Mesoporous bioactive glass composition effects on degradation and bioactivity.

Mesoporous bioactive glasses (MBGs) are promising materials for regenerative medicine, due to their favorable properties including bioactivity and degradability. These key properties, but also their surface area, pore structure and pore volume are strongly dependent on synthesis parameters and glass stoichiometry. However, to date no systematic study on MBG properties covering a broad range of possible compositions exists. Here, 24 MBG compositions in the SiO2-CaO-P2O5 system were synthesized by varying SiO2 (60-90 mol %), CaO and P2O5 content (both 0 to 40 mol-%), while other synthesis parameters were kept constant. Mesopore characteristics, degradability and bioactivity were analysed. The results showed that, within the tested range of compositions, mesopore formation required a molar SiO2 content above 60% but was independent of CaO and P2O5 content. While mesopore size did not depend on glass stoichiometry, mesopore arrangement was influenced by the SiO2 content. Specific surface area and pore volume were slightly altered by the SiO2 content. All materials were degradable; however, degradation as well as bioactivity, i.e. the ability to form a CaP mineral on the surface, depended on stoichiometry. Major differences were found in early surface reactions in simulated body fluid: where some MBGs induced direct hydroxyapatite crystallization, high release of calcium in others resulted in calcite formation. In summary, degradation and bioactivity, both key parameters of MBGs, can be controlled by glass stoichiometry over a broad range while leaving the unique structural parameters of MBGs relatively unaffected. This allows targeted selection of material compositions for specific regenerative medicine applications.