In vitro degradation studies on bioactive calcium fluoroborophosphate glasses mixed with some modifier oxides-influence of therapeutically active vanadium ions

Abstract

The main objective of the study is to investigate the influence of therapeutically active vanadium ions on the in vitro bio-active properties of calcium oxy fluoro borophosphate glasses mixed with different modifier oxides viz., BaO, SrO, ZnO and MgO. The investigations mainly include the degradation studies of the chosen glasses in simulated body fluid (SBF) for a prolonged period (about 800 h). The rate of degradation was estimated by measuring the weight loss of the samples and by measuring the pH of the residual SBF solution at regular intervals of immersion time. During the immersion of the samples in SBF solution, a thin layer of crystalline hydroxy apatite layer (HAp) is observed to develop on the surface of the glass samples. The comparison of the results of XRD, SEM, EDS and IR spectral studies of pre and post immersed samples confirmed the formation of HAp layer embedded with calcium vanadate crystal phases. From the XRD studies it is understood that the magnitude of HAp layer developed on the surface of the samples is the highest for BaO modifier mixed glasses. The optical absorption as well as EPR spectral studies of pre and post immersed samples confirmed that vanadium ions existed in different oxidation states, mainly in V4+ and V5+ states, in the bulk glass samples. The ratio of the concentration of these two ions is predicted to be different for different modifier oxides mixed glasses and such variation is predicted to play a vital role in the variations of the magnitude of HAp layer formed on the surface of the samples. The bioactivity of the samples is estimated from the qualitative information on the magnitude of HAp layer formed on the surface of the samples and also the degradability of the samples in SBF solution which is estimated by measuring weight loss as well as pH of the residual SBF. The overall analysis of the results of in vitro bioactivity studies (degradability studies together with spectroscopic studies) revealed that among various glasses mixed with different modifier oxides, the glass mixed with BaO is found to be the superior bioactive material. Such glasses may be useful in improving the osteogenic activity in the human body if used as bone implants since it contains HAp layer embedded with calcium vanadate crystal phases. However quantitative in vitro cell culture studies are required to establish this.