AVS 53rd International Symposium
    Biomaterial Interfaces Thursday Sessions
       Session BI+AS-ThA

Paper BI+AS-ThA7
Effects of Annealing and Sample Processing Methods on Surface Molecular Orientation of Ultra-high Molecular Weight Polyethylene

Thursday, November 16, 2006, 4:00 pm, Room 2014

Session: Biomolecule-Surface Characterization I
Presenter: S. Sambasivan, National Institute of Standards and Technology
Authors: S. Sambasivan, National Institute of Standards and Technology
D.A. Fischer, National Institute of Standards and Technology
M.C. Shen, National Institute of Standards and Technology
J.A. Tesk, National Institute of Standards and Technology
S.M. Hsu, National Institute of Standards and Technology
Correspondent: Click to Email
Ultra-high molecular weight polyethylene (UHMWPE) has remained the dominant polymer in artificial joints due to its outstanding wear resistance properties. It has been have demonstrated in the past that the molding and annealing the ultra-high molecular weight polyethylene (UHMWPE) at a safe elevated temperature resulted in increased mechanical strength. Also, cross-linking of UHMWPE has been shown to reduce wear significantly. This novel study utilizes resonant absorption of linearly polarized soft x-rays at a synchrotron beamline to characterize the molecular orientation of the UHMWPE surface layer (top 10 nm) which is understood to be a precursor to wear. Carbon-K-edge x-ray absorption measurements were done on the UHMWPE samples, which were annealed in nitrogen atmosphere. Effects of annealing and cross-linking on the wear characteristics were also examined. It was found that the degree of orientation after annealing the sample at 130°C in nitrogen, the average molecular orientation in UHMWPE decreased significantly (about 80% reduction) compared to the un-annealed UHMWPE. These studies show a promising new insight into how UHMWPE wears and will aid in the development of new materials for artificial joints. In addition to the annealing and cross-linking studies, it was observed that routine surface preparation methods such as molding, polishing and microtoming also induced surface molecular orientation to various degrees.