ASTM F732-17

Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses

SIGNIFICANCE AND USE
4.1 This test method is intended to be performed in conjunction with pin-on-flat wear machines or similar machines that are designed to evaluate simplified specimen geometries.
Note 1: See Haider & Baykal (1)3 for useful considerations and potential pitfalls in conducting pin on disk testing, interpreting test results and the complex and sometimes conflicting effects of lower stress and higher contact area on wear.  
4.2 This test method is designed to evaluate combinations of materials with respect to the amount of polymer wear, where quantifiable wear occurs primarily on the polymeric component. With some combinations of materials, significant wear of the counterface may occur, with subsequent embedding of counterface debris particles in the polymer. Such an occurrence will render the weight loss of the polymer specimen unreliable as an indicator of the polymer wear.  
4.3 Wear is reported as volume loss of the polymeric specimen as a function of sliding distance; however, if the sliding distance is not constant across the polymeric specimen surface due to complex motion patterns, wear may be reported as volume loss of the polymeric specimen as a function of wear cycles (in which case a “wear cycle” shall be defined). Volume loss of the polymer specimen is determined by dividing the experimental weight loss by the density of the polymer. For ease of interpretation, wear should be reported as a function of both the number of wear cycles and the sliding distance, when possible.  
4.4 The reference for the comparative evaluation of candidate materials shall be the wear rate of ultra-high-molecular-weight polyethylene (UHMWPE) conforming to Specification F648 bearing against counterfaces of cobalt-chromium-molybdenum alloy (in accordance with Specifications F75, F799, or F1537), having prosthetic-quality surface finish and lubricated with bovine blood serum (see 5.2).
SCOPE
1.1 This test method describes a laboratory method for evaluating the wear properties of combinations of materials that are being considered for use as bearing surfaces of human total joint prostheses. The body of this test method contains general methods which apply to all types of prosthesis wear applications while individual annexes describe specific wear test methods and clinical validation criteria tailored to each distinct wear application (for example, linear reciprocating motion, ball-cup (“hip-type”) wear, delamination wear, and so forth). It is the intent of this test method to rank materials, within each wear application, for polymer wear rates under simulated physiological conditions. It must be recognized, however, that contact geometries and wear motions are simplified using such methods. This test method, therefore, represents only an initial stage in the full wear characterization of a candidate material.  
1.2 All candidate materials should be tested in an appropriate joint simulator apparatus using prototype prostheses before being used in clinical trials in patients. The tests described in this test method are used to quickly and reliably screen material combinations for wear performance in different orthopaedic wear applications prior to committing them to more expensive and time-consuming joint simulator testing. In addition, these simplified tests can be used to relate material, surface finish, or other parameters to wear behavior on a more practical basis than is possible in joint simulator tests.  
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Developmen...

General Information

• Status: Published
• Publication Date: 31-Aug-2017
• ICS: 11.040.40 - Implants for surgery, prosthetics and orthotics
• Technical Committee: F04 - Medical and Surgical Materials and Devices
• Drafting Committee: F04.15 - Material Test Methods

Relations

• Replaces: ASTM F732-00(2011) - Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses
• Effective Date: 01-Sep-2017
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM F1537-20 - Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, UNS R31538, and UNS R31539)
• Effective Date: 01-Mar-2020
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM F799-19 - Standard Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Forgings for Surgical Implants (UNS R31537, R31538, R31539)
• Effective Date: 15-May-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM G40-15 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Nov-2015
• Refers: ASTM F648-13 - Standard Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants
• Effective Date: 01-Jul-2013
• Refers: ASTM G40-13 - Standard Terminology Relating to Wear and Erosion
• Effective Date: 01-Jun-2013

Overview

ASTM F732-17 is the Standard Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses, developed by ASTM International. This standard specifies laboratory procedures to evaluate the wear properties of material combinations considered for use as bearing surfaces in human total joint prostheses. The test method is essential for accurately ranking and screening polymeric materials, especially those used in orthopaedic implants under simulated physiological conditions. By utilizing pin-on-flat or similar wear testing machines, ASTM F732-17 helps manufacturers, researchers, and regulatory bodies identify suitable materials and predict their long-term performance in joint prostheses.

Key Topics

• Polymeric Material Wear Rate: Measures the progressive loss of material from polymer specimens due to sliding motion against a counterface, simulating the movement in joint prostheses.
• Testing Apparatus: Focuses on simplified geometries using pin-on-flat or pin-on-disk machines, imitating real prosthesis operations.
• Wear Measurement: Wear is reported as volume loss of the polymeric specimen as a function of sliding distance and/or wear cycles. Experimental weight loss data is converted to volumetric loss using material density.
• Material Combinations: Evaluates combinations where quantifiable wear occurs primarily on the polymer. The standard reference uses ultra-high-molecular-weight polyethylene (UHMWPE) against cobalt-chromium-molybdenum alloy counterfaces.
• Simulated Physiological Conditions: Wear tests are conducted in lubricated environments (typically using bovine serum) to mimic the body’s internal conditions.
• Screening and Ranking: Provides comparative evaluation against known material standards to facilitate fast and reliable initial screening before costly joint simulator and clinical testing.

Applications

ASTM F732-17 is widely used in the medical device industry for:

• Development of Orthopaedic Implants: Ensures potential materials for knee, hip, and other joint replacements demonstrate satisfactory wear resistance prior to clinical trials.
• Research and Material Selection: Guides researchers and manufacturers in selecting the most promising polymeric materials for improved prosthesis longevity.
• Quality Assurance: Supports regulatory submission by providing standardized, reproducible wear data that meets international requirements.
• Comparative Performance Studies: Enables manufacturers to benchmark novel polymers and alternative counterface materials against established standards like UHMWPE and cobalt-chromium alloys.
• Process Validation and Optimization: Assists engineers in understanding the influence of material changes, processing conditions, surface finish, and lubrication on wear behaviors.

Related Standards

ASTM F732-17 references several important ASTM standards relevant to the wear testing of medical polymers, including:

• ASTM F75 – Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings for Surgical Implants
• ASTM F648 – Specification for Ultra-High-Molecular-Weight Polyethylene for Surgical Implants
• ASTM F799 – Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Forgings for Surgical Implants
• ASTM F1537 – Specification for Wrought Cobalt-28 Chromium-6 Molybdenum Alloys for Surgical Implants
• ASTM F2025 – Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
• ASTM F86 – Practice for Surface Preparation and Marking of Metallic Surgical Implants
• ASTM D883 – Terminology Relating to Plastics
• ASTM G40 – Terminology Relating to Wear and Erosion

Practical Value

Implementing ASTM F732-17 ensures the predictable performance and safety of polymeric materials used in joint prostheses. It streamlines laboratory screening, reduces clinical risk, and supports regulatory compliance. By adhering to this wear testing standard, manufacturers can deliver more durable and reliable orthopaedic implants, directly translating into improved patient outcomes and extended service life of artificial joints.

