ASTM F2025-00
(Practice)Standard Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
Standard Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
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, or both. 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 as found in vivo.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:F2025–00
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope surement was originally developed (3) for pin-on-disk wear
studies (Practice F732) and has been extended to total hip
1.1 This practice describes a laboratory method using a
replacements (4,5, and Guide F1714) and to femoro-tibial
weight-loss (that is, mass-loss; see X1.4) technique for evalu-
knee prostheses (6 and Guide F1715), and to femoro-patellar
ating the wear properties of polymeric materials or devices
knee prostheses (6,7).
which are being considered for use as bearing surfaces of
3.2 While wear results in a change in the physical dimen-
human joint replacement prostheses, or both. The test speci-
sions of the specimen, it is distinct from dimensional changes
mens are evaluated in a device intended to simulate the
due to creep or plastic deformation, in that wear results in the
tribological conditions encountered in the human joint; for
removal of material in the form of polymeric debris particles,
example, use of a fluid such as bovine serum, or equivalent
causing a loss in weight of the specimen.
pseudosynovial fluid shown to simulate similar wear mecha-
3.3 This practice for measuring wear of the polymeric
nisms and debris generation as found in vivo.
component is suitable for various simulator devices. These
2. Referenced Documents
techniquescanbeusedwithmetal,ceramic,carbon,polymeric,
and composite counter faces bearing against a polymeric
2.1 ASTM Standards:
material (for example, polyethylene, polyacetal, and so forth).
D792 TestMethodsforDensityandSpecificGravity(Rela-
Thus, this weight-loss method has universal application for
tive Density) of Plastics by Displacement
wear studies of human joint replacements which feature
D1505 Test Method for Density of Plastics by the Density-
polymeric bearings. This weight-loss method has not been
Gradient Technique
validated for non-polymeric material bearing systems, such as
F732 Practice for Pin-on-Flat Evaluation of Friction and
metal-metal, carbon-carbon, or ceramic-ceramic. Progressive
Wear Properties of Polymeric Materials for Use in Total
wear of such rigid bearing combinations has generally been
Joint Prostheses
monitoredusingalinear,variable-displacementtransducers,or
F1714 Guide for Gravimetric Wear Assessment of Pros-
by other profilometric techniques.
thetic Hip-Designs in Simulator Devices
F1715 Guide for Gravimetric Wear Assessment of Pros-
4. Components and Materials
thetic Knee-Designs in Simulator Devices
4.1 Hip Prosthesis Components—The hip joint prosthesis
3. Significance and Use
comprises a ball-and-socket configuration in which materials
such as polymers, composites, metal alloys, ceramics, and
3.1 This practice uses a weight-loss method of wear deter-
carbon have been used in various combinations and designs.
mination for the polymeric components or materials used in
4.1.1 Component Configurations—The diameter of the
human joint prostheses, using serum or demonstrated equiva-
prosthetic ball may vary from 22 to 54 mm or larger. The
lent fluid for lubrication, and running under a load profile
design may include ball-socket, trunnion, bipolar, or other
representative of the appropriate human joint application
configurations. If applicable, the normal metal backing for the
(1,2). The basis for this weight-loss method for wear mea-
polymeric component shall be used provided disassembly and
reassembly of these components for the measurement does not
ThispracticeisunderthejurisdictionofASTMCommitteeF-4onMedicaland
haveanunrepresentativeeffectontheweightmeasurementsor
Surgical Materials and Devices and is the direct responsibility of Subcommittee
wear behavior. Otherwise, a modified backing may be used,
F04.22 on Arthroplasty.
again provided this has no unrepresentative effect on the
Current edition approved May 10, 2000. Published Aug. 2000.
Annual Book of ASTM Standards, Vol 08.01. weight measurements or wear behavior (see X1.5).
Annual Book of ASTM Standards, Vol 13.01.
