September 2001

MORPHOLOGY INDEX ROUND ROBIN (ISO/WD 5834-2, Technical Contact: S. Kurtz)

A scoring system for rating the morphology of UHMWPE has been implemented in ASTM F648 and is under consideration for inclusion in ISO 5834-2. A round robin is proposed to assess the repeatability and reproducibility of the "morphology index." Based on input provided to the group so far, the variables that are expected to control the apparent Morphology Index include not only the presence of defects, but also the thickness of the sample. S. Kurtz will coordinate the distribution of a set of UHMWPE samples with varying thickness and defect content.

At present, 10 institutions from Germany, United States, Great Britain, Romania, and Turkey have volunteered to participate in the round robin. It is desired to recruit up to 15 performance sites to participate, so if you are interested, please contact me. The round robin will be organized and launched no later than November 2001.

ACCELERATED AGING STANDARD (ISO/WD 5834-3, Technical Contact: S. Kurtz)

In light of the reproducibility documented** for the existing ASTM aging standard (ASTM F2003-00), there is a desire by the ISO working group to more narrowly define the experimental conditions (and perhaps the apparatus) associated with the standard aging methods. Potential variables which may influence aging results are believed to include:

• Heating/cooling rates
• Timing between specimen irradiation and start of aging
• Timing between aging and specimen evaluation
• Validation of temperature/pressure settings
• Validation of aging results
• Test interruptions/oxygen flow out of a pressure vessel
• Total mass loading of bomb/oven
• Acceptable tolerances for temperature, time, variation, etc.

At present, the goal is to identify institutional knowledge which may be useful in establishing acceptable limits for these test parameters. The goal at present is to collect information from the current end users of the aging standard for consideration in developing the next working draft for the ISO standard. If consensus can be reached regarding the next iteration of the aging standard, then it would be reasonable to begin organizing a new round robin to evaluate what effect, if any, the proposed procedural details may have on the reproducibility/repeatability.

**Kurtz SM, Muratoglu OK, Buchanan F, Currier B, Gsell R, Greer K, Gualtieri G, Johnson R, Schaffner S, Sevo S, Spiegelberg S, Shen FW, Yau SS. Interlaboratory reproducibility of standard accelerated aging methods for oxidation of UHMWPE. Biomaterials 2001; 22: 1731-1737.

OXIDATION INDEX STANDARD (ISO/WD 5834-4, Technical Contact: R. Gsell)

The first draft of the standard was informally distributed at Canberra and discussed. The revised draft will be officially circulated and debated at the ISO meeting next year in Alexandria, Va.

Acknowledgement

Special thanks to Marta Villarraga, Exponent, Inc., for providing coverage of the ISO meetings in Canberra and for contributing to this summary.

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