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: F732 − 17
Standard Test Method for
Wear Testing of Polymeric Materials Used in Total Joint
Prostheses
ThisstandardisissuedunderthefixeddesignationF732;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method describes a laboratory method for
mendations issued by the World Trade Organization Technical
evaluating the wear properties of combinations of materials
Barriers to Trade (TBT) Committee.
that are being considered for use as bearing surfaces of human
total joint prostheses. The body of this test method contains
2. Referenced Documents
general methods which apply to all types of prosthesis wear
2.1 ASTM Standards:
applications while individual annexes describe specific wear
D883Terminology Relating to Plastics
test methods and clinical validation criteria tailored to each
F75Specification for Cobalt-28 Chromium-6 Molybdenum
distinct wear application (for example, linear reciprocating
Alloy Castings and Casting Alloy for Surgical Implants
motion, ball-cup (“hip-type”) wear, delamination wear, and so
(UNS R30075)
forth). It is the intent of this test method to rank materials,
F86Practice for Surface Preparation and Marking of Metal-
within each wear application, for polymer wear rates under
lic Surgical Implants
simulated physiological conditions. It must be recognized,
F648Specification for Ultra-High-Molecular-Weight Poly-
however, that contact geometries and wear motions are sim-
ethylene Powder and Fabricated Form for Surgical Im-
plified using such methods. This test method, therefore, repre-
plants
sents only an initial stage in the full wear characterization of a
F799Specification for Cobalt-28Chromium-6Molybdenum
candidate material.
Alloy Forgings for Surgical Implants (UNS R31537,
1.2 All candidate materials should be tested in an appropri-
R31538, R31539)
ate joint simulator apparatus using prototype prostheses before
F1537 Specification for Wrought Cobalt-28Chromium-
being used in clinical trials in patients. The tests described in
6Molybdenum Alloys for Surgical Implants (UNS
thistestmethodareusedtoquicklyandreliablyscreenmaterial
R31537, UNS R31538, and UNS R31539)
combinations for wear performance in different orthopaedic
F2025Practice for Gravimetric Measurement of Polymeric
wear applications prior to committing them to more expensive
Components for Wear Assessment
and time-consuming joint simulator testing. In addition, these
G40Terminology Relating to Wear and Erosion
simplifiedtestscanbeusedtorelatematerial,surfacefinish,or
other parameters to wear behavior on a more practical basis
3. Terminology
than is possible in joint simulator tests.
3.1 Definitions of Terms Specific to This Standard:
1.3 The values stated in either SI units or inch-pound units
3.1.1 wear—forthepurposeofthistestmethod,theprogres-
are to be regarded separately as standard. The values stated in
sive loss of material from the polymer specimen as a result of
each system may not be exact equivalents; therefore, each
theoscillatingmotionagainstthecounterfaceunderload.Wear
system shall be used independently of the other. Combining
may be generated by several mechanisms including adhesion,
values from the two systems may result in non-conformance
twoorthreebodyabrasion,surfacefatigue,orotherprocesses.
with the standard.
3.1.2 wearrate—thevolumeofmateriallostduetowearper
1.4 This international standard was developed in accor-
unit of sliding distance (or per million wear cycles if complex
dance with internationally recognized principles on standard-
motion patterns result in a non-uniform sliding distance across
the specimen; see 4.3).
ThistestmethodisunderthejurisdictionofASTMCommitteeF04onMedical
andSurgicalMaterialsandDevicesandisthedirectresponsibilityofSubcommittee
F04.15 on Material Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Sept. 1, 2017. Published October 2017. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1982. Last previous edition approved in 2011 as F732–00 (2011). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/F0732-17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F732 − 17
4. Significance and Use 5.2.2 A filter-sterilized serum rather than pooled serum
should be used since the former is less likely to contain
4.1 This test method is intended to be performed in con-
hemolyzed blood material, which has been shown to adversely
junction with pin-on-flat wear machines or similar machines
affect the lubricating properties of the serum (2). Serum must
that are designed to evaluate simplified specimen geometries.
be filtered to remove hard, abrasive, particulate contaminants
NOTE 1—See Haider & Baykal (1) for useful considerations and
that might otherwise affect the wear properties of the speci-
potentialpitfallsinconductingpinondisktesting,interpretingtestresults
and the complex and sometimes conflicting effects of lower stress and
mens being tested.
higher contact area on wear.
5.2.3 Maintain the volume, concentration, and temperature
4.2 Thistestmethodisdesignedtoevaluatecombinationsof
of the lubricant nearly constant throughout the test. This may
materials with respect to the amount of polymer wear, where
be accomplished by sealing the chambers so that water does
quantifiable wear occurs primarily on the polymeric compo-
notevaporate,byperiodicallyorcontinuouslyreplacingevapo-
nent.Withsomecombinationsofmaterials,significantwearof
rated water with deionized water, or by recirculating the
the counterface may occur, with subsequent embedding of
lubricant in a sealed environment.
counterfacedebrisparticlesinthepolymer.Suchanoccurrence
5.2.4 To retard bacterial degradation, freeze and store the
will render the weight loss of the polymer specimen unreliable
serum between -10 and -40 °C until it is used for testing. Prior
as an indicator of the polymer wear.
totesting,itisrecommended,butnotmandatory,thatasuitable
4.3 Wear is reported as volume loss of the polymeric
antibacterial agent be added at an appropriate volume fraction.
specimen as a function of sliding distance; however, if the
A commonly used antibacterial agent is sodium azide. If
sliding distance is not constant across the polymeric specimen
sodium azide is used, it is recommended to use a volume
surface due to complex motion patterns, wear may be reported
fraction of 0.11 to 0.16 % (mass fraction of 0.2 to 0.3 %). The
asvolumelossofthepolymericspecimenasafunctionofwear
volumeandmassfractionsoftheantibacterialagentreferences
cycles(inwhichcasea“wearcycle”shallbedefined).Volume
the volume and mass of the final test solution which may be
loss of the polymer specimen is determined by dividing the
diluted or undiluted serum.
experimental weight loss by the density of the polymer. For
NOTE 3—Sodium azide is a poison and must be handled very carefully.
ease of interpretation, wear should be reported as a function of
NOTE 4—It has been shown that the addition of sodium azide may
both the number of wear cycles and the sliding distance, when
reduce wear, and sodium azide may not inhibit all types of bacterial
possible.
growth (3).
4.4 The reference for the comparative evaluation of candi-
