Improving the fatigue properties of poly(methyl methacrylate) orthopaedic cement containing radiopacifier nanoparticles

For over 40 years, poly(methyl methacrylate) (PMMA) based bone cement has been widely used for fixation of total joint replacement prostheses. Such cements usually comprise two components: (1) liquid MMA monomer and (2) a powder component containing prepolyrnerized 50-100 mum diameter beads of PMMA, along with 1 mum diameter radiopacifier particles of barium sulfate or zirconium oxide and benzoyl peroxide reaction initiator. Upon mixing the two components, the liquid MMA polymerizes and fuses the prepolymerized beads, and the cement slowly hardens in the patient over a period of approximately 30 minutes. The 3 volume percent of radiopacifier particles are necessary to enable orthopaedic surgeons to monitor fatigue fracture of cement in the patient using x-ray radiographs. A major problem associated with these particles is that their incomplete dispersion leads to the presence of large defects, ultimately decreasing the fatigue properties of the cement. In this study, we replaced the 0.5-3 mum size barium sulfate particles with an identical quantity of 50-100 run size barium sulfate particles. The dispersion and size distribution of barium sulfate particles in PMMA cement was characterized using low voltage scanning electron microscopy and ultra-small angle x-ray scattering performed at the UNICAT beamline of the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. The fatigue life of notched dogbone shaped cement specimens was measured by subjecting them to cyclic loading. The nanocomposite cement had a fatigue life of over twice that of the microcomposite cement. LVSEM of fracture surfaces showed evidence of plastic deformation in the regions containing the nanoparticle fillers which resulted in it's higher fracture toughness.