ASTM F2003-02(2008)
(Practice)Standard Practice for Accelerated Aging of Ultra-High Molecular Weight Polyethylene after Gamma Irradiation in Air
Standard Practice for Accelerated Aging of Ultra-High Molecular Weight Polyethylene after Gamma Irradiation in Air
SIGNIFICANCE AND USE
This practice summarizes a method that may be used to accelerate the oxidation of UHMWPE components using elevated temperature and elevated oxygen pressure. Under real-time conditions, such as shelf aging and implantation, oxidative changes to UHMWPE after sterilization using high energy radiation may take months or years to produce changes that may result in deleterious mechanical performance. The method outlined in this practice permits the evaluation of oxidative stability in a relatively short period of time (for example, weeks).
This practice may also be used to oxidize UHMWPE test specimens and joint replacement components prior to characterization of their physical, chemical, and mechanical properties. In particular, this practice may be used for accelerated aging of UHMWPE components prior to evaluation in a hip or knee joint wear simulator as outlined in Guide F 1714 (hip wear), Guide F 1715 (knee wear), ISO 14242 (hip wear), or ISO 14243 (knee wear), or combination thereof.
SCOPE
1.1 It is the intent of this practice to permit an investigator to evaluate the oxidative stability of UHMWPE materials as a function of processing and sterilization method. This practice describes a laboratory procedure for accelerated aging of ultra-high molecular weight polyethylene (UHMWPE) specimens and components for total joint prostheses. The UHMWPE is aged at elevated temperature and at elevated oxygen pressure, to accelerate oxidation of the material and thereby allow for the evaluation of its long-term chemical and mechanical stability.
1.2 Although the accelerated-aging method described by this practice will permit an investigator to compare the oxidative stability of different UHMWPE materials, it is recognized that this method may not precisely simulate the degradative mechanisms for an implant during real-time shelf aging and implantation.
1.3 The accelerated aging method specified herein has been validated based on oxidation levels exhibited by certain shelf-aged UHMWPE components packaged in air and sterilized with gamma radiation. The method has not been shown to be representative of shelf aging when the UHMWPE is packaged in an environment other than air. For example, this practice has not been directly correlated with the shelf life of components that have been sealed in a low-oxygen package, such as nitrogen. This practice is not intended to simulate any change that may occur in UHMWPE following implantation.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F2003 − 02(Reapproved 2008)
Standard Practice for
Accelerated Aging of Ultra-High Molecular Weight
Polyethylene after Gamma Irradiation in Air
This standard is issued under the fixed designation F2003; 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 priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 It is the intent of this practice to permit an investigator
to evaluate the oxidative stability of UHMWPE materials as a
2. Referenced Documents
function of processing and sterilization method. This practice
2.1 ASTM Standards:
describes a laboratory procedure for accelerated aging of
D883 Terminology Relating to Plastics
ultra-high molecular weight polyethylene (UHMWPE) speci-
F648 Specification for Ultra-High-Molecular-Weight Poly-
mens and components for total joint prostheses. The UHM-
ethylene Powder and Fabricated Form for Surgical Im-
WPE is aged at elevated temperature and at elevated oxygen
plants
pressure, to accelerate oxidation of the material and thereby
F1714 GuideforGravimetricWearAssessmentofProsthetic
allow for the evaluation of its long-term chemical and me-
Hip Designs in Simulator Devices
chanical stability.
F1715 Guide for Wear Assessment of Prosthetic Knee De-
1.2 Although the accelerated-aging method described by
signs in Simulator Devices (Withdrawn 2006)
this practice will permit an investigator to compare the
2.2 ISO Standards:
oxidative stability of different UHMWPE materials, it is
ISO 5834 Implants for surgery—Ultra-high molecular
recognized that this method may not precisely simulate the
weight polyethylene
degradative mechanisms for an implant during real-time shelf
ISO 14242 Implants for surgery—Wear of total hip joint
aging and implantation.
prostheses
1.3 The accelerated aging method specified herein has been
ISO 14243 Implants for surgery—Wear of total knee joint
validated based on oxidation levels exhibited by certain shelf-
prostheses
aged UHMWPE components packaged in air and sterilized
3. Terminology
with gamma radiation. The method has not been shown to be
representative of shelf aging when the UHMWPE is packaged
3.1 Definitions—For definitions of terms in this practice
in an environment other than air. For example, this practice has
relating to plastics, refer to Terminology D883. For definitions
not been directly correlated with the shelf life of components
of terms in this practice relating to UHMWPE, refer to
that have been sealed in a low-oxygen package, such as
Specification F648 and ISO 5834.
nitrogen. This practice is not intended to simulate any change
3.2 Definitions of Terms Specific to This Standard:
that may occur in UHMWPE following implantation.
