Evidence of catalase mimetic activity in Ce³⁺/Ce⁴⁺ doped bioactive glasses

The ability of Ce-containing bioactive glasses to inhibit oxidative stress in terms of reduction of hydrogen peroxide, by mimicking the catalase enzyme activity is demonstrated here for the first time. The antioxidant properties of three bioactive glasses containing an increasing amount of CeO₂ have been evaluated by following the degradation of hydrogen peroxide with time after immersion in H₂O₂ aqueous solutions with different concentration. XPS and UV-vis measurements allowed us to determine the Ce³⁺/Ce⁴⁺ ratio in the bulk and on the glass surface, and to correlate it with the ability of the samples to show catalase mimetic activity. Interestingly, we have found that the bioactive glass with composition 23.2Na₂O-25.7CaO-43.4SiO₂-2.4P₂O₅-5.3CeO₂ immersed in 0.1 M H₂O₂ aqueous solution is able to degrade 90% of it in 1 week. The reduction in bioactivity of the glasses with increasing CeO₂ content is here rationalized in terms of a lower amount of phosphate groups available for the hydroxyapatite layer formation, after binding with cerium ions. In fact, classical molecular dynamics simulations revealed that the addition of CeO₂ leads to the formation of cerium phosphate rich regions. The formation of an insoluble CePO₄ crystalline phase is also observed by XRD analysis after thermal treatment of the glass samples.