5.2.5 It is recommended, but not mandatory, that ethylene-
date materials shall be the wear rate of ultra-high-molecular-
diaminetetraacetic acid (EDTA) be added to the serum at a
weight polyethylene (UHMWPE) conforming to Specification
concentration of 20 mM [7.45 g/L] to bind calcium in solution
F648 bearing against counterfaces of cobalt-chromium-
and minimize precipitation of calcium phosphate onto the
molybdenum alloy (in accordance with Specifications F75,
bearing surfaces. The latter event has been shown to strongly
F799,or F1537), having prosthetic-quality surface finish and
affect the friction and wear properties, particularly of
lubricated with bovine blood serum (see 5.2).
polyethylene/ceramic combinations (4). The molar concentra-
tion of the EDTA references the volume of the final test
5. Apparatus and Materials
solution which may be diluted or undiluted serum.
5.1 Orthopaedic Wear Application:
5.1.1 For linear reciprocating wear motion applications,
NOTE 5—There are multiple forms of EDTAcommonly available, such
as pure EDTA, EDTA dipostassium salt dihydrate, and so forth. All of
refer to Annex A1.
thesecompoundshavedifferentmolecularweights,andadifferentamount
5.1.2 For fixed-bearing ball-cup (“hip-type”) wear motion
of each compound is required to achieve the same EDTA concentration.
applications, refer to Annex A2.
Pure EDTA has a very low solubility in water, and EDTA disodium salt
5.1.3 For nominally linear motion delamination wear
dihydrate is recommended.
applications, refer to Annex A3.
5.2.6 Additives such as sodium azide and EDTA shall be
NOTE 2—Other types of applications may be addressed in later
dissolvedindeionizedwaterandpassedthrougha0.2-µmfilter
revisions.
before adding to bovine serum.
5.2 Lubricant (see also Annex A4):
5.2.7 The appropriate interval for replacing used serum
5.2.1 The specimen shall be lubricated with bovine blood
depends on how long the serum maintains its composition (for
serum unless an alternative medium can be justified as de-
example, lubricating properties) under the specific test
scribed in section 5.2.8. Since different sera differ in compo-
conditions/materialsbeingusedandtheadditivespresentinthe
sition (protein concentration, and so forth), dilution with
serum. There is no minimum replacement interval. The maxi-
deionized water of up to 75 % (volume fraction) may be
mum replacement interval is two weeks. The selected interval
appropriate. The appropriate dilution shall be based on satis-
must meet the validation requirements in the appropriate
faction of the clinical validation criteria in the appropriate
annex.
annex.
5.2.8 Alubricantotherthanbovineserumshallbeusedonly
when it can be shown that the lubricant reproduces clinical
wear mechanisms as well or better than bovine serum. In such
The boldface numbers in parentheses refer to a list of references at the end of
this test method. case the lubricant shall be specified in the test report.
F732 − 17
6. Preparation of Specimens erties relevant to wear (for example, grain structure, hardness,
and percentage of contaminants).
6.1 The governing rule for specimen preparation is that the
6.4.2 Surface Finish—In tests that are intended to evaluate
fabricationprocessparallelsthatusedorintendedforuseinthe
an alternate counterface material bearing against the standard
productionofactualprostheses,inordertoproduceaspecimen
UHMWPE,ensurethatthecounterfacefinishisappropriatefor
with comparable bulk material properties and surface charac-
components intended for clinical use. In test of alternate
teristics (see Practice F86).
materialswhereareferencemetalorceramicisused,polishthe
6.2 Polymers and Composites:
counterface to the prosthesis quality.
6.4.3 Ensure that cleaning of specimens produces a surface
6.2.1 Obtain a fabrication history for each polymeric or
free of any particles, oils, greases, or other contaminants that
composite specimen, including information such as grade,
batch number, and processing variables, including method of might influence the wear process.
forming (extruding, molding, and so forth), temperature,
pressure, and forming time used, articulation surface prepara- 7. Procedure
tionmethods(seeAnnexA5)andanypost-formingtreatments,
7.1 Make any initial measurements required to determine
including sterilization.
thesubsequentamountofwearofthepolymericspecimen(see
6.2.2 Pre-test characterization may include measurement of
Practice F2025 for the gravimetric measurement method).
bulk material properties, such as molecular-weight range and
7.2 Placethecontrolsoakspecimen(s)inasoakchamberof
distribution, percent crystallinity, density, or others. The sur-
test lubricant, such that the total surface area exposed to the
face finish of specimens may be characterized by profilometry,
lubricant is equal to that of the wear specimens when mounted
photomicrography, replication by various plastics, or other
in the test chambers. Maintain the soak chamber lubricant
techniques.
temperature at the same nominal temperature as the test
6.2.3 Sterilization—Sterilize the specimens in a manner
chambers. This temperature shall be 37 6 3°C unless justifi-
typical of that in clinical use for such devices unless it can be
cation can be provided that use of a different temperature will
proven that this has no effect on wear properties of the
not affect the results.
materials. Report sterilization processing parameters with the
7.3 Placetheweartestspecimensintheirtestchambers,add
aging time prior to each test, if known. Sterilization of all test
the lubricant, and activate load(s) and motion(s).
and control specimens within a specific test group should be
done simultaneously (in a single container), when possible, to
7.4 As testing is commenced, monitor the specimens for
minimize variation among the specimens.
signsoferraticbehaviorthatmightrequireearlyterminationof
6.2.4 Cleaning of Polymer Specimens—Prior to wear the test.
testing,carefulcleaningofthepolymerspecimensisimportant
7.5 Remove the wear and soak specimens at desired
to remove any contaminants that would not normally be
intervals, wash, rinse, concurrently in accordance with the
present on an actual prosthesis. During the wear test, the
procedure in Annex A6 (also defined in Practice F2025). It is
specimens must be re-cleaned and dried before each wear
important that both the wear and soak components be treated
measurement to remove any extraneous material that might
identically to ensure that they have the same exposure to the
affect the accuracy of the measurement. The required proce-
wash, rinse, and drying fluids. This will provide the most
dure for cleaning and drying of polymeric specimens, as
accurate correction for fluid sorption by the wear specimens,
defined in Practice F2025, is given in Annex A6.
and correction for any other factors which could affect wear
measurements.
6.3 Soaking of Polymeric and Composite Specimens:
6.3.1 Polymeric and composite specimens should be pre-
7.6 After rinsing and drying, conduct wear measurements.
soaked in the wear test lubricant to minimize fluid-sorption
