In vitro properties of magnesium and strontium containing bioactive borosilicate glasses

Bioactive glasses are promising material utilized in tissue engineering, mainly in bone-related applications. Borosilicate glasses are especially interesting, as they have been shown to have faster conversion to hydroxyapatite (HA) in physiological conditions compared to the traditional silica-based bioactive glasses, while also possessing thermal properties enabling e.g. 3D scaffolds processing. However, borosilicate glasses are known to lead to a decrease in the cells activity.

In this study, we investigated new borosilicate glasses with molar composition of 47.1 SiO2 - 6.7 B2O3 - 22.7 Na2O – (21.8-x-y) CaO - 1.7 P2O5 – x MgO – y SrO, where x,y varied from 0 to 10 mol-%.

The objective was to assess if a decreased Ca release and presence of Sr and/or Mg can enhance the cellular activity on these materials. The in vitro dissolution of the glasses was studied in simulated body fluid. Change in dissolution rate evidenced by pH and ICP-OES measurement are correlated to changes in the glass structure. Additionally, cell activity at the surface of the glass discs was tested using mesenchymal stem cells.

It was found that the glass dissolution rate decreased with increasing Ca substitution. The formation of HA layer appeared quite rapidly on all of the studied glasses, while Mg and Sr were suspected to be introduced in the precipitated HA layer. With mesenchymal stem cells, Mg and/or Sr containing glasses exhibited enhanced cell viability and proliferation.