Characterization of network parameters for UHMWPE by plane strain compression

Area of Science:

• Biomaterials Science
• Polymer Science
• Orthopedic Engineering

Background:

• Ultra-high molecular weight polyethylene (PE) is a critical bearing material in joint replacements due to its toughness and wear resistance.
• Wear debris from PE components can lead to osteolysis, a bone inflammation that can cause implant loosening.
• Crosslinking PE via ionizing radiation enhances wear resistance by introducing chemical crosslinks and physical entanglements.

Purpose of the Study:

• To compare crosslink densities and molecular weights between crosslinks in irradiated PE using equilibrium swelling versus a Gaussian and Eight-Chain model.
• To evaluate the effectiveness of a melt compression modeling approach in characterizing crosslinked PE.

Main Methods:

• Irradiation of PE to doses ranging from 0-200 kGy.
• Characterization of crosslink density and molecular weight between crosslinks using equilibrium swelling.
• Application of the Gaussian and Eight-Chain model to plane strain compression data of the PE melt.

Main Results:

• Crosslink density increased monotonically with radiation dose, while molecular weight between crosslinks decreased.
• The Gaussian and Eight-Chain model yielded higher crosslink density values compared to equilibrium swelling.
• The model-derived molecular weight between crosslinks was lower than that obtained from equilibrium swelling.

Conclusions:

• The Gaussian and Eight-Chain model provides a more comprehensive characterization of crosslinked PE by including entanglements, which are often neglected in solvent-based methods.
• This advanced characterization can lead to a better understanding and optimization of crosslinked PE for improved wear resistance in joint prostheses.