7.7 Thoroughly rinse all test assembly surfaces which have
during the wear test. Without presoaking, specimens made
contacted bovine serum using deionized water.
from very low-wear polymers such as UHMWPE could show
7.8 Inspect the bearing surfaces of the test specimens and
a net increase in weight or volume during the initial wear
note the characteristics of the wear process. Visual,
intervals due to fluid sorption (2, 5). The error due to fluid
microscopic, profilometric, replication, or other inspection
sorption can be reduced through presoaking and use of control
techniques can be used. Care must be taken, however, that the
soak specimens. The length of presoaking depends on the
surfaces do not become contaminated or damaged by any
variability and magnitude of fluid sorption encountered (5).A
substance or technique that might affect the subsequent wear
minimum of one control soak specimen per material condition
properties. If contamination occurs, thoroughly reclean the
is required.
specimens prior to restarting the wear test.
6.4 Counterfaces of Metal Alloys, Ceramic, or Other Mate-
7.9 Replace the wear specimens, maintaining original
rials:
couples and orientation, and soak control(s) in fresh lubricant
6.4.1 Characterization—Pretest characterization of the
and continue wear cycling.
counterface material shall include recording of fabrication
variables, such as composition, forming method (forging, 7.10 The appropriate wear test duration depends on the
casting, molding, and so forth) and any postforming objective of the specific test, the duration of run-in effects, the
processing, such as annealing. Obtain data on material prop- linearity of wear rates, and the potential for wear mechanism
F732 − 17
transitions. The minimum duration shall be two million wear 8.3.4 At the discretion of the investigator, more complex,
cycles. The minimum number of wear measurements, subse- nonlinear models may be fit to the wear-test data.
quent to the initial measurement shall be four.
8.3.5 Report the test duration in cycles. Explain why the
selected test duration was used.
8. Report
8.3.6 Report the method of calculating polymer sliding
8.1 Materials:
distance per wear cycle. Report the test duration in polymer
8.1.1 Provide material traceability information from a raw
sliding distance in addition to cycles.
material and fabrication or manufacturing standpoint for each
8.3.7 An explanation of how the wear rates meet the
material counterface. Examples of such information include
designatedcriteria(intheappropriateannex)shallbereported.
material grade, batch number, and processing variables.
8.4 Wear Mechanisms:
8.1.2 Pretest characterization for a plastic counterface may
8.4.1 Provide a description of the articulating surfaces of
include measurement of bulk material properties, such as
both components.
molecular-weight average, range, and distribution, percent
8.4.2 Anexplanationofhowthewearmechanismsmeetthe
crystallinity, density, degree of oxidation, or others. The
designatedcriteria(intheappropriateannex)shallbereported.
surface finish of both counterfaces may be characterized by
profilometry, photomicrography, replication, or other appli-
8.5 Accuracy and Repeatability:
cable techniques. Surface finish of the harder counterface shall
8.5.1 In multiple tests where the wear rate is determined
be reported.
from the slope of the graph comparing wear versus test
8.1.3 Reportthemethodofsterilization,thesterilizationand
duration(cycles)foreachspecimen,reporttheindividualrates,
testdates,ifknown,andthemeansofstoragepost-sterilization
mean wear rate, and the 95 % confidence intervals for each
and pretest.
rate.
8.2 Test Apparatus—Report the number of stations on the
8.5.2 Incaseswherethemeanwearratefortwomaterialsis
machineandthenumberofstationsusedforthistest.Reportif
different,evaluateandreportthelevelofstatisticalsignificance
replicatetestswereconductedduringmorethanonetestseries.
of this difference.
Describe the mechanisms used to generate motions and forces,
8.6 Since the accumulation of wear debris in the lubricant
the systems used to measure motions and forces, the arrange-
mayinfluencethewearrate,reportanyfilteringofthelubricant
ment for mounting specimens, a detailed description of the
during operation (continuously or periodically) and the lubri-
lubricant used, the arrangement for lubricating the articulating
cant replacement intervals.
surfaces, arrangement for lubricant temperature control, the
measured lubricant temperatures, total lubricant volume per 8.7 Reporttheloadingconditions,ifany,onthesoakcontrol
station,lubricantreplacementinterval,andarrangementforthe specimen(s). Load soaking, which is defined as a pulsing load
exclusion of contaminant particles. Report the nature and profile equivalent to the wear profile without the tangential
frequency of all calibrations conducted on the test apparatus. movement, may increase the fluid sorption rate.
Define what constitutes one wear cycle. Confirm and explain
8.8 Includeareferencetothistestmethodandtothemethod
howthistestmethodsatisfiesalleleventestparameterrequire-
used for wear measurement.
ments set forth in the corresponding annex.
8.3 Wear Rates:
9. Precision and Bias
8.3.1 Graphically plot the wear of each specimen as a
9.1 Inorderthatthescreeningtestweardatabereproducible
function of sliding distance and/or wear cycles. Wear shall be
andcomparableamonglaboratories,itisessentialthatuniform
reported as the volumetric loss of the bearing component(s) as
procedures be established. Sufficient data has not yet been
afunctionofslidingdistanceand/orthenumberofwearcycles.
produced using identical materials in different laboratories to
If weight measurements were made, this will require knowing
permit determining the precision and bias of this procedure.
the density of the wear specimen(s).
The publication of this test method is intended, in part, to
8.3.2 Intestswherethewearrateisnearlyconstantoverthe
facilitate uniform testing and reporting of data from screening
test run, calculate the volumetric wear rate by the method of
test wear studies. Validation of this methodology, may be
least squares linear regression.
achieved through round-robin testing.
8.3.3 If the wear rate changes during the test, as with a
decreaseduetowearing-inofthespecimensoranincreasedue
10. Keywords
totheonsetoffatiguewear,linearregressionmaybeappliedto
separateintervalsofthetesttoindicatethechangeinwearrate. 10.1 joint prosthesis materials; pin-on-disk; wear testing
F732 − 17
ANNEXES
(Mandatory Information)
A1. TEST METHOD FOR LINEAR RECIPROCATING WEAR MOTION APPLICATIONS
A1.1 Scope A1.2.3 Reproduction of in vivo Wear Mechanisms—The
baseline test wear mechanisms should be representative of
A1.1.1 The “linear reciprocating wear motion” test method
those seen clinically. For linear reciprocating wear motion
describes a laboratory method for evaluating the friction and
applications, a baseline CoCr/UHMWPE test should exhibit
wear properties of combinations of materials that are being
mild microadhesive/micro-abrasive wear mechanisms, result-
considered for use as the bearing surfaces of human total joint
