Synthesis and characterization of poly(methyl methacrylate)-based experimental bone cements reinforced with TiO2–SrO nanotubes

In an attempt to overcome existing limitations of experimental bone cements we here demonstrate a simple approach to synthesizing strontium-modified titania nanotubes (n-SrO–TiO2 tubes) and functionalize them using the bifunctional monomer methacrylic acid. Then, using ‘grafting from’ polymerization with methyl methacrylate, experimental bone cements were produced with excellent mechanical properties, radiopacity and biocompatibility. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy mapping and backscattered SEM micrographs revealed a uniform distribution of SrO throughout the titanium matrix, with retention of the nanotubular morphology. Nanocomposites were then reinforced with 1, 2, 4 and 6 wt.% of the functionalized metal oxide nanotubes. Under the mixing and dispersion regime employed in this study, 2 wt.% appeared optimal, exhibiting a more uniform dispersion and stronger adhesion of the nanotubes in the poly(methyl methacrylate) matrix, as shown by TEM and SEM. Moreover, this optimum loading provided a significant increase in the fracture toughness (KIC) (20%) and flexural strength (40%) in comparison with the control matrix (unfilled) at P < 0.05. Examination of the fracture surfaces by SEM showed that toughening was provided by the nanotubes interlocking with the acrylic matrix and crack bridging during fracture. On modifying the n-TiO2 tubes with strontium oxide the nanocomposites exhibited a similar radiopacity to a commercial bone cement (CMW® 1), while exhibiting a significant enhancement of osteoblast cell proliferation (242%) in vitro compared with the control at P < 0.05.