Backscattered Electron Imaging to Enhance Microstructural Contrast in Poly(Methyl Methacrylate) Bone Cement Fracture Analysis

Poly(methyl methacrylate) (PMMA) bone cement is used as a grout to secure joint replacement prostheses into bone. It has a distinct microstructure made up of: prepolymerized beads, an interbead matrix polymer, a radiopacifier {barium sulphate (BaS04) or zirconium dioxide (Zr02)}, and pores or voids; the radiopacifier is fmmd only in the interbead matrix of the cured bone cement. The mechanism of slow or fatigue crack growth appears to be initial micro-cracking through the interbead matrix, followed by coalescence of the microcracks to form a continuous crack. Thus, distinguishing the interbead matrix from the pre-polymerized beads is important for investigating fatigue crack behavior in bone cement. Backscattered electron (BE) imaging theoretically facilitates discrimination of the radiopacifier, and thus , interbead matrix polymer, from the prepolymerized beads. The purpose of this study was to investigate the use of BE imaging and secondary electron (SE) imaging to enhance the contrast between the microstructural components in PMMA bone cement. Electron microscopy revealed that: (1) the damage zone in fatigue fracture of PMMA was characterized by microcracks ahead of the crack tip, and (2) in the BE micrographs, it was easy to differentiate the prepolymerized beads from the interbead matrix . Therefore, BE imaging can be successfully used to contrast the radiopacifier with other constituents of the cement.