The numbers in parentheses refer to the list of references at the end of this
standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2025
4.2 Knee Prosthesis Components—The knee joint com- 5.3 Polymer Specimen Weighing Procedure—The poly-
prises femoral, tibial, and patellar configurations in which meric components shall be weighed on an analytical balance
materialssuchasmetalalloys,ceramics,polymers,andcarbon having a sensitivity on the order of 10 µg. This degree of
materials have been used in various combinations in different sensitivity is necessary to detect the slight loss in weight of
designs. polymerssuchasUHMWpolyethylene,whichmaywear1mg
4.2.1 Component Configurations—The polymeric compo- or less per million cycles. Specimens shall always be weighed
nents may be backed by either metal, ceramic, or composite in the clean, dry condition (AnnexA1). The components shall
reinforcements. If applicable, the normal metal backing shall bekeptinadust-freecontainerandhandledwithcleantoolsto
be used provided disassembly and reassembly of these com- prevent contamination which might affect the weight measure-
ponentsforthemeasurementdoesnothaveanunrepresentative ment.Eachwearandcontrolcomponentshallbeweighedthree
effect on the weight measurements or wear behavior. Other- times in rotation to detect random errors in the weighing
wise, a modified backing may be used, again provided this has process.
nounrepresentativeeffectontheweightmeasurementsorwear 5.4 Pre-soaking of Test Specimens:
behavior (see X1.5). 5.4.1 Polymeric and composite components made from
4.3 Other prosthesis components and test coupons may be materials which absorb fluid initially, but saturate within a few
used to represent other human joint replacement applications. weeks, should be presoaked in the test lubricant to reduce the
error due to fluid sorption during the wear run. If the fluid
5. Specimen Preparation
sorption behavior of a particular material is unknown, the
5.1 Polymers and Composites—Material Condition:
investigator shall conduct a preliminary study to determine
5.1.1 A fabrication history shall be obtained for each poly-
whether or not the material is exempt from presoaking.
meric or composite component, including information such as
5.4.2 Preliminary Study—A minimum of three soak speci-
grade, batch number and processing variables, method of
mens(thesecanbetestcouponsoractualdevices)permaterial
forming (extruding, molding, and so forth), temperature, pres-
shall be cleaned and dried in accordance with the procedure in
sure and forming time used, and any post-forming treatments,
Annex A1, and then weighed by precisely controlled and
including sterilization method and parameters.
repeatable methods (Annex A1). The specimens shall then be
5.1.2 Pretest characterization may include measurement of
placed in a container of test lubricant and removed, cleaned,
bulk material properties such as molecular-weight range and
dried, and weighed (in accordance with Annex A1) once or
distribution,percentcrystallinity,orother.Densityisaparticu-
twice a week. The weight change shall be calculated in
larly important property because of the conversion of weight
accordance with Annex A1. The procedure shall be repeated
measurements to volumetric wear (see 7.4). Density measure-
until the specimens have soaked for five weeks. Specimen
ments shall be obtained in accordance with Test Methods or
weight change shall be averaged at each interval and plotted
Test Method D792 or D1505. If it can be justified that
versus time. Data points shall be fit using a second or third
previous density measurements are representative of the mate-
order polynomial or hyperbolic function, connecting through
rial used in the current wear test, reference to these previous
zero. The fit of this curve should have an R value of 0.8 or
measurements and suitable justification shall be provided (see
greater. If the slope of this curve at five weeks is ten or more
also X1.6). The surface finish of specimens may be character-
times less than the slope of the curve at zero (see X1.7), then
ized by profilometry, photomicrography, and replication by
this material must be subjected to presoaking before wear
various plastics or other techniques.
testing (if gravimetric wear measurement is to be used).
5.1.3 Sterilization—The components shall be sterilized in a
Otherwise, it is exempt.
manner typical of that in clinical use for such devices, as this
NOTE 1—Even if presoaking is not required, one to three soak control
may affect the wear properties of the materials. Sterilization of
components are still necessary per material condition to account for fluid
all test and control components within a specific test group
sorption by the wear components during the wear test.
should be done simultaneously (in a single container) when
5.4.3 Pre-soaking Procedure (if Required)—After fabrica-
possibletominimizevariationamongthespecimens.Thewear
tion and characterization, the wear components and one to
testing procedure makes no attempt to maintain the sterility of
three soak-control components of each test material shall be
specimens during the wear test.
cleaned in accordance with the procedure in Annex A1. The
5.2 Polymer Specimen Cleaning Procedure—Prior to
wear components and soak control(s) shall then be placed in a
weighing and wear testing, careful cleaning of the polymer
container of test lubricant for a minimum of five weeks (35
specimensisimportanttoremoveanycontaminantsthatwould
days).
