Design, synthesis and structural properties of borate glasses: Towards an alkali-free bioactive glass

Glasses in the system (14-x) Na2O-(54+x) B2O3-22CaO-8MgO-2P2O5 with 0 <= x <= 14 mol%, have been prepared by the classic method, fast quenching of high-temperature melts. Multiples techniques were used to investigate their physical and structural properties such as X-ray diffraction, Density measurements, Differential scanning calorimetry, Infrared spectroscopy, Raman spectroscopy, and Isothermal heat treatment. The results found by Raman and Infrared spectroscopy show that the addition of boron oxide in different proportion and the pro-gressive reduction of sodium oxide affect clearly the glass structure, wherewith the total elimination of Na2O the glass network exhibit the formation of an interconnected large cluster (pentaborate) at the detriment of the isolated unit containing non-bridging oxygen, thus promoting groups with four coordinated boron. The physical parameters and thermal analysis confirm the structural results found revealing an increase in the oxygen packing density and glass transition temperature from 510 degrees C to 640 degrees C indicating compactly packed structure and a reinforcement of the glass network. The isothermal treatment confirms the role of boron by maintaining the vitreous aspect until (800 degrees C) for the alkali-free glass, in addition to a much higher thermal stability. The bioactivity test was achieved by immersion glass samples in simulated body fluids solution (SBF) at 37 degrees C, these latter within a few days reveals the growth of the hydroxyapatite phase confirmed by X-ray diffraction, FT-IR, and scanning electron microscope. Also, the conversion process was proved with the increase in pH and the weight loss values as well as the consumption of Ca and P concentration in simulated body fluids solution. However, the kinetics of the reaction decreases with the substitution of Na2O with B2O3 in the glass system which is quite related to the creation of more interconnected bonds and less non-bridging oxygens. Thus the properties found of the alkali-free glass in correlation with the formation of hydroxyapatite layer indicate a potential glass for tissue engineering application.