ASTM F2102-01
(Guide)Standard Guide for Evaluating the Extent of Oxidation in Ultra-High-Molecular-Weight Polyethylene Fabricated Forms Intended for Surgical Implants
Standard Guide for Evaluating the Extent of Oxidation in Ultra-High-Molecular-Weight Polyethylene Fabricated Forms Intended for Surgical Implants
SCOPE
1.1 This guide describes a method for the measurement of the relative extent of oxidation present in ultra-high-molecular-weight polyethylene (UHMWPE) intended for use in medical implants. The material is analyzed by infrared spectroscopy. The intensity (area) of the carbonyl absorptions (>C=O) centered near 1720 cm-1 is related to the amount of chemically bound oxygen present in the material. Other forms of chemically bound oxygen (C-O-C, C-O-O-C, C-O-H, and so forth) are not captured by this method.
1.2 Although this method may give the investigator a means to compare the relative extent of carbonyl oxidation present in various UHMWPE samples, it is recognized that other forms of chemically bound oxygen may be important contributors to these materials' characteristics.
1.3 The applicability of the infrared method has been demonstrated by many literature reports. This particular method, using the intensity (area) of the C-H absorption centered near 1370 cm-1 to normalize for the sample's thickness, has been validated by an Interlaboratory Study (ILS) conducted according to Practice E691.
1.4 The following precautionary caveat pertains only to the test method portion, Section 5, of this specification:This standard may involve hazardous materials, operations, and equipment. 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 requirements prior to use.
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Designation: F 2102 – 01
Standard Guide for
Evaluating the Extent of Oxidation in Ultra-High-Molecular-
Weight Polyethylene Fabricated Forms Intended for Surgical
Implants
This standard is issued under the fixed designation F 2102; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 bulk oxidation index (BOI)—a sample’s bulk oxida-
tion index (BOI) is the average of the oxidation indices
1.1 This guide describes a method for the measurement of
collected over a 500-μm section at the center of the sample.
the relative extent of oxidation present in ultra-high-molecular-
3.1.1.1 Discussion—Typically, this is a plateau region with
weight polyethylene (UHMWPE) intended for use in medical
the smallest oxidation indices.
implants. The material is analyzed by infrared spectroscopy.
3.1.1.2 Discussion—For samples less than about 8 to 10
The intensity (area) of the carbonyl absorptions (>C=O)
-1
mm thick, this central region may display the sample’s highest
centered near 1720 cm is related to the amount of chemically
oxidation indices, depending on its state of oxidation.
bound oxygen present in the material. Other forms of chemi-
3.1.2 depth locator (DL)—a measurement of the distance
cally bound oxygen (C-O-C, C-O-O-C, C-O-H, and so forth)
from the articular surface, or surface of interest, that a spectrum
are not captured by this method.
was collected and a corresponding OI calculated.
1.2 Although this method may give the investigator a means
3.1.3 oxidation index (OI)—an oxidation index (OI) is
to compare the relative extent of carbonyl oxidation present in
defined as the ratio of the area of the absorption peak(s)
various UHMWPE samples, it is recognized that other forms of
-1
between 1650 and 1850 cm to the area of the absorption
chemically bound oxygen may be important contributors to
-1
peak(s) between 1330 and 1396 cm , as shown in Fig. 1.
these materials’ characteristics.
3.1.4 oxidation index profile—an oxidation index profile is
1.3 The applicability of the infrared method has been
the graphical representation of variation of the sample’s
demonstrated by many literature reports. This particular
oxidation index with distance from its articular surface or the
method, using the intensity (area) of the C-H absorption
-1
surface of interest. This is a plot of an OI versus DL. Typically,
centered near 1370 cm to normalize for the sample’s thick-
the graph will show the profile through the entire thickness of
ness, has been validated by an Interlaboratory Study (ILS)
the sample.
conducted according to Practice E 691.
3.1.5 surface oxidation index (SOI)—a sample’s surface
1.4 The following precautionary caveat pertains only to the
oxidation index (SOI) is the average of the oxidation indices
test method portion, Section 5, of this specification: This
from the sample’s articular surface, or the surface of interest, to
standard may involve hazardous materials, operations, and
a depth of 3-mm subsurface.
equipment. This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Apparatus
responsibility of the user of this standard to establish appro-
4.1 Infrared Spectrometer:
priate safety and health practices and determine the applica-
4.1.1 A calibrated infrared spectrometer capable of record-
bility of regulatory requirements prior to use.
ing a transmission absorption spectrum over the range of about
-1
2. Referenced Documents 1200 to about 2000 cm using about 200-mm-thick films at a
-1
resolution of 4 cm and an aperture of about 200 by 200 μm.
2.1 ASTM Standards:
4.1.1.1 Other modes of collection (that is, percent reflection,
E 691 Practice for Conducting an Interlaboratory Study to
attenuated total reflection (ATR), and so forth) and aperture
Determine the Precision of a Test Method
and increment sizes may be used to generate the sample’s
3. Terminology absorption spectrum provided they can be demonstrated to
produce equivalent results. Too large an aperture can result in
3.1 Definitions:
a loss of profile accuracy.