ing in a mild burnished or smeared UHMWPE wear surface
replacement prostheses which experience only linear recipro-
and no significant loss of material. The wear motion direction
cating (straight or rotatory) wear motion. Such applications
should be apparent on this wear surface. A very thin transfer
include hinged knees, other hinged joints, trunnion bearings,
film may be visible on the CoCr surface.
axlebearings,somemobilebearingkneeapplicationsinwhich
the insert/tibial tray attachment mechanisms allow for linear
A1.2.4 Repeatability and Reproducibility of Results—A
motion only, and any other application in which the wear path
minimum of three replicate tests per condition should be
at any given contact point reciprocates along a fixed line.
conducted; more if the repeatability relative to mean wear or
Applications which are not relevant to this test method include
aggregate wear rate is poor. If the same specimen condition
head/socket articulation in hips and shoulders, fossa/condyle
were tested in separate series, there should be no significant
articulation in temporomandibular joints, liner/shell relative
difference in results.
motion in hips, all patellofemoral and femorotibial articulation
A1.3 Apparatus and Materials
in knees where internal-external rotation may occur, and tibial
insert/tibial tray relative motion in knees where rotation may
A1.3.1 Description of Specimens and Test Parameters:
occur. It is the intent of this test method to rank the materials
A1.3.1.1 Polymer Specimen—The standard polymer speci-
with regard to friction levels and polymer wear rates under
menisaflat-endedcircularcylinder13mm[0.50in.]longand
simulated physiological conditions. However, it must be rec-
9.00 mm [0.354 in.] in diameter, providing a cross-sectional
ognized that, since any one design of joint replacement, even 2 2
area of 63.6 mm [0.0986 in. ]. In the wear machine, the
within this restricted scope, performs under unique conditions
polymer specimen is loaded end-wise against the counterface
of load, motion, and contact geometry, there can be no single
in a flat-on-flat configuration. This specimen geometry pro-
universally applicable wear screening test. This test method
vides a known contact area that remains constant as the test
therefore represents only the first stage in the full character-
progresses and wear occurs. Care should be taken to ensure
ization of a candidate material.
alignment of the specimen end face with the counter face.
A1.1.2 All candidate materials should be tested in a joint
A1.3.1.2 Counterface—The wear counterface may be fabri-
simulator apparatus using prototype prostheses before being
cated in any convenient shape, provided that the contact
usedinclinicaltrialsinpatients.Thepin-on-disktestdescribed
surface is flat in the plane of motion of the polymer specimen
inthistestmethodisusedtoquicklyandreliablyidentifythose
and extends beyond the extremes of travel of the polymer
low-friction, low-wear materials for which the more expensive
specimen.
and time-consuming joint simulator testing is justified. In
A1.3.1.3 Wear Machine:
addition, the pin-on-disk test can be used to relate wear to
(1) Specimen Chambers—In the case of a multiple speci-
material parameters such as polymer molecular weight or
men machine, the specimens shall be contained in individual
counterface surface finish, on a more practical basis than is
isolated chambers to prevent contamination of one set of
possible in joint simulator tests.
specimens with debris from another test specimen. The cham-
bershallbemadeentirelyofcorrosion-resistantmaterialssuch
A1.2 Criteria for Appropriate Test Results
as acrylic plastic and shall be easily removable from the
A1.2.1 Rationale—Because there are subtle test method
machine for thorough cleaning between tests. The wear cham-
variables which will exist, even for a highly detailed test
bers shall be designed such that the specimen surfaces are
methodsuchasthis,itisnecessarytoidentifycharacteristicsof
immersed in the lubricant for the duration of the test.
test results which must be met to ensure that they are
(2) Load—The test load of 225 N [50.6 lbf] shall be
representative of clinical results. Baseline testing should be
applied along the longitudinal axis of the polymer specimen,
conducted utilizing material combinations with significant
such that the average contact stress is 3.54 MPa [513 psi].The
clinical history such as cast CoCr and gamma-sterilized UH-
loading apparatus must be free to follow the specimen as wear
MWPE.
occurs, such that the applied load is constant to within 63%
A1.2.2 Reproduction ofinvivo Wear Quantities—Thebase- for the duration of the test.
linetestwearquantitiesshouldbecomparedtoclinicalresults. (3) Motion—Relative motion between the specimen and
Clinical data for linear reciprocating wear motion applications the counterface shall be oscillatory. The orientation between
are quite sparse.At this time, a suitable guideline for relevant sliding direction and the lay of the surface roughness in each
wear quantities is not clear. test should be noted. It is recommended that the relative
F732 − 17
orientation of the pin and disk be maintained by suitable A1.3.2.3 Metal concave/flat/convex: flat.
specimen-holder keying.
A1.3.2.4 Contact stress: 3.54 MPa.
(4) Sliding Speed—Specimens shall be run through a 25
A1.3.2.5 Lubricant exclusion/exposure: metal re-exposed,
mm stroke at a rate of 1 cycle/s, producing an average sliding
polymer not.
speed of 50 mm/s.
A1.3.2.6 Contact “coverage”: polymer surface 100% cov-
(5) Cycle Counter—The machine shall include a cycle
erage.
counter to record the total number of wear cycles.
A1.3.2.7 Contact area interaction ratio: metal wear surface
(6) Friction—It is recommended that the machine include
area at least 100% greater than polymer wear surface area.
strain gage instrumentation or other transducers capable of
A1.3.2.8 Cross-shearofpolymer(changeinangleofmotion
providingacontinuousreadoutofthetangential(friction)force
relative to metal surface) during a wear cycle: none (0°).
transmitted across the specimen interface during the test
A1.3.2.9 Wear cycle frequency: 1 Hz.
A1.3.2 Summary of Test Parameter Requirements:
A1.3.2.10 Meanpolymerslidingdistanceperwearcycle:50
A1.3.2.1 Motion track: linear reciprocating sliding.
mm.
A1.3.2.2 Polymer concave/flat/convex: flat-ended cylindri-
cal pin. A1.3.2.11 Mean polymer sliding speed: 50 mm/s.
A2. TEST METHOD FOR FIXED-BEARING BALL-CUP (“HIP-TYPE”) WEAR APPLICATIONS
A2.1 Scope A2.2.2 Reproduction ofinvivo Wear Quantities—Thebase-
linetestwearquantitiesshouldbecomparedtoclinicalresults:
A2.1.1 The “hip-type” wear test method describes a labo-
3 3
69 6 33 mm /yr for 22 mm balls, 85 6 33 mm /yr for 28 mm
ratorymethodforevaluatingthefrictionandwearpropertiesof 3
balls, and 90 6 44 mm /yr for 32 mm balls (6).The wear area
combinations of materials that are being considered for use as
of the UHMWPE pin for this test method is roughly ten times
the bearing surfaces of fixed-bearing ball/cup devices for total
smaller than that of a 22 mm cup, so
...

