Effective role of P2O5 on in vitro bioactivity of CaO–ZnO–P2O5/P2O5 glass composites

Abstract

Abstract

Composite glass systems without SiO₂ have attracted research interest to solve the challenges associated with SiO₂ glass-based bioactive materials. Herein, we synthesized phosphate glass composites, which involves CaO–ZnO–P₂O₅ glass (composed of orthophosphate (Q⁰) or pyrophosphate (Q¹) groups)) and a small amount of P₂O₅ glass (composed of metaphosphate (Q²) groups), by melt quenching. The effects of the added P₂O₅ glass content on the in vitro bioactivity were then investigated. From the simulated body fluid (SBF) test, the maximum weight gain values were obtained regardless of the base glass, and spherical precipitates were observed on the sample surface with 2 wt.% added P₂O₅ by SEM. The addition of ≥ 3 wt.% P₂O₅ glass decreased the weight gain, retained the structure of the sample, and increased the size of the spherical precipitates. The spherical precipitates were Ca–Zn phosphate compounds presumed by XRD analysis to be a mixture of Ca–Zn hydroxyapatite and parascholzite. Among the samples comprising P₂O₅ glass, the Q⁰ group glass-based composites exhibited larger weight gain than the Q¹ group glass-based composites. Therefore, three factors are crucial in the precipitation and growth of phosphate compounds on the sample surface in the in vitro test: (1) promoted dissolution of the P component in the SBF solution; (2) increased abundance of Q⁰, which is the starting point of precipitation; and (3) co-existence of dissolution and precipitation in separate glasses.