Individual and combined effects of the elements Zn, Mg and Sr on the surface reactivity of a SiO2·CaO·Na2O·P2O5 bioglass system

This study had two aims: to determine how the elements Zn, Mg and Sr can affect the reactivity of a bioglass system, and to determine the mechanism of dissolution/precipitation when this material is immersed in a complex medium such as cell culture medium. To answer these questions, we synthesized a standard bioglass (SiO2·CaO·Na2O·P2O5, BV), a bioglass containing Zn (BV-Zn), Mg (BV-Mg) or Sr (BV-Sr) and a bioglass containing all three elements (BV-SrZnMg) by the sol-gel route. A typical cell culture medium (McCoy's 5A modified medium) was used for the dissolution/precipitation assays. Thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) and N2-adsorption measurements were performed to characterize the obtained glasses. Inductively coupled plasma optical emission spectrometry (ICP-OES), diffuse reflectance infrared Fourier transform (DRIFT), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses were performed to determine the bioglass reactivity after immersion in McCoy's 5A modified medium. The mechanism of ionic change responsible for the initial increase in pH after immersion in cell culture medium was independent of the modifier elements (Zn, Mg and Sr) present in the samples. The addition of Sr to the bioglass composition did not significantly change the SiO44 − release compared to the control. The presence of Zn increased SiO44 − release by decreasing the crystallization temperature Tc. In contrast, the SiO44 − release decreased upon the addition of Mg to the glass system, despite a remarkable decrease in Tc. The presence of Mg in the McCoy's 5A medium most likely generated a saturation state close to the surface, avoiding SiO44 − release. While SiO44 −, Zn2 + and Sr2 + were released from the bioglasses upon immersion, Ca2 +, Mg2 + and PO43 − were captured from the medium. As a consequence, the formation of a CaMg phosphate layer containing CO32 − was observed for all samples, regardless of which elements were present.