1、Designation: F3268 18F3268 18aStandard Guide forin vitro Degradation Testing of Absorbable Metals1This standard is issued under the fixed designation F3268; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 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 The purpose of this standard is to outline appropriate experimental approaches for conducting an initial evaluation of thein vitro d
3、egradation properties of a device or test sample fabricated from an absorbable metal or alloy.1.2 The described experimental approaches are intended to control the corrosion test environment through standardization ofconditions and utilization of physiologically relevant electrolyte fluids. Evaluati
4、on of a standardized degradation control materialis also incorporated to facilitate comparison and normalization of results across laboratories.1.3 The obtained test results may be used to screen materials and/or constructs prior to evaluation of a more refined fabricateddevice. The described tests
5、may also be utilized to define a devices performance threshold prior to more extensive in vitroperformance evaluations (e.g. fatigue testing) or in vivo evaluations.1.4 This standard is considered to be applicable to all absorbable metals, including magnesium, iron, and zinc-based metals andalloys.1
6、.5 The described tests are not considered to be representative of in vivo conditions and could potentially provide a more rapidor slower degradation rate than an absorbable metals actual in vivo corrosion rate. The herein described test methods are to beused for material comparison purposes only and
7、 are not to act as either a predictor or substitute for evaluation of the in vivodegradation properties of a device.1.6 This standard only provides guidance regarding the in vitro degradation of absorbable metals and does not address anyaspect regarding either in vivo or biocompatibility evaluations
8、.1.7 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, health, and environmental practices and determine the applicability ofregulatory limitations prior to use.
9、1.8 This 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 Tr
10、ade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B943 Specification for Zinc and Tin Alloy Wire Used in Thermal Spraying for Electronic ApplicationsB954 Test Method for Analysis of Magnesium and Magnesium Alloys by Atomic Emission SpectrometryE2375 Practice for Ultrasonic Testing of Wr
11、ought ProductsF1854 Test Method for Stereological Evaluation of Porous Coatings on Medical ImplantsF2129 Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the Corrosion Suscepti-bility of Small Implant DevicesF2739 Guide for Quantifying Cell Viability within Bi
12、omaterial ScaffoldsF3160 Guide for Metallurgical Characterization of Absorbable Metallic Materials for Medical ImplantsG1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test SpecimensG3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing1 This guide i
13、s under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee F04.15on Material Test Methods.Current edition approved April 1, 2018Oct. 1, 2018. Published May 2018November 2018. Originally approved in 2018. Last previous
14、 edition approved in 2018 asF326818. DOI: 10.1520/F3268-18.vb h10.1520/F3268-18A.2 For referencedASTM standards, visit theASTM 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
15、on the ASTM website.This document is not 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 use
16、rs consult prior editions as appropriate. 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 States1G4 Guide for Conducting Corr
17、osion Tests in Field ApplicationsG16 Guide for Applying Statistics to Analysis of Corrosion DataG31 Guide for Laboratory Immersion Corrosion Testing of MetalsG46 Guide for Examination and Evaluation of Pitting CorrosionG59 Test Method for Conducting Potentiodynamic Polarization Resistance Measuremen
18、tsG102 Practice for Calculation of Corrosion Rates and Related Information from Electrochemical MeasurementsG106 Practice for Verification of Algorithm and Equipment for Electrochemical Impedance MeasurementsG215 Guide for Electrode Potential Measurement2.2 DIN Standards:3DIN 50918 Elektrochemische
19、Korrosionsuntersuchungen. Deutsche Normen. Berlin: Beuth Verlag; 1978. p. 1-62.3 ISO Standards:4ISO 10993-15 Biological evaluation of medical devices Part 15: Identification and quantification of degradation products frommetals and alloysISO 13485 Medical devices Quality management systems Requireme
20、nts for regulatory purposes3. Terminology3.1 Definitions:3.1.1 absorbable, adjin the body, referring to an initially distinct foreign material or substance that either directly or throughintended degradation can be excreted, metabolized or assimilated by cells and/or tissue.3.1.2 surface roughness,
21、RA, nthe arithmetic average deviation of the surface profile from the centerline, normally reportedin micrometers.3.2 Definitions of Terms Specific to This Standard:3.2.1 degradation, nthe breakdown of a metallic test material or metallic device principally due to corrosion in an electrolytesolution
22、 relevant to physiologic conditions.3.2.2 degradation control material, nmultiple batches of a defined metallic compositon with sufficiently uniform corrosionproperties to verify an experimental setup and to compare relative intra-laboratory and/or inter-laboratory corrosion rates.4. Summary of Guid
23、e4.1 Guidance is given on in vitro evaluation of the corrosion/degradation properties of absorbable metal materials and devicesfabricated from absorbable metals. Considerations specific to the application of corrosion testing methods to absorbable metalmaterials are outlined for both immersion and e
24、lectrochemical methods.4.1.1 Electrolyte composition is a critical factor in corrosion experiments. Several electrolytes are commonly used to mimic invivo conditions. Electrolyte selection may also take into consideration the alloy being tested.4.1.2 Control of the experimental conditions (i.e., tem
25、perature, pH and fluid movement around the test piece(s) can markedlyaffect the corrosion rates and experimental outcomes. Controlling and documenting these factors are important with regard togenerating consistent, reproducible results. Experimental conditions may be altered, depending on the inten
26、t of the experiment.4.1.3 The surrounding atmosphere may interact with the electrolyte solution (liquid-gas interface), depending on electrolytecomposition, particularly if the electrolyte contains a carbonate buffer or if oxygen in the electrolyte is consumed during thecorrosion process, as with ir
27、on-based alloys. Measurement and control of the atmospheric composition may be important,depending on the specific circumstances of the experiment.4.1.4 Measurements of corrosion may include weight loss of the sample, accumulation of corrosion products in the experiment,generation of H2 gas, and cha
