Fast Cure of Bone Cement Based on Poly(Methyl Methacrylate)/Hydroxyapatite Nanocomposite for Application in Cranioplasty

Novel initiation systems for the production of poly(methyl methacrylate) (PMMA) bone cements based on low-toxicity tertiary amine initiators and hydroxyapatite nanoparticles were investigated. Bicomponent systems formed by a solid component containing PMMA and benzoyl peroxide (BPO) and a liquid component containing methylmethacrylate and low-toxicity aliphatic (dimethylamino-ethoxy-ethane) (DMEE) and aromatic (dimethylamino-benzaldehyde) (DMAB) tertiary amines were tested at two amine concentrations (0.75 and 3.75 wt%) and compared with the standard tertiary amine dimethyl-p-toluidine (DMT). The components were mixed in a 2:1 ratio (solid/liquid) for 60 s. Nanocomposites were prepared using nano-hydroxyapatite inserted into the PMMA-based polymer matrix at various concentrations between 1.0 and 3.75 wt%, aiming to increase the biocompatibility of bone cements applied in cranioplasty. The concentration of tertiary amines directly affects the reaction rate, and increasing the concentration accelerates the curing reaction. Thermal analyses (DSC and TGA) revealed that the produced polymers did not show significant changes in glass transition temperature (113 °C and 115 °C), nor in onset (150–158 °C) or peak degradation temperatures (353 °C and 355 °C). The reaction with the aliphatic amine proved to be slow, as no polymerization occurred within the time period stipulated in the study. However, drastic changes did take place when the cure occurred in the presence of nano-hydroxyapatite. The cure with DMAB (3.75 wt%) that presented an exothermic peak at 37 min (53 °C) showed a peak at 16 min (70 °C), and the cure with DMEE (3.75 wt%) a peak at 11 min (62.5 °C) after the addition of nano-hydroxyapatite. In conclusion, addition of nano-hydroxyapatite significantly influenced both the time and the temperature of cure reaction in all amines studied, expanding the possibility of using new initiators in polymerization systems for cranioplasty flaps.