Essential role of calcium phosphate heterogeneities in 2D-hexagonal and 3D-cubic SiO2-CaO-P2O5 mesoporous bioactive glasses

Abstract

Mesoporous bioactive glasses (MBGs) with a compoisition of 85SiO2-10CaO-5P2O5 (mol %) have been prepared through the evaporation-induced self-assembly (EISA) method, using P123 as a structure directing agent. For the first time, SiO2-CaO-P2O5 MBGs with identical composition and textural properties, but exhibiting different bicontinuous 3D-cubic and 2D-hexagonal structures, have been prepared. These materials allow us to discriminate the role of the structure on the bioactivity, from other parameters. To understand the role of each component on the mesostructure, local environment, and bioactive behavior, mesoporous 100SiO2, 95SiO2-5P2O5,and 90SiO2-10CaO (mol %) materials were also prepared under the same conditions. The results demonstrate that the joint presence of CaO and P2O5 results in amorphous calcium phosphate (ACP) clusters sited at the pore wall surface. This heterogeneity highly improves the bioactive behavior of these materials. In addition, the presence of ACP clusters within the silica network leads to different mesoporous structures. The mesoporous order can be tuned through a rigorous control of the solvent evaporation temperature during the mesophase formation, resulting in p6mm, p6mm/Ia3d coexistence, and Ia3d phases for 20, 30, and 40 C, respectively. Preliminary results indicate that, in the case of identical composition and textural properties, the mesoporous structure does not have influence on the apatite formation, although initial ionic exchange is slightly enhanced for 3D cubic bicontinuous structures.