Nanoparticulate fillers improve the mechanical strength of bone cement

Polymethylmethacrylate (PMMA-) based bone cement contains micrometer-size barium sulfate or zirconium oxide particles to radiopacify the cement for radiographic monitoring during follow-up. Considerable effort has been expended to improve the mechanical qualities of cements, largely through substitution of PMMA with new chemical structures. The introduction of these materials into clinical practice has been complicated by concerns over the unknown long-term risk profile of these new structures in vivo. We investigated a new composite with the well characterized chemical composition of current cements, but with nanoparticles instead of the conventional, micrometer-size barium sulfate radiopacifier.

In this study, we replaced the barium sulfate microparticles that are usually present in commercial PMMA cements with barium sulfate nanoparticles. The resultant "microcomposite" and "nanocomposite" cements were then characterized through morphological investigations such as ultra-small angle X-ray scattering (USAXS) and scanning electron microscopy (SEM). Mechanical characterization included compression, tensile, compact tension, and fatigue testing.

SEM and USAXS showed excellent dispersion of nanoparticles. Substitution of nanoparticles for microparticles resulted in a 41% increase in tensile strain-to-failure (p = 0.002) and a 70% increase in tensile work-of-fracture (p = 0.005). The nanocomposite cement also showed a two-fold increase in fatigue life compared to the conventional, microcomposite cement.

In summary, nanoparticulate substitution of radiopacifiers substantially improved the in vitro mechanical properties of PMMA bone cement without changing the known chemical composition.