In vivo and in vitro surface changes in a highly cross-linked polyethylene

Area of Science:

• Biomaterials Science
• Orthopedic Engineering
• Polymer Science

Background:

• Conventional ultrahigh-molecular-weight polyethylenes (UHMWPEs) are prone to wear in arthroplasty.
• Advancements in UHMWPE processing aim to enhance wear resistance and implant longevity.
• Highly cross-linked UHMWPEs represent a significant development in orthopedic materials.

Purpose of the Study:

• To investigate the surface morphology and wear mechanisms of highly cross-linked UHMWPEs used in arthroplasty.
• To characterize novel surface features observed on retrieved UHMWPE components.
• To understand the formation and implications of microcracks in advanced UHMWPE materials.

Main Methods:

• Analysis of retrieved UHMWPE components from arthroplasty implants.
• In vitro investigation of UHMWPE specimens under simulated loading conditions.
• Microscopic examination to identify and measure surface features, including ripples and microfissures.

Main Results:

• Highly cross-linked UHMWPEs demonstrated superior wear resistance compared to conventional materials.
• Surface examination revealed characteristic ripples with associated microfissures, described as folds with microcracks.
• Microcrack depth reached up to 5 micrometers and was independent of loading cycles (up to 27 million).

Conclusions:

• The observed folds with microcracks represent a distinct surface phenomenon in highly cross-linked UHMWPEs.
• These features accumulate on the surface due to the material's extreme wear resistance.
• Further research is needed to fully elucidate the clinical significance of these microcracks in long-term arthroplasty performance.