Structural and in vitro study of cerium, gallium and zinc containing sol–gel bioactive glasses

Abstract

Sol–gel derived glasses comprised of bioactive materials exhibit a high in vitro response, i.e., the capability to form a hydroxycarbonate apatite (HCA) layer that is claimed to be responsible for the bonding between the glass and the host bone. In this paper, the sol–gel bioactive glass 80% SiO₂–15% CaO–5% P₂O₅ (B_BG) was modified by adding the biologically relevant elements cerium, gallium and zinc. Structural characterization of the glasses was performed by ²⁹Si MAS NMR and their in vitro response was investigated by soaking them in simulated body fluid (SBF) for up to 15 days at 37 °C. The HCA formation was monitored by XRD, FTIR, SEM-EDS and ICP measurements. Ce³⁺, Ga³⁺, and Zn²⁺ can be classified as “intermediate ions”. However, ²⁹Si NMR revealed that Ce³⁺ ions have a more marked role of “modifier ions” than Ga³⁺ ions, while the behavior of Zn²⁺ lies between those of Ce³⁺ and Ga³⁺. On the other hand, in spite of the decrease in the in vitro response of B_BG by substitution, the glasses show HCA formation after 15 days of soaking. In addition, an increase in substitution of zinc accelerated the formation of HCA along with the formation of the mixed phase CaZn₂(PO₄)₂·2H₂O (scholzite) acting as nucleating agent for HCA. Moreover, the therapeutic effect of optimum Zn released as an ionic dissolution product from Zn-glasses could be beneficial to stimulate osteogenesis.