3.2.1 oxidation, n—theincorporationofoxygenintoanother
1.4 The values stated in SI units are to be regarded as
molecule (for example, UHMWPE) by means of a chemical
standard. The values given in parentheses are mathematical
reaction, resulting in the formation of a chemical covalent
conversions to inch-pound units that are for information only
bond.
and are not considered standard.
3.2.2 oxygen bomb, n—a pressure vessel suitable for pre-
1.5 This standard does not purport to address all of the
conditioning of UHMWPE at an elevated temperature and
safety concerns, if any, associated with its use. It is the
partial pressure of oxygen.
responsibility of the user of this standard to establish appro-
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
ThispracticeisunderthejurisdictionofASTMCommitteeF04onMedicaland Standards volume information, refer to the standard’s Document Summary page on
Surgical Materials and Devices and is the direct responsibility of Subcommittee the ASTM website.
F04.15 on Material Test Methods. The last approved version of this historical standard is referenced on
Current edition approved May 1, 2008. Published June 2008. Originally www.astm.org.
approved in 2002. Last previous edition approved in 2002 as F2003 – 02. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/F2003-02R08. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2003 − 02 (2008)
4. Significance and Use controller, capable of controlling the heating rate with an
accuracy of 0.1°C/min.
4.1 This practice summarizes a method that may be used to
accelerate the oxidation of UHMWPE components using NOTE 2—Temperature stability and test interruption has been shown to
significantly influence the outcome of accelerated aging studies.
elevated temperature and elevated oxygen pressure. Under
Consequently, the pressure vessel must maintain nearly constant tempera-
real-time conditions, such as shelf aging and implantation,
ture (that is, within 61°C) throughout the duration of the testing period,
oxidative changes to UHMWPE after sterilization using high
or the results may not be reproducible or may be unreliable.
energy radiation may take months or years to produce changes
that may result in deleterious mechanical performance. The
6. Test Specimens
method outlined in this practice permits the evaluation of
6.1 The test specimens shall be prepared in final form
oxidative stability in a relatively short period of time (for
according to the requirements of any subsequent physical,
example, weeks).
chemical, or mechanical tests to be performed after accelerated
4.2 This practice may also be used to oxidize UHMWPE
aging. For example, if the specimens will ultimately be
test specimens and joint replacement components prior to
subjected to hip joint simulation, they should be prepared in
characterization of their physical, chemical, and mechanical
final form according to Guide F1714 and ISO 14242.
properties. In particular, this practice may be used for acceler-
6.2 Finished specimens shall not be machined after accel-
ated aging of UHMWPE components prior to evaluation in a
erated aging of (bulk) stock materials, because the accelerated
hip or knee joint wear simulator as outlined in Guide F1714
oxidation procedure outlined in this practice will result in an
(hipwear),GuideF1715(kneewear),ISO 14242(hipwear),or
inhomogeneous distribution of chemical, physical, and hence
ISO 14243 (knee wear), or combination thereof.
mechanical properties through the thickness of an aged part.
5. Apparatus
6.3 Test specimens shall be removed from their packaging
prior to accelerated aging, because this practice is not intended
5.1 Combined Apparatus—An oxygen bomb (pressure ves-
to reproduce the aging of UHMWPE that is stored in a low
sel) apparatus that is capable of maintaining the desired
oxygen environment.
temperature with an accuracy of 62°C by itself may be used,
providing it incorporates the requirements of 5.2-5.4.
7. Validation of Apparatus
5.2 Pressure Vessel—If a combined apparatus is not used, it
7.1 Thermal Chamber Validation—Using the calibrated
will be necessary to enclose the specimens within a pressure
temperature sensor, validate the temperature of the accelerated
vessel, also known as an “oxygen bomb,” capable of with-
aging apparatus to within 61°C of the aging temperature.
standing a static pressure of 690 kPa (100 psi). The pressure
7.1.1 Verify the calibration of the temperature sensor(s) that
vessel shall be manufactured from stainless steel. The pressure
will be used to validate the thermal conditions in the acceler-
vessel shall be equipped with either a regulator or a safety
ating aging apparatus. The temperature sensor shall be cali-
release valve to maintain the internal pressure to the desired
brated as defined in the manufacturer’s instructions.
value,whenatequilibrium,toanaccuracyof 67kPa(61psi).
