Zinc-containing bioactive glasses: surface reactivity and behaviour towards endothelial cells

This paper reports a physico-chemical study devoted to reactivity towards hydroxo-carbonate apatite (HCA) formation of bioactive glass 45S5 (H glass; commercially known as Bioglass) and of two preparations of zinc-doped 45S5-derived systems (HZ5, HZ20), immersed in Tris(hydroxymethyl)aminomethane (Tris) and Dulbecco's modified Eagle's medium (DMEM) buffer solutions. The activity/toxicity of the glasses was also tested using endothelial cells (EC). Zn caused a drastic reduction in the overall leaching activity of glasses and, at high Zn concentration (HZ20), the formation of HCA on the glass surface was thoroughly inhibited. The presence of Zn also decreased the increment of pH after glass immersion in both Tris and DMEM solution. EC are known to be very sensitive to pH changes and, for this reason, the rapid increase in pH brought about by H glass dissolution is likely to affect cell adhesion and spreading, whereas the high zinc release from HZ20 causes a drastic reduction in cell proliferation after a long contact time (approximately 1 week). This study shows that only HZ5 glass containing 5 wt.% Zn presents at the same time: reduced solubility, bioactivity (monitored by HCA formation) and conditions allowing EC growth over a 6-day period.