Molecular anatomy of freeze-fractured ultra-high-molecular-weight polyethylene as determined by low-voltage scanning electron microscopy

Morphological similarities between virgin ultra-high-molecular-weight polyethylene (UHMWPE) powder and debris retrieved from failed UHMWPE total joint implants motivated this study's objective: to establish the internal microstructural features of consolidated UHMWPE. Cylindrical specimens were cored from a γ-irradiation-sterilized tibial component (extruded from GUR 415 resin), and then these specimens were freeze-fractured at high strain rates. Low-voltage scanning electron microscopy was used to examine these surfaces. Two types of areas were observed. The first were uniform, homogeneous, and continuous with microridge structures (45-70 nm wide) and hillocks (0.1-0.3 μm in diameter). The second was nonhomogeneous and discontinuous with fibrils (10-200 nm long), microridges, fenestra as small as 20 nm, and large crater-like structures (6-12 μm in diameter). Many of the submicron-sized structures observed were similar to the structures observed in virgin powder, as well as those observed by others from wear debris retrieval studies. These data support the hypotheses that wear debris originates, in part, from structures originally present in the powder resin, and that these structures retain their identity throughout consolidation, machining, and in vive wear, and are released into periprosthetic tissues as wear debris.