not normally be present on the actual prosthesis. During the
wear test, the components must be re-cleaned and dried before
6. Measurement Procedure
each weighing to remove any extraneous material that might
affecttheaccuracyoftheweighing.Theprocedureforcleaning 6.1 After fabrication, characterization, and the completion
and drying of polymeric components is given in Annex A1. of the presoak period (if required), the wear components and
With some combinations of materials, wear may result in the soak control(s) should be cleaned, dried, and weighed by
transfer of particulate debris which may then become re- precisely controlled and repeatable methods (Annex A1).
imbedded or otherwise attached to polymeric, metal, or com- These weights shall be recorded as the initial weights of the
positesurfaces.Suchanoccurrencewillrendertheweight-loss specimens for purposes of calculating the progressive weight
assessment of wear less reliable. lossduringtheweartest.Thesoakcontrolspecimen(s)shallbe
F2025
placed in holders in a soak chamber of test lubricant, such that may be preferable to compare these on the basis of volumetric
thetotalsurfaceareaexposedtothelubricantisequaltothatof wear,ratherthanweightloss.Thevolumetricwearratemaybe
the wear components when mounted in the test chamber. The obtained by dividing the weight loss data by the density of the
soak chamber temperature shall be maintained at the same material, in appropriate units. The accuracy of this calculation
temperature as the bulk lubricant in the wear test, or specified is dependent on the material being reasonably homogeneous
if different. It is recommended that the soak chamber be (that is, having a constant density with wear depth). The
attached to the test machine or otherwise agitated in the same density value used in this conversion shall be reported.
manner as the actual wear chambers. In addition, it may be
8. Report
advantageous to apply a cyclic load to the soak control
8.1 Materials:
specimen(s) (without tangential motion) comparable to that
8.1.1 Material traceability information shall be provided for
appliedtothewearspecimens,sincethiscanalsoaffecttherate
each material counter face and shall include pertinent details
of fluid sorption.
related to raw material and fabrication or manufacturing
6.2 The wear and soak component(s) shall be removed at
history. Examples of such information include material grade,
specified intervals, washed, rinsed, and dried concurrently, in
batch number, and processing variables.
accordancewiththeprocedureinAnnexA1.Itisimportantthat
8.1.2 Pretest characterization for a plastic counter face may
both the wear and soak component(s) be treated identically to
include measurement of bulk material properties such as
ensurethattheyhavethesameexposuretothewash,rinse,and
molecular-weightaverage,rangeanddistribution,percentcrys-
dryingfluids.Thiswillprovidethemostaccuratecorrectionfor
tallinity, density, degree of oxidation, or others. The surface
fluid sorption by the wear specimens.
finish of both counter faces may be characterized by profilo-
6.3 Afterrinsinganddrying,thewearcomponentsandsoak
metry, photomicrography, replication, or other applicable tech-
controls shall be weighed on an analytical balance in accor-
niques.
dance with 5.3.
8.1.3 The method of sterilization, the sterilization date and
6.4 The wear chambers and component surfaces shall be
testdate,andthemeansofstoragepost-sterilizationandpretest
thoroughly rinsed with distilled or deionized water.
shall be reported. For irradiation-sterilized specimens, total
6.5 The bearing surfaces of the components shall be in-
dose and dose rate shall be reported.
spected, and the characteristics of the wear process noted.
8.1.4 If presoaking was not conducted, justification shall be
Visual,microscopic,profilometric,replication,orotherinspec-
provided.
tion techniques can be used. However, care must be taken that
8.2 Wear Rates:
the surfaces do not become contaminated or damaged by any
8.2.1 The weight loss of each specimen shall be plotted
substanceortechniquewhichmightaffectthesubsequentwear
graphicallyasafunctionofwearcycles.Wearmaybereported
properties. If contamination occurs, the specimens shall be
astheweightlossofthebearingcomponentasafunctionofthe
thoroughly re-cleaned prior to restarting the wear test.
number of wear cycles, but is preferentially converted to
6.6 The wear components and soak control(s) shall be
volumetric wear if the density of the material is known (see
replaced in fresh lubricant and wear cycling continued.
X1.6 and X1.8)
7. Determination of Wear Rates
8.2.2 In tests where the wear rate is nearly constant, the
7.1 Test Length—The accuracy of the test method depends volumetric(orgravimetric)wearra
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.