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. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: F732 − 00 (Reapproved 2011) F732 − 17
Standard Test Method for
Wear Testing of Polymeric Materials Used in Total Joint
Prostheses
This standard is issued under the fixed designation F732; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method describes a laboratory method for evaluating the wear properties of combinations of materials that are
being considered for use as bearing surfaces of human total joint prostheses. The body of this test method contains general methods
which apply to all types of prosthesis wear applications while individual annexes describe specific wear test methods and clinical
validation criteria tailored to each distinct wear application (for example, linear reciprocating motion, ball-cup (“hip-type”) wear,
delamination wear, etc.). and so forth). It is the intent of this test method to rank materials, within each wear application, for
polymer wear rates under simulated physiological conditions. It must be recognized, however, that contact geometries and wear
motions are simplified using such methods. This test method, therefore, represents only an initial stage in the full wear
characterization of a candidate material.
1.2 All candidate materials should be tested in an appropriate joint simulator apparatus using prototype prostheses before being
used in clinical trials in patients. The tests described in this test method are used to quickly and reliably screen material
combinations for wear performance in different orthopaedic wear applications prior to committing them to more expensive and
time-consuming joint simulator testing. In addition, these simplified tests can be used to relate material, surface finish, or other
parameters to wear behavior on a more practical basis than is possible in joint simulator tests.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.4 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.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
F75 Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants (UNS
R30075)
F86 Practice for Surface Preparation and Marking of Metallic Surgical Implants
F648 Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants
F799 Specification for Cobalt-28Chromium-6Molybdenum Alloy Forgings for Surgical Implants (UNS R31537, R31538,
R31539)
F1537 Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, UNS
R31538, and UNS R31539)
F2025 Practice for Gravimetric Measurement of Polymeric Components for Wear Assessment
G40 Terminology Relating to Wear and Erosion
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.15 on Material Test Methods.
Current edition approved June 1, 2011Sept. 1, 2017. Published July 2011October 2017. Originally approved in 1982. Last previous edition approved in 20062011 as
F732 – 00 (2006).(2011). DOI: 10.1520/F0732-00R11.10.1520/F0732-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F732 − 17
3.1.1 wear—for the purpose of this test method, the progressive loss of material from the polymer specimen as a result of the
oscillating motion against the counterface under load. Wear may be generated by several mechanisms including adhesion, two or
three body abrasion, surface fatigue, or other processes.
3.1.2 wear rate—the volume of material lost due to wear per unit of sliding distance (or per million wear cycles if complex
motion patterns result in a non-uniform sliding distance across the specimen; see 4.3).
4. Significance and Use
4.1 This test method is intended to be performed in conjunction with pin-on-flat wear machines or similar machines that are
designed to evaluate simplified specimen geometries.
NOTE 1—See Haider & Baykal (1) for useful considerations and potential pitfalls in conducting pin on disk testing, interpreting test results and the
complex and sometimes conflicting effects of lower stress and higher contact area on wear.
4.2 This test method is designed to evaluate combinations of materials with respect to the amount of polymer wear, where
quantifiable wear occurs primarily on the polymeric component. With some combinations of materials, significant wear of the
counterface may occur, with subsequent embedding of counterface debris particles in the polymer. Such an occurrence will render
the weight loss of the polymer specimen unreliable as an indicator of the polymer wear.
4.3 Wear is reported as volume loss of the polymeric specimen as a function of sliding distance; however, if the sliding distance
is not constant across the polymeric specimen surface due to complex motion patterns, wear may be reported as volume loss of
the polymeric specimen as a function of wear cycles (in which case a “wear cycle” shall be defined). Volume loss of the polymer
specimen is determined by dividing the experimental weight loss by the density of the polymer. For ease of interpretation, wear
should be reported as a function of both the number of wear cycles and the sliding distance, when possible.
4.4 The reference for the comparative evaluation of candidate materials shall be the wear rate of ultra-high-molecular-weight
polyethylene (UHMWPE) conforming to Specification F648 bearing against counterfaces of cobalt-chromium-molybdenum alloy
(in accordance with Specifications F75, F799, or F1537), having prosthetic-quality surface finish and lubricated with bovine blood
serum (see 5.2).
5. Apparatus and Materials
5.1 Orthopaedic Wear Application:
5.1.1 For linear reciprocating wear motion applications, refer to Annex A1.
5.1.2 For fixed-bearing ball-cup (“hip-type”) wear motion applications, refer to Annex A2.
5.1.3 For nominally linear motion delamination wear applications, refer to Annex A3.
NOTE 2—Other types of applications may be addressed in later revisions.
5.2 Lubricant (see also Annex A4):
5.2.1 The specimen shall be lubricated with bovine blood serum unless an alternative medium can be justified as described in
section 5.2.8. Since different sera differ in composition (protein concentration, etc.), and so forth), dilution with deionized water
of up to 75 % (volume fraction) may be appropriate. The appropriate dilution shall be based on satisfaction of the clinical validation
criteria in the appropriate annex.
5.2.2 A filter-sterilized serum rather than pooled serum should be used since the former is less likely to contain hemolyzed blood
material, which has been shown to adversely affect the lubricating properties of the serum (12)). Serum must be filtered to remove
hard, abrasive, particulate contaminants that might otherwise affect the wear properties of the specimens being tested.
5.2.3 Maintain the volume, concentration, and temperature of the lubricant nearly constant throughout the test. This may be
accomplished by sealing the chambers so that water does not evaporate, by periodically or continuously replacing evaporated water
with deionized water, or by recirculating the lubricant in a sealed environment.
5.2.4 To retard bacterial degradation, freeze and store the serum until needed for testing. In addition, it is recommended that
the serum contains a mass fraction of between -10 and -40 °C until it is used for testing. Prior to testing, it is recommended, but
not mandatory, that a suitable antibacterial agent be added at an appropriate volume fraction. A commonly used antibacterial agent
is sodium azide. If sodium azide is used, it is recommended to use a volume fraction of 0.11 to 0.16 % (mass fraction of 0.2 to
0.3 % sodium azide (or other suitable antibacterial agent) to minimize bacterial degradation.%). The volume and mass fractions
of the antibacterial agent references the volume and mass of the final test solution which may be diluted or undiluted serum.
NOTE 3—Sodium azide is a poison and must be handled very carefully.
NOTE 4—It has been shown that the addition of sodium azide may reduce wear, and sodium azide may not inhibit all types of bacterial growth (3).
5.2.5 It is recommended recommended, but not mandatory, that ethylene-diaminetetraacetic acid (EDTA) be added to the serum
at a concentration of 20 mM [7.45 g/L] to bind calcium in solution and minimize precipitation of calcium phosphate onto the
The boldface numbers in parentheses refer to a list of references at the end of this test method.
F732 − 17
bearing surfaces. The latter event has been shown to strongly affect the friction and wear properties, particularly of
polyethylene/ceramic combinations (24). The molar concentration of the EDTA references the volume of the final test solution
which may be diluted or undiluted serum.
NOTE 5—There are multiple forms of EDTA commonly available, such as pure EDTA, EDTA dipostassium salt dihydrate, and so forth. All of these
compounds have different molecular weights, and a different amount of each compound is required to achieve the same EDTA concentration. Pure EDTA
has a very low solubility in water, and EDTA disodium salt dihydrate is recommended.
5.2.6 Additives such as sodium azide and EDTA shall be dissolved in deionized water and passed through a 0.2-μm filter before
adding to bovine serum.
5.2.7 The appropriate interval for replacing used serum depends on how long the serum maintains its composition (for example,
lubricating properties) under the specific test conditions/materials being used and the additives present in the serum. There is no
minimum replacement interval. The maximum replacement interval is two weeks. The selected interval must meet the validation
requirements in the appropriate annex.
5.2.8 A lubricant other than bovine serum shall be used only when it can be shown that the lubricant reproduces clinical wear
mechanisms as well or better than bovine serum. In such case the lubricant shall be specified in the test report.
6. Preparation of Specimens
6.1 The governing rule for specimen preparation is that the fabrication process parallels that used or intended for use in the
production of actual prostheses, in order to produce a specimen with comparable bulk material properties and surface
characteristics (see Practice F86).
6.2 Polymers and Composites:
6.2.1 Obtain a fabrication history for each polymeric or composite specimen, including information such as grade, batch
number, and processing variables, including method of forming (extruding, molding, etc.), and so forth), temperature, pressure, and
forming time used, articulation surface preparation methods (see Annex A5) and any post-forming treatments, including
sterilization.