4.1.1.2 When a Fourier Transform Infrared (FTIR) spec-
This guide is under the jurisdiction of ASTM Committee F04 on Medical and
trometer is used, a minimum of 32 scans shall be collected per
Surgical Materials and Devicesand is the direct responsibility of Subcommittee
spectrum.
F04.15on Material Test Methods.
4.1.1.3 The FTIR instrument and sample compartment
Current edition approved May 10, 2001. Published June 2001.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F 2102
6.1.1 For each absorbance spectrum calculate the total area
-1
of the peak absorptions between 1650 and 1850 cm (see Fig.
1).
6.1.1.1 This is the area below the sample’s absorption curve
and above the straight line baseline drawn between the same
-1
starting and ending points, namely, 1650 and 1850 cm .
6.2 Normalization Peak Area:
6.2.1 For each absorbance spectrum, calculate the total area
-1
of the peak absorptions between 1330 and 1396 cm (see Fig.
1).
6.2.1.1 This is the area below the sample’s absorption curve
and above the straight line baseline drawn between the same
-1
starting and ending points, namely, 1330 and 1396 cm .
6.3 Oxidation Index (OI):
6.3.1 For each absorbance spectrum, calculate its OI by
dividing the area of its oxidation peak (6.1) by the area of its
FIG. 1 Typical FTIR Spectra of Oxidized UHMWPE, Showing the
normalization peak (6.2), as shown in Fig. 1.
Definition of an Area-Based Oxidation Index Based on
-1
6.4 Oxidation Index Depth Locator (DL):
Normalization Using the 1370-cm Peak
6.4.1 Calculate the distance from the articular surface, or
surface of interest (DL), for each spectrum and its correspond-
should be purged with a moisture- and carbon-dioxide-free
ing OI from the following equation.
inert gas (for example, nitrogen, helium, or argon) to minimize
spectral interference from these components.
DL 5 0.5~A! 1 n~S!
4.2 Specimen Holder:
where:
4.2.1 Equipment capable of accurately positioning the
A = the size of the aperture in micrometres in the step
sample under the orifice in increments at the scale of the
direction,
aperture dimensions.
n = the number of steps (increments) the aperture had been
4.3 Microtome:
moved from its initial location at the articular surface
4.3.1 Equipment capable of producing about 200-μm-thick
or surface of interest, and
slices (films) of a sample perpendicular to the articular surface
S = the step (increment) size in micrometres.
or the surface of interest.
6.5 Sample’s Oxidation Index Profile:
5. Procedure 6.5.1 Construct a plot of a sample’s oxidation indices (OI)
versus their corresponding depth locators (DL).
5.1 Preparation of the Infrared Spectrometer:
6.6 Surface Oxidation Index (SOI):
5.1.1 Prepare the infrared spectrometer for collection of a
6.6.1 Calculate a sample’s SOI by calculating the average of
transmission absorption spectrum from a thin film of the
the sample’s oxidation indices (OI) with depth locator (DL)
UHMWPE sample according to the manufacturer’s recommen-
values between 0 and 3000.
dations and the conditions described in Section 4 above.
6.7 Bulk Oxidation Index (BOI):
5.1.2 Collect the sequence of spectra per 5.2 and 5.3.
6.7.1 Calculate a sample’s BOI by calculating the average
5.2 Preparation of Test Specimen:
of the sample’s oxidation indices (OI) corresponding to the
5.2.1 Using a microtome, or other appropriate device, pre-
center 500 mm of material.
pare a thin slice of the sample about 200 μm thick.
5.2.2 The slice shall typically be taken near the center of the
7. Report
sample’s articular surface or the surface of interest.
7.1 The report shall contain at least the following experi-
5.2.3 The orientation of the slice shall typically be perpen-
mental details and results:
dicular to the articular surface or the surface of interest.
7.1.1 Material Information:
5.3 Configuration of the Test Specimen in the Spectrometer:
7.1.1.1 Resin type and resin lot number.
5.3.1 The test film (slice) shall be first configured in the
7.1.1.2 Consolidation method and manufacturer and manu-
spectrometer (after an appropriate background spectrum has
facturer lot number.
been collected) such that the aperture is positioned over the
7.1.1.3 Any special postconsolidation treatments, for ex-
first 200 μm of the film starting at the surface of interest.
ample, HIPing, annealing, sterilization, cross-linking, stabili-
5.3.2 Subsequent spectra shall be collected sequentially at
zation, accelerated aging, and storage conditions.
increments matching the aperture size (that is, about 200 μm)
7.1.2 Sample Information:
from the articular surface, or surface of interest, across the
7.1.2.1 Orthopedic implant or laboratory test specimen.
width of the film to the opposite surface.
7.1.2.2 Articular surface or nonarticulator surface.
5.3.2.1 Larger increments may be used; however, too large
7.1.2.3 Test sample’s original dimensions.
an increment size may result in a loss of profile accuracy.
7.1.2.4 Any special posttreatments of the original test
6. Calculations
sample, for example, annealing, sterilization, cross-linking,
6.1 Oxidation Peak Area: stabilization, accelerated aging, and storage conditions.
F 2
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