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Published on: January 30, 2015
Subsurface oxidation of polyethylene
1Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755-8000, USA.
Journal of Biomedical Materials Research
|November 25, 1998
Summary
Gamma radiation sterilization of ultrahigh molecular weight polyethylene (UHMWPE) medical implants causes degradation. Oxidation profiles reveal maximum degradation occurs below the surface, impacting orthopedic prostheses longevity.
Area of Science:
- Biomaterials Science
- Polymer Chemistry
- Orthopedic Engineering
Background:
- Ultrahigh molecular weight polyethylene (UHMWPE) is a critical bearing material in orthopedic prostheses since the 1960s.
- Gamma radiation sterilization, commonly used for UHMWPE, promotes material degradation in the presence of oxygen, linked to implant failure.
- Understanding UHMWPE degradation mechanisms is crucial for improving the longevity of orthopedic implants.
Purpose of the Study:
- To investigate the oxidation profiles of aged ultrahigh molecular weight polyethylene components.
- To elucidate the mechanism of oxidative degradation in gamma-sterilized UHMWPE.
- To develop a predictive model for UHMWPE degradation based on oxidation patterns.
Main Methods:
- Shelf-aged UHMWPE components (5.8 and 10.9 years) were sectioned.
- Fourier-transform infrared (FTIR) spectroscopy was used to quantify ketone concentrations (primary oxidation products).
- Oxidation profiles were analyzed, and a computational model incorporating radical reactions and oxygen diffusion was developed.
Main Results:
- Maximum ketone concentrations were observed several millimeters below the component surface.
- Surface ketone levels were low due to oxygen-driven alkyl radical depletion.
- Bulk ketone levels were low due to limited oxygen availability, while subsurface levels peaked due to a balance of radical concentrations.
Conclusions:
- A model explaining subsurface oxidation peaks in UHMWPE was proposed, involving the interplay of alkyl radicals, peroxyl radicals, and oxygen diffusion.
- The model accurately predicted observed oxidation profiles, enhancing understanding of UHMWPE degradation.
- Findings provide insights into improving the long-term performance and reliability of UHMWPE-based orthopedic implants.
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