ASTM F2025-06(2018)
(Practice)Standard Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
Standard Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
SIGNIFICANCE AND USE
3.1 This practice uses a weight-loss method of wear determination for the polymeric components or materials used in human joint prostheses, using serum or demonstrated equivalent fluid for lubrication, and running under a load profile representative of the appropriate human joint application (1,2) .4 The basis for this weight-loss method for wear measurement was originally developed (3) for pin-on-disk wear studies (Practice F732) and has been extended to total hip replacements (4, 5, ISO 14242–2, and Guide F1714), and to femoro-tibial knee prostheses (6 and ISO 14243–2), and to femoro-patellar knee prostheses (6,7).
3.2 While wear results in a change in the physical dimensions of the specimen, it is distinct from dimensional changes due to creep or plastic deformation, in that wear results in the removal of material in the form of polymeric debris particles, causing a loss in weight of the specimen.
3.3 This practice for measuring wear of the polymeric component is suitable for various simulator devices. These techniques can be used with metal, ceramic, carbon, polymeric, and composite counter faces bearing against a polymeric material (for example, polyethylene, polyacetal, and so forth). Thus, this weight-loss method has universal application for wear studies of human joint replacements which feature polymeric bearings. This weight-loss method has not been validated for non-polymeric material bearing systems, such as metal-metal, carbon-carbon, or ceramic-ceramic. Progressive wear of such rigid bearing combinations has generally been monitored using linear, variable-displacement transducers, or by other profilometric techniques.
SCOPE
1.1 This practice describes a laboratory method using a weight-loss (that is, mass-loss; see X1.4) technique for evaluating the wear properties of polymeric materials or devices which are being considered for use as bearing surfaces of human joint replacement prostheses. The test specimens are evaluated in a device intended to simulate the tribological conditions encountered in the human joint; for example, use of a fluid such as bovine serum, or equivalent pseudosynovial fluid shown to simulate similar wear mechanisms and debris generation found in vivo.
1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F2025 − 06 (Reapproved 2018)
Standard Practice for
Gravimetric Measurement of Polymeric Components for
Wear Assessment
This standard is issued under the fixed designation F2025; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ISO14243–2Implants for Surgery—Wear of Total Knee-
Joint Prostheses—Part 2: Methods of Measurement
1.1 This practice describes a laboratory method using a
weight-loss (that is, mass-loss; see X1.4) technique for evalu-
3. Significance and Use
ating the wear properties of polymeric materials or devices
3.1 This practice uses a weight-loss method of wear deter-
which are being considered for use as bearing surfaces of
mination for the polymeric components or materials used in
human joint replacement prostheses. The test specimens are
human joint prostheses, using serum or demonstrated equiva-
evaluated in a device intended to simulate the tribological
lent fluid for lubrication, and running under a load profile
conditionsencounteredinthehumanjoint;forexample,useof
representative of the appropriate human joint application
a fluid such as bovine serum, or equivalent pseudosynovial
(1,2). The basis for this weight-loss method for wear mea-
fluid shown to simulate similar wear mechanisms and debris
surement was originally developed (3) for pin-on-disk wear
generation found in vivo.
studies (Practice F732) and has been extended to total hip
1.2 This international standard was developed in accor-
replacements (4, 5, ISO14242–2, and Guide F1714), and to
dance with internationally recognized principles on standard-
femoro-tibial knee prostheses (6 and ISO14243–2), and to
ization established in the Decision on Principles for the
femoro-patellar knee prostheses (6,7).
Development of International Standards, Guides and Recom-
3.2 While wear results in a change in the physical dimen-
mendations issued by the World Trade Organization Technical
sions of the specimen, it is distinct from dimensional changes
Barriers to Trade (TBT) Committee.
due to creep or plastic deformation, in that wear results in the
2. Referenced Documents removal of material in the form of polymeric debris particles,
causing a loss in weight of the specimen.
2.1 ASTM Standards:
D792Test Methods for Density and Specific Gravity (Rela- 3.3 This practice for measuring wear of the polymeric
tive Density) of Plastics by Displacement component is suitable for various simulator devices. These
D1505Test Method for Density of Plastics by the Density- techniquescanbeusedwithmetal,ceramic,carbon,polymeric,
Gradient Technique and composite counter faces bearing against a polymeric
F732Test Method for Wear Testing of Polymeric Materials material (for example, polyethylene, polyacetal, and so forth).
Used in Total Joint Prostheses Thus, this weight-loss method has universal application for
F1714GuideforGravimetricWearAssessmentofProsthetic wear studies of human joint replacements which feature
Hip Designs in Simulator Devices polymeric bearings. This weight-loss method has not been
2.2 Other Standards: validated for non-polymeric material bearing systems, such as
metal-metal, carbon-carbon, or ceramic-ceramic. Progressive
ISO14242–2ImplantsforSurgery—WearofTotalHip-Joint
Prostheses—Part 2: Methods of Measurement wear of such rigid bearing combinations has generally been
monitored using linear, variable-displacement transducers, or
by other profilometric techniques.
