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Comparison of Cross-Linked and Conventional UHMWPE Wear Debris
Wimmer, M. A., Sprecher, C.
Abstract
Cross-linking of UHMWPE has provided a considerable reduction in wear volume. The purpose of the study was to compare the particle morphology (size and shape) of commercially available cross-linked UHMWPE against conventional (standard) UHMWPE.
A hip wear simulation device was used to generate wear debris. Biaxial motion of 1.8 Hz was carried out in 33% diluted calf serum (37°C) at a constant compressive load of 1000N for 5 million cycles. The two PE-materials tested were a commercially available cross-linked PE (Durasul) and the so-called "HSS Reference PE" (conventional, ram-extruded polyethylene). Both materials were not sterilized.
The generated wear particles were separated from the serum according to a previously published method using a polycarbonate filter of 0.1µm pore size. Isolated particles on filters were sputter coated with 10nm Au/Pd (80/20%) for Scanning Electron Microscopy (SEM) analysis. The parameters circularity and equivalent circle diameter (ECD) were determined.
SEM images of reference PE showed circular-round and elongated particles. Larger particles were more fibrillar and twisted. In general, the particles of cross-linked PE were smaller in size compared with reference PE and more round in shape. There were no fibrils. Over 96% of reference PE and over 98% of cross-linked PE particles were smaller than 1µm. Nearly 95% of the cross-linked PE particles were smaller than 0.35 µm (compared with 50% of reference PE). The average ECD of cross-linked PE was 0.19±0.06 µm versus 0.36±0.15 µm for reference PE. Classifying the particles into size groups of 0.1, 0.2, 0.3 µm demonstrated a clear relationship between size and shape: larger particles are more elongated on average. The cross-linked particle fraction seems to display a subgroup of the standard UHMWPE wear debris.
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