Mixed Network Former Effect on Structure, Physical Properties, and Bioactivity of 45S5 Bioactive Glasses: An Integrated Experimental and Molecular Dynamics Simulation Study.

Boron-containing bioactive glasses display a strong potential in various biomedical applications lately due to their controllable dissolution rates. In this paper, we prepared a series of B2O3/SiO2-substituded 45S5 bioactive glasses and performed in vitro biomineralization tests with both simulated body fluid and K2HPO4 solutions to evaluate the bioactivities of these glasses as a function of boron oxide to silica substitution. The samples were examined with scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectrometry after immersing them in the two solutions (simulated body fluid and K2HPO4) up to 3 weeks. It was found that introduction of boron oxide delayed the formation of hydroxyapatite, but all the glasses were shown to be bioactive. Molecular dynamics (MD) simulations were used to complement the experimental efforts to understand the structural changes due to boron oxide to silica substitution by using newly developed partial charge composition-dependent potentials. Local structures around the glass network formers, medium-range structural information, network connectivity, and self-diffusion coefficients of ions were elucidated from MD simulation. Relationships between boron content and glass properties such as structure, density, glass transition temperature, and in vitro bioactivity were discussed in light of both experimental and simulation results.