scan direction is reversed.3.2.8 it = Threshold Current Density (mA/cm2)a preset current density, at which the scan direction is reversed. Typically, thescan is reversed when a current density two decades higher than the
24、 current density at the breakdown potential (Eb) is reached.4. Summary of Test Method4.1 The device is placed in an appropriate deaerated simulated physiological solution, and the rest potential (Er) is recorded for1 h or, alternatively, until the rest potential stabilizes to a rate of change less t
25、han 3 mV/min. The potentiodynamic scan is thenstarted at Er and scanned in the positive or noble (forward) direction. The scan is reversed after either the vertex potential (Ev) isreached or the current density has reached a value approximately two decades greater than the current density measured a
26、t thebreakdown potential.The reverse scan is stopped after the current has become less than that in the forward direction or the potentialreaches Er. The data is plotted with the current density in mA/cm2 on the x axis (logarithmic axis) versus the potential in mV onthe y axis (linear axis).5. Signi
27、ficance and Use5.1 Corrosion of implantable medical devices can have deleterious effects on the device performance or may result in the releaseof corrosion products with harmful biological consequences; therefore it is important to determine the general corrosion behavioras well as the susceptibilit
28、y of the devices to localized corrosion.5.2 The forming and finishing steps used to create an implantable device may have significant effects on the corrosion resistanceof the material out of which the device is fabricated. During the selection process of a material for use as an implantable device,
29、testing the corrosion resistance of the material is an essential step; however, it does not necessarily provide critical data regardingdevice performance.5.3 To accommodate the wide variety of device shapes and sizes encountered, a variety of holding devices can be used.5.4 Note that the method is i
30、ntentionally designed to reach conditions that are sufficiently severe to cause breakdown anddeterioration of the medical devices and that these conditions may not necessarily be encountered in vivo. The results of thiscorrosion test conducted in artificial physiological electrolytes can provide use
31、ful data for comparison of different device materials,designs, or manufacturing processes. However, note that this test method does not take into account the effects of cells, proteins,and so forth on the corrosion behavior in vivo.6. Apparatus6.1 Potentiostat, calibrated in accordance with Referenc
32、e Test Method G5.6.2 Working Electrode, to be used as the test specimen, as described in Section 9. Its configuration and holder will depend onthe type of specimen being tested, as described in Section 7. In all cases, the metallurgical and surface condition of a specimensimulating a device must be
33、in the same condition as the device.F2129 17b26.3 Reference ElectrodeA saturated calomel electrode (SCE), as described in Reference Test Method G5, shall be used as areference electrode.6.4 Salt Bridge, such as a Luggin probe, shall be used between the working and reference electrode, such as the ty
34、pe shownin Reference Test Method G5.6.5 Auxiliary Electrodes:6.5.1 Two platinum auxiliary electrodes may be prepared from high-purity rod stock. The surfaces may be platinized, as perReference Test Method G5.6.5.2 Alternatively, high-purity graphite auxiliary electrodes may be used in accordance wit
35、h Reference Test Method G5. Careshould be taken to ensure that they do not get contaminated during a test.6.5.3 The auxiliary electrode surface area should be at least four times greater than the sample surface area. Use of wire-meshplatinum might be more cost-effective than platinum cylinders when
36、testing larger specimens or whole devices.6.6 Suitable Polarization Cell, with a sufficient volume to allow the solution to cover the sample and the counter electrode, andto prevent changes in pH during testing. Furthermore, the cell needs to be appropriately sealed to avoid oxygen access and includ
37、ea secondary bubbler for the release of exhaust gas without the back diffusion of oxygen. The test cell must be able to hold aminimum of 500 ml.6.7 Water Bath, or other heating appliance capable of maintaining the test solution temperature at 37 6 1C (see X1.5).6.8 Purge Gas Delivery System, capable
38、 of delivering nitrogen gas at 150 cm3/min.7. Specimen Holders7.1 There are a variety of holders that may be used in this test method. Each is designed for a specific type or class of device.7.2 Short wire or coil specimens:7.2.1 Specimens can be held suspended from a clamping device. For example, t
39、he threaded end of a Reference Test Method G5holder can be used to hold two stainless steel nuts. The wire test specimen is clamped between these nuts and bent so as to enterthe test solution.7.2.2 The surface area of the test specimen shall be calculated based on the length of wire or coil immersed
40、 in the test solution.7.2.3 This type of holder exposes the specimen to the air-liquid interface, which is subject to localized crevice corrosion. Testspecimens should be examined carefully after testing to ensure that there is no localized corrosion at or just below the interface.If specimens show
41、evidence of localized corrosion at the air-liquid interface, then the portion of the specimen passing across thisinterface shall be sealed with an impervious coating.7.2.4 Alternatively, one may choose to coat the portion of the specimen out of the solution and the connection to the specimenholder w
42、ith a suitable coating. The surfaces out of solution will tend to have test solution condensed on them and this may leadto undesirable results.7.3 One method for holding stents or cylindrical devices is shown in Appendix X3.8. Reagents8.1 Reagent grade chemicals shall be used for this test method wh
43、en they are commercially available (for example, somecomponents in bile solutions are not available in reagent grade). Such reagents shall conform to the specifications of the Committeeon Analytical Reagents of the American Chemical Society.48.1.1 The water shall be distilled or deionized conforming
44、 to the purity requirements of Specification D1193, Type IV reagentwater.8.1.2 Unless otherwise specified, phosphate buffered saline (PBS) should be used as the standard test solution.ArepresentativePBS formulation is given in Appendix X2, along with the formulations of two simulated bile solutions
45、for testing implantablemedical devices intended for use in the biliary system, the formulations of two artificial urine solutions for testing implantableindwelling materials intended for use in the urinary tract, and the compositions of two other commonly used physiologicalsolutions.8.1.3 The pH of
46、the electrolyte should be adjusted as needed based 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) or Na2HPO4 (base). When the electrolyte is deaerated, its pH maychange significantly if it is not sufficiently buffered. Several pH
47、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.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing of reage
48、nts not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.F2129 17b39. Test Specimen9.1 Unless otherwise justified,
49、all samples selected for testing should be taken from finished, clinical-quality product. Cosmeticrejects or other nonclinical samples may be used if the cause for rejection does not affect the corrosion behavior of the device.Sterilization may be omitted if it can be demonstrated that prior sterilization has no effect on the corrosion behavior of the device.9.1.1 Test specimens used for design parameter studies can be prepared as detailed in Reference Test Method G5 for workingelectrodes, with the requirement that the metallurgical and surface conditions of the
