Structural and chemical changes in ultra-high-molecular-weight polyethylene due to gamma radiation-induced crosslinking and annealing in air .

Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) is used to fabricate one of the articulating surfaces used in many total joint replacements. Various sterilization and annealing methods affect the mechanical wear properties in ways still unknown at the microscopic and molecular levels. We have investigated crosslinking induced by gamma irradiation and annealing time (both done in air). TEM was used to probe the organization of crystalline lamellae in the polymer. Pyrolysis interfaced with GC-MS was used to quantify the extent of crosslinking by identifying peaks that correlate with crosslinking structures along its backbone. Changes in lamellar stacking and the extent of the crosslinking suggest two types of crosslinking occuring in the material. Lamellar mobility is enhanced during the transitions from one type of bonding to the other, and this appears to optimize near eight hours of annealing time. Results from decomposition experiments and percent crystallinity measuresments provide further support for this postulated theory.