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Wear Surfaces of Highly Crosslinked Components
Rieker, C., Schneider, W., Konrad, R., Schn, R.
Abstract
Highly crosslinked UHMWPEs were developed to significantly lower the amount of UHMWPE wear in arthroplasty. These UHMWPEs have demonstrated a significant improvement in the in-vitro adhesive - abrasive wear resistance of total joint prostheses.
One commercially available highly crosslinked UHMWPE (DURASUL) is manufactured as follows: The raw material, GUR 1050 pressed sheets, is crosslinked by irradiation at 125°C using a 10-MeV electron-beam accelerator at a total dose level of 9.5 Mrad. Following irradiation, the samples are melt-annealed at 150°C.
The SEM surface analysis of knee simulator DURASULô mobile inserts tested according to ISO/FDIS 14'243-1 kinematics showed the presence of microcracks at the distal interface. These microcracks were also episodically seen on some retrieved DURASUL acetabular liners revised for reasons unrelated to wear. The depth of these microcracks was examined under an optical microscope and TEM on perpendicular sections. The maximum measured depth was smaller than 2 µm. To investigate the relevance of these microcracks, a specific test was developed using two DURASUL acetabular liners articulating on a metallic head with a load of 2060 N. All tests were conducted at 37°C in a lubricant containing 33% calf serum and 67% Ringer's solution. The same microcracks could be reproduced on the liners after 100,000 cycles. A higher number of cycles (up to 1 million) did not increase the density of these microcracks. Perpendicular sections of the liners were examined optically to determine the depth of these microcracks. The maximum measured depth was consistently smaller than 2 µm as well as independent of the number of cycles.
Due to their stable behaviour (density and depth not influenced by the number of cycles), these microcracks can be described as a surface feature without detrimental influences on the mechanical performance of components manufactured with DURASUL.
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