6.2.2 Pre-test characterization may include measurement of bulk material properties, such as molecular-weight range and
distribution, percent crystallinity, density, or others. The surface finish of specimens may be characterized by profilometry,
photomicrography, replication by various plastics, or other techniques.
6.2.3 Sterilization—Sterilize the specimens in a manner typical of that in clinical use for such devices unless it can be proven
that this has no effect on wear properties of the materials. Report sterilization processing parameters with the aging time prior to
each test, if known. Sterilization of all test and control specimens within a specific test group should be done simultaneously (in
a single container), when possible, to minimize variation among the specimens.
6.2.4 Cleaning of Polymer Specimens—Prior to wear testing, careful cleaning of the polymer specimens is important to remove
any contaminants that would not normally be present on an actual prosthesis. During the wear test, the specimens must be
re-cleaned and dried before each wear measurement to remove any extraneous material that might affect the accuracy of the
measurement. The required procedure for cleaning and drying of polymeric specimens, as defined in Practice F2025, is given in
Annex A6.
6.3 Soaking of Polymeric and Composite Specimens:
6.3.1 Polymeric and composite specimens should be presoaked in the wear test lubricant to minimize fluid-sorption during the
wear test. Without presoaking, specimens made from very low-wear polymers such as UHMWPE could show a net increase in
weight or volume during the initial wear intervals due to fluid sorption (12, 35). The error due to fluid sorption can be reduced
through presoaking and use of control soak specimens. The length of presoaking depends on the variability and magnitude of fluid
sorption encountered (35). A minimum of one control soak specimen per material condition is required.
6.4 Counterfaces of Metal Alloys, Ceramic, or Other Materials:
6.4.1 Characterization—Pretest characterization of the counterface material shall include recording of fabrication variables,
such as composition, forming method (forging, casting, molding, etc.) and and so forth) and any postforming processing, such as
annealing. Obtain data on material properties relevant to wear (for example, grain structure, hardness, and percentage of
contaminants).
6.4.2 Surface Finish—In tests that are intended to evaluate an alternate counterface material bearing against the standard
UHMWPE, ensure that the counterface finish is appropriate for components intended for clinical use. In test of alternate materials
where a reference metal or ceramic is used, polish the counterface to the prosthesis quality.
6.4.3 Ensure that cleaning of specimens produces a surface free of any particles, oils, greases, or other contaminants that might
influence the wear process.
7. Procedure
7.1 Make any initial measurements required to determine the subsequent amount of wear of the polymeric specimen (see
Practice F2025 for the gravimetric measurement method).
F732 − 17
7.2 Place the control soak specimen(s) in a soak chamber of test lubricant, such that the total surface area exposed to the
lubricant is equal to that of the wear specimens when mounted in the test chambers. Maintain the soak chamber lubricant
temperature at the same nominal temperature as the test chambers. This temperature shall be 37 6 3°C unless justification can be
provided that use of a different temperature will not affect the results.
7.3 Place the wear test specimens in their test chambers, add the lubricant, and activate load(s) and motion(s).
7.4 As testing is commenced, monitor the specimens for signs of erratic behavior that might require early termination of the
test.
7.5 Remove the wear and soak specimens at desired intervals, wash, rinse, concurrently in accordance with the procedure in
Annex A6 (also defined in Practice F2025). It is important that both the wear and soak components be treated identically to ensure
that they have the same exposure to the wash, rinse, and drying fluids. This will provide the most accurate correction for fluid
sorption by the wear specimens, and correction for any other factors which could affect wear measurements.
7.6 After rinsing and drying, conduct wear measurements.
7.7 Thoroughly rinse all test assembly surfaces which have contacted bovine serum using deionized water.
7.8 Inspect the bearing surfaces of the test specimens and note the characteristics of the wear process. Visual, microscopic,
profilometric, replication, or other inspection techniques can be used. Care must be taken, however, that the surfaces do not become
contaminated or damaged by any substance or technique that might affect the subsequent wear properties. If contamination occurs,
thoroughly reclean the specimens prior to restarting the wear test.
7.9 Replace the wear specimens, maintaining original couples and orientation, and soak control(s) in fresh lubricant and
continue wear cycling.
7.10 The appropriate wear test duration depends on the objective of the specific test, the duration of run-in effects, the linearity
of wear rates, and the potential for wear mechanism transitions. The minimum duration shall be two million wear cycles. The
minimum number of wear measurements, subsequent to the initial measurement shall be four.
8. Report
8.1 Materials:
8.1.1 Provide material traceability information from a raw material and fabrication or manufacturing standpoint for each
material counterface. Examples of such information include material grade, batch number, and processing variables.
8.1.2 Pretest characterization for a plastic counterface may include measurement of bulk material properties, such as
molecular-weight average, range, and distribution, percent crystallinity, density, degree of oxidation, or others. The surface finish
of both counterfaces may be characterized by profilometry, photomicrography, replication, or other applicable techniques. Surface
finish of the harder counterface shall be reported.
8.1.3 Report the method of sterilization, the sterilization and test dates, if known, and the means of storage post-sterilization and
pretest.
8.2 Test Apparatus—Report the number of stations on the machine and the number of stations used for this test. Report if
replicate tests were conducted during more than one test series. Describe the mechanisms used to generate motions and forces, the
systems used to measure motions and forces, the arrangement for mounting specimens, a detailed description of the lubricant used,
the arrangement for lubricating the articulating surfaces, arrangement for lubricant temperature control, the measured lubricant
temperatures, total lubricant volume per station, lubricant replacement interval, and arrangement for the exclusion of contaminant
particles. Report the nature and frequency of all calibrations conducted on the test apparatus. Define what constitutes one wear
cycle. Confirm and explain how this test method satisfies all eleven test parameter requirements set forth in the corresponding
annex.
8.3 Wear Rates:
8.3.1 Graphically plot the wear of each specimen as a function of sliding distance and/or wear cycles. Wear shall be reported
as the volumetric loss of the bearing component(s) as a function of sliding distance and/or the number of wear cycles. If weight
measurements were made, this will require knowing the density of the wear specimen(s).
8.3.2 In tests where the wear rate is nearly constant over the test run, calculate the volumetric wear rate by the method of least
squares linear regression.
8.3.3 If the wear rate changes during the test, as with a decrease due to wearing-in of the specimens or an increase due to the
onset of fatigue wear, linear regression may be applied to separate intervals of the test to indicate the change in wear rate.
8.3.4 At the discretion of the investigator, more complex, nonlinear models may be fit to the wear-test data.
8.3.5 Report the test duration in cycles. Explain why the selected test duration was used.
8.3.6 Report the method of calculating polymer sliding distance per wear cycle. Report the test duration in polymer sliding
distance in addition to cycles.
8.3.7 An explanation of how the wear rates meet the designated criteria (in the appropriate annex) shall be reported.
8.4 Wear Mechanisms:
F732 − 17
8.4.1 Provide a description of the articulating surfaces of both components.
8.4.2 An explanation of how the wear mechanisms meet the designated criteria (in the appropriate annex) shall be reported.
8.5 Accuracy and Repeatability:
8.5.1 In multiple tests where the wear rate is determined from the slope of the graph comparing wear versus test duration
(cycles) for each specimen, report the individual rates, mean wear rate, and the 95 % confidence intervals for each rate.
8.5.2 In cases where the mean wear rate for two materials is different, evaluate and report the level of statistical significance
of this difference.
8.6 Since the accumulation of wear debris in the lubricant may influence the wear rate, report any filtering of the lubricant
during operation (continuously or periodically) and the lubricant replacement intervals.
8.7 Report the loading conditions, if any, on the soak control specimen(s). Load soaking, which is defined as a pulsing load
profile equivalent to the wear profile without the tangential movement, may increase the fluid sorption rate.
8.8 Include a reference to this test method and to the method used for wear measurement.
9. Precision and Bias
9.1 In order that the screening test wear data be reproducible and comparable among laboratories, it is essential that uniform
procedures be established. Sufficient data has not yet been produced using identical materials in different laboratories to permit
determining the precision and bias of this procedure. The publication of this test method is intended, in part, to facilitate uniform
testing and reporting of data from screening test wear studies. Validation of this methodology, may be achieved through
round-robin testing.
10. Keywords
10.1 joint prosthesis materials; pin-on-disk; wear testing
ANNEXES
(Mandatory Information)
A1. TEST METHOD FOR LINEAR RECIPROCATING WEAR MOTION APPLICATIONS
A1.1 Scope
A1.1.1 The “linear reciprocating wear motion” test method describes a laboratory method for evaluating the friction and wear
properties of combinations of materials that are being considered for use as the bearing surfaces of human total joint replacement