7.2 Pressure Vessel Validation—Verify the integrity of the
5.3 Because oxygen-air mixtures will be maintained at
pressure vessel to within 67 kPa (61 psi) by conducting the
elevated temperatures for weeks at a time, it is recommended
following 14-day (336 6 1 h) validation test:
that a laboratory that is performing aging at elevated pressure
7.2.1 Increase the pressure of pure oxygen inside the vessel
take appropriate safety precautions. For this reason, the use of
by 503 kPa (73 psi) at 70 6 1°C.
a commercially available and properly validated “oxygen
7.2.2 Throughout the duration of the validation test, the
bomb” is recommended. The pressure vessel must be of
gage pressure shall not vary by 67 kPa (61 psi).
suitable construction such that it does not leak, thereby leading
7.2.3 Pressure vessels that are not capable of maintaining
to the reduction of pressure during the two-week aging period.
the target gage pressure within the stated tolerance shall be
NOTE 1—Oxygen flow and test interruption have been shown to
significantly influence the outcome of accelerated aging studies. considered invalid for the purposes of accelerated aging until
Consequently, the pressure vessel must maintain nearly constant pressure
the excessive leaking has been rectified.
(that is, within 67 kPa or 1 psi) throughout the duration of the testing
period, or the results may not be reproducible or may be unreliable. 7.3 The thermal chamber and pressure vessel shall be
validated at least once per year, unless otherwise indicated by
5.4 ThermalChamber—Ifacombinedapparatusisnotused,
a specification or customer.
accelerated aging of the UHMWPE shall be conducted using a
thermal chamber that can maintain the desired temperature
8. Conditioning
withanaccuracyof 62°C.Thespatial
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:F2003–00
Standard Guide for Accelerated Aging of Ultra-High Molecular
Weight Polyethylene Designation:F2003–02 (Reapproved
2008)
Standard Practice for
Accelerated Aging of Ultra-High Molecular Weight
Polyethylene after Gamma Irradiation in Air
This standard is issued under the fixed designation F 2003; 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
1.1It is the intent of this guide to permit an investigator to investigate the oxidative stability of ultra-high molecular weight
polyethylene (UHMWPE) materials as a function of processing and sterilization method. This guide describes a laboratory test
method for accelerated aging of UHMWPE specimens and components for total joint prostheses. The UHMWPE is aged at
elevated temperatures and, alternatively, at elevated partial pressures of oxygen, to accelerate oxidation of the material and thereby
allow for the evaluation of its long-term chemical and mechanical stability.
1.2Although the accelerated-aging test methods described by this guide will permit an investigator to compare the oxidative
stability of UHMWPE, it is recognized that these test methods may not precisely simulate the degradative mechanisms for an
implant during real-time shelf aging and implantation. However, these accelerated oxidation methods have been successfully used
to rank UHMWPE materials for their long-term oxidative stability.
1.3The accelerated aging test methods specified herein have been validated based on oxidation levels exhibited by certain
shelf-aged UHMWPE components packaged in air and sterilized with gamma radiation. The methods have not been shown to be
representative of shelf aging when the UHMWPE is packaged in an environment other than air. For example, these test methods
have not been directly correlated with the shelf life of components that have been sealed in a low-oxygen package, such as
nitrogen.
1.4
1.1 It is the intent of this practice to permit an investigator to evaluate the oxidative stability of UHMWPE materials as a
function of processing and sterilization method. This practice describes a laboratory procedure for accelerated aging of ultra-high
molecular weight polyethylene (UHMWPE) specimens and components for total joint prostheses. The UHMWPE is aged at
elevated temperature and at elevated oxygen pressure, to accelerate oxidation of the material and thereby allow for the evaluation
of its long-term chemical and mechanical stability.
1.2 Although the accelerated-aging method described by this practice will permit an investigator to compare the oxidative
stabilityofdifferentUHMWPEmaterials,itisrecognizedthatthismethodmaynotpreciselysimulatethedegradativemechanisms
for an implant during real-time shelf aging and implantation.
1.3 The accelerated aging method specified herein has been validated based on oxidation levels exhibited by certain shelf-aged
UHMWPE components packaged in air and sterilized with gamma radiation. The method has not been shown to be representative
of shelf aging when the UHMWPE is packaged in an environment other than air. For example, this practice has not been directly
correlated with the shelf life of components that have been sealed in a low-oxygen package, such as nitrogen. This practice is not
intended to simulate any change that may occur in UHMWPE following implantation.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions
to inch-pound units that are for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
This guide is under the jurisdiction of ASTM Committee F-4 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee F04.15
on Test Material Methods.
