Bioactive glasses are commonly studied in vitro to estimate their reactions in vivo. Usually, the in vitro tests are conducted by immersing the bioactive glass in static buffered solutions. However, the environment around dissolving bioactive glass particles is not static and might be affected by bone infections leading to an acidic environment. Also, limited solution circulation might increase the ion concentrations around the dissolving implants and thus cause elevated pH levels locally.

In our previous in vitro study conducted in dynamic flow conditions, the increased ion concentrations decreased the overall dissolution, thus delaying reaction layer formation on bioactive glass particles. This work studies the impact of increased ion concentrations in buffered solutions on the overall dissolution of bioactive glass S53P4 particles.

Alkaline (pH 9), physiological (pH 7.4) and acidic (pH 5) Tris solutions and an acetic acid sodium hydroxide-buffer solution (pH 5) were used to immerse bioactive glass S53P4 particles (Ø 300-500 µm) for 120 hours. Additionally, new particles were immersed in extracts after 24 and 72 h of dissolution to measure the effect of common ions in the solution on the glass dissolution. The as-prepared solution was assumed to mimic the solution in first contact with an implanted particle bed, while the extracts mimicked conditions inside the bed. The changes in the solutions’ pH were measured as functions of time. The ion concentrations were analysed using ICP-OES at several time points. Finally, the particle surfaces and cross-sections were analysed with SEM-EDX.

The overall dissolution of the bioactive glass S53P4 decreased with the common ions present in all immersion solutions, independent of the original pH. At 120 h, the dissolution decreased from 4.9% to 2.6% in the 72 h extract of the Tris-solution buffered at pH 7.4. In the solutions buffered at pH 9, the dissolution was less than at pH 7.4. Correspondingly, the highest dissolution was measured in the solutions with pH = 5. In the alkaline solutions, the glass particles dissolved congruently, with some signs of glass corrosion on the surfaces. In contrast, distinct layers were formed in all other solutions, with the thickest silica-rich layers in the acidic solutions. The results indicate that the particles do not dissolve and react uniformly in an implanted bed, but the reaction behaviour depends on their mutual placement and, thus, the composition of the surrounding solution.