EN
Ion release of Mg- and Zn-substituted Bioglass
45S5 (46.1 SiO2-2.6 P2O5-26.9 CaO-24.3Na2O; mol%; with 0,
25, 50, 75 or 100% of calcium replaced bymagnesium/zinc)
was investigated at pH 7.4 (Tris buffer) and pH 4 (acetic
acid/sodium acetate buffer) in static and dynamic dissolution
experiments. Despite Mg2+ and Zn2+ having the same
charge and comparable ionic radii, they influenced the
dissolution behaviour in very different ways. In Tris, Mgsubstituted
glasses showed similar ion release as 45S5,
while Zn-substituted glasses showed negligible ion release.
At low pH, however, release behaviour was similar,
with all glasses releasing large percentages of ions within
a few minutes. Precipitation of crystalline phases also varied,
as Mg- and Zn-substitution inhibited apatite formation,
and Zn-substitution resulted in formation of zinc
phosphate phases at low pH. These results are relevant
for glasses used in aluminium-free glass ionomer bone cements,
as they show that Zn/Mg-substituted glasses release
ions similarly fast as glasses containing no Zn/Mg,
suggesting that these ions are no prerequisite for ionomer
glasses. Zn-substituted glasses may potentially be used as
controlled-release materials, which release antibacterial
zinc ions when needed only, i.e. at low pH conditions (e.g.
bacterial infection), but not at normal physiological pH
conditions.