Produção e caracterização de biocimentos de apatitas nanométricas incorporados com dióxido de silício para aplicações biomédicas

Abstract

Calcium phosphate biocements exhibit high osteoconductivity, ease of molding and handling, as well as excellent biocompatibility and bioactivity. However, their use is limited to applications in which they are submitted to small loads, mainly due to their low mechanical strength. This study aimed at developing and characterizing biocements made from calcium phosphate bioceramics obtained by precipitation in aqueous solution, with the incorporation of nanometric silicion dioxide. The biocements were produced in the laboratory by adding nanometric silicon dioxide (in the proportions 10%, 20%, 30% and 40% by weight) to nanometric beta tricalcium phosphate. The samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, pH testing, testing of mechanical strength by diametrical compression and biological characterizations. X-ray results exhibited peaks identified as brushite as well as peaks representative of beta tricalcium phosphate, besides traces of tricalcium silicate and calcium carbonate. It is observed that the additive interferes with dissociation of beta tricalcium phosphate for the formation of brushite, and favors the formation of tricalcium silicate, which reduces the dissociation of beta tricalcium phosphate. In the analysis of infrared it was possible to identify functional groups of the phosphates and silicon dioxide bands present in biocements. Results of the morphological analysis showed a surface formed by brushite crystals in the form of plates surrounded by agglomerated particles (probably beta tricalcium phosphate / silicon dioxide). Tensile tests by diametrical compression for the various compositions of biocements showed that the percentage of silicon dioxide present influences the mechanical strength of the material. Additions of silicon dioxide improve mechanical strength up to a certain level, after which they become deleterious to strength. The pH of the obtained biociments remained 6.0 and 6.5, close to the neutral range. Analysis of citotoxicity of biocements showed that they did not affect the metabolism of mitochondrial enzymes, neither in the structural integrity of the nucleus nor in the cytoplasmic enzymatic activity of cells. In SBF solution, formation of an apatite on the surface of the material indicates that the biocement produced is bioactive. In general, the biocements produced are considered viable for biomedical applications.