NIST Reference Materials
Reference UHMWPE is intended to be a consistent material that can be used as a control in experiments, thereby serving as a common reference for academia and industry. Reference materials are subjected to extensive testing, stored in a controlled environment, and are accompanied by a test report documenting their properties. Historically, there have been two widely used reference materials in orthopedics. The first was organized by the Hospital for Special Surgery in the mid 1990s, and later, when the initial supply of reference material was exhausted, the torch was passed to the National Institutes of Standards and Technology (NIST) to maintain a common reference of medical grade UHMWPE. This section of the website provides an overview for both HSS and NIST reference materials, along with relevant links.
-S.M. Kurtz, August 14, 2009
HSS Reference Material
In the mid 1990s, it was recognized that variability in processing conditions and different resins resulted in variations in the properties of consolidated UHMWPE, and that "these variations make comparative data between experiments and other research groups inaccurate or inconclusive" (Bennett et al., Trans ORS 1996). Researchers at the Hospital for Special Surgery (HSS) in New York organized a grandly titled, "Global Reference UHMWPE" to be used as a control in experiments. Informally, this material was also known as HSS Reference Material.
Researchers agreed with Ticona to donate GUR 415 resin from a single lot to the program, and consolidator Poly Hi Solidur agreed to donate 1000 feet of ram extruded material. The single extrusion run was characterized, stored, and distributed in 5-foot lengths by HSS. The properties of this reference material were published at the 1996 meeting of the Orthopedic Research Society:
Bennett AP, Wright TM, Li S. Global reference UHMWPE: Characterization and comparison to commercial UHMWPE. Transactions of the 1996 ORS, p. 472.
Around this time, HSS reference material was distributed internationally to 75 research laboratories. This program lasted until the late 1990s, when the program was disbanded. The costs of storing and shipping the material internationally for free proved to be impractical for HSS to duplicate, so the next round of reference material was orchestrated by NIST.
NIST Reference Materials
The National Institutes of Standards and Technology has developed a standard reference biomaterial based on ram extruded GUR 1050. Researchers from the National Institutes of Standards and Technology presented the characterization of Reference Material No. 8456 in Poster No. 472 at the Society for Biomaterials:
F. C. Eichmiller, J. Tesk, C. M. Croarkin, "Mechanical Properties of Ultra High Molecular Weight Polyethylene NIST Reference Material #8456"
Reference medical grade UHMWPE is currently available from NIST in three forms, as extruded rod, 5-mm cubes, and as wear particles. All three types of reference UHMWPE can be purchased from NIST reference material program via the NIST website.
Extruded Rod Reference Material:
Reference biomaterial (RM 8456) is currently supplied as a 7.6 cm (3-inch) diameter, 152 cm (5-foot) length rod sample of GUR 1050, which can be used to make bulk specimens. Click here to download the PDF certificate of analysis for the extruded rod sample of medical grade, UHMWPE reference material (RM 8456).
Machined Cube Reference Material:
The same GUR 1050 reference UHMWPE biomaterial has been machined into 5 mm cubes as reference samples (RM 8457) to be used in swell ratio measurements. Click here to download the PDF certificate of analysis for the 5 mm cube samples of medical grade, UHMWPE reference material (RM 8457).
Wear Particulate Reference Material:
Most recently, in 2007, NIST created a third reference particulate material generated using pins fabricated from gamma-sterilized, HSS reference UHMWPE (GUR 415). These gamma-sterilized pins were used to generate particles in a pin-on-disc apparatus. Thus, the microscopic UHMWPE wear particles are supplied in sealed vials (RM 8385). Click here to download the PDF certificate of analysis for the NIST reference wear particles (RM 8385). Note that this material should be considered a historical reference only; the current designation for GUR 415 is now GUR 4150 and the resin is now only available for industrial applications.