Injectable acrylic bone cements for vertebroplasty based on a radiopaque hydroxyapatite. Bioactivity and biocompatibility.

Radiopaque bone cements have been formulated to provide injectable pastes with improved bioactivity to be applied in vertebroplasty and kyphoplasty techniques. The bioactive compound was strontium containing hydroxyapatite salt, which was introduced as obtained (SrHA) or after treatment with MMA monomer (SrHA-t). The in vitro bioactivity of the cements was tested in cement films or in cement pastes introduced directly in a simulated body fluid (SBF) solution at 37 degrees C to mimic the in vivo conditions. Precipitation of an apatite-like layer was observed for the 20 wt %-SrHA-t containing cement in the first experiments, and in all formulations in the second ones. The deposited particles were characterized by FTIR spectroscopy and by EDAX analysis. Radiopacity of cements after immersion in SBF was confirmed. The biocompatibility exhibited by the SrHA containing cements was, in some cases, superior to that shown by a formulation with 10 wt % of BaSO(4). The new formulations prepared with the treated filler exhibited the lowest cytotoxicity and enhanced cellular proliferation. The in vivo biocompatibility tested by an intramuscular model in rats indicated the formation of a membrane formed by collagen fibers containing fibroblasts with no inflammatory cells, such as macrophages, giant cells or lymphocytes in all formulations.