Low-temperature mineralization sintering process for fabrication of fluoridated hydroxyapatite-containing bioactive glass

Abstract

Bioactive glasses and glass-ceramics are receiving wide attention for their biomedical applications. We present a novel route to obtain fluoridated hydroxyapatite-containing bioactive glass (FHBG) through a low-temperature mineralization sintering process (LMSP). LMSP is a low-temperature densification procedure that can provide a functionalization of pristine materials through the formation and growth of new phases induced by mineralization. Here, SiO2–CaO–P2O5 bioactive glass nanoparticles (BGNPs) were prepared and mixed with fluorine-containing simulated body fluid (F–SBF) to induce mineralization. Under a uniaxial pressure of 330 MPa and temperature of 120 °C, BGNPs were densified up to 89% of their theoretical density, and the Vickers hardness and fracture toughness of the sintered BGNPs increased to 4.15 ± 0.11 GPa and 1.32 ± 0.12 MPa m1/2, respectively. This densification behavior was strongly influenced by the mineralization that forms nanoscale crystalline phase such as carbonated fluoridated hydroxyapatite (HAp), where part of PO43− and OH− in HAp (Ca10(PO4)6(OH)2) was replaced by CO32− and F−, respectively. The fluorides formed as minor phases in the sintered BGNPs by mineralization were identified as calcium fluorosilicate (CaSiF6) and calcium fluoride (CaF2). After an acid resistance test, because of the presence of fluorides, the sintered BGNPs containing fluorides presented a 38% weight loss, which is lower than that of sintered BGNPs containing no fluorides (54% weight loss). By employing LMSP, we successfully fabricated FHBG from non-fluoride-containing BGNPs and F–SBF at an extremely low temperature at 120 °C. Therefore, this study offers a more efficient method for the manufacturing of glasses and glass-ceramics.