prostheses which experience only linear reciprocating (straight or rotatory) wear motion. Such applications include hinged knees,
other hinged joints, trunnion bearings, axle bearings, some mobile bearing knee applications in which the insert/tibial tray
attachment mechanisms allow for linear motion only, and any other application in which the wear path at any given contact point
reciprocates along a fixed line. Applications which are not relevant to this test method include head/socket articulation in hips and
shoulders, fossa/condyle articulation in temporomandibular joints, liner/shell relative motion in hips, all patellofemoral and
femorotibial articulation in knees where internal-external rotation may occur, and tibial insert/tibial tray relative motion in knees
where rotation may occur. It is the intent of this test method to rank the materials with regard to friction levels and polymer wear
rates under simulated physiological conditions. However, it must be recognized that, since any one design of joint replacement,
even within this restricted scope, performs under unique conditions of load, motion, and contact geometry, there can be no single
universally applicable wear screening test. This test method therefore represents only the first stage in the full characterization of
a candidate material.
A1.1.2 All candidate materials should be tested in a joint simulator apparatus using prototype prostheses before being used in
clinical trials in patients. The pin-on-disk test described in this test method is used to quickly and reliably identify those
low-friction, low-wear materials for which the more expensive and time-consuming joint simulator testing is justified. In addition,
the pin-on-disk test can be used to relate wear to material parameters such as polymer molecular weight or counterface surface
finish, on a more practical basis than is possible in joint simulator tests.
A1.2 Criteria for Appropriate Test Results
A1.2.1 Rationale—Because there are subtle test method variables which will exist, even for a highly detailed test method such as
F732 − 17
this, it is necessary to identify characteristics of test results which must be met to ensure that they are representative of clinical
results. Baseline testing should be conducted utilizing material combinations with significant clinical history such as cast CoCr and
gamma-sterilized UHMWPE.
A1.2.2 Reproduction of in vivo Wear Quantities—The baseline test wear quantities should be compared to clinical results. Clinical
data for linear reciprocating wear motion applications are quite sparse. At this time, a suitable guideline for relevant wear quantities
is not clear.
A1.2.3 Reproduction of in vivo Wear Mechanisms—The baseline test wear mechanisms should be representative of those seen
clinically. For linear reciprocating wear motion applications, a baseline CoCr/UHMWPE test should exhibit mild microadhesive/
micro-abrasive wear mechanisms, resulting in a mild burnished or smeared UHMWPE wear surface and no significant loss of
material. The wear motion direction should be apparent on this wear surface. A very thin transfer film may be visible on the CoCr
surface.
A1.2.4 Repeatability and Reproducibility of Results—A minimum of three replicate tests per condition should be conducted; more
if the repeatability relative to mean wear or aggregate wear rate is poor. If the same specimen condition were tested in separate
series, there should be no significant difference in results.
A1.3 Apparatus and Materials
A1.3.1 Description of Specimens and Test Parameters:
A1.3.1.1 Polymer Specimen—The standard polymer specimen is a flat-ended circular cylinder 13 mm [0.50 in.] long and 9.00 mm
2 2
[0.354 in.] in diameter, providing a cross-sectional area of 63.6 mm [0.0986 in. ]. In the wear machine, the polymer specimen is
loaded end-wise against the counterface in a flat-on-flat configuration. This specimen geometry provides a known contact area that
remains constant as the test progresses and wear occurs. Care should be taken to ensure alignment of the specimen end face with
the counter face.
A1.3.1.2 Counterface—The wear counterface may be fabricated in any convenient shape, provided that the contact surface is flat
in the plane of motion of the polymer specimen and extends beyond the extremes of travel of the polymer specimen.
A1.3.1.3 Wear Machine: (1) Specimen Chambers—In the case of a multiple specimen machine, the specimens shall be contained
in individual isolated chambers to prevent contamination of one set of specimens with debris from another test specimen. The
chamber shall be made entirely of corrosion-resistant materials such as acrylic plastic and shall be easily removable from the
machine for thorough cleaning between tests. The wear chambers shall be designed such that the specimen surfaces are immersed
in the lubricant for the duration of the test.
(1) Specimen Chambers—In the case of a multiple specimen machine, the specimens shall be contained in individual isolated
chambers to prevent contamination of one set of specimens with debris from another test specimen. The chamber shall be made
entirely of corrosion-resistant materials such as acrylic plastic and shall be easily removable from the machine for thorough
cleaning between tests. The wear chambers shall be designed such that the specimen surfaces are immersed in the lubricant for
the duration of the test.
(2) Load—The test load of 225 N [50.6 lbf] shall be applied along the longitudinal axis of the polymer specimen, such that
the average contact stress is 3.54 MPa [513 psi]. The loading apparatus must be free to follow the specimen as wear occurs, such
that the applied load is constant to within 63 % for the duration of the test.
(3) Motion—Relative motion between the specimen and the counterface shall be oscillatory. The orientation between sliding
direction and the lay of the surface roughness in each test should be noted. It is recommended that the relative orientation of the
pin and disk be maintained by suitable specimen-holder keying.
(4) Sliding Speed—Specimens shall be run through a 25 mm stroke at a rate of 1 cycle/s, producing an average sliding speed
of 50 mm/s.
(5) Cycle Counter—The machine shall include a cycle counter to record the total number of wear cycles.
(6) Friction—It is recommended that the machine include strain gage instrumentation or other transducers capable of providing
a continuous readout of the tangential (friction) force transmitted across the specimen interface during the test
(2) Load—The test load of 225 N [50.6 lbf] shall be applied along the longitudinal axis of the polymer specimen, such that the
average contact stress is 3.54 MPa [513 psi]. The loading apparatus must be free to follow the specimen as wear occurs, such that
the applied load is constant to within 63 % for the duration of the test
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(3) Motion—Relative motion between the specimen and the counterface shall be oscillatory. The orientation between sliding
direction and the lay of the surface roughness in each test should be noted. It is recommended that the relative orientation of the
pin and disk be maintained by suitable specimen-holder keying.
(4) Sliding Speed—Specimens shall be run through a 25 mm stroke at a rate of 1 cycle/s, producing an average sliding speed
of 50 mm/s.
(5) Cycle Counter—The machine shall include a cycle counter to record the total number of wear cycles.
(6) Friction—It is recommended that the machine include strain gage instrumentation or other transducers capable of providing
a continuous readout of the tangential (friction) force transmitted across the specimen interface during the test.
A1.3.2 Summary of Test Parameter Requirements:
A1.3.2.1 Motion track: linear reciprocating sliding.
A1.3.2.2 Polymer concave/flat/convex: flat-ended cylindrical pin.
A1.3.2.3 Metal concave/flat/convex: flat.
A1.3.2.4 Contact stress: 3.54 MPa.
A1.3.2.5 Lubricant exclusion/exposure: metal re-exposed, polymer not.
A1.3.2.6 Contact “coverage”: polymer surface 100 % coverage.
A1.3.2.7 Contact area interaction ratio: metal wear surface area at least 100 % greater than polymer wear surface area.
A1.3.2.8 Cross-shear of polymer (change in angle of motion relative to metal surface) during a wear cycle: none (0°).
A1.3.2.9 Wear cycle frequency: 1 Hz.
A1.3.2.10 Mean polymer sliding distance per wear cycle: 50 mm.
A1.3.2.11 Mean polymer sliding speed: 50 mm/s.
A2. TEST METHOD FOR FIXED-BEARING BALL-CUP (“HIP-TYPE”) WEAR APPLICATIONS
A2.1 Scope
A2.1.1 The “hip-type” wear test method describes a laboratory method for evaluating the friction and wear properties of
combinations of materials that are being considered for use as the bearing surfaces of fixed-bearing ball/cup devices for total hip
replacement. It is the intent of this test method to rank the materials with regard to friction levels and wear rates under simulated
physiological conditions. However, it must be recognized that, since any one design of fixed-beating ball-cup joint replacement,
even within this restricted scope, performs under slightly different conditions of load, motion, and contact geometry, there may be
no single universally applicable wear screening test for this application. This test method therefore represents only the first stage
in the full characterization of a candidate material.
A2.1.2 All candidate materials should be tested in a joint simulator apparatus using prototype prostheses before being used in
clinical trials in patients. The pin-on-disk test described in this test method is used to quickly and reliably identify those
low-friction, low-wear materials for which the more expensive and time-consuming joint simulator testing is justified. In addition,
the pin-on-disk test can be used to relate wear to material parameters such as polymer molecular weight or counterface surface
finish, on a more practical basis than is possible in joint simulator tests.
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A2.2 Criteria for Appropriate Test Results
A2.2.1 Rationale—Because there are test method variables which will exist, even for a highly detailed method such as this, it is
necessary to identify characteristics of test results which must be met to ensure that they are representative of clinical results.
Clinical history of ball-cup wear predominantly involves th
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