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Radiation-induced physical changes in UHMWPE implant components
S H Naidu1, B L Bixler, M J Moulton
1Department of Orthopedics, Pennsylvania State University, Hershey, USA.
Orthopedics
|February 1, 1997
Summary
Post-irradiation aging in ultra-high molecular weight polyethylene (UHMWPE) is driven by chain scission, not just oxidation. This leads to crystallization and unclear mechanical property changes, warranting caution with gamma sterilization.
Area of Science:
- Polymer Science
- Materials Science
- Biomaterials Engineering
Background:
- Post-irradiation aging of ultra-high molecular weight polyethylene (UHMWPE) is not fully understood.
- Retrieval studies and in vitro aging show oxidative changes and increased crystallinity.
- Existing literature suggests oxidation is key initially, but other factors dominate later aging.
Purpose of the Study:
- To critically analyze and review the polymer science and physics literature on UHMWPE aging.
- To elucidate the mechanisms driving post-irradiation aging in UHMWPE.
- To clarify the impact of aging on UHMWPE mechanical properties.
Main Methods:
- Literature review and critical analysis of polymer science and physics studies.
- Examination of findings from retrieval studies and in vitro aged UHMWPE specimens.
- Synthesis of existing data to propose aging mechanisms.
Main Results:
- Oxidation is significant in the first year post-irradiation.
- Subsequent aging is primarily due to gamma radiation-induced chain scission.
- Chain scission leads to isothermal crystallization in amorphous regions of UHMWPE.
- Mechanical property changes in aged UHMWPE remain unclear.
Conclusions:
- Gamma radiation-induced chain scission is the primary driver of long-term UHMWPE aging.
- Isothermal crystallization follows chain scission in the amorphous regions.
- The effects of aging on mechanical properties require further investigation.
- Gamma irradiation sterilization of UHMWPE should be approached with caution due to unclear aging effects.