Abstract
Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) is the material of choice for one of the articulating surfaces in many total joint replacements, notably hip and knee prostheses. The various methods used by the orthopaedic biomaterials industry to sterilize and anneal UHMWPE components, and the resulting oxidation and crosslinking, affect the mechanical wear resistance properties in ways still unknown at the microscopic and molecular levels. Transmission electron microscopy and chemical pyrolysis were used to quantify crosslinking induced by gamma irradiation and annealing in air. Changes in lamellar stacking and the amount of crosslinking suggest two types of crosslinking: relatively unstable crosslinks in the amorphous region initially resulting from gamma irradiation which are later replaced by more thermally stable crosslinks resulting from rearrangements at the annealing temperature. Lamellar mobility, the ability of crystalline lamellae to flow in the material, is enhanced during the transition from one type of bond to the other, and this appears to optimize near eight hours of annealing time. Results from decomposition and percent crystallinity measurements provide further support for this theory.