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland
Surgical Materials and Devices and is the direct responsibility of Subcommittee
4. Components and Materials
F04.22 on Arthroplasty.
Current edition approved April 1, 2018. Published May 2018. Originally
4.1 Hip Prosthesis Components—The hip joint prosthesis
approved in 2000. Last previous edition approved in 2012 as F2025–06 (2012).
comprises a ball-and-socket configuration in which materials
DOI: 10.1520/F2025-06R18.
2 such as polymers, composites, metal alloys, ceramics, and
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM carbon have been used in various combinations and designs.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
4th Floor, New York, NY 10036. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2025 − 06 (2018)
4.1.1 Component Configurations—The diameter of the specimensisimportanttoremoveanycontaminantsthatwould
prosthetic ball may vary from 22 to 54 mm or larger. The not normally be present on the actual prosthesis. During the
design may include ball-socket, trunnion, bipolar, or other wear test, the components must be re-cleaned and dried before
configurations. If applicable, the normal metal backing for the each weighing to remove any extraneous material that might
polymeric component shall be used provided disassembly and affecttheaccuracyoftheweighing.Theprocedureforcleaning
reassembly of these components for the measurement does not and drying of polymeric components is given in Annex A1.
haveanunrepresentativeeffectontheweightmeasurementsor With some combinations of materials, wear may result in the
wear behavior. Otherwise, a modified backing may be used, transfer of particulate debris which may then become re-
again provided this has no unrepresentative effect on the imbedded or otherwise attached to polymeric, metal, or com-
weight measurements or wear behavior (see X1.5). positesurfaces.Suchanoccurrencewillrendertheweight-loss
assessment of wear less reliable.
4.2 Knee Prosthesis Components—Thekneejointcomprises
femoral, tibial, and patellar configurations in which materials
5.3 Polymer Specimen Weighing Procedure—Thepolymeric
suchasmetalalloys,ceramics,polymers,andcarbonmaterials
components shall be weighed on an analytical balance having
have been used in various combinations in different designs.
a sensitivity on the order of 10 µg.This degree of sensitivity is
4.2.1 Component Configurations—The polymeric compo- necessary to detect the slight loss in weight of polymers such
nents may be backed by either metal, ceramic, or composite as ultra-high-molecular-weight polyethylene (UHMWPE),
reinforcements. If applicable, the normal metal backing shall which may wear 1 mg or less per million cycles. Specimens
be used provided disassembly and reassembly of these com- shall always be weighed in the clean, dry condition (Annex
ponentsforthemeasurementdoesnothaveanunrepresentative A1).Thecomponentsshallbekeptinadust-freecontainerand
effect on the weight measurements or wear behavior. handledwithcleantoolstopreventcontaminationwhichmight
Otherwise, a modified backing may be used, again provided affect the weight measurement. Each wear and control compo-
thishasnounrepresentativeeffectontheweightmeasurements
nent shall be weighed three times in rotation to detect random
or wear behavior (see X1.5). errors in the weighing process.
4.3 Other prosthesis components and test coupons may be
5.4 Pre-Soaking of Test Specimens:
used to represent other human joint replacement applications.
5.4.1 Polymeric and composite components made from
materials which absorb fluid initially, but saturate within a few
5. Specimen Preparation
weeks, should be presoaked in the test lubricant to reduce the
error due to fluid sorption during the wear run. If the fluid
5.1 Polymers and Composites—Material Condition:
sorption behavior of a particular material is unknown, the
5.1.1 A fabrication history shall be obtained for each poly-
investigator shall conduct a preliminary study to determine
meric or composite component, including information such as
whether or not the material is exempt from presoaking.
grade, batch number and processing variables, method of
5.4.2 Preliminary Study—A minimum of three soak speci-
forming (extruding, molding, and so forth), temperature, pres-
mens(thesecanbetestcouponsoractualdevices)permaterial
sure and forming time used, and any post-forming treatments,
shall be cleaned and dried in accordance with the procedure in
including the sterilization method and parameters.
