Molecular Orientation of Ultrahigh Molecular Weight Polyethylene Induced by Various Sliding Motions

Published

August 1, 2004

Author(s)

S Sambasivan, Daniel A. Fischer, M C. Shen, Stephen M. Hsu

Abstract

Wear and wear debris of ultra-high molecular weight polyethylene (UHMWPE) in joint replacements has been recognized as one of the major contributors to the failure of orthopaedic implants. Detailed wear mechanisms of the polyethylene under biomechanic motions is not well understood. In simulation wear bench tests, it was found that unidirectional sliding produces the least amount of wear, reciprocating motion increases wear significantly, and cross-shear motion (similar to human body motion) produces the highest amount of wear. Conventional wear theories are inadequate to explain this observation. This study utilizes resonant absorption of linearly polarized soft x-rays at a synchrotron radiation beamline to measure the molecular orientation of UHMWPE surface layer subjected to different wear motions. Carbon-K-edge partial electron yield x-ray absorption measurements were done on the UHMWPE worn samples. X-ray absorption measurements show conclusively that the molecular chains of UHMWPE align preferentially parallel to the direction of sliding. When examined under various wear motions, it was observed that unidirectional shear produced the maximum chain orientation, while cross shearing wear motions produced the least amount of orientation. When polymeric chains align, the surface layer tends to be more brittle and hard, thus resisting wear. When they do not align, loose chains may be subjected to both mode I and mode II fracture, hence increasing the wear rate.

Citation

Journal of Biomedical Materials Research

Volume

70

Issue

No. 2

Pub Type

Journals

Keywords

cross-shear motions, molecular orientation, orthopaedic joint replacement, wear, wear mechanisms, XANES

Citation

Sambasivan, S. , Fischer, D. , Shen, M. and Hsu, S. (2004), Molecular Orientation of Ultrahigh Molecular Weight Polyethylene Induced by Various Sliding Motions, Journal of Biomedical Materials Research (Accessed May 6, 2024)