Current edition approved Jan. 10, 2000. Published April 2000.
This practice is under the jurisdiction ofASTM 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 May 1, 2008. Published June 2008. Originally approved in 2002. Last previous edition approved in 2002 as F 2003 – 02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2003–02 (2008)
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D 883 Terminology Relating to Plastics
F 648 Specification ofor Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants
F 1714 Guide for Gravimetric Wear Assessment of Prosthetic Hip-Designs in Simulator Devices
F 1715 Guide for Gravimetric Wear Assessment of Prosthetic Knee- Designs in Simulator Devices
2.2 ISO Standards:
ISO 5834 Implants for surgery—Ultra-high molecular weight polyethylene
ISO 14242 Implants for surgery—Wear of total hip joint prostheses
ISO 14243 Implants for surgery—Wear of total knee joint prostheses
3. Terminology
3.1 Definitions— For definitions of terms in this guidepractice relating to plastics, refer to Terminology D 883. For definitions
of terms in this guidepractice relating to UHMWPE, refer to Specification F 648 and ISO 5834.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 oxidation, n—the incorporation of oxygen into another molecule (for example, UHMWPE) by means of a chemical
covalent bond. —the incorporation of oxygen into another molecule (for example, UHMWPE) by means of a chemical reaction,
resulting in the formation of a chemical covalent bond.
3.2.2 oxygen bomb, n—a pressure vessel suitable for preconditioning of UHMWPE at an elevated temperature and partial
pressure of oxygen.
4. Significance and Use
4.1 This guidepractice summarizes test methodsa method that may be used to accelerate the oxidation of UHMWPE
components using elevated temperatures and, alternatively, temperature and elevated partial pressures of oxygen. oxygen pressure.
Under real-time conditions, such as shelf aging and implantation, oxidative changes to UHMWPE after sterilization using high
energy radiation may take months or years to produce changes that may result in deleterious mechanical performance. The test
methods method outlined in this guide permitpractice permits the evaluation of oxidative stability in a relatively short period of
time (for example, weeks).
4.2 This guidepractice may also be used to preconditionoxidize UHMWPE test specimens and joint replacement components
prior to characterization of their physical, chemical, and mechanical properties. In particular, this guidepractice may be used for
preconditioningaccelerated aging of UHMWPE components prior to evaluation in a hip or knee joint wear simulator as outlined
in Guide F 1714 (hip wear), Guide F 1715 (knee wear), ISO 14242 (hip wear), or ISO 14243 (knee wear), or combination thereof.
5. Apparatus and Materials Apparatus
5.1 UHMWPE Test Specimens—The test specimens shall be prepared in final form in accordance with the requirements of any
subsequent physical, chemical, or mechanical tests to be performed after preconditioning. For example, if the specimens will
ultimately be subjected to hip joint simulation, they should be prepared in final form in accordance with Guide F1714 and
ISO14242. Because the accelerated oxidation methods outlined in this guide result in inhomogeneous distribution of chemical,
physical, and hence mechanical properties through the thickness of a preconditioned part, it is not recommended that finished test
specimens be machined after preconditioning of (bulk) stock materials. Because this guide is not intended to reproduce the aging
of UHMWPE that is stored in a low-oxygen environment, test specimens should be removed from their packaging prior to
preconditioning.
5.2Preconditioning Chamber—Accelerated oxidation (preconditioning) of the UHMWPE shall be conducted in a convection,
air circulating oven that can maintain the desired temperature with an accuracy of 62°C. The spatial variation of temperature
within the oven shall be measured using thermocouples and verified to be less than 61°C.The chamber will need to be sufficiently
large to accommodate a pressure vessel, if it is desired to precondition the UHMWPE at an elevated partial pressure of oxygen.
An oxygen bomb (pressure vessel) that is capable of maintaining the desired temperature with an accuracy of 62°C by itself may
beused.CombinedApparatus—Anoxygenbomb(pressurevessel)apparatusthatiscapableofmaintainingthedesiredtemperature
with an accuracy of 62°C by itself may be used, providing it incorporates the requirements of 5.2-5.4.
5.2 Pressure Vessel—Ifacombinedapparatusisnotused,itwillbenecessarytoenclosethespecimenswithinapressurevessel,
also known as an “oxygen bomb,” capable of withstanding a static pressure of 690 kPa (100 psi). The pressure vessel shall be
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
, Vol 08.01.volume information, refer to the standard’s Document Summary page on the ASTM website.