Annex A1, and then weighed by precisely controlled and
5.1.2 Pretest characterization may include measurement of
repeatable methods (Annex A1). The specimens shall then be
bulk material properties such as molecular-weight range and
placed in a container of test lubricant and removed, cleaned,
distribution,percentcrystallinity,orother.Densityisaparticu-
dried, and weighed (in accordance with Annex A1) once or
larly important property because of the conversion of weight
twice a week. The weight change shall be calculated in
measurements to volumetric wear (see 7.4). Density measure-
accordance with Annex A1. The procedure shall be repeated
mentsshallbeobtainedinaccordancewithTestMethodsD792
until the specimens have soaked for five weeks. Specimen
or Test Method D1505. If it can be justified that previous
weight change shall be averaged at each interval and plotted
densitymeasurementsarerepresentativeofthematerialusedin
versus time. Data points shall be fit using a second or third
thecurrentweartest,referencetothesepreviousmeasurements
order polynomial or hyperbolic function, connecting through
andsuitablejustificationshallbeprovided(seealsoX1.6).The
zero. The fit of this curve should have an R value of 0.8 or
surface finish of specimens may be characterized by
greater. If the slope of this curve at five weeks is ten or more
profilometry, photomicrography, and replication by various
times less than the slope of the curve at zero (see X1.7), then
plastics or other techniques.
this material shall be subjected to presoaking before wear
5.1.3 Sterilization—The components shall be sterilized in a
testing (if gravimetric wear measurement is to be used).
manner typical of that in clinical use for such devices, as this
Otherwise, it is exempt.
may affect the wear properties of the materials. Sterilization of
all test and control components within a specific test group
NOTE 1—Even if presoaking is not required, one to three soak control
should be done simultaneously (in a single container) when
components are still necessary per material condition to account for fluid
possibletominimizevariationamongthespecimens.Thewear sorption by the wear components during the wear test.
testing procedure makes no attempt to maintain the sterility of
5.4.3 Pre-soaking Procedure (if Required)—After fabrica-
specimens during the wear test.
tion and characterization, the wear components and one to
5.2 Polymer Specimen Cleaning Procedure—Prior to three soak-control components of each test material shall be
weighing and wear testing, careful cleaning of the polymer cleaned in accordance with the procedure in Annex A1. The
F2025 − 06 (2018)
wear components and soak control(s) shall then be placed in a cycles or more may be required to clearly establish the
container of test lubricant for a minimum of five weeks (35 long-term wear properties.
days).
7.2 Number of Measurements per Test—When specimens
can be removed for intermediate weight measurement, at least
6. Measurement Procedure
three measurements per test series shall be made.
6.1 After fabrication, characterization, and the completion
7.3 Correcting for Fluid Sorption—The average gain (or
of the presoak period (if required), the wear components and
loss) of the soak control component(s) shall be added to (or
soak control(s) should be cleaned, dried, and weighed by
subtracted from) the measured weight loss of each wear
precisely controlled and repeatable methods (Annex A1).
component (Annex A2.6). This procedure corrects both for
These weights shall be recorded as the initial weights of the
systematic sorption as well as random differences in the
specimens for purposes of calculating the progressive weight
amount of surface drying (of the entire set of test and control
lossduringtheweartest.Thesoakcontrolspecimen(s)shallbe
specimens) and balance fluctuations due to environmental or
placed in holders in a soak chamber of test lubricant, such that
other variables at each interval of weighing.
thetotalsurfaceareaexposedtothelubricantisequaltothatof
7.4 Conversion to Volumetric Wear—Intestswherethewear
the wear components when mounted in the test chamber. The
rates of materials with different densities are evaluated, it may
soak chamber temperature shall be maintained at the same
bepreferabletocomparetheseonthebasisofvolumetricwear,
temperature as the bulk lubricant in the wear test, or specified
rather than weight loss. The volumetric wear rate may be
if different. It is recommended that the soak chamber be
obtained by dividing the weight loss data by the density of the
attached to the test machine or otherwise agitated in the same
material, in appropriate units. The accuracy of this calculation
manner as the actual wear chambers. In addition, it may be
is dependent on the material being reasonably homogeneous
advantageous to apply a cyclic load to the soak control
(that is, having a constant density with wear depth). The
specimen(s) (without tangential motion) comparable to that
density value used in this conversion shall be reported.
appliedtothewearspecimens,sincethiscanalsoaffecttherate
of fluid sorption.
8. Report
6.2 The wear and soak component(s) shall be removed at
8.1 Materials:
specified intervals, washed, rinsed, and dried concurrently, in
8.1.1 Material traceability information shall be provided for
accordance with the procedure in Annex A1. It is important
each material counter face and shall include pertinent details
thatboththewearandsoakcomponent(s)betreatedidentically
related to raw material and fabrication or manufacturing
to ensure that they have the same exposure to the wash, rinse,
history. Examples of such information include material grade,
and drying fluids. This will provide the most accurate correc-
batch number, and processing variables.
tion for fluid sorption by the wear specimens.
8.1.2 Pretest characterization for a plastic counter face may
6.3 Afterrinsinganddrying,thewearcomponentsandsoak
include measurement of bulk material properties su
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