28、nges to physical and mechanical properties.4.2 Electrochemical methods, Polarization Resistance, and Electrochemical Impedance Spectroscopy also can be used tomeasure relative corrosion rates and generate additional insight into the corrosion process. The electrolyte used in these methodsmay not be
29、relevant to in vivo conditions and may not mimic the process in vivo. It is important to fully document relevantexperimental conditions (e.g. electrolyte composition, current, current density and atmosphere), so that their impact on the testresults can be understood.4.3 Use of a degradation control
30、material to monitor the consistency of the experimental system is recommended, but notmandatory. See Annex A1 for details.5. Significance and Use5.1 This standard provides an itemization of potential in vitro test methods to evaluate the degradation of absorbable metals.The provided approach defers
31、to the user of this standard to pick most appropriate method(s) based on the specific requirements3 Available from Deutsches Institut fr Normung e.V.(DIN), Am DIN-Platz, Burggrafenstrasse 6, 10787 Berlin, Germany, http:/www.din.de.4 Available from International Organization for Standardization (ISO)
32、, ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.F3268 18a2of the intended application. However, a minimum of at least two different corrosion evaluation methods is considered necessaryfor basic profiling of the material or devic
33、e, with additional methods potentially needed for an adequate characterization. However,in some instances there may be only one method that correlates to in vivo degradation results.5.2 It is recognized that not all test methods will be meaningful for every situation. In addition, some methods carry
34、 differentpotential than others regarding their relative approximation to the in vivo conditions within which actual use is to occur.As a result,some discussion and ranking of the relevance of the described methods is provided by this guidance.5.3 It should be noted that degradation of absorbable me
35、tals is not linear. Thus, precautions should be taken that evaluationsof the degradation profile of a metal or metal device are appropriately adapted to reflect the varying stages and rates of degradation.Relevant factors can include the amount or percentage (%) of tissue coverage of the implanted d
36、evice and the metabolic rate ofsurrounding tissue, which is not necessarily accompanied by a high perfusion rate.5.4 It is recognized that in vivo environments will impart specialized considerations that can directly affect the corrosion rate,even when compared with other in vivo locations. Thus, a
37、basic understanding of the biochemistry and physiology of the specifictargeted implant location (e.g. hard tissue; soft tissue; high, low or zero perfusion areas/tissue; high, low or zero loadingenvironments) is needed to optimize in vitro and in vivo evaluations.5.5 Within the evaluation of absorba
38、ble metals, rate uniformity is considered to be the principle concern and design goal. Therecognized primary value for the herein described in vitro testing under static (i.e. not dynamic) conditions is to monitor and screenmaterials and/or devices for their corrosion consistency. Such an evaluation
39、 may provide a practical understanding of theuniformity of the device prior to any subsequent in vivo testing - where device consistency is considered to be critical foroptimizing the quality of the obtained observations.5.6 Once a suitable level of device corrosion consistency has been established
40、(either directly or historically), static and/ordynamic fatigue testing can then be undertaken, if needed, to further enhance the understanding of the corrosion process withinthe context of the devices overall design and its intended application/use.5.7 Depending on the intended application, appropr
41、iate levels of implant loading may range from minimal to severe. Thus, thisstandard does NOT directly address the appropriate level of loading of absorbable metallic devices, guidance for which may befound in documents specific to the intended implant application and the design requirements for the
42、product.5.8 This standard does NOT directly address dynamic fatigue testing of absorbable metallic devices.6. Material/Metallurgical Characterization6.1 A full understanding of the compositional and morphological features of the material or device to be tested is needed priorto conducting any in vit
43、ro degradation evaluation. Lack of control of critical material features (e.g. elemental composition,contamination, grain size, etc.) may lead to inconsistent results both in vitro and/or in vivo. Characterization of the test materialshould be undertaken in accordance with ASTM F3160.6.2 Depending o
44、n the goals of the experiment, selected mechanical tests may be repeated at various intervals during thecorrosion experiment. In most cases, it would be appropriate to retire mechanically tested samples.7. General Testing Conditions7.1 The intention of the following listing of general considerations
45、 is to provide a fundamental overview of the critical factorsinvolved with generating consistent in vitro corrosion characterization results.7.2 Fluid Composition:7.2.1 For all in vitro test systems, fluid composition is a critical factor that requires both control and disclosure. Additionally,pH (w
46、hich can be influenced by degradation product composition and generation rate), fluid flow, and solution buffer capacity aresignificant variables that can affect an absorbable metals corrosion rate. While it is desirable to maintain an in vitro pH at a levelthat is representative of the in vivo cond
47、ition, it is important to note that the composition of a buffers anions can significantly affectthe corrosion rate. Critical electrolytes and biomolecules that are known to directly affect the corrosion rate of Mg alloys includephosphate, carbonate, chloride, calcium, serum proteins, and lipids see
48、references (1-7). As a result, solutions with aphysiologically relevant combination of electrolytes should be used.NOTE 1If the intention of the experiment is to provide an in vitro approximation to an in vivo system, the use of a well-controlled, simpler electrolytesystem that has been correlated t
49、o in vivo data may be preferable to a more complex, less stable system.7.2.2 Numerous formulations exist for simulated body fluids (SBFs) or buffering solutions that are intended to mimic the in vivocondition. Hanks Solution, which is phosphate-based and designed to buffer in a normal atmosphere, provides an approximationof the electrolyte composition found in the body. However, while it does provide a reasonable approximation of inorganic moieties,F3268 18a3it does NOT provide the bodys buffer capacity (as enhanced through carbonate equilibria5) or the pres