Annual Book of ASTM Standards, Vol 13.01.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
F2003–02 (2008)
manufacturedfromstainlesssteel.Thepressurevesselshallbeequippedwitheitheraregulatororasafetyreleasevalvetomaintain
the internal pressure to the desired value, when at equilibrium, to an accuracy of 67 kPa (61 psi).
5.3 Because oxygen-air mixtures will be maintained at elevated temperatures for weeks at a time, it is recommended that a
laboratory that is performing aging at elevated pressure take appropriate safety precautions. For this reason, the use of a
commercially available and properly validated “oxygen bomb” is recommended. The pressure vessel must be of suitable
construction such that it does not leak, thereby leading to the reduction of pressure during the two-week aging period.
NOTE1—Itmaybedesirabletouseanovenwiththecapabilityofheatingthetestspecimenatacontrolledheatingratewithanaccuracyof 60.1°C/min.
5.3Pressure Vessel—When preconditioning UHMWPE at elevated partial pressures of oxygen, it will be necessary to enclose
the specimens within a pressure vessel, also known as an oxygen bomb, capable of withstanding a static pressure of 690 kPa (100
psi).The pressure vessel shall be manufactured from stainless steel or aluminum.The pressure vessel shall be equipped with either
a regulator or a safety release valve to maintain the internal pressure to the desired value, when at equilibrium, to an accuracy of
67 kPa (61 psi). Because oxygen-air mixtures will be maintained at elevated temperatures for weeks at a time, it is recommended
that appropriate safety precautions be taken by a laboratory performing preconditioning at elevated partial pressures. For this
reason, the use of a commercially available and properly validated oxygen bomb is recommended.
6.Preconditioning Test Methods 1—Oxygen flow and test interruption have been shown to significantly influence the
outcome of accelerated aging studies. Consequently, the pressure vessel must maintain nearly constant pressure (that
is, within 67 kPa or 1 psi) throughout the duration of the testing period, or the results may not be reproducible or
may be unreliable.
5.4 Thermal Chamber— If a combined apparatus is not used, accelerated aging of the UHMWPE shall be conducted using a
thermal chamber that can maintain the desired temperature with an accuracy of 62°C. The spatial variation of temperature within
the thermal chamber shall be measured using thermocouples and verified to be less than 61°C. Note that the thermal chamber will
need to be sufficiently large to accommodate the pressure vessel, described in 5.2.
5.5 Test Method A (Ambient Air Preconditioning)—Conduct Test Method A in a suitable thermal chamber. Precondition test
specimens at a constant temperature of 80°C for 3 weeks prior to subsequent testing. Temperature Controller—The combined
apparatus or thermal chamber shall be equipped with a temperature controller, capable of controlling the heating rate with an
accuracy of 0.1°C/min.
NOTE2—To maximize the extent and penetration of oxidative degradation into bulk hip or knee components using Test MethodA, it is recommended
that specimens be inserted into the thermal chamber while at room temperature, and that the chamber be elevated to the constant preconditioning
temperature at a slow constant heating rate, ranging from 0.1 to 0.6°C/min (1) 2—Temperature stability and test interruption has been shown to
significantly influence the outcome of accelerated aging studies. Consequently, the pressure vessel must maintain nearly constant temperature (that is,
within 61°C) throughout the duration of the testing period, or the results may not be reproducible or may be unreliable.
6. Test Specimens
6.1 The test specimens shall be prepared in final form according to the requirements of any subsequent physical, chemical, or
mechanical tests to be performed after accelerated aging. For example, if the specimens will ultimately be subjected to hip joint
simulation, they should be prepared in final form according to Guide F 1714 and ISO 14242.
6.2Test Method B (Preconditioning at Elevated Partial Pressures of Oxygen)—Conduct Test Method B using an oxygen bomb
placed inside a suitable thermal chamber. Precondition test specimens at a constant temperature of 70°C and at an equilibrium
pressure of 503 kPa (73 psi, 5 atmospheres) of pure oxygen for 2 weeks prior to subsequent testing.
6.3Regardless of the preconditioning test method used (Test Method A or B), array the test specimens within the test chamber
or oxygen bomb such that all relevant surfaces have equivalent access to oxygen during the test. For example, with hip and knee
components, the articulating surface which may subsequently be subjected to wear simulation shall not be obstructed or covered
by other parts or mate
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