1、Designation: F2129 08F2129 15Standard 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
2、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 susceptibili
3、ty 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, s
4、upport 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 is
5、 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 metho
6、d 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 s
7、tandard.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.2. Refere
8、nced 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 StentsG3 Practice for Con
9、ventions 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 Potentiodynamic Polarization
10、Measurements for Localized Corrosion Susceptibility ofIron-, Nickel-, or Cobalt-Based Alloys3. Terminology3.1 Definitions:3.1.1 potentiostat, nan instrument for automatically maintaining an electrode in an electrolyte at a constant potential orcontrolled potentials with respect to a suitable referen
11、ce electrode (see Terminology G15).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 SubcommitteeF04.15 on Material Test Methods.Current edition approved Oct. 1, 2008March 1, 2015. Published November 2
12、008May 2015. Originally approved in 2001. Last previous edition approved in 20062008 asF2129 06.F2129 08. DOI: 10.1520/F2129-08.10.1520/F2129-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsv
13、olume information, refer to the standardsstandards 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 not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what
14、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 appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the o
15、fficial document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 potentiodynamic cyclic polarization (forward and reverse polarization), na technique in which the potential of the testspecimen is controlled and the corrosion cur
16、rent 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 reached, and the
17、specimen no longer demonstrates passivity, asdefined in Practice G3. The potential scan direction then is then reversed until the specimen repassivates or the potential reachesa preset value.3.1.3 scan rate, nthe rate at which the controlling voltage is changed.3.2 Symbols:3.2.1 Eb = Breakdown or Cr
18、itical 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 working elect
19、rode 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 the scan is
20、 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 is no break
21、down. 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 difference between E
22、b 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 current de
23、nsity 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 than 3 mV/mi
24、n. 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 at thebreakd
25、own 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. Significance and
26、 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,therefore it is important to determine the general corrosionbehavior as well as the susceptibility
27、 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,t
28、esting 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 in
29、tentionally designed to reach conditions that are sufficiently severe to cause breakdown anddeterioration of the medical devices and that these conditions may not be necessarily be encountered in vivo. The results of thiscorrosion test conducted in artificial physiological electrolytes can provide u
30、seful 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 Refere
31、nce 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 b
32、e in the same condition as the device.6.3 Reference ElectrodeA saturated calomel electrode (SCE), as described in Reference Test Method G5, shall be used as areference electrode.F2129 1526.4 Salt Bridge, such as a Luggin probe, shall be used between the working and reference electrode, such as the t
33、ype 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 wi
34、th 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
35、 testing larger specimens or whole devices.6.6 Suitable Polarization Cell, with a volume of about 1000 cm3, equivalent to or similar to that recommended in ReferenceTest Method G5. Furthermore, the cell needs to be appropriately sealed to avoid oxygen access and include a secondary bubblerfor the re
36、lease of exhaust gas without the back diffusion of oxygen.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 of delivering nitrogen gas at 150 cm3/min.7. Specimen Holders7.1 There are a variety
37、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, the threaded end of a Reference Test Method G5holder can be used to hold two stainless
38、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 in the test solution.7.2.3 This type of holder exposes the specimen to the air-liquid
39、 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 evidence of localized corrosion at the air-liquid interface, then the portion of the s
40、pecimen 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 with a suitable coating. The surfaces out of solution will tend to have test solution c
41、ondensed 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. Such reagents shall conform to the specifications of theCommittee on Analytical Reagent
42、s of the American Chemical Society.48.1.1 The water shall be distilled or deionized conforming 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. A standard PBSformula
43、tion is given in Appendix X2, along with the formulations of two simulated bile solutions for testing implantable medicaldevices intended for use in the biliary system, the formulations of two artificial urine solutions for testing implantable indwellingmaterials intended for use in the urinary trac
44、t, and the compositions of two other commonly used physiological solutions.8.1.3 The pH of the electrolyte should be adjusted as needed based on the nature of the solution (e.g., for PBS, adjust the pHby the addition of NaOHNaH2PO4 (acid) or HCl.Na2HPO4 (base). When the electrolyte is deaerated, its
45、 pH may changesignificantly if it is not sufficiently 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 f
46、or 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 o
47、n 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 specimens are the same as the intendedimplantable med
48、ical device.4 Reagent Chemicals, American Chemical Society Specifications, , American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed bythe American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United
49、States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.F2129 15310. Procedure10.1 Prepare the specimen such that the portion exposed to the test solution is in the same metallurgical and surface conditionas the implantable form of the medical device being studied.10.1.1 Calculate the total surface area of the specimen exposed to the solution in order to determine the current density (currentper surface area) generated by the specimen during the test.10.2 Prepare enough test solution to immerse the device and auxiliar
