Development and characterization of multi-solution bone cements containing cross-linked PMMA nanospheres and nanospherical polymer brushes

High viscosity two-solution cements exhibit several advantages over other commercial powder-liquid formulations. Nevertheless, the high concentration of monomer required for the preparation of the standard formulation, which consequently leads to high concentrations of residual monomer, polymerization shrinkage and high exothermal temperatures, is considered a major limitation to the use of this material. Novel two-solution cements containing cross-linked PMMA microspheres and nanospheres, as part of the polymer phase, have been developed as the first step for optimization of cement viscosity, targeting the application of the material in the treatment of vertebral compression fractures using kyphoplasty and vertebroplasty. Such procedures require the use of cements with reduced viscosities and extended setting times to allow for adequate augmentation and to reduce the risk of cement extravasation. Two-solution cements containing cross-linked nanospheres exhibited reduced viscosity, high pseudoplasticity, lower polymerization exotherm, longer setting times and lower concentration of residual monomer in comparison to a standard two-solution bone cement formulation. Subsequently, the surface of the cross-linked nanospheres was decorated with functional groups following a novel synthetic strategy, which allowed for efficient grafting of PMMA brushes to the surface of the PMMA nanospheres. The goal of the addition of brushes in the two-solution cement is to improve interfacial bonding of the beads to the cement matrix, allowing for complete substitution of the linear phase of the cement mixture. The ultimate goal of this study was to evaluate the viability of preparing two-solution cements with reduced monomer concentration and lower viscosities by the complete substitution of linear PMMA with PMMA brushes at higher polymer-to-monomer ratios. The addition of brushes resulted in a further decrease of cement viscosity and the same level of residual monomer, in comparison to cements prepared with a mixture of nanospheres and linear polymer at the same polymer-to-monomer ratios. These cements require further optimization of the hydrodynamic properties of the brush compositions added to the mixture for enhancement of the mechanical properties of the material. In summary, novel two-solution cements were developed exhibiting a combination of attractive properties and the potential to serve as platforms for addition of other elements that will ultimately prolong the life and performance of arthroplasties and vertebral augmentation.