1.1 This guide covers a method for the measurement of the relative extent of oxidation present in HDPE homopolymers and 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 guide.

1.2 Although this guide 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.

FIG. 1 Typical FTIR Spectra of Oxidized UHMWPE, Showing the Definition of an Area-Based Oxidation Index Based on Normalization Using the 1370-cm^-1 Peak

FIG. 2 FTIR Spectra Showing the Carbonyl Absorption Bands

Note 1: Note that both reagents effectively extracted the lipids (the lipid absorption peak is centered at approximately 1740 cm^-1). The tibial insert was fabricated from highly crosslinked and remelted UHMWPE followed by terminal sterilization in EtO gas (Ref. 